. ..
C()
(/N
ITIH
PS
YC
HO
LOG
Y 1
8,86 (1986)
0010
-028
5/86
$7.
50C
o"yr
i~hl
~ 1
9II~
hy
Aca
dem
ic P
re...
Inc,
All
ri~h
.. or
r."
rodu
clio
n in
any
ror
m r
e""r
yed.
MC
CLE
LLA
ND
AN
D E
LMA
N
Cm
"'I'1
?i.f
!-M
elltm
U"i,
'er,f
;/Y
the
abili
ty to
trad
e cu
es o
ff a
gain
st e
ach
othe
r in
pho
nem
e id
entif
icat
ion.
At t
hew
ord
leve
l. th
e m
odel
cap
ture
s Ih
e m
a.io
r po
sitiv
e fe
atur
e of
Mar
slen
-Wils
on
CO
HO
RT
mod
el o
f spe
ech
perc
eptio
n. in
that
it s
how
s im
med
iate
sen
sitiv
ity to
info
rmat
ion
favo
ring
one
wor
d or
set
of w
ords
ove
r ot
hers
. At t
he s
ame
time,
itov
erco
mes
a d
iffi
culty
with
the
CO
HO
RT
mod
el: i
t can
rec
over
fro
m u
nder
spec
-, i
fica
lion
or m
ispr
onun
ciat
ion
of a
wor
d's
begi
nnin
g. T
RA
CE
II
also
use
s le
xica
lin
form
atio
n to
seg
men
t a s
trea
m o
f sp
eech
into
a s
eque
nce
of w
ords
and
to f
ind
wor
d be
ginn
ings
and
end
ings
, and
it s
imul
ates
a n
umbe
r of
rec
ent f
indi
ngs
rela
ted
to th
ese
poin
ts. T
he T
RA
CE
mod
el h
as s
ome
limita
tions
, but
we
belie
ve it
is a
step
tow
ard
a ps
ycho
logi
cally
and
com
puta
tiona
lly a
dequ
ate
mod
el o
f th
e pr
oces
sof speech perception. ~
1986
Aca
dem
ic P
re..,
Inc,
The
TR
AC
E M
odel
of S
peec
h P
erce
ptio
n
JAM
ES
L. M
CC
LELL
AN
D
AN
DC
onsi
der
the
perc
eptio
n of
the
phon
eme
/g/ i
n th
e se
nten
ce "
She
re-
ceiv
ed a
val
uabl
e gi
ft; "
The
re a
re a
larg
e nu
mbe
r of
cue
s in
this
sen
tenc
eto
the
iden
tity
of th
is p
hone
me,
Fir
st, t
here
are
the
acou
stic
cue
s to
the
iden
tity
of th
e /g
/ its
elf,
Sec
ond.
the
othe
r ph
onem
es in
the
sam
e w
ord
prov
ide
anot
her
sour
ce o
f cu
es. f
or if
we
know
the'
res
t of t
he p
hone
mes
in th
is w
ord.
ther
e ar
e on
ly a
few
pho
nem
es th
at c
an f
orm
a w
ord
with
, them, Third. the semantic and syntactic context further constrain the
poss
ible
wor
ds w
hich
mig
ht o
ccur
. and
thus
lint
it st
ill f
urth
er th
e po
ssib
lein
terp
reta
Jion
of
the
firs
t pho
nem
e in
"gi
ft,
The
re is
am
ple
evid
ence
that
all
of th
ese
diffe
rent
sou
rces
of i
nfor
-m
atio
n ar
e us
ed in
rec
ogni
zing
wor
ds a
nd th
e ph
onem
es th
ey c
onta
in,
In~
eed.
as
Col
e an
d R
udni
cky (1983) have recently noted. these basic
fact
s w
ere
desc
ribed
in e
arly
.exp
erim
ents
by
Bag
ley
(190
0) o
ver
80 y
ears
ago,
Col
e an
d R
udni
cky
poin
t out
that
rec
ent w
ork
(whi
ch w
e c~
msi
der
in d
etai
l bel
ow)
has
adde
d cl
arity
and
det
ail t
o th
ese
basi
c fi
ndin
gs b
utha
s no
t lea
d to
a th
eore
tical
syn
thes
is th
at p
rovi
des
a sa
tisfa
ctor
y ac
coun
tof
thes
e an
d m
any
othe
r ba
sic
aspe
cts
of s
peec
h pe
rcep
tion,
In th
is p
aper
. we
desc
ribe
a m
Ode
l who
se p
rim
ary
purp
ose
is to
acc
ount
for
the
inte
grat
ion
of m
ultip
le s
ourc
es o
f in
form
atio
n. o
r co
nstr
aint
, in
spee
ch p
erce
ptio
n, T
he m
odel
is c
onst
ruct
ed w
ithin
a f
ram
ewor
k w
hich
appe
ars
to b
eid
eal f
or th
e ex
ploi
tatio
n of
sim
',lta
neou
s. a
nd o
ften
mut
ual,
cons
trai
nts.
Thi
s fr
amew
ork
is th
e in
tera
ctiv
e ac
tivat
ion
fram
ewor
k(M
cCle
lland
& R
umel
hart
. 198
1; R
umel
hart
& M
cCle
lland
. 1981. 1982),
Thi
s ap
proa
ch g
rew
out
of
a nu
mbe
r of
ear
lier
idea
s. s
ome
com
ing
firs
tfr
om r
esea
rch
on s
poke
n la
ngua
ge r
ecog
nitio
n (M
arsl
en-W
ilson
& W
elsh
.19
78; M
orto
n. 1
969;
Red
dy. 1
976) and others arising from m
ore
gene
ral
cons
ider
atio
ns o
f in
tera
ctiv
e pa
ralle
l pro
cess
ing
(And
erso
n. 1
977;
Gro
ss-
berg
. 197
8; M
cCle
lland
. 197
9),
Acc
ordi
ng to
the
inte
ract
ive-
activ
atio
n ap
proa
ch. i
nfor
mat
ion
pro-
cess
ing
take
s pl
ace
thro
ugh
the
exci
tato
ry a
nd in
hibi
tory
inte
ract
ions
amon
g a
larg
e nu
mbe
r of
pro
cess
ing
elem
ents
cal
led
units
, Eac
h un
it is
a ve
ry s
impl
e pr
oces
sing
dev
ice,
It s
tand
s fo
r a
hypo
thes
is a
bout
the
inpu
t bei
ng p
roce
ssed
. The
act
ivat
ion
of a
uni
t is
mon
oton
ical
ly r
elat
ed
,. q, ~
JEF
FR
EY
L. E
LMA
N
U"i
t'er.fi/y of C(/l((omi(/. Stili Dif!1!O
We
desc
ribe
a m
odel
cal
led
the
TR
AC
E m
odel
of
spee
ch p
erce
ptio
n. T
he m
odel
is b
ased
on
the
prin
cipl
es o
f in
tera
ctiv
e ac
tivat
ion.
Inf
orm
atio
n pr
oces
sing
take
spl
ace
thro
ugh
the
e xci
tato
ry a
nd in
hibi
tory
inte
ract
ions
of
a la
rge
num
ber
ofsimple processing u
rtits
, eac
h w
orki
ng c
ontin
uous
ly to
upd
ate
its o
wn
activ
atio
non
the
basi
s of
the
activ
atio
ns o
f ot
her
units
to w
hich
it is
con
nect
ed. T
he m
odel
is c
alle
d th
e T
RA
CE
mod
el b
ecau
se th
e ne
twor
k of
uni
ts f
orm
s a
dyna
mic
pro
-cessing structure called "the Trace."
whi
ch s
erve
s at
onc
e as
the
perc
eptu
alpr
oces
sing
mec
hani
~m
and
as
the
syst
ems
wor
king
mem
ory.
The
mod
el is
in-
stan
tiate
d in
two
sim
ulat
ion
prog
ram
s. T
RA
CE
I, d
escr
ibed
in d
etai
l els
ewhe
re,
deals with short seg~ents orreal speech. and suggests a m
echa
nism
for
cop
ing
with
the
fact
that
the
cues
to th
e id
entit
y, o
f pho
nem
es v
ary
as a
fun
ctio
n of
cont
ext.
TR
AC
E II
_th
e fo
cus
of th
is a
rtic
le, s
imul
ates
a la
rge
num
ber
of e
mpi
rica
lfin
ding
s on
the
perc
:ept
ion
of p
hone
mes
and
wor
ds a
nd o
n th
e in
tera
ctio
ns o
fph
onem
e ;m
d w
ord
perc
eptio
n. A
t the
pho
nem
e le
vel,
TR
AC
E I
I si
mul
ates
the
innu
ence
of l
exic
al j
nfor
mat
ion
on th
e id
entif
icat
ion
of p
hone
mes
and
acc
ount
sfor Ihe fact that le
xic:
ial e
ffect
s ar
e fo
und
unde
r ce
rtai
n co
nditi
ons
but n
ot o
ther
s.T
he m
odel
als
o sh
ows
how
kno
wle
dge
of p
hono
logi
cal c
onst
rain
ts c
an b
e em
-bo
died
in p
artic
ular
lexi
cal i
tem
s bu
t can
stil
l be
used
to in
nuen
ce p
roce
ssin
g of
nove
l. no
nwor
d ul
lera
nces
. The
mod
el a
lso
exhi
bits
cat
egor
ical
per
cept
ion
and
The
wor
k re
port
ed h
ere
was
sup
port
ed in
par
t by
a co
ntrd
ct fr
om th
e O
ffice
of N
aval
Research CN-
tKK
II4-
!l2-
'13741. in part by a grant from the National Science Foundation
IHN
S-79
-240
621.
and
in p
art b
y a
.Res
earc
h Sc
ient
ists
Car
eer
Dev
elop
men
t Aw
ard
to th
efi
rst a
utho
r fr
om th
e N
atjo
nalln
stitu
te o
f M
enta
l Hea
lth (
5-K
OI-MHOO3851. We thank
Dr.
Joan
ne M
iller
for
a ve
ry u
5efu
l dis
cuss
ion
whi
ch in
spire
d us
to w
rite
this
art
icle
in it
s pr
esen
tfo
rm. D
avid
Pis
oni w
as e
~tre
mel
y he
lpfu
l in
mak
ing
us d
eal m
ore
fully
with
sev
eral
impo
rtan
tis
sues
, and
in .I
erlin
g us
to a
larg
e nu
mbe
r of
use
ful p
aper
s in
the
liter
atur
e, W
e al
so th
ank
Dav
id R
umel
hart
for
use~
ul d
iscu
ssio
ns d
urin
g th
e de
velo
pmen
t of t
he b
asic
arc
hite
ctur
e of
TR
AC
E a
nd E
ileen
Con
way
, Mar
k Jo
hnso
n. D
ave
Pare
, and
pod
ul S
mith
for
thei
r as
sist
ance
in p
rogr
amin
g an
d gr
aphi
cs. S
end
requ
esls
for
rep
rint
s to
Jam
es L
McC
lella
nd. D
epar
tmen
tof
I)sy
chol
ogy.
Car
negi
e..'.
Mel
lon
Uni
vers
ity. S
chen
ley
Par
k. P
illsb
urgh
, PA
152
13.
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
to th
e st
reng
th o
f th
e hy
poth
esis
for
whi
ch th
e un
it st
ands
, Con
stra
ints
amon
g hy
poth
eses
are
rep
rese
nted
by
conn
ectio
ns. U
nUs
whi
ch a
re m
u-tu
ally
con
sist
ent a
re m
utua
lly e
xcita
tory
, and
uni
ts th
at a
re m
utua
lly in
-co
nsis
tent
are
mut
ually
inhi
bito
ry. T
hus,
the
unit
for
/g/ h
as m
utua
llyex
cita
tory
con
nect
ions
with
uni
ts f
or w
ords
con
tain
ing
/g/,
and
has
mu-
tual
ly in
hibi
tory
con
nect
ions
with
uni
ts f
or o
ther
pho
nem
es, W
hen
the
activ
atio
n of
a u
nit e
xcee
ds s
ome
thre
shol
d ac
tivat
ion
valu
e, it
beg
ins
toinfluence the
activ
atio
n of
oth
er u
nits
via
its
outg
oing
con
nect
ions
; the
stre
ngth
of
th~s
e si
gnal
s de
pend
s on
the
degr
ee o
f th
e se
nder
s ac
tivat
ion,
The
sta
te o
f the
sys
tem
at a
giv
en p
oint
in ti
me represents the current
stat
us o
f the
var
ious
pos
sibl
e hy
poth
eses
abo
ut th
e in
put;
info
rmat
ion
proc
essi
ng a
mou
nts
to th
e ev
olut
ion
of th
at s
tate
, ove
r tim
e, T
hrou
ghou
tthe course
of
proc
essi
ng, e
ach
unit
is c
ontin
ually
rec
eivi
ng in
put f
rom
othe
r un
its, c
ontin
ually
upd
atin
g its
act
ivat
ion
on th
e ba
sis
of th
ese
inpu
ts,
and,
if it
is o
ver
thre
shol
d, i
t is
cont
inua
lly s
endi
ng e
xcita
tory
and
inhi
b-ito
ry s
igna
ls to
oth
er u
nits
. Thi
s " i
nter
activ
e-ac
tivat
ion
" ,p
roce
ss a
llow
sea
ch h
ypot
he~
is b
oth
to c
onst
rain
and
be
cons
trai
ned
by o
ther
mut
ually
cons
iste
nt o
r in
cons
iste
nt h
ypot
hese
s,
Cri
teri
ll lI
nd C
olls
tmill
ts O
il M
odel
Dev
elop
men
t
The
re a
re g
ener
ally
two
kind
s of
mod
els
of th
e sp
eech
per
cept
ion
pro-
cess
, One
kin
d of
mod
el, w
hich
gro
ws
out o
f speech engineering and
artif
ical
inte
llige
nce,
atte
mpt
s to
pro
vide
a m
achi
ne s
olut
ion
to th
epr
oble
m o
f s~
eech
rec
ogni
tion,
Exa
mpl
es o
f th
is k
ind
of m
odel
are
HE
AR
SA
Y (
Erm
an &
Les
ser,
198
0; R
eddy
, Erm
an, F
enne
ll. &
Nee
ly,
1973
) H
WIM
(Wol
f &
Woo
ds, 1
978)
, HA
RPY
(L
ower
re, 1
976)
, and
LA
FS/S
CR
IBE
R (
Kla
tt, 1
980)
, A s
econ
d ki
nd o
f m
odel
, gro
win
g ou
t of
expe
rimen
tal ~
sych
olog
y, a
ttem
pts
to a
ccou
nt fo
r as
pect
s of
psy
chol
og-
ical
dat
a on
the
perc
eptio
n of
spe
ech.
Exa
mpl
es o
f th
is c
lass
of
mod
els
incl
ude
Mar
sl~
n-W
ilson
s C
OH
OR
T M
odel
(M
arsl
en- W
ilson
& T
yler
,19
80; M
arsl
en~
Wils
on &
Wel
sh, 1
978;
Nus
baum
& S
iow
iacz
ek, 1
982)
;M
assa
ros
feat
ure
inte
grat
ion
mod
el (
Mas
saro
, 198
1; M
assa
ro &
Ode
n,I
980a
, 198
0b; O
den
& M
assa
ro, 1
978)
; Col
e an
d Ja
kim
ik' s
(1978, 1980)
mod
el o
f au
dito
ry w
ord
proc
essi
ng, a
nd th
e m
odel
of
audi
tory
and
pho
-ne
tic m
emor
y es
pous
ed b
y Fu
jisak
i and
Kaw
ashi
ma
(196
8) a
nd P
ison
i(1973, 1975).
Eac
h ap
proa
ch h
onor
s a
diff
eren
t cri
teri
on f
or s
ucce
ss. M
achi
nemodels are ju4ged in terms of actual performance in
rec
ogni
zing
rea
lsp
eech
. Psy
chol
ogic
al m
odel
s ar
e ju
dged
in te
rms
of th
eir
abili
ty to
ac-
coun
t for
det
ails
of
hum
an p
erfo
rman
ce in
spe
ech
reco
gniti
on, W
e ca
llthese two criteria
ompi
llllti
mw
i an
d pj
iych
olog
;cal
ad
equa
cy.
In e
xten
ding
the
inte
ract
ive
activ
atio
n ap
proa
ch to
spe
ech
perc
eptio
n,w
e ha
d es
sent
ially
two
ques
tions
: Firs
t, co
uld
the
inte
ract
ive-
activ
atio
n
appr
oach
con
trib
ute
tow
ard
the
deve
lopm
ent o
f a c
ompu
tatio
nally
suf
fi-ci
ent f
ram
ewor
k fo
r sp
eech
per
cept
ion?
Sec
ond
, cou
ld it
acc
ount
for
wha
tis
kno
wn
abou
t the
psy
chol
ogy
of s
peec
h pe
rcep
tion?
In
shor
t, w
e w
ante
dto
kno
w, w
as th
e ap
proa
ch f
ruitf
ul, b
oth
on c
ompu
tatio
nal a
nd p
sych
o-lo
gica
l gro
unds
.T
wo
fact
s im
med
iate
ly b
ecam
e ap
pare
nt. F
irst
, spo
ken
lang
uage
intr
o-du
ces
man
y ch
alle
nges
that
mak
e it
far
from
cle
ar h
ow w
ell t
he in
tera
c-tiv
e-ac
tivat
ion
appr
oach
will
ser
ve w
hen
exte
nded
fro
m p
rint
to s
peec
h.Se
cond
, the
app
roac
h its
elf i
s to
o br
oad
to p
rovi
de a
con
cret
e m
odel
,w
ithou
t fur
ther
ass
umpt
ions
, Her
e w
e re
view
sev
eral
fac
ts a
bout
spe
ech
that
pla
yed
a ro
le in
sha
ping
the
spec
ific
ass
umpt
ions
em
bodi
ed in
TR
AC
E.
Som
e Im
port
ant F
acts
abo
ut S
peec
h
Our
inte
ntio
n he
re is
not
to p
rovi
de a
n ex
tens
ive
surv
ey o
f th
e na
ture
of s
peec
h an
d its
per
cept
ion,
but
rat
her
to p
oint
to s
ever
al fu
ndam
enta
las
pect
s of
spe
ech
that
hav
e pl
ayed
impo
rtan
t rol
es in
the
deve
lopm
ent
of th
e m
odel
we
desc
ribe
'her
e, A
ver
y us
eful
dis
cuss
ion
of s
ever
al o
fth
ese
poin
ts is
ava
ilabl
e in
Kla
tt (1
980)
.T
empo
ral n
atur
e of
the
speec'h stimulus,
It d
oes
not,
of c
ours
e, ta
ke a
scie
ntis
t to
obse
rve
one
fund
amen
tal d
iffe
renc
e be
twee
n sp
eech
and
prin
t: sp
eech
is a
sig
nal w
hich
is e
xten
ded
in ti
me,
whe
reas
pri
nt is
. ast
imul
us w
hich
is e
xten
ded
in s
pace
, The
seq
uent
ial n
atur
e of
spe
ech
pose
s pr
oble
ms
for
a m
odel
er, i
n th
at to
acc
ount
for
con
text
eff
ects
, one
need
s to
kee
p a
reco
rd o
f the
con
text
, It w
ould
be
a si
mpl
e m
atte
r to
proc
ess
spee
ch if
eac
h su
cces
sive
por
tion
of th
e sp
eech
inpu
t wer
e pr
o-ce
ssed
inde
pend
ently
of
all o
f th
e ot
hers
, but
in f
act,
this
is c
lear
ly ri
otth
e ca
se. T
he p
rese
nce
of c
onte
xt e
ffec
ts in
spe
ech
perc
eptio
n re
quir
esa
mec
hani
sm th
at k
eeps
som
e re
cord
of
that
con
text
, in
a fo
rm th
at a
llow
sit
to in
flue
nce
th~
inte
rpre
tatio
n of
sub
sequ
ent i
nput
.A
fur
ther
poi
nt, a
nd o
ne th
at h
as b
een
muc
h ne
glec
ted
in c
erta
in. m
odel
s, is
that
it is
not
onl
y pr
ior
cont
ext b
ut a
lso
subs
eque
nt c
onte
xtth
at in
flue
nces
per
cept
ion,
(T
his
and
rela
ted
poin
ts h
ave
rece
ntly
bee
nm
ade
by G
rosj
ean
& G
ee, 1
984;
Sal
asoo
& P
ison
i, 19
85; a
nd T
hom
pson
,19
84).
For
exa
mpl
e, G
anon
g (1
980)
rep
orte
d th
at th
e id
entif
icat
ion of a
sylla
ble-
initi
al s
peec
h so
und
that
was
con
stru
cted
to b
e be
twee
n /g
I an
d/k
/ was
;ptlu
ence
d by
whe
ther
the
rest
of t
he s
ylla
ble
was
Iisl
(as
inki
ss)
or /l
ftl (
as in
"gi
ft" )
, Suc
h' "
righ
t con
text
eft
ects" (Thompson,
1984) indicate that the pe
rcep
tion
of w
hat c
omes
in n
ow b
oth
infl
uenc
esan
d is
infl
uenc
ed b
y th
e pe
rcep
tion
of w
hat c
omes
in la
ter.
Thi
s fa
cisu
gges
ts th
at th
e re
cord
of
wha
t has
alr
eady
bee
n pr
esen
ted
cann
ot n
otbe
a s
tatic
rep
rese
ntat
ion
, but
sho
uld
rem
ain
in a
mal
leab
le f
orm
. sub
ject
to a
ltera
tion
as a
res
ult o
f inf
luen
ces
aris
ing
from
sub
sequ
ent c
on/e
x!.
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
::.-
LL
I
LL
I0:
:
:.....
..
wor
d se
gmen
tatio
n (B
ond
& G
arne
s, 1
980)
. and
cer
tain
seg
men
tatio
nde
cisi
ons
are
easi
ly in
flue
nced
by
cont
extu
al f
acto
rs (
Col
e &
Jak
iinik
.19
80),
Thu
s. it
is c
lear
that
wor
d re
cogn
ition
can
not c
ount
on
an a
ccur
ate
segm
enta
tion
of th
e ph
onem
e st
ream
into
sep
arat
e w
ord
units
. and
m
any
case
s su
ch a
seg
men
tatio
n w
ould
per
forc
e ex
clud
e fr
om o
ne o
f th
ew
ords
a s
hare
d se
gmen
t tha
t is
doin
g do
uble
dut
y in
eac
h of
two
succ
es-
sive
wor
ds, .
CO
fltex
t-se
miti
t'ity
of m
e.f,
A
thir
d m
ajor
fac
t abo
ut s
peec
h is
that
the
cues
for
a p
artic
ular
uni
t var
y co
nsid
erab
ly w
ith th
e co
ntex
t in
whi
chth
ey o
ccur
. For
exa
mpl
e, th
e tr
ansi
tion oftht second formant carries a
great deal of information about the identity of the stop consonant
Ibl
Fig,
I. b
ut th
at f
orm
ant w
ould
look
qui
te d
iffe
rent
had
the
sylla
ble
been
big"
or "
bog" instead of "
bag.
" T
hus
the
cont
ext .
in w
hich
a p
hone
me
occu
rs r
estr
uctu
res
the
cues
to th
e id
entit
y of
that
pho
nem
e (L
iber
man
,19
70).
The
ext
ent o
f th
e re
stru
ctur
ing
depe
..ds
on th
e un
it se
lect
ed a
ndon
the
part
icul
ar c
ue in
volv
ed. B
ut th
e pr
oble
m is
ubi
quito
us in
spe
ech,
Not
onl
y ar
e th
e cu
es f
or e
ach
phon
eme
dram
atic
ally
aff
ecte
d by
prec
edin
g an
d fo
llow
ing
cont
ext.
they
are
als
o al
tere
d by
. mor
e gl
obal
fact
ors
such
as
rate
of
spee
ch (
Mill
er. 1
981)
. by
mor
phol
ogic
al a
nd p
ro-
sodi
c fa
ctor
s su
ch a
s po
sitio
n in
wor
d an
d in
the
stre
ss c
onto
ur o
f th
eut
tera
nce.
and
by
char
acte
rist
ics
of th
e sp
eake
r su
ch a
s si
ze a
nd s
hape
of th
e vo
cal t
ract
. fun
dam
enta
l fre
quen
cy o
f th
e sp
eaki
ng v
oice
. and
dialectical variations (see Klatt, 1980. an
d R
epp
& L
iber
man
. 1984. for
disc
ussi
ons)
, .A
num
ber
of d
iffe
rent
app
roac
hes
to th
e pr
oble
m h
ave
been
trie
d by
diff
eren
t inv
estig
ator
s. O
ne a
ppro
ach
is to
try
to find relatively invar-
iant
-generally relational-
feat
ures
(e.
g.. S
teve
ns &
Blu
mst
ein.
198
1),
Ano
ther
appr
oach
has
bee
n to
red
efin
e th
e un
it so
that
it e
ncom
pass
esth
e co
ntex
t and
ther
efor
e be
com
es m
ore
inva
rian
t (Fu
jimur
a &
Lov
ins.
1982
; Kla
tt. 1
980;
Wic
kelg
ren,
196
9), W
hile
thes
e ar
e bo
th s
ensi
ble
and
usef
ul a
ppro
ache
s, th
e fi
rst h
as n
ot y
et s
ucce
eded
in e
stab
lishi
ng a
suf
-fi
cien
tly in
vari
ant s
et o
f cu
es, a
nd th
e se
cond
may
alle
viat
e bu
t doe
s no
tel
imin
ate
the
prob
lem
; eve
n un
its s
uch
as d
emis
ylla
bles
(F
ujim
ura
&L
ovin
s, .1
982)
, con
text
-sen
sitiv
e al
loph
ones
(W
icke
lgre
n, 1
969)
. or
even
who
le w
ords
(K
latt,
198
0) a
re s
till i
nflu
ence
d by
con
text
. We
have
cho
sen
to f
ocus
inst
ead
on a
thir
d po
ssib
ility
: tha
t the
per
cept
ual s
yste
m u
ses
info
rmat
ion
from
the
cont
ext i
n w
hich
an
utte
ranc
e oc
curs
to a
lter
con-
nect
ions
, the
reby
eff
ectiv
ely
allo
win
g th
e co
ntex
t to
retu
ne th
e pe
rcep
tual
mec
hani
sm o
n th
e fly
.Noise and indeterminacy
in
the speech signal.
To
com
poun
d al
l the
prob
lem
s al
lude
d to
abo
ve, t
here
is th
e ad
ditio
nal f
act t
hat s
peec
h is
ofte
ilpe
rcei
ved
unde
r le
ss th
an id
eal c
ircum
stan
ces.
Whi
le a
slo
w a
nd c
aref
ulsp
eake
r in
a q
uiet
roo
m m
ay p
rodu
ce s
uffic
ient
cue
s to
allo
w c
orre
ct
Lack
(~
r hOllllc!a/";es alld te
mpo
/"al
OI'C
'r/ap
. A
sec
ond
fund
amen
tal p
oint
abou
t spe
ech
.is th
at th
e cu
es to
successive units of speech frequently
over
lap
in ti
me.
The
pro
blem
is p
artic
ular
ly s
ever
e at
the
phon
eme
leve
l. A glance at a schematic speech spectrogram (Liberman. 19
70; F
ig. I
)cl
earl
y ill
ustr
ates
this
pro
blem
. The
re o
are
no s
epar
able
pac
kets
of i
nfor
-m
atio
n in
the
spec
trog
ram
like
the
sepa
rate
fea
ture
bun
dles
that
mak
e up
letlt
~rs
in p
rinte
d w
ords
,B
ecau
se o
f th
e ov
erla
p of
suc
cess
ive
phon
emes
. it i
s di
ffic
ult a
nd. w
ebelieve. counterproductive to try to divide the speech st
ream
up
into
sepa
rate
pho
nem
e un
its in
adv
ance
of
iden
tifyi
ng th
e un
its. A
num
ber
ofot
her
rese
arch
ers
(e.g., Fowler, 1984: Klatt, 1980) have m
ade
muc
h th
esa
me
poin
t. A
sup
erio
r ap
proa
ch s
eem
s to
be
to a
llow
the
phon
eme
ide;
n-
tific
atio
n pr
oces
s to
dam
ine
the
spee
ch s
trea
m fo
r ch
arac
teris
tic p
at-
tern
s. w
ithou
t fir
st s
egm
entin
g th
e st
ream
into
sep
arat
e u!
1its
,
The
pro
blem
of
over
lap
is le
ss s
ever
e fo
r w
ords
than
for
pho
nem
es.
but i
t doe
s no
t go
away
com
plet
e.ly
, In
rapi
d sp
eech
. wor
ds r
un in
to e
ach
othe
r. a
nd th
ere
are
no p
ause
s be
twe~
n w
ords
in r
unni
ng s
peec
h, T
o be
sure
. the
re a
re o
ften
cues
that
sig
nal t
he lo
catio
ns o
f bou
ndar
ies
betw
een
words-stop consona
hts
are
gene
rally
asp
irate
d at
the
begi
nnin
gs o
fst
ress
ed w
ords
in E
nglis
h. a
nd w
ord
initi
al v
owel
s ar
e ge
nera
lly p
rece
ded,
by g
lotta
l sto
ps. f
or e
xam
ple.
The
se c
ues
have
bee
n st
udie
d by
a n
umbe
rof
inve
stig
ator
s. p
artic
tllar
ly L
ehis
te (
e,g,. Lehiste, 1960, 1964) an
d N
ak-
atan
i and
col
labo
rato
rs, N
akat
ani a
nd D
ukes
(197
7) .
dem
onst
rate
d th
atpe
rcei
vers
exp
loit
som
e of
thes
e cu
es b
ut f
ound
that
cer
tain
utte
ranc
esdo
not
pro
vide
suf
fici
ent c
ues
to w
ord
boun
dari
es to
per
mit
relia
ble
per-
cept
ion
of th
e in
tend
ed u
ttera
nce,
Spe
ech
erro
rs o
ften
invo
lve
erro
rs o
f
TIM
EFI
G, I
, A ~
chcm
alic
spc
clrn
gram
ror
the ~yJlab'e "
bag,
" indicating the overtap or the
inro
rmat
ion
~pe
ciry
ing
the
diffe
rent
pho
nem
es. R
eprin
ted
with
per
mis
sion
rro
m L
iber
man
1197
01,
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
perc
eptio
n of
all
of th
e ph
onem
es in
an
utte
ranc
e w
ithou
t the
aid
of l
exic
alor
oth
er h
ighe
r le
vel c
onst
rain
ts, t
hese
con
ditio
ns d
o no
t alw
ays
obta
in,
People can correctly perceive speech under quite impoverished condi-
tions
, if
it is
sem
antic
ally
coh
eren
t and
syn
tact
ical
ly w
ell f
orm
ed (
G,
Mill
er, H
eise
, & L
icht
en, 1
951)
, Thi
s m
eans
that
the
spee
ch m
echa
nism
sm
ust b
e ab
le to
fun
ctio
n, e
ven
with
a h
ighl
y de
grad
ed s
timul
us, I
n pa
r-tic
ular
, as
Tho
mps
on (
1984
), N
orri
s (1
982)
, and
Gro
sjea
n an
d G
ee (
1984
)ha
ve p
oint
edou
t, th
e m
echa
nism
s of
spe
ech
perc
eptio
n ca
nnot
cou
nt o
nac
cura
te in
form
atio
n ab
out a
ny p
art o
f a
wor
d, A
s w
e sh
all s
ee, t
his
fact
pose
s a
serio
us p
robl
em fo
r on
e of
the
best
cur
rent
psy
chol
ogic
al m
odel
sof
the
proc
ess
of s
poke
n w
ord recognition (Marslen-Wilson & Welsh,
1978
),M
any
of th
e ch
arac
teri
stic
s th
at w
e ha
ve r
evie
wed
dif
fere
ntia
te s
peec
hfrom print-
at le
ast,
from
ver
y hi
gh q
ualit
y pr
int o
n w
hite
pap
er-b
utit
wou
ld b
e a:
mis
take
to th
ink
that
sim
ilar
prob
lem
s ar
e no
t enc
ount
ered
in o
ther
dom
ains
. Cer
tain
ly, t
he s
eque
ntia
l nat
ure
of s
poke
n in
put s
ets
. speech apart from vi
sion
, in
whi
ch th
ere
can
be s
ome
degr
ee o
f si
mul
-ta
neity
of p
erce
ptio
n, H
owev
er, t
he p
robl
ems
of il
l-defined boundaries,
cont
ext s
ells
itivi
ty o
f cu
es, a
nd n
oise
and
inde
term
inac
y ar
e ce
ntra
lpr
oble
ms
in v
isio
n ju
st a
s m
uch
as th
ey a
re in
spe
ech
(cf.
Bal
lard
, Hin
ton,
an
d S
ejno
wsk
i, 19
83; B
arro
w &
Ten
enba
um, 1
978; Marr, 19
82),
Thu
s,th
ough
the
mod
el w
e pr
esen
t her
e is
foc
usse
d on
spe
ech
perc
eptio
n, w
ew
ould
hop
e th
at th
e w
ays
in w
hich
it d
eals
with
the
chal
leng
es p
osed
by
the
spee
ch s
igna
l are
app
licab
le in
oth
er d
omai
ns.
activ
atio
n m
odel
s th
an w
ith m
odel
s in
any
oth
er computational frame-
wor
k, s
uch
as e
xper
t sys
tem
s or
pro
duct
ion
syst
ems.
.0
-
TH
E T
RA
CE
MO
DE
L
The
Im
porl
twce
of
the
Rig
ht A
rchi
tect
ure
All
four
of
the
cons
ider
atio
ns li
sted
abo
ve p
laye
d an
impo
rtan
t rol
e in
the
form
ulat
ion
of th
e T
RA
CE
mod
el. T
he m
odel
is a
n in
stan
ce o
f an
inte
ract
ive
activ
atio
n m
odel
, but
it is
. by
no m
eans
the
only
inst
ance
of
such
a m
odel
that
we
have
con
side
red
or th
at c
ould
be
cons
ider
ed, O
ther
form
ulat
ions
,we
cons
ider
ed s
impl
y di
d no
t app
ear
to o
ffer
a s
atis
fact
ory
fram
ewor
k fo
r de
alin
g w
ith th
ese
four
asp
ects
of
spee
ch (
see
Elm
an &
McC
lella
nd, ,
1984
, for
dis
cuss
ion)
. Thu
s, th
e T
RA
CE
mod
el h
inge
s as
muc
h on
the
part
icul
ar p
roce
ssin
g ar
chite
ctur
e it
prop
oses
for
spe
ech
perc
eptio
n as
it d
oes
on th
e in
tera
ctiv
e ac
tivat
ion
proc
esse
s th
at o
ccur
with
in th
is a
rchi
tect
ure.
Inte
ract
ive~
activ
atio
n m
echa
nism
s ar
e a
clas
s to
o br
oad
to s
tand
or
fall
on th
e m
erits
of a
sin
gle
mod
el, T
o th
e ex
tent
that
com
puta
tiona
lly a
ndps
ycho
logi
cally
ade
quat
e m
odel
s ca
n be
bui
lt w
ithin
the
fram
ewor
k, th
eat
trac
tiven
ess
of th
e fr
amew
ork
as a
who
le is
, of
cour
se, i
ncre
ased
, but
the
adeq
uacy
of
any
part
icul
ar m
odel
will
gen
eral
ly d
epen
d on
the
par-
ticul
ar a
ssum
ptio
ns th
at m
odel
em
bodi
es. I
t is
no d
iffer
ent w
ith in
tera
ctiv
e-
Ove
rvie
w
The
TR
AC
E m
odel
con
sist
s pr
imar
ily o
f a
very
larg
e nu
mbe
r of
uni
tsorganized into three levels,
thefealllre. phoneme,
and
It'o
rd
leve
ls, E
ach
unit
stan
ds f
or a
hyp
othe
sis
abou
t a p
artic
ular
per
cept
ual o
bjec
t occ
urri
ngat
!a p
artic
ular
poi
nt in
tim
e de
fined
rel
ativ
e to
the
begi
nnin
g of
the
ut-
.te
ranc
e.A
sm
all s
ubse
t of
the
units
in T
RA
CE
II,
the
vers
ion
of th
e m
odel
we
focu
s on
in th
is p
aper
, is
illus
trat
ed in
Fig
s, 2
,3,
and
4, E
ach
of th
e th
ree
figu
res
repl
icat
es th
e sa
me
set o
f un
its, i
llust
ratin
g a
diff
eren
t pro
pert
yof
the
mod
el in
eac
h ca
se. I
n th
e fi
gure
s, e
ach
rect
angl
e co
rres
pond
s to
a se
para
te p
roce
ssin
g un
it, T
he la
belS
on
the
units
and
alo
ng th
e si
dein
dica
te th
e sp
oken
obj
ect (
feat
ure,
pho
nem
e, o
r w
ord)
for
whi
ch e
ach
unit
stan
ds, T
he le
flan
d ri
ght e
dges
of
each
rec
tang
le in
dica
te th
e po
rtio
nof
the
inpu
t the
uni
t spa
ns,
At t
he f
eatu
re le
vel,
ther
e ar
e se
vera
l ban
ks o
f fe
atur
e de
tect
ors,
one
for
each
of
seve
ral d
imen
sion
s of
spe
ech
soun
ds. E
ach
bank
is r
eplic
ated
for'
each
of s
ever
dl s
ucce
ssiv
e m
omen
ts in
tim
e, o
r tim
e sl
ices
, At.
the
phon
eme
leve
l, th
ere
are
dete
ctor
s fo
r ea
ch o
f th
e ph
onem
es, T
here
ison
e co
py o
f ea
ch p
hone
me
dete
ctor
cen
tere
d ov
er e
very
thre
e tim
e sl
ices
.E
ach
unit
span
s si
x tim
e sl
ices
, so
units
with
adj
acen
t cen
ters
spa
n ov
er-
lapp
ing
rang
es o
f sl
ices
, At t
he w
ord
leve
l, th
ere
are
dete
ctor
s fo
r ea
chw
ord.
The
re is
one
cop
y of
eac
h w
ord
dete
ctor
cen
tere
d ov
er e
very
thre
efe
atur
e sl
ices
. Her
e ea
ch d
etec
tor
span
s a
stre
tch
of fe
atur
e sl
ices
cor
-re
spon
ding
to th
e en
tire
leng
th o
f ' th
e w
ord.
Aga
in, t
hen,
uni
ts w
ith a
d-ja
cent
cen
ters
spa
n ov
erla
ppin
g ra
nges
of s
lices
,In
put t
o th
e m
odel
, in
the
form
of
a pa
ttern
of
activ
atio
n to
be
appl
ied
to th
e un
its a
t the
fea
ture
leve
l, is
pre
sent
ed s
eque
ntia
lly to
the
feat
urc-
leve
l uni
ts in
suc
cess
ive
sliC
es, a
s it
wou
l(J if
it w
ere
a re
al s
peec
h st
ream
,un
fold
ing
in ti
me.
Moc
k-sp
eech
inpu
ts o
n th
e th
ree
illus
trat
ed d
imen
sion
sfo
r th
e ph
rase
"te
a cu
p" (/tik"p/
)' ar
e sh
own
in F
ig. 2
, A
t any
inst
ant,
inpu
t is
arri
ving
onl
y at
the
units
in o
ne s
lice
at th
e fe
atur
e le
vel.
In te
rms
of th
e di
spla
y in
Fig
, 2, t
hen,
we
can
visu
aliz
e th
e in
put b
eing
app
lied
tosu
cces
sive
slic
es o
f th
e ne
twor
k at
~uc
cess
ive
mom
ents
in ti
me.
How
ever
,it
is im
port
ant t
o re
mem
ber
that
all
the
units
are
con
tinua
lly in
volv
ed in
proc
essi
ng, a
nd p
roce
ssin
g of
the
inpu
t arr
ivin
g at
one
tim
e is
just
beg
in-
ning
as
the
inpu
t is
mov
ed a
long
to th
e ne
xt ti
me
slic
e.. T
he e
ntir
e ne
twor
k of
uni
ts is
cal
led
"the
Tra
ce,"
bec
ause
the
patte
rnof
act
ivat
ion
left
by
a sp
oken
inpu
t is
a tr
ace
of th
e an
alys
is o
f th
e in
put
at e
ach
of th
e th
ree
proc
essi
ng le
vels
. Thi
s tr
ace
is u
nlik
e m
~i\y
trac
es
TR
AC
E M
OD
EL
kAp
i~i~
i~i~
i~i~
i~i
. p
rlnr
~t~t
~t~t
~t'
1111
: , :
: : I
: III
1'rn
n:l:!
t!t!
,!t'
1111
1: , III
IIII I
'r~
r~r~
r~r~
I~.r
~I'
.L:-
a..
i~i~
i~i~
i~i~
i~i'
, - 11-
I:h;
ctl~
A. P
-Fl
o. 2
, A s
ubse
l of
the
units
in T
RA
CE
II.
Eac
h re
ctan
gle
repr
esen
ts a
dif
fere
nt u
nit,
The
labe
ls in
dica
te th
e ite
m fo
r w
hich
the
unit
stan
ds, a
nd th
e ho
rizo
ntal
edg
es o
f th
e re
ctan
gle
indi
cale
the
port
ion
of th
e T
race
spa
nned
by
each
uni
t. T
he in
put f
eatu
re s
peci
fica
tions
for
the
phra
se "
tea
cup.
" pr
eced
ed a
nd f
ollo
wed
by
sile
nce.
are
indi
cate
d fo
r th
e th
ree
iIIu
s-tr
ated
dim
ensi
ons
by th
e bl
acke
ning
of
the
corr
espo
ndin
g fe
atur
e un
its.
thou
gh, i
n th
at it
is d
ynam
ic, s
ince
it c
onsi
sts
of a
ctiv
atio
ns o
f pr
oces
sing
elem
ents
. and
thes
e pr
o ces
sing
ele
men
ts ' c
ontin
ue to
inte
ract
as
time
goes
on. T
he d
istin
ctio
n be
t!w
een
perc
eptio
n an
d (p
rim
ary)
mem
ory
is c
om-
plet
ely
blur
red~
.sin
ce th
e pe
rcep
t is
unfo
ldin
g in
the
sam
e st
ruct
ures
that
serv
e as
wor
king
mem
ory,
and
per
cept
ual p
roce
ssin
g of
old
er p
ortio
ns o
fth
e in
put c
ontin
ues
even
as
new
er p
ortio
ns a
re c
omin
g in
to th
e sy
stem
,T
hese
con
tinui
ng in
tera
ctio
ns p
erm
it th
e m
odel
to in
corp
orat
e rig
ht c
on-
text
eff
ects
, and
allo
w ~
he m
odel
to a
ccou
nt d
irec
tly f
or c
erta
in a
spec
ts
MC
CLE
LLA
ND
AN
D E
LMA
N
kAp
i~i~
i~i~
i~i~
i~i'
.L:-
a..
rlrA
r~'A
rArA
rlr'
I :1
11: I
II. :
I :
I : I
',t'
ttt'l,
!,t'l
t'11111: III! I
:1 :
I'II
r:
flf~
ilr:I
:I:I
'i~
i~i~
T~i
!i!i
!i'
~ ~
I~ :
, .
JI-
FIG. 3. The connections orthe unit for the phoneme
Ik/,
cent
ered
ove
r T
ime
Slic
e :!4
. The
rectangle for this unit is highlighted with a bold outline. The
Ikl
unit
has
mut
ually
exc
iluto
ryco
nnec
tions
to a
ll th
e w
ord-
and
fea
ture
- lev
el u
nits
col
ored
eith
er p
urtly
or
who
lly in
blu
ck;
The
mor
e co
lorin
g on
a u
nits
' rec
tang
le. t
he g
reat
er th
e st
reng
th o
f the
con
nect
ion.
The
Ikl
unit
has
mut
ually
inhi
bito
ry c
onne
ctio
ns to
all
of th
e ph
onem
e-le
vel u
nits
col
ored
pur
tlyor
who
lly in
gre
y. A
gain
. the
rel
ativ
e am
ount
of
inhi
bitio
n is
indi
cate
d by
the
exte
nt o
f th
eco
lori
ng o
f th
e un
it: it
is d
irec
tly p
ropo
rtio
nal t
o th
e ex
tent
of
the
tem
pora
l ove
rlap
of
the
units
. of short-te
rm m
emor
y, s
uch
as th
e fa
ct th
at m
ore
info
rmat
ion
can
bere
tain
ed f
or s
hort
per
iods
of
time
if it
han
gs to
geth
er to
for
m a
coh
eren
tw
hole
, Pr
oces
sing
take
s pl
ace
thro
ugh
the
exci
tato
ry a
nd inhibitory interac-
tions
of t
he u
nits
in th
e T
race
. Uni
ts o
n di
ffere
nt le
vels
that
are
mut
ually
cons
iste
nt h
ave
mut
ually
exc
itato
ry c
onne
ctio
ns. w
hile
uni
ts o
n th
e sa
me
TR
AC
E M
OD
EL
MCCLELLAND AND ELMAN
. kl\p
visu
al m
o.de
l elim
inat
e th
ese
betw
een-
leve
l inh
ibito
.ry
co.n
nect
ions
. sin
ceth
ese
co.n
nect
io.n
s ca
n in
terf
ere
with
suc
c~ss
ful u
se o
.f pa
rti~
1 in
form
atio
n(McClelland, 1985; McClelland
, 198
6), L
ike
thes
e ne
wer
ver
sio.
ns o
.f th
evi
sual
mo.
del,
TR
AC
E li
kew
ise
co.n
tain
s , n
o. b
etw
een-
leve
l inh
ibiti
o.n.
We
will
see
that
this
fea
ture
o.f
TR
AC
E p
lays
a v
ery
impo
.rta
nt r
ole
in it
sab
ility
to. s
imul
ate
a nu
mbe
r o.
f em
piri
cal p
heno
.men
a.SO
Im:e
s of
TR
AC
E' s
lIrL'hitectllre,
The
insp
iratio
.n fo
.r th
e ar
chite
ctur
eo.
f T
RA
CE
go.
es b
ack
to. t
he H
EA
RSA
Y S
peec
h un
ders
tand
ing
syst
em(E
rman
& L
esse
r, 1
980;
Red
dy e
t al..
197
3), H
EA
RSA
Y in
trod
uced
the
no.ti
o.n
o.f a
Bla
ckbo
.ard
, a s
truc
ture
sim
ilar
to. t
he T
race
in th
e T
RA
CE
mo.
del.
The
mai
n di
ffer
ence
is th
at th
e T
race
is a
dyn
amic
pro
cess
ing
stru
ctur
e th
at is
sel
f-up
datin
g, w
hile
the
Bla
ckbo
.ard
in H
EA
RSA
Y w
asa
pass
ive
data
str
uctu
re th
ro.u
gh w
hich
ant
o.no
.mo.
us p
roce
sses
sha
red
info
.rm
atio
.n.
The
arc
hite
ctur
e o.
fTR
AC
E b
ears
a s
tro.
ng r
esem
blan
ce to
. the
"ne
ural
spec
trog
ram
" propo.sed by Cro.wder (1978, 1981) to
. acc
o.un
t fo.
r in
terf
er-
ence
eff
ects
bet
wee
n su
cces
sive
item
s in
sho.rt-term memo.ry.
. Lik
e ~
UI'
Tra
ce, C
row
ders neural spectro.gram pro.vides a dy
nam
ic w
o.rk
ing
mem
o.ry
rep
rese
ntat
io.n
o.f
a sp
oken
inpu
t. T
here
are
two.
impo
.rta
nt d
if-fe
renc
es b
etw
een
the
Tra
ce a
nd C
ro.w
der
s ne
ural
spe
ctro
gram
, ho.
wev
er.
Firs
t o.f
all,
the
neur
al s
pect
ro.g
ram
was
ass
umed
o.n
ly to
. rep
rese
nt th
efr
eque
ncy
spec
trum
o.f
the
spee
ch w
ave
o.ve
r tim
e; th
e T
race
, o.n
the
othe
rha
nd, r
epre
sent
s th
e sp
eech
wav
e in
:term
s o.
fa la
rge
num
ber
o.f d
itfer
ent
feature dimensio.ns, as well as in terms of the ph
o.ne
mes
and
wo.
rds
co.n
-si
sten
t with
the
patte
rn o
.f activatio.n at the feature level, In this re
gard
TR
AC
E m
ight
be
seen
as
an e
xten
sio.
n o.
f the
neu
ral s
pect
rogr
am id
ea,
The
sec
o.nd
dif
fere
nce
is th
at C
row
der
po.s
tula
tes
inhi
bito
.ry
inte
ract
io.n
sbe
twee
n de
tect
o.rs
fo.r
spe
ctra
l co.
mpo
.nen
ts s
pace
d up
to. s
ever
al h
undr
edm
illis
eco.
nds
apar
t. T
hese
inhi
bito
.ry
Inte
ract
io.n
s ex
tend
co.
nsid
erab
ly fa
r-th
er th
an th
o.se
we
have
incl
uded
in th
e fe
atur
e le
vel o
.f th
e T
race
. Thi
sdi
ffer
ence
do.
es n
o.t r
efle
ct a
' dis
agre
emen
t with
Cro
wde
rsa
ssum
ptio
.ns.
Tho
.ugh
we
have
no.
t , fo
.und
it n
eces
sary
, to.
ado
.pt t
his
assu
mpt
io.n
to. a
c-co
unt f
o.r
the
phen
o.m
ena
we fo.cus on in this article, lateral extensio.n o.f
inhi
bitio
.n in
the
time
do.m
ain
mig
ht w
ell a
llo.w
the
TR
AC
E fr
amew
o.rk
to.
inco
.rpo
.rat
e m
any
o.f
the
find
ings
Cro
.wde
r di
scus
ses
in th
e tw
o. a
rtic
les
cite
d.
i~i~
i~i~
;~;~
i~i'
Q.)
Q.)
..c:.
a..
~ 10
ID S
hi
j i '?
.
FI(j
, 4. T
he c
onne
clio
ns o
f Ih
e hi
ghlig
hled
uni
l for
Ihe
hig
h va
lue
on I
he V
ocal
ic f
elllu
redi
men
sion
in T
ime'
Slic
e 9
and
for
Ihe
high
lighl
ed u
nil f
or I
he w
ord
Ik' p
l starling in Slice
24. E
xcila
lory
con
necl
ions
are
rf(
rese
nled
in b
lack
. inh
ibito
ry c
onne
ctio
ns in
gre
y. a
s in
Fig. 3.
leve
l tha
t are
inco
.nsi
sten
t hav
e m
utua
lly in
hibi
to.r
y co.nnectio.ns, All co.n-
nect
io.n
s ar
e bi
dire
ctio
.nal
. Bid
irect
io.n
al e
xcita
to.r
y an
d in
hibi
to.r
y'co
.n-
nect
io.n
s o.
f the
unit fo.r
Ikl
cent
ered
o.v
er F
eatu
re-s
lice
24 (
co.u
ntin
g fr
om. 0
) ar
e sho.wn ,n Fig. 3; co.nnectio.ns far the high
valu
e o.
f the feature
Vo.
calic
in S
lice
9.an
d fo
.r th
ewo.
rd Ik
" pl with the
Ikl
cent
ered
o.v
er S
lice
24 a
re s
ho.w
n i~
Fig
. 4.
The
inte
ract
ive
activ
atio
.n mo.del o.f visual w
ard
reco
.gni
tio.n
(M
c-C
lella
nd &
Rum
elha
rt, 1
981)
incl
uded
inhi
bito
.ry
co.n
nect
io.n
s be
twee
nea
ch u
nit o
.n th
e fe
atur
e le
vel a
nd le
tters
that
did
no.
t co.
ntai
n th
e fe
atur
e,an
d be
twee
n ea
ch le
tter
unit
and
the
wo.
rds
that
did
no.
t co.
ntai
n th
e le
tter.
Thu
s th
e un
its f
o.r
T in
the
firs
t let
ter
po.s
itio.
n in
hibi
ted
the
units
fo.r
all
wo.rds that did no
.t be
gin
with
T. H
o.wever, mo.re recent versio.ns
o.f
the
Con
text
-Sen
sitiv
e T
lIni
ngof
Pho
nem
e U
nits
The
co.
nnec
tio.n
s, b
etw
een
the
feat
ure
and
pho.
nem
e le
vel d
eter
min
ewhat pattern
of activations o.ver the feature units will mo.st slrongly ac-
tivate the detecto.r fo
.r e
ach
phon
eme.
To. co.pe with the fact that the
feat
ures
rep
rese
ntin
g ea
ch p
ho.n
eme
vary
acc
o.rd
ing
to. t
he p
ho.n
emes
sur
-ro
undi
ng th
em, t
he m
odel
adj
usts
the
conn
ectio
ns f
rom
uni
ts a
l the
fea
-tu
re le
vel t
o. u
nits
at t
he n
hone
me
leve
l as
a fu
nctio
n nf
Iu'tiv:llinn" al 'hI"
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
TRACE land TRACE
In d
evel
opin
g T
RA
CE
, and
i(l t
ryin
g to
test
its
com
puta
tiona
l and
psy
-ch
olog
ical
ade
quac
y, w
e fo
und
that
we
wer
e so
met
imes
led
in r
athe
rdi
ffer
ent d
irec
tions
, We
wan
ted
to s
how
that
TR
AC
E c
ould
pro
cess
rea
lsp
eech
, but
to b
uild
a m
odel
that
did
so
it w
as n
eces
sary
to w
orry
abo
utex
actly
wha
t fea
ture
s m
ust b
e ex
trac
ted
from
the
spee
ch s
igna
l, ab
out
diff
eren
ces
in d
urat
ion
of d
iffe
rent
fea
ture
s of
dif
fere
nt p
hone
mes
, and
abou
t how
to c
ope
with
the
way
s in
whi
ch f
eatu
res
and
feat
ure
dura
tions
vary as a function of context. Obviously, these are important pr
oble
ms,
wor
thy
of c
onsi
dera
ble
atte
ntio
n. H
owev
er, c
once
rn w
ith th
ese
issu
este
nded
to o
bscu
re a
ttent
ion
to th
e fu
ndam
enta
l pro
pert
ies
of th
e m
odel
and
the
mod
el's
abi
lity
to a
ccou
nt f
or b
asic
asp
ects
of
the
psyc
h(jlo
gica
l
data
obt
aine
d in
man
y ex
perim
ents
.T
o co
pe w
ith th
ese
conf
lictin
g go
als,
we
have
dev
elop
ed tw
o di
ffer
ent
vers
ions
of
the
mod
el, c
alle
d T
RA
CE
1 a
nd T
RA
CE
II,
Bot
h m
odel
s
spri
ng f
rom
the
sam
e ba
sic
assu
mpt
ions
, but
foc
us o
n di
ffer
ent a
spec
tsof
spe
ech
perc
eptio
n. T
RA
CE
1 w
as d
esig
ned
to a
ddre
ss s
ome
of th
ech
alle
nges
pos
ed b
y th
e ta
sk o
f rec
ogni
zing
pho
nem
es f
rom
rea
l spe
ech,
Thi
s ve
rsio
n of
the
mod
el is
des
crib
ed in
det
ail i
n E
lman
and
McC
lella
nd(i
n pr
ess)
. With
this
ver
sion
of
the
mod
el, w
e w
ere
able
to s
how
that
the
TR
AC
E f
ram
ewor
k co
uld
inde
ed b
e us
ed to
pro
cess
rea
l spe
ech-
albe
itfr
om a
sin
gle
spea
ker
utte
ring
isol
ated
mon
osyl
labl
es a
t thi
s po
int.
We
wer
e al
so a
ble
to d
emon
stra
te th
e ef
ficac
y of
the
idea
of a
djus
ting
feat
ure
to p
hone
me
conn
ectio
ns o
n th
e ba
sis
of a
ctiv
atio
ns p
rodu
ced
by s
ur-
roun
ding
con
text
. With
con
nect
ion
stre
ngth
adj
ustm
ent i
n pl
ace
' the
mod
el w
as a
ble
to id
entif
y th
e st
op c
onso
nant
in 9
0% o
f a
set b
f is
olat
edm
onos
ylla
bles
cor
rect
ly, u
p fr
om 7
9% w
ith a
n in
vari
ant s
et o
f co
nnec
-tio
ns. T
his
leve
l of
perf
orm
ance
is c
ompa
rabl
e to
wha
t has
bee
n ac
hiev
edby other machine-ba
sed
phon
eme
iden
tific
atio
n sc
hem
es (
e,g.
, Kop
ec,
1984
) an
d ill
ustr
ates
the
prom
ise
of th
e co
nnec
tion
stre
ngth
adj
ustm
ent
sche
me
for
copi
ng w
ith v
aria
bilit
y du
e to
loca
l pho
netic
con
text
. Ide
asfo
r ex
tend
iqg
the
conn
ectio
n st
reng
th a
djus
tmen
t sch
eme
to d
eal w
ith th
ew
ays
in w
hich
cue
s to
pho
nem
e id
entif
icat
ion
vary
with
glo
bal v
aria
bles
(rat
e, s
peak
er c
hara
cter
istic
s, e
Jc,)
are
con
side
red
in th
e ge
nera
l dis
cus-
sion
.T
RA
CE
II,
the
vers
ion
desc
ribe
d in
the
pres
ent p
aper
, was
des
igne
dto
acc
ount
prim
arily
for
lexi
cal i
nflu
ence
s on
pho
nem
e pe
rcep
tion
and
for
wha
t is
know
n ab
out o
n-lin
e re
cogn
ition
of
wor
ds, t
houg
h w
e us
e it
to il
lust
rate
how
cer
tain
oth
er a
spec
ts o
f ph
onem
e pe
rcep
tion
fall
out o
fth
e T
RA
CE
fra
mew
ork,
Thi
s ve
rsio
n of
the
mod
el is
act
ually
a s
impl
ifie
dve
rsio
n of
TR
AC
E 1
. Mos
t im
port
antly
, we
elim
inat
ed th
e co
nnec
tion-
stre
ngth
adj
ustm
ent f
acili
ty, a
nd w
e re
plac
ed th
e re
al s
peec
h in
puts
toT
RA
CE
I w
ith m
ock
spee
ch, T
his
moc
k sp
eech
inpu
t con
sist
ed o
f ov
er-
lapp
ing
but c
onte
xtua
lly in
vari
ant s
peci
fica
tions
of
the
feat
ures
of
suc-
cess
ive
phon
emes
, Obv
ious
ly, t
hen,
TR
AC
E I
I si
dest
eps
man
y fu
nda-
mental issues about speech, But it makes "it
muc
h ea
sier
to s
ee h
ow th
em
echa
nism
can
acc
ount
for
a nu
mbe
r of
asp
ects
of p
hone
me
and
wor
dre
cogn
ition
, A n
umbe
r of
furt
her
sim
plify
ing
assu
mpt
ions
wer
e m
ade
tofa
cilit
ate
exam
inat
ion
of b
asic
pro
pert
ies
of th
e in
tera
ctiv
e ac
tivat
ion
pro-
cess
es ta
king
pla
ce w
ithin
the
mod
el,
The
fol
l9w
ing
sect
ions
des
crib
e T
RA
CE
II
in m
ore
deta
il, F
irst
we
cons
ider
the
spec
ific
atio
ns o
f th
e m
ock-
spee
ch in
()ut
to th
e m
odel
, and
then
we
cons
ider
the
units
and
con
nect
ions
that
mak
e up
the
Tra
ce a
t
each
of t
he th
ree
leve
ls,
Moc
k-Sp
eech
Inp
uts
The
inpu
t to
TR
AC
E I
I w
as a
ser
ies
of s
peci
fica
tions
for
inpu
ts to
uni
tsat
the
feat
ure
leve
l, on
e fo
r ea
ch 2
5-m
s tim
e sl
ice
of th
e m
ock
utte
ranc
e,T
hese
spe
cific
atio
ns w
ere
gene
rate
d by
a s
impl
e co
mpu
ter
prog
ram
from
a se
quen
ce o
f to
-be-
pres
ente
d se
gmen
ts p
rovi
ded
by th
e hu
man
use
r of
the
sim
ulat
ion
prog
ram
. The
allo
wed
seg
men
ts c
onsi
sted
of
the
stop
con
-so
nant
s Ib
l, Ip
l, Id
l, It/
,lgI,
an
d Ik
l, the fricatives
Isl
and
ISI
sh" as in
ship
), the liquids
III
and
Irl,
and the vowels
Ia!
(as
in "
pot"
),
IiI
(as
in
beet
),
lul
(as
in "
boot
"), and
rI
(as
in "
but
).
rI
was
als
o us
ed to
repr
esen
t red
uced
vow
els
such
as
the
seco
nd v
owel
in "
targ
et." There
was
als
o a
"sile
nce"
segment represented by
I-I.
Sp
ecia
l seg
men
ts, s
uch
as a segment halfway between
Ibl
and
Ipl,
wer
e al
so u
sed;
thei
r pr
oper
ties
are
desc
ribed
in d
escr
iptio
ns o
f the
rel
evan
t sim
ulat
ions
,A
set
of
seve
n di
men
sion
s w
as u
sed
in T
RA
CE
lIto represent the
feat
ure-
leve
l inp
uts,
Fiv
e of
the'
dim
ensi
ons
(Con
sona
ntal
, Voc
alic
, Dif-
fuse
ness
, Acu
tene
ss, a
nd V
oici
ng)
wer
e ta
ken
from
cla
ssic
al w
ork
inph
onol
ogy
(Jak
obso
n, F
ant,
& H
alle
, 195
2), t
houg
h w
e tr
eat e
ach
of th
ese
dim
ensi
ons
as c
ontin
ua, i
n th
e sp
irit
ofO
den
and
Mas
saro
(197
8), r
athe
rth
an a
s bi
nary
fea
ture
s, A
six
th d
imen
sion
, Pow
er, w
as in
clud
ed b
ecau
seit
has
been
foun
d us
eful
for
phon
eme
iden
tific
atio
n in
var
ious
mac
hine
syst
ems
(e,g
., R
eddy
, 197
6), a
nd it
was
inco
rpor
ated
her
e to
add
an
ad-
ditio
nal d
imen
sion
to in
crea
se th
e di
ffer
entia
tion
of th
e vo
wel
s an
d co
n-so
nant
s, T
he s
even
th d
imen
sion
, the
am
plild
de o
f th
e bu
rst o
f no
ise
that
occu
rs a
t the
beg
inni
ng o
f w
ord
initi
al s
tops
, was
incl
uded
to p
rovi
de a
nad
ditio
nal b
asis
for
dist
ingu
ishi
ng th
e st
op c
onso
nant
s, w
hich
oth
erw
ise
diff
ered
fro
m e
ach
othe
r on
onl
y on
e or
two
dim
ensi
ons,
Of
cour
se, t
hese
phon
eme
leve
l in
prec
edin
g an
d fo
llow
ing
time
slic
es, F
or e
xam
ple,
whe
nthe phoneme
It I
is preceded or followed by the vowel
Iii,
the feature
pattern corresponding to the
It I
is very different than it is when the
It I
preceded or followed by another vowel, such as
la/.
Acc
ordi
ngly
, whe
n
the unit for
Iii
in a particular sl
ice:
is a
ctiv
e, it
cha
nges
the pattern of
connections for units for
It I
in
pre
cedi
ng a
nd fo
llow
ing
slic
es.
TR
AC
E M
OD
EL
dim
ensi
ons
an;:
inte
ntio
nal s
impl
ific
atio
ns o
f th
e re
al a
cous
tid s
truc
ture
of s
peec
h, in
muc
h th
e sa
me
way
that
the
font
use
d by
McC
lella
nd a
ndR
umel
hart
(19
81)
in th
e in
tera
ctiv
e-ac
tivat
ion
mod
el o
f vi
sual
wor
d re
c-og
nitio
n W
as a
n in
tent
iona
l sim
plifi
catio
n. o
f the
rea
l str
uctu
re o
f pr
int.
Eac
h di
men
sion
was
div
ided
into
eig
ht v
alue
ran
ges.
Eac
h ph
onem
ew
as a
ssig
ned
a va
lue
on e
ach
dim
ensi
on; t
he v
alue
s on
the
Voc
alic
, Oif
-fu
sene
ss, a
nd A
cute
ness
dim
ensi
ons
for
the
phon
emes
in th
e ut
tera
nce
!tik
.p!
are
show
n in
Fig
. 2, T
he f
ull s
et o
f va
lues
are
sho
wn
in T
able
I,N
umbe
rs in
the
cells
of t
he ta
ble
indi
cate
whi
ch v
alue
on
the
indi
cate
ddi
men
sion
was
mos
t str
ongl
y ac
tivat
ed b
y th
e fe
atur
e pa
ttern
for
the
indi
cate
d ph
onem
e, V
alue
s ra
nge
from
I
very low
to 8 =
very high,
The
last
two
dim
ensi
ons
wer
e al
tere
d fo
r th
e ca
tego
rica
l per
cept
ion
and
trad
ing
rela
tions
sim
ulat
ions
,V
alue
s w
ere
assi
gned
to a
ppro
xim
ate
the
valu
es r
eal p
hone
mes
wou
ldha
ve o
n th
ese
dim
ensi
ons
and
to m
ake
phon
emes
that
fall
into
the
. sam
eph
onet
ic c
ateg
ory
have
iden
tical
val
ues
on m
any
of th
e di
men
sion
s, T
hus,
.fo
r ex
ampl
e, a
ll st
op c
onso
nant
s w
ere
assi
gned
the
sam
e va
lues
on
the
Pow
er, V
ocal
ic, a
nd C
onso
nant
al d
imen
sion
s, W
e do
not
cla
im to
hav
eca
ptur
ed th
e de
tails
of p
hone
me
sim
ilarit
y ex
actly
, Ind
eed,
one
can
not
do s
o in
a fi
xed
feat
ure
set b
ecau
se th
e si
mila
ritie
s va
ry a
s a
func
tion
ofco
ntex
t. H
owev
er, t
he f
eatu
re s
ets
do h
ave
the
prop
erty
that
the
feat
ure
patte
rn f
or o
ne p
hone
me
is m
ore
sim
ilar
to th
e fe
atur
e pa
ttern
for
oth
erph
onem
es in
the
sam
e ph
gnet
ic c
ateg
ory
(sto
p, f
rica
tive,
liqu
id, o
r vo
wel
)th
an it
is to
the
patte
rns
for
phon
emes
in o
ther
cat
egor
ies.
Am
ong
the
stop
s, th
ose
phon
emes
sha
ring
pla
ce o
f ar
ticul
atio
n or
voi
cing
are
mor
esi
mila
r th
an th
ose
shar
ing
neith
er a
ttrib
ute.
The
cor
rela
tions
of
the
feat
ure
patte
rns
for
the
15 p
hone
mes
use
d ar
esh
own
in T
able
2. I
t is
thes
e co
rrel
atio
ns o
f th
e pa
ttern
s as
sign
ed to
the
~ -
!II :J
, !II
II:)
I:!
1.1:
1 is '"
:;;
'")
~ 1
!
"" ~
~~
~~
~ ~
~~
~~
I~
....
-D - -D
..., ~
"0 "1
r-; r-; I ~
0 -
;:::~
I~~~
~T
AB
LE I
Phon
eme
Feal
ure
Val
ues
Use
d in
TR
AC
E I
I
Phun
eme
Pow
Voc
alic
Dif
fuse
AC
Ule
CO
Ins.
Voi
ced
Our
s.
11.
Co,
r)
- "0
~ "
" on
II:
) ..
01 ,- :J,.
,r)
~ I~
;:::~
~
I~;::
:~~~
:;;
~8~~
~
00...
.
"! '")
~~ I
~
~ I
~~
~8 I
~~
~
~ 18
I ~~
~ I I ~"'!
"',
....
'")
r--
'") '"
).:.
:;;.
,
,r)
"ii .
,r) :0-
..c !II
..!!
.... !II
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
diff
eren
t pho
nem
es. r
athe
r th
an th
e ac
tual
val
ues
assi
gned
to p
artic
ular
phon
emes
or
even
the
labe
ls a
ttach
ed to
the
diff
eren
t moc
k-sp
eech
di-
men
sion
s. th
at d
eter
min
e th
e be
havi
or o
f the
sim
ulat
ion
mod
el.
sinc
e it
is th
ese
corr
elat
ions
that
det
erm
ine
how
muc
h an
inst
ance
of o
ne p
ho-
nem
e w
ill te
nd to
exc
ite th
e de
tect
or f
or a
noth
er,
The
feat
ure
patte
rns
wer
e co
nstr
u~t
ed in
suc
h a
way
that
it w
as p
ossi
ble
to c
reat
e fe
atur
e pa
ttern
s th
at w
ould
act
ivat
e tw
o di
ffere
nt p
hone
mes
inth
e sa
me
cate
gory
(st
op. l
iqui
d. f
rica
tive.
or vowel) to an equal extent
by a
vera
ging
the
valu
es o
f th
e tw
o ph
onem
es o
n on
e or
mor
e di
men
sion
s,In
this
way
, it w
as a
sim
ple
mat
ter
to m
ake
up a
mbi
guou
s in
puts
. hal
fway
betw
een
two
phon
times
. or
to c
onst
ruct
con
tinua
var
ying
bet
wee
n ' tw
oph
onem
es o
n on
e or
mor
e di
men
sion
s.T
he f
eatu
re s
peci
fica
tion
of e
ach
phon
eme
in th
e in
put s
trea
m e
xten
ded
over
II
time
slic
es o
f th
e in
put.
The
str
engt
h of
the
patte
rn g
rew
to a
peak
at t
he 6
th s
lic~
and
fell
off a
gain
. as
illus
trat
ed in
Fig
, 2, P
eaks
of
succ
essi
ve p
hone
mes
wer
e se
para
ted
by 6
slic
es, T
hus.
spe
cifi
catio
ns o
fsu
cces
sive
pho
nem
es o
verl
appe
d. a
s th
ey d
o in
rea
l spe
ech
(Fow
ler.
198
4;L
iber
man
, 197
0).
Gen
eral
ly. t
here
wer
e no
cue
s to
wor
d boundaries in the speech
stre
am- t
he fe
atU
lie s
peci
ficat
ion
for
the
last
pho
nem
e of
one
wor
dov
erla
pped
with
the
, fir
st p
hone
me
of th
e ne
xt in
just
the
sam
e w
ay f
eatu
resp
ecif
icat
ions
of
adj~
\cen
t pho
nem
es o
verl
ap w
ithin
wor
ds, H
owev
er. e
n-tir
e ut
tera
nces
pre
sent
ed to
the
mod
el fo
r pr
oces
sing
-whe
ther
they
wer
ein
divi
dual
syl
labl
es.,
wor
ds. o
r st
rings
of w
ords
-wer
e pr
eced
ed a
nd fo
l-lo
wed
by
sile
nce,
Sile
nce
was
nol
sim
ply
the
abse
nce
ofan
y in
put;
rath
er.
it w
as a
pat
tern
of
feat
ure
valu
es. j
ust l
ike
the
phon
emes
, Thu
s. a
nin
thva
lue
on e
ach
of th
e is
even
dim
ensi
ons
was
ass
ocia
ted
with
sile
nce,
The
seva
lues
wer
e ac
tual
ly o
utsi
de th
e ra
nge
of v
alue
s w
hich
occ
urre
d in
the
phon
emes
them
selv
es. s
o th
at th
e fe
atur
es o
f si
lenc
e w
ere
com
plet
ely
unco
rrel
ated
with
the
feat
ures
of
any
of th
e ph
onem
es u
sed,
The
Pho
nem
e Le
vel a
nd F
eatu
re- P
hone
me
Con
nect
ions
At t
he p
hone
me
leve
l. th
ere
is a
set
of detectors for each of the 15
phon
emes
list
ed a
bove
, In
addi
tion.
ther
e is
a s
et of detectors for the
pres
ence
of
sile
nce,
The
se s
ilenc
e de
tect
ors
are
trea
ted
like
all o
ther
phon
eme
dete
ctor
s. E
ach
mem
ber
of th
e se
t of
dete
ctor
s fo
r a
part
icul
arph
onem
e is
cen
tere
d ov
er a
diff
eren
t tim
e ~
;ce
at th
e fe
atur
e le
vel,
and
the
cent
ers
are
spac
ed th
ree
time
slic
es a
part
. The
uni
t cen
tere
d ov
er a
part
icul
ar s
lice
rece
ived
exc
itato
ry in
put f
rom
fea
ture
uni
ts in
a r
ange
of
slic
es, e
xten
ding
bot
h fo
rwar
d an
d ba
ckw
ard
from
the
slic
e in
whi
ch th
eph
onem
e un
it is
loca
ted,
It a
lso
send
s ex
cita
tory
fee
dbac
k do
wn
to th
esame feature units in the same range of slices.
The
con
nect
ion
stre
ngth
s be
twee
n th
e fe
atur
e-le
vel u
nits
and
a p
artic
-ul
ar p
hone
me-
leve
l uni
t exa
ctly
mat
ch th
e fe
atur
e pa
ttern
the
phon
eme
is g
iven
in it
s in
put s
peci
fica
tion,
Thu
s. a
s ill
ustr
ated
in F
ig. 3
. the
strengths of the connections between the node for
Ikl
cent
ered
ove
r T
ime
Slic
e 24
and
the
node
s at
the
feat
ure
leve
l are
exa
ctly
pro
port
iona
l to
the
patte
rn o
f in
put t
o th
e fe
atur
e le
vel p
rodu
ced
by a
n in
put s
peci
ficat
ion
containing the featur~s of
Ikl
cent
ered
in th
e sa
me
time
slic
e.T
here
are
inhi
bito
ry c
onne
ctio
ns b
etw
een
units
at t
he p
hone
me
leve
l.U
nits
inhi
bit e
ach
othe
r to
the
exte
nt th
at th
e sp
eech
obj
ects
they
sta
ndfo
r re
pres
ent a
ltern
ativ
e in
terp
reta
tions
of
the
cont
ent o
f th
e sp
eech
stre
am a
t the
sam
e po
int i
n th
e ut
tera
nce.
Not
e th
at. a
lthou
gh th
e fe
atur
esp
ecif
icat
ion
of a
pho
nem
e is
spr
ead
over
a w
indo
w o
f II
slic
es, s
ucce
s-si
ve p
hone
mes
in th
e in
put h
ave
thei
r , c
ente
rs 6
slic
es a
part
. Thu
s ea
chph
onem
e-le
vel u
nit i
s th
ough
t of a
s sp
anni
ng 6
feat
ure-
level slices. as
illus
trat
ed in
Fig
. 3. E
ach
unit
inhi
bits
oth
ers
in p
ropo
rtio
n to
thei
rov
erla
p, T
hus,
a p
hone
me
dete
ctor
inhi
bits
oth
er p
hone
me
dete
ctor
scen
-te
red
over
the
sam
e sl
ice
twic
e as
muc
h as
it in
hibi
ts d
etec
tors
cen
tere
d3
slic
es a
way
, and
inhi
bits
det
ecto
rs c
ente
red
6 or
mor
e sl
ices
aw
ay n
otat all, (
Fc'
lIlIIr
e Le
l'el V
nit.
f and
Co"
"ect
ion.
The
uni
ts a
t the
fea
ture
leve
l are
det
ecto
rs f
or f
eatu
res
of th
e sp
eech
stre
am a
t par
ticul
ar , m
omen
ts in
tim
e. I
n T
RA
CE
II.
ther
e w
as a
uni
t for
each of the nine values on each of the seven dimensions in each time
slic
e of
the
Tra
ce, T
he f
igur
es s
how
thre
e se
ts o
f fe
atur
e un
its in
sev
eral
time
slic
es, U
nits
for
fea
ture
s on
the
sam
e di
men
sion
with
in th
e sa
me
time
slic
e ar
e m
utua
lly in
hibi
tory
, Thu
s, th
e un
it fo
r th
e hi
gh v
alue
of
the
Voc
alic
dim
ensi
on in
Tim
e Sl
ice
9 in
hibi
ts th
e un
its f
or o
ther
val
ues
onth
e sa
me
dilJ
lens
ion
in th
e sa
me
time
slic
e. a
s ill
ustr
ated
in F
ig. 4
. Thi
sfig
ure
also
illu
stra
tes
the
mut
ually
exc
itato
ry c
onne
ctio
ns o
f th
is s
ame
feat
ure
unil
with
uni
ts a
t the
pho
nem
e le
vel.
In th
e ne
xt s
ectio
n w
e re
-de
scri
be th
ese
conn
ectio
ns f
rom
the
poin
t of
view
of
the
phon
em~
leve
l,
Wor
d V
nits
and
Wor
d-P
hone
me
Con
nec'
tions
The
re is
a u
nit f
or e
very
wor
d in
eve
ry ti
me
slic
e, E
ach
of th
ese
units
repr
esen
ts a
dif
fere
nt h
ypot
hesi
s ab
out a
wor
d id
entit
y an
d st
artin
g lo
-cation in the 'Irace. For example, the unit for the word
Ik.p
l in Slice 24
. (hi
ghlig
hted
in F
ig, 4
) re
pres
ents
the
hypo
thes
is th
at th
e in
put c
onta
ins
the
wor
d " c
up"
star
ting
in S
lice
24, M
ore
exac
tly, i
t rep
rese
nts
the
hy-
poth
esis
that
the
inpu
t con
tain
s th
e w
ord
" cup
" w
ith it
s fi
rst p
hone
me
centered in Time Slice 24.
Wor
d un
its r
ecei
ve e
xcita
tion
from
the
units
for
the
phon
emes
they
cont
ain
in a
ser
ies
of o
verl
appi
ng w
indo
ws.
Thu
s, th
e un
it fo
r " c
up" in
Time Slice 24 will receive excitation from
Ikl
in s
lices
nei
ghbo
ring
Slic
e
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
24, from
rI
in slices neighboring Slice 30, and from
Ipl
in slices neigh-
bori
ng S
lice
36. A
s w
ith th
e fe
atur
e-ph
onem
e co
nnec
tions
, the
se c
on-
nect
ions
are
str
onge
st a
t the
cen
ter
of th
e w
indo
w a
nd fa
ll of
f lin
earl
y on
either side,
The
inhi
bito
ry c
onne
ctio
ns a
t the
wor
d le
vel a
re s
imila
r to
thos
e at
the
phon
eme
leve
l, A
gain
, the
str
engt
h of
the
inhi
bitio
n be
twee
n tw
o w
ord
units
dep
ends
on
the
num
ber
of ti
me
slic
es in
whi
ch th
ey o
verl
ap. T
hus,
units
rep
rese
ntin
g al
tern
ativ
e in
terp
reta
tions
of
the
sam
e st
retc
h of
pho
-ne
me
units
are
str
ongl
y co
mpe
titiv
e, b
ut u
nits
repr
esen
ting
inte
rpre
ta-
tions
of
nono
verl
appi
ng s
eque
nces
of
phon
emes
~o
not c
ompe
te a
t all.
TR
AC
E I
I ha
s de
tect
ors
for
the 211 words found in a computerized
phon
etic
wor
d lis
t tha
t met
all
of th
e fo
llow
ing
cons
trai
nts:
(a)
the
wor
dco
nsis
ted
only
of t
he p
hone
mes
list
ed a
bove
; (b)
it w
as n
ot a
n in
flect
ion
of s
ome
othe
r w
ord
that
cou
ld b
e m
ade
by a
ddin
g "-
ed," "
os, " or
ing
; (c)
the
wor
d to
geth
er w
ith it
s "-
ed,"
" -s," and "
ing" inflections
occu
rred
wiih
a f
requ
ency
of
20 o
r m
ore
per
mill
ion
in th
e K
ucer
a an
dFr
anci
s (1
967)
wor
d co
unt.
It is
not
cla
imed
that
the
mod
el's
lexi
con
is a
nex
haus
tive
list o
f w
ords
mee
ting
this
cri
teri
on, s
ince
the
com
pute
rize
dph
onet
ic le
xico
n w
as n
ot c
ompl
ete,
but
it is
rea
sona
bly
clos
e to
this
, To
mak
e sp
ecif
ic p
oint
s ab
out t
he b
ehav
ior
of th
e m
odel
, det
ecto
rs f
or th
efo
llow
ing
thre
e w
ords
not
in th
e m
ain
list w
ere
adde
d: "
blus
h,
" "
rega
l,an
d "
slee
t."
The
mod
el a
lso
had
dete
ctor
s at
the
wor
d le
vel f
or s
ilenc
e(I
-I),
w
hich
was
trea
ted
like
it on
e-ph
onem
e w
ord,
inde
fini
tely
, tho
ugh
for
prac
tical
pur
pose
s it
is a
lway
s te
rmin
ated
. aft
er
som
e pr
edet
erm
ined
num
ber
of ti
me
cycl
es h
as ~
Iaps
ed,
...
Pres
enta
tion
tlnd
Proc
e!jti
'ing
of tm
Ulle
rtln
c'
Bef
ore
proc
essi
ng o
f an
utte
ranc
e be
gins
, the
act
ivat
ions
of
all o
f th
eun
its a
re s
et a
t the
ir r
estin
g va
lues
. At t
he s
tart
of processing, the input
to th
e in
itial
slic
e of
feat
ure
units
is a
pplie
d, A
ctiv
atio
ns a
re th
en u
pdat
ed,
endi
ng th
e in
itial
tim
e cy
cle,
On
the
next
tim
e cy
cle,
the
inpu
t to
the
next
slic
e of
fea
ture
uni
ts is
app
lied
, and
exc
itato
ry a
nd in
hibi
tory
inpu
ts to
each
uni
t res
ultin
g fr
om th
e pa
ttern
of
activ
atio
n le
ft a
t the
end
of
the
prev
ious
tim
e sl
ice
are
com
pute
d,It
is im
port
ant t
o re
mem
ber
that
the
inpu
t is
appl
ied
, one
slic
e at
atim
e, p
roce
edin
g fr
om le
ft to
rig
ht a
s th
ough
it w
ere
an ongoing stream
of s
peec
h "w
ritin
g on
" the successive time sl
ices
of t
he T
race
, The
in-
tera
ctiv
e-ac
tivat
ion
proc
ess
is o
ccur
ring
thrc
ugho
ut th
e Trace on each
time
slic
e, e
ven
thou
gh th
e ex
tern
al b
otto
m-u
p in
put i
s on
ly c
omin
g in
toth
e fe
atur
e un
its o
ne s
lice
at a
tim
e. P
roce
ssin
g in
tera
ctio
ns c
an c
ontin
ueev
en a
fter
the
left
to r
ight
sw
eep
thro
ugh
the
inpu
t rea
ches
the
end
of th
eT
race
. Onc
e th
is h
appe
ns, t
here
are
sim
ply
no n
ew in
put s
peci
fica
tions
appl
ied
to th
e T
race
; the
con
tinui
ng in
tera
ctio
ns a
re b
ased
on
wha
t has
alre
ady
been
pre
sent
ed. T
his
inte
ract
ion
proc
ess
is a
ssum
ed to
con
tinue
Det
ails
of P
roce
ssin
g D
ynam
kti,
The
inte
ract
ive
activ
atio
n pr
oces
s in
the
Tra
ce m
odel
follo
ws
thed
y-na
mic
ass
umpt
ions
laid
out
in M
cCle
lland
and
Rum
elha
rt (
1981
), E
ach
unit
has
a re
stin
g ac
tivat
ion
valu
e ar
bitr
arily
set
at 0
, a m
axim
um a
ctiv
atio
nvalue arbitrarily set at 1,0,
and
a m
inim
um a
ctiv
atio
n se
t at -
.3.
On
ever
y tim
e cy
cle
of p
roce
ssin
g, a
ll th
e w
eigh
ted
exci
tato
ry a
nd in
hibi
tory
sign
als
impi
ngin
g up
on a
uni
t are
add
ed to
geth
er, T
he s
igna
l fro
m o
neun
it to
ano
ther
is ju
st th
e ex
tent
to w
hich
its
activ
atio
n ex
ceed
s 0;
if it
sac
tivat
ion
is le
ss th
an 0
, the
sig
nal '
is 0
.1 G
loba
l lev
el-s
peci
fic
exci
tato
ry,
inhi
bito
ry, a
nd d
ecay
par
amet
ers
scal
e th
e re
lativ
e m
agni
tude
s of
dilf
eren
ttypes of influences on the activation of each unit. Values for these pa-
ram
eter
s ar
e gi
ven
belo
w,
Aft
er th
e ne
t inp
ut to
eac
h un
it ha
s be
en d
eter
min
ed b
ased
on
the
prio
rac
tivat
ions
of
the
units
, the
act
ivat
ions
of
the
units
arc
all
upda
ted
for
the
next
pro
cess
ing
cycl
e, T
he n
ew v
alue
of
the
activ
atio
n of
the
unit
isa
func
tion
of it
s ne
t inp
ut f
rom
oth
er u
nits
and
its
prev
ious
act
ivat
ion
valu
e, T
he e
xact
fun
ctio
n us
ed (
see
McC
lella
nd &
Rum
elha
rt, 1
981)
kee
ps
unit
activ
atio
ns b
ound
ed b
etw
een
thei
r m
axim
um a
nd m
inim
um v
alue
s.G
iven
a c
onst
ant i
nput
, the
act
ivat
ion
of a
uni
t will
sta
biliz
e at
a p
oint
betw
een
its m
axim
um a
nd m
inim
um th
at d
epen
ds o
n th
e st
reng
th a
ndsi
gn (
exci
tato
ry o
r in
hibi
tory
) of
the
inpu
t. W
ith a
net
inpu
t of 0, the
activ
atio
n of
the
unit
will
gra
dual
ly r
etur
n to
its
rest
ing
leve
l.E
ach
proc
essi
ng ti
me
cycl
e co
rres
pond
s to
a s
ingl
e tim
e sl
ice
at th
efe
atur
e le
vel.
Thi
s is
act
ually
a p
aram
eter
of
the
mod
el-t
here is no
intr
insi
c re
ason
why
ther
e sh
ould
be
a si
ngle
cyc
le o
f th
e in
tera
ctiv
e-ac
tivat
ion
proc
ess
sync
hron
ized
with
the
arri
val o
f ea
ch s
ucce
ssiv
e sl
ice
of th
e in
put.
A h
ighe
r ra
te o
f cy
clin
g w
ould
spe
ed th
e pe
rcol
atio
n of
effe
cts
of n
ew in
put t
hrou
gh th
e ne
twor
k re
lativ
e to
the
rate
of
pres
en-
tatio
n,
Out
put A
ssum
ptio
ns
Act
ivat
ions
of
units
in th
e T
race
ris
e an
d fa
ll as
the
inpu
t sw
eeps
acr
oss
the
feat
ure
leve
l. A
t any
tim
e, a
dec
isio
n ca
n be
mad
e ba
sed
on th
e pa
ttern
of a
ctiv
atio
n as
it s
tand
s at
that
mom
ent.
The
dec
isio
n m
echa
nism
can
,w
e as
sum
e, b
e di
rect
ed to
con
side
r th
e se
t of u
nits
loca
ted
with
in a
sm
all
win
dow
of
adja
cent
slic
es w
ithin
any
leve
l. T
he u
nits
in th
is s
et th
enI
At t
he w
ord
leve
l, th
e in
hibi
tory
sig
nal f
rom
one
wor
d to
ano
ther
is ju
st. t
he s
quar
e of
the
exte
nt to
whi
ch th
e se
nder
s ac
tivat
ion
exce
eds
zero
. Thi
s te
nds
to s
moo
th I
he e
fli:.
:hof
man
y un
its s
udde
nly
beco
min
g sl
ight
ly a
ctiv
ated
. and
of
cour
se il
als
o in
crea
ses
Ihe
dom
inan
ce o
f on
e ac
tive
wor
d ov
er m
any
wea
kly
activ
ated
one
s,
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
Sj =
kaj,
Eve
n w
ith a
ll th
e si
mpl
ifica
tions
des
crib
ed a
bove
. the
TR
AC
E m
odel
still
has
a n
umbe
r of
free
par
amet
ers.
The
se p
aram
eter
s ar
e lis
ted
in T
hble
3, I
t sho
uld
be n
oted
that
par
amet
ers
are
not i
f'! g
ener
al d
irect
ly c
ompa
-ra
blea
cros
s le
vels
, For
exa
mpl
e. p
hone
me-
to-p
hone
me
and
wor
d-to
-w
ord
inhi
bitio
n ar
e no
t dir
ectly
com
para
ble
to e
ach
othe
r or
to f
eatu
re-
to-p
hone
me
inhi
bitio
n. s
ince
fea
ture
-lev
el u
nits
con
lpet
e on
ly w
ithin
asi
ngle
slic
e. w
hile
pho
nem
e an
d w
ord
units
com
pete
in p
ropo
rtio
n to
thei
rov
erla
p,T
here
was
som
e tr
ial a
od e
rror
in fi
ndin
g 'h
e se
t of p
aram
eter
s us
ed in
the
repo
rted
sim
ulat
ions
. but
. in
gene
ral.
the
qual
itativ
e be
havi
or o
f the
mod
el w
as r
emar
kabl
y ro
bust
und
er p
aram
eter
var
iatio
ns. a
nd n
o sy
s~te
mat
ic s
earc
h of
the
spac
e of
par
amet
ers
was
nec
essa
ry, G
ener
ally
. ma-
nipu
latio
ns o
f pa
ram
eter
s si
mpl
y in
flue
nce
t hem
agni
tude
or
the
timin
gof
one
eff
ect o
r an
othe
r w
ithou
t cha
ngin
g th
e ba
sic
natu
re o
f th
e ef
fect
sob
serv
ed, F
or e
xam
ple.
str
onge
r bo
ttom
-up
exci
tatio
n sp
eeds
thin
gs u
pan
d ca
n in
dire
ctly
influ
ence
the
si~
e of
top-
dow
n ef
fects. since. for ex-
ampl
e. s
tron
ger
wor
d le
vel a
ctiv
atio
ns p
rodu
ce s
tron
ger
feed
back
to th
e. p
hone
me
leve
l. St
rong
er to
p-do
wn
exci
tatio
n. o
f cou
rse.
dire
ctly
influ
-en
ces
the
mag
nitu
de o
f le
xica
l eff
ects
, The
one
par
amet
er th
at a
ppea
red
to in
fluen
ce th
e qu
alita
tive
beha
vior
of t
he m
odel
was
the
stre
ngth
of
with
in- l
evel
inhi
bitio
n, S
tron
ger
with
in-l
evel
inhi
bitio
n m
ake
the
mod
elco
mm
it its
elf
mor
e st
rong
ly to
slig
ht e
arly
dif
fere
nces
in a
ctiv
atio
n am
ong
com
petin
g al
tern
ativ
es. T
here
was
. the
refo
re. s
ome
tuni
ng o
f thi
s pa
ram
-et
er to
avo
id e
arly
ove
rcom
mitm
ent t
hat w
ould
pre
vent
rig
ht c
onte
xt fr
omex
ertin
g an
infl
uenc
e un
der
som
e ci
rcum
stan
ces,
Fin
ally
. a lo
w r
ate
offe
atur
e-le
vel d
ecay
was
use
d to
allo
w f
eatu
re-l
evel activations to persist
, aft
er th
e in
put m
oved
on
to la
ter
slic
es,
The
par
amet
er v
alue
s w
ere
held
con
stan
t at t
he v
alue
s sh
own
in th
e
cons
titut
e th
e se
t of
resp
onse
alte
rnat
ives
. des
igna
ted
by th
e id
entit
y of
the
item
for
whi
ch th
e un
it st
ands
(no
te th
at w
ith s
ever
al a
djac
ent s
lices
incl
uded
in th
e se
t. se
vera
l uni
ts in
the
alte
rnat
ive
set m
ay c
orr~
spon
d to
the
sam
e ov
ert r
espo
nse)
, Wor
d id
entif
icat
ion
resp
onse
s ar
e as
sum
~d
tobe based on
. rea
dout
fro
m th
e w
ord
leve
l. an
d ph
onem
e id
entif
icat
ion
resp
onse
s ar
e as
sum
ed to
be
base
d. o
n re
adou
t fro
m th
e ph
onem
e le
vel.
As
far
as p
hone
me
iden
tific
atio
n is
con
cern
ed, t
hen.
it h
Ol:n
~gen
eous
mec
hani
sm is
ass
umed
to b
e us
ed w
ith b
oth
wor
d an
d no
nwor
d st
imul
i.T
he d
ecis
ion
mec
hani
sm c
an b
e as
ked
to m
ake
a re
spon
se e
ither
(a)
at a
criterialtime during processirig
or (
b) w
hen
a un
it in
the
alte
rnat
ive
set
reac
hes
a cr
iteri
al s
tren
gth
rela
tive
to th
e ac
tivat
ion
of o
ther
alte
rnat
ive
units
. Onc
e a
deci
sion
has
bee
n m
ade
to m
ake
a re
spon
se. o
ne o
f the
alte
rnat
ives
is c
hose
n fr
om th
e m
embe
rs o
f th
e se
t, T
he p
roba
bilit
y of
choo
sing
a p
artic
ular
alte
rnat
ive
i is
then
given by the Luce (1959)
choi
ce r
ule:
peR
i~ S
whe
n in
dexe
s th
e m
embe
rs o
f th
e al
tern
ativ
e se
t. an
d
The
exp
onen
tial t
rans
form
atio
n en
sure
s th
at a
ll ac
tivat
ions
are
pos
itive
and
give
s gr
eat w
eigh
t to
stro
nger
act
ivat
ions
. and
the
Luc
e ru
le e
nsur
esth
at th
e su
m o
f al
l of
the
resp
onse
pro
babi
litie
s ad
ds u
p to
1, 0
. Sub
stan
-tia
lly th
e sa
me assumptions were used by McClelland and Rumelhart
(198
1),
Mil1
imiz
il1R
the
Num
ber
of P
aram
eter
sA
t the
exp
ense
oC
cons
ider
able
rea
lism
. we
have
trie
d to
kee
p T
RA
CE
II s
impl
e by
usi
ng h
omog
eneo
us p
aram
eter
s w
here
ver
poss
ible
. Thu
s, a
sal
read
y no
ted.
the
feat
ure
spec
ific
atio
ns o
f al
l pho
nem
es w
ere
spre
ad o
utov
er th
e sa
me
num
ber
of ti
me
slic
es. e
ffect
ivel
y gi
ving
all
phon
emes
the
sam
e du
ratio
n, T
he s
tren
gth
of th
e to
tal e
xcita
tion
com
ing
into
a p
artic
-ul
ar p
hone
me
unit
~rom
the
feat
ure
units
was
nor
mal
ized
to, t
he s
ame
value for all phonelT1es. thus m
akin
g ea
ch p
hone
me
equa
lly e
xcita
ble
byits
ow
n ca
noni
cal p
atte
rn, O
ther
sim
plif
ying
ass
umpt
ions
sho
uld
be n
oted
as w
ell.
For
exa
mpl
e. th
ere
wer
e no
diff
eren
ces
in c
onne
ctio
ns o
r re
stin
gle
vels
for
wor
ds o
f d~
ffere
nt fr
eque
ncy,
It w
ould
hav
e be
en a
sim
ple
mat
ter
to in
corp
orat
e fr
eque
ncy
as M
cCle
lland
and
Rum
elha
rt (
1981
) di
d. a
nd a
com
plet
e m
ltdel
wou
ld. o
f co
urse
. inc
lude
som
e ac
coun
t for
the
ubiq
uito
usef
fect
s of
wor
d fr
eq~e
ncy.
We
left
it o
ut h
ere
to f
acili
tate
an
exam
inat
ion
of th
e m
any
othe
r f~
ctor
s th
at a
ppea
r to
influ
ence
the
proc
ess
of w
ord
reco
gniti
on in
spe
ech
perc
eptio
n,
TA
BL
E 3
Para
met
ers
of T
RA
CE
II
Para
met
erV
alue
Feat
ure-
phon
eme
exci
tatio
nP
hone
me-
wor
d ex
cita
tion
Wor
d-ph
onem
e ex
cita
tion
Phon
eme-
feature excitation
Feat
ure-
leve
l inh
ibiti
onPh
onem
e-le
vel i
nhib
ition
"W
ord-
leve
l inh
ibiti
on"
Feat
ure-
leve
l dec
ayPh
onem
e-le
vel d
ecay
Wor
d-le
vel d
ecay
" P
er th
ree
time-
slic
es o
f ove
rlap.
TR
AC
E M
OD
EL
tabl
e th
roug
hdut
the
sim
ulat
ions
, exc
ept i
n th
e si
mul
atio
ns o
f cat
egor
ical
perc
eptio
n an
d tr
adi' n
g re
latio
ns, S
ince
we
wer
e no
t exp
licitl
y co
ncer
ned
with
the
effe
ds o
f fe
edba
ck to
the
feat
ure
leve
l in
any
of th
e ot
her
sim
-ul
atio
ns, w
e st
h th
e fe
edba
ck fr
om th
e ph
onem
e le
vel t
o th
e fe
atur
e le
vel
to z
ero
to s
peed
up
the
sim
ulat
ions
in a
ll ot
her cases. In the categorical
perc
eptio
n an
d tr
adin
g re
latio
ns s
imul
atio
ns th
is p
aram
eter
was
set
at ,
OS,
Phon
eme-
to- f
eatu
re f
eedb
ack
tend
ed to
slo
w th
e ef
fect
ive
rate
of
deca
yat
the
feat
ure
leve
l and
to in
crea
se th
e ef
fect
ive
dist
inct
iven
ess
of d
iffe
rent
feat
ure
patte
rris
, Rat
e of
dec
ay o
f fea
ture
- lev
el a
ctiv
atio
ns a
nd s
tren
gth
of p
hone
me-
to'-
phon
eme
com
petit
ion
wet
e se
t to
, 03
and
.05
to c
ompe
n-sa
te fo
r th
ese
effe
cts,
No
lexi
con
was
use
d in
the
cate
goric
al p
erce
ptio
nan
d tr
adin
g re
liitio
ns s
imul
atio
ns, w
hich
is e
quiv
alen
t to
setti
ng th
e ph
o-ne
me
to w
ord
~xdt
atio
n pa
ram
eter
to z
ero,
't!
C 0
.
:: g~
+
-4;
QJ
.c:
Il.
MC
CLE
LLA
ND
AN
D E
LMA
N
045+
II'!
.
1.1 Ii
! !
~ ~I
1IliI
~.:
r '
fl!f
tlllf
l!I
:.~t!
1
I -
B I
a- b
g.. b~ b
I' F
IG. S
. Pho
nem
e- a
nd w
ordc
levet activiltions at several points in Ihe un'tllding of iI ~cgl1lCl1t
ambiguous between
Ibl
and
Ipl
followed by
III, 0
and
Ig!.
See
texl
Itlr
ilfu
ll cx
plal
1aliu
l1,
TH
E D
YN
AM
ICS
OF
PHO
NE
ME
PE
RC
EPT
ION
In th
e in
trod
uctio
n, w
e m
otiv
ated
the
appr
oach
take
n in
the
TR
AC
Em
odel
in g
ener
al te
rms.
In
this
sec
tion,
we
see
. that
the
sim
ple
conc
epts
that
lead
to T
RA
CE
pro
vide
a c
oher
ent a
nd s
ynth
etic
acc
ount
of
a la
rge
num
ber
of d
iffe
rent
kin
ds o
f fin
ding
s on
the
perc
eptio
n of
pho
nem
es,
Prev
ious
mod
e:ls
hav
e be
en a
ble
to p
rovi
de f
airl
y ac
cura
te a
ccou
nts
of a
num
ber
of th
ese
phen
omen
a, F
or e
xam
ple,
Mas
saro
and
Ode
ns
feat
ure
inte
grat
ion
mod
el (
Mas
saro
, 198
1; M
assa
ro &
Ode
n, 1
980a
, 198
0b; O
den
& M
assa
ro, 1
978)
acc
ount
s in
det
ail f
or a
larg
e bo
dy o
f da
ta o
n th
ein
flue
nces
of
mul
tiple
cue
s to
pho
nem
e id
entit
y, a
nd th
e Pi
soni
/Fuj
isak
i-Kawashima m
bdel
of
cate
gori
cal p
erce
ptio
n (F
ujis
aki &
Kaw
ashi
ma,
1968; Pisoni, 1973, 1975) accounts for a large bo
dy o
f dat
a on
the
con-
ditio
ns u
nder
whi
ch s
ubje
cts
can
disc
rim
inat
e so
unds
with
in th
e sa
me
phon
etic
cat
egor
y. M
arsl
er, W
ilson
s C
OH
OR
T m
odel
can
acc
ount
for
the
time
cour
se o
f lex
ical
influ
ence
s on
pho
nem
e id
entif
icat
ion.
Wha
t we
hope
to s
how
her
e is
that
TR
AC
E b
ring
s th
ese
phen
omen
a, a
nd s
ever
alot
hers
not
con
side
red
by e
ither
mod
el, t
oget
her
into
a c
oher
ent p
ictu
reof
the
proc
ess
of p
hone
me
perc
eptio
n as
it u
nfol
ds in
tim
e,T
he p
rese
nt s
ectio
n co
nsis
ts o
f th
ree
mai
n pa
rts.
The
fir
st f
ocus
es o
nle
xica
l effe
Cts
On
phon
eme
iden
tific
atio
n an
d th
e co
nditi
ons
unde
r w
hich
thes
e ef
fect
s ar
e ob
tain
ed. H
ere,
we
see
how
TR
AC
E c
an a
ccou
nt fo
rth
e ba
sic
lexi
cal e
ffect
, and
we
mak
e it
clea
r w
hy le
xica
l effe
cts
are
only
obta
ined
und
er s
ome
cond
ition
s, T
he s
econ
d pa
rt o
f th
is s
ectio
n fo
cuse
son
the
ques
tion
of th
e ro
le o
f pho
nota
ctic
rul
es- t
hat i
s, r
ules
spe
cify
ing
whi
ch p
hone
mes
can
occ
ur to
geth
er in
Eng
lish-
in p
hone
me
iden
tific
a-tio
n, H
ere,
we
see
how
TR
AC
E m
imic
s , th
e ap
pare
ntly
rul
e-go
vern
edbe
havi
or o
f hu
man
sub
ject
f. in
term
s of
a "
cons
pira
cy" of the le
xica
lite
ms
that
inst
antia
te th
e ru
le. T
he. t
hird
par
t foc
uses
on
two
aspe
cts
ofph
onem
e id
entif
icat
ion
ofte
n co
nsid
ered
qui
te s
epar
atel
y fr
om le
xica
l ef-
fect
s-na
mel
y, th
e co
ntra
stin
g ph
enom
ena
of c
ue tr
adeo
fTs
in p
hone
me
perc
eptio
n an
d ca
tego
rica
l per
cept
ion,
Her
e w
e se
e th
at T
RA
CE
pro
vide
san
acc
ount
of
both
eff
ects
as
wel
l as
deta
ils o
f th
eir
time
cour
se, A
ll th
ree
part
s of
this
sec
tion
illus
trat
e 'h
ow th
e si
mpl
e m
echa
nism
s of
mut
ual e
x-ci
tatio
n an
d in
hibi
tion
amon
g th
e pr
oces
sing
uni
ts o
f th
e T
race
pro
vide
ana
tura
l way
of
acco
untin
g fo
r th
e re
leva
nt p
heno
men
a, T
he s
ectio
n en
dsw
ith a
bri
ef c
onsi
dera
tion
of th
e w
ays
in w
hich
TR
AC
E m
ight
be
ex-
tend
ed to
cop
e w
ith s
ever
al o
ther
asp
ects
of p
hone
me
iden
tific
atio
n an
dpe
rcep
tion,
Lexical EffeL'
YO
ll ca
n te
ll a
phon
eme
by Ih
e co
mpa
ny Ih
m il
keep
j'2
In th
is s
ectio
n,we describe a simple simulation of the basic lexical effect
on
phon
eme
iden
tific
atio
n re
port
ed b
y G
anon
g (1
980)
, We
star
t with
this
phe
nom
enon
beca
use
it. a
nd th
e re
late
d ph
onem
ic r
esto
ratio
n ef
fect
, wer
e am
ong
the
prim
ary
reas
ons
why
we
felt
that
the
inte
ract
ive-
activ
atio
n ap
proa
chw
ould
be
appr
opri
ate
for
spee
ch p
erce
ptio
n as
wel
l as
visu
al w
ord
rec-
ogni
tion
and
read
ing,
For
the
firs
t sim
ulat
ion,
the
inpu
t to
the
mod
el c
onsi
sted
of a
feat
ure
specification which activated
Ibl
and
Ipl
equa
lly, f
ollo
wed
by
(am
I par
tially
overlapping with) the feature specifications for
III
then
n,
th
en
Ig!.
Fi
gure
5 sh
ows
phon
eme
and
wor
d-level activations at several points in the
unfo
ldin
g of
this
inpu
t spe
cifi
catio
n. E
ach
pane
l of
the
figu
re r
epre
sent
s
2 T
his
titte
is a
dapJ
ed f
rom
the
tille
of
a ta
lk b
y D
-dvi
d E
, Rum
elha
rl on
rel
illcd
phe
nol1
lcni
lin
telle
r pe
rcep
tion.
The
se f
indi
ngs
are
desc
ribe
d in
Rom
elha
rt a
nd M
cCle
lland
(198
2/, W
eIh
ank
Dav
e fo
r hi
s pe
rmis
sion
to a
dapt
the
title
TR
AC
E M
OD
EL
a di
ffere
nt p
oint
in ti
me
durin
g th
e pr
esen
tatio
n an
d co
ncom
itant
pro
-ce
ssin
g of
the
inpu
t. T
he u
pper
por
tion
of e
ach
pane
l is
used
to d
ispl
ayac
tivat
ions
at t
he w
ord
leve
l; th
e lo
wer
pan
el is
use
d fo
r ac
tivat
ions
at
the
phon
eme
leve
l. E
ach
unit
is r
epre
sent
ed b
y a
rect
angl
e, la
bele
d w
ithth
e id
entit
y of
the
item
the
unit
stan
ds f
or, T
he h
oriz
onta
l ext
ensi
on o
fth
e re
ctan
gle
indi
cate
s th
e po
rtio
n of
the
inpu
t spa
nned
by
the
unit.
The
vert
ical
pos
ition
of
the
rect
angl
e in
dic
ates
the
degr
ee o
f ac
tivat
ion
of th
eun
it. I
n th
is a
nd s
ubse
quen
t fig
ures
, act
ivat
ions
of
the
phon
eme
units
loca
ted
betw
een
the
peak
s of
the
inpu
t spe
cifi
catio
ns o
f th
e ph
onem
es(at Slices 3, 9, 15. etc,)
have
bee
n de
lete
d fr
om th
e di
spla
y fo
r cl
arity
(the activations of these units genera1ly get suppressed by the model,
sinc
e th
e un
its o
n th
e pe
aks
tend
to d
omin
ate
them
), T
he in
put i
tsel
f is
indi
cate
d be
low
eac
h pa
nel,
with
the
succ
essi
ve p
hone
mes
pos
ition
ed a
tth
e te
mpo
ral p
ositi
ons
of th
e ce
nter
s of
thei
r in
put s
peci
fica
tions
, The
rt
along the
axis represents the point in the presentation of the input
stre
am a
t whi
ch th
e sn
apsh
ot w
as t!
lken
,T
he fi
gure
illu
stra
tes
the
gradual' buildup of activation of the tw
o in
-te
rpre
tatio
ns o
f th
e fi
rst p
hone
me,
fol
low
ed b
y gr
adua
l bui
ldup
s in
act
i-va
tion
for
subs
eque
nt p
hone
mes
, As
thes
e pr
oces
ses
unfo
ld, t
hey
begi
nto
pro
duce
wor
d-le
vel a
ctiv
atio
ns, I
t is
diff
icul
t to
reso
lve
any
wor
d-le
v~1
activ
atio
ns in
the
firs
t few
fra
mes
,. h
owev
er, s
ince
in these frames, the
info
rmat
ion
at th
e p~
onem
e le
vel s
impl
y ha
s no
t evo
lved
to th
e po
int
whe
re it
pro
vide
s en
ough
con
stra
int t
o se
lect
any
one
part
icul
ar w
ord.
In this case, it is only after the
Igl
has
com
e in
that
the
mod
el h
as in
for-
mat
ion
telli
ng it
whe
~he
r th
e in
put i
s cl
oser
to "
plug
," " pl
us," "
blus
h,or "bl
ood"
(T
RA
CE
's le
xico
n co
ntai
ns n
o ot
her
wor
ds beginning with
Iprt
or fbr/), After that point, as ill
ustr
ated
in th
e fo
urth
pan
el, "
plug
win
s th
e co
mpe
titio
n at
the
wor
d le
vel a
nd, t
hrou
gh f
eedb
ack
supp
ort t
oIp
/, ca
uses
Ip
l to dominate
Ibl
at the ph
onem
e le
vel.
The
mod
el, t
hen,
prov
ides
an
expl
icit
acco
unt f
or th
e w
ay in
whi
ch le
xica
l inf
orm
atio
n ca
nin
fluen
ce p
hone
me
iden
tific
atio
n,T
wo
thin
gs a
bout
the
lexi
cal e
ffec
t obs
erve
d in
this
cas
e ar
e w
orth
y of
note
. Firs
t. th
e ef
fect
is r
athe
r sm
all,
Sec
ond,
it d
oes
not e
mer
ge u
ntil
wel
l aft
er th
e am
bigu
ous
segm
ent i
tsel
f ha
s co
me
and
gone
, The
re is
aslight advantage of
Ipl
over
Ib
l in
Fra
mes
2 a
nd 3
of
the
figu
re. I
n th
ese
case
s, h
owev
er, t
he a
dvan
tage
is n
ot d
ue to
the
spec
ific
info
rmat
ion
that
this
item
is th
e w
ord
"plu
gth
e m
odel
can
hav
e no
way
of k
now
ing
this at these points in processing, The slight advantage for
Ipl
at these
earl
y po
ints
is d
ue to
the
fact
that
ther
e ar
e m
ore
wor
ds b
egin
ning
with
Ipll
than Ibltin the model's
lexi
con,
and
in p
artic
ular
, the
re a
re m
ore
beginning with
Iprl
th
an
Ibrt
. So, when the input is
nrd/
, w
ith th
e?standing for the ambiguous
Ib/-
/pl
segm
ent,
the
mod
el m
ust a
ctua
lly o
ver-
com
e th
is s
light
Ip/
-war
d bi
as, E
vent
ually
, it d
oes
so,
. Fig
ure
6 sh
ows
the
tem
pora
l cou
rse
of b
uild
up o
f th
e st
reng
th o
f th
e
MCCLELLAND AND ELMAN
:-.. 1.00
::: :0 0.
!II
6: 0.
1/1 C 0
.
1/1 ~ 0.
00
12 18 24 30 38 42 48 54 80 88 72
Processing Cycles
FIG. 6. The time course or the buitdup in the strength or the
Ipl
resp
onse
bas
ed o
n ac
ti-va
tions
or
phon
eme
units
in S
lice
12. i
n proces1iing an ambiguous
Ibl-
lpl
segm
ent i
n '-I
'g/,
and the same segment in
I'SI.
T
he a
mbi
guou
s se
gmen
t is
indi
cate
d by
the
"?,' .
AI~o
show
n is
the
build
up o
r re
spon
se s
tren
gth
ror
proc
essi
ng a
n un
ambi
guou
~ Ip
l se
gmen
t in
Ipl'g
/. T
he v
ertic
al li
ne to
pped
with
"?" indicates the point in time co
rres
pond
ing
to th
ece
nter
or
the
initi
al s
egm
ent i
n th
e in
put s
trea
m. S
ucce
ssiv
e ve
rtic
al li
nes
indi
cate
cen
ters
or s
ucce
ssiv
e ph
onem
es.
Ipl
resp
onse
bas
ed o
n ac
tivat
ions
of
the
phon
eme
units
. in Slice 12 for
two cases in which the initial segment is ambiguous between
Ipl
and
Ib/.
In one case, the ambiguous segment is followed by
Irgl
(a
s in
"pl
ugin
the
othe
r, it
is fo
llowed by
IrSI
(a
s in
"bl
ush"
), G
iven
the
mod
el's
rest
rict
ed le
xico
n, w
hich
doe
s no
t con
tain
the
~ord
"pl
ush,
" the lexical
effect should lead to eventual dominance of the
Ipl
resp
onse
in th
e fi
rst
case, but a suppression of the
Ipl
resp
onse
in th
e se
cond
cas
e, T
he d
if-fe
renc
es b
etw
een
the
cont
exts
do
not b
egin
to s
how
up
until
aft
er th
ece
nter
of
the
fina
l pho
nem
e, w
hich
occ
urs
at S
lice
30. T
he r
easo
n fo
r th
isis
sim
ply
that
the
info
rmat
ion
is. n
ot a
vaila
ble
until
that
poi
nt, b
ecau
seth
e ph
onem
e th
at s
igna
ls w
hat t
he w
ord
will
be
com
es a
t the
ver
y en
d of
the
wor
d. T
he e
ffect
take
s an
othe
r fe
w ti
me
slic
es to
beg
in to
influ
ence
the activation of the
' ini
tial p
hone
me,
bec
ause
it p
erco
lat~
s to
the
firs
tph
onem
e by
way
of
the
feed
back
fro
m th
e w
ord
or w
ords
that
con
-ta
in it
, .Elimination of the lexical effect by time pressure,
Fox
(198
2) h
as r
e-po
rted
that
the
lexi
cal e
ffect
on
wor
d in
itial
seg
men
ts is
elim
inat
ed if
subj
ects
are
giv
en a
dea
dlin
e to
res
pond
with
in 5
00 m
s of
the
ambi
guou
sse
gmen
t. T
houg
h th
ey c
an c
orre
ctly
iden
tify
unam
bigu
ous
segm
ents
inre
spon
ses
mad
e be
fore
the
dead
line,
thes
e ea
rly r
espo
nses
sho
w n
o se
n-
sitiv
ity to
the
lexi
cal s
tatu
s of
the
alte
rnat
ives
, Sim
ilar findings are also
repo
rted
by
Fox
(198
4).
Our
mod
el is
com
plet
ely
cons
iste
nt w
ith F
oxs
resu
lts, I
ndee
d, w
e ha
ve
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
alre
ady
seen
that
the
activ
atio
ns in
the 1i"ace only begin to reflect the
lexi
cal e
ffec
t abo
ut o
ne p
hone
me
or s
o af
ter
the
phon
eme
that
est
ablis
hes
the
lexi
cal i
dent
ity o
f th
e ite
m, G
iven
that
this
seg
men
t doe
s no
t occ
ur,
in F
oxs experiments, until the second or third segment after the ambig-
uous
seg
men
t, th
ere
is n
o w
ay th
at a
lexi
cal e
ffect
cou
ld b
e ob
serv
ed in
earl
y re
spon
ses.
But
wha
t abq
ut th
e fa
ct th
at e
arly
res
pons
es to
una
mbi
guou
s se
gmen
tsca
n be
acc
urat
e? T
RA
CE
acc
ount
s fo
r th
is to
o. I
n Fi
gure
7 w
e sh
ow th
est
ate
of th
e T
race
at v
ario
us d
iffe
rent
poi
nts
afte
r th
e un
ambi
guou
s Ib
l
Ibrgl, Here, the
Ibl
dominates the
Ipl
from
the
earl
iest
poi
nt. T
he a
nal-
ogou
s re
sult
is !
obtained, when the stimulus is
Ipl
in Iprgl, and the actio
vatio
n fo
r th
e ih
itial
pho
nem
e is
qui
te in
depe
nden
t of
whe
ther
or
not t
heite
m is
a w
ord.
The
res
pons
e st
reng
th f
or th
e ca
se w
hen
Iprg
l is
pres
enttd
in F
ig, 6
sho
ws
that
the
prob
abili
ty o
f cho
osin
g Ip
l is
nea
r un
ity w
ithin
12 processing cycles, or 300 ms of the in
itia,
seg
men
t, w
ell b
efor
e th
ede
adlin
e w
ould
be
reac
hed-
and
wel
l bef
ore
wor
d id
entit
y sp
ecif
ying
info
rmat
ion
is I
/.vai
labl
e,Lexictll effec'ts Itlte in tI word.
In th
e m
odel
, lex
ical
effe
cts
on w
ord-
initi
al s
egm
ents
! dev
elop
rat
her
late
, at l
east
in th
e ca
se w
here
ther
e is
no
cont
ext p
rece
dIng
the
wor
d, O
f cou
rse,
the
exac
t tim
ing
of th
e de
velo
p-m
ent o
f any
lexi
cal e
ffect
wou
ld b
e de
pend
ent u
pon
the
set o
f wor
dsac
tivat
ed b
y th
b st
imul
us; i
f on
e w
ord
pred
omin
ated
ear
ly o
n, a
lexi
cal
effe
ct c
ould
dev
elop
rat
her.
ear
lier,
In
gene
ral,
thou
gh, w
ord-
initi
al a
m-
bigu
ities
will
req
uire
tim
e to
res
olve
on
the
basi
s of
lexi
cal i
nfor
mat
ion,
How
ever
, whe
n th
e am
bigu
ous
segm
ent c
omes
late
in th
e w
ord
, and
the
info
rmat
ion
that
pre
cede
s th
e am
bigu
ous
segm
ent h
as a
lrea
dy e
stab
lishe
dw
hich
of t
he tw
o al
tern
ativ
es fo
r th
e am
bigu
ous
segm
ent i
s co
rrec
tT
RA
CE
sho
ws
a le
xica
l effe
ct th
at d
evel
ops
as th
e di
rect
per
cept
ual
info
rmat
ion
rele
vant
to th
e id
entit
y of
the
targ
et s
egm
ent i
s be
ing
pro-
cess
ed. T
his
phen
omen
on is
illu
Str
ated
in F
ig, 8
, whi
ch s
how
s th
e st
ate
of th
e 1i
"ace
at s
ever
al p
oint
s in
tim
e re
lativ
e to
an
ambi
guou
s fin
al s
eg-
ment tha~ could be a
It I
or a
Idl,
at th
e en
d of
the
cont
ext I
targ
I, W
ithin
the
dura
tion
of a
sin
gle
phon
eme
afte
r th
e ce
nter
of
the
ambi
guou
s se
g-m
ent,
It!
already has an advantage over
Idl,
We
ther
efor
e pr
edic
t tha
tFo
xs
resu
lts w
ould
com
e ou
t diff
eren
tly, w
ere
he to
use
wor
d-fi
nal,
asop
pose
d to
wor
d-in
itial
, am
bigu
ous
segm
ents
, In
such
a c
ase
we
wou
ldex
pect
the
lexi
cal e
ffec
t to
show
up
wel
l with
in th
e 50
0-m
s de
adlin
e,D
epen
denc
'e o
f the
lexi
CtlI
effe
ct o
n ph
onol
ogic
' (11
tlmbi
gllit
y,
One
fur-
ther
asp
ect o
fthe
lexi
cal e
ffect
that
was
not
ed b
y G
anon
g (1
980)
des
erve
sco
mm
ent,
Thi
s is
the
fact
that
the
lexi
cal e
ffect
on
the
iden
tity
of a
. pho
nem
e on
ly o
ccur
s w
ith s
egm
ents
whi
ch f
all i
n th
e bo
unda
ry r
egio
nb~
twee
ntw
o ph
onem
es. F
or s
egm
ents
whi
ch a
re u
nam
bigu
ous
exam
ples
of o
ne c
ateg
ory
or th
e ot
her,
the
effe
ct is
not
obt
aine
d, T
RA
CE
is e
ntir
ely
cons
iste
nt w
ith th
is a
spec
t of t
he d
ata,
The
influ
ence
of t
he le
xico
n is
sim
ply
anot
her
sour
ce o
f ev
iden
ce, l
ike
that
com
ing
from
the
feat
ure
- b
- b
Har
ll-lf
Eli . FLIl
8 ff
:Wff
:WiI
:W!i
lW
- t
- t
a r
1a I'
a 1"1
I k
klSI
-
I 1
I' k
- f
- B .
-tar
-tar
g--t
ara-
- t a
r a
- t -
-bl-a-
-bl
- I- -
bl- I- -
bl-
FIG
, 7. T
he s
tate
of
the
Tra
ce a
t var
ious
sta
ges
of p
roce
ssin
g th
e st
ream
Ibr
gl.
FIG
. 8. T
he s
tale
of
the
Tra
ce a
l sev
eral
sta
ges
of p
roce
ssin
g Ih
e st
ream
con
sisl
ing
ofIt
arg
' followed by Ii segment ambiguous bel ween
III
and
Id/.
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
leve
l, in
fluc
ncin
g th
e ac
tivat
ion
of o
ne p
hone
me
unit
or a
noth
er. W
hen
the
botto
m-u
p in
put i
s de
cisi
ve, i
t can
pre
empt
any
lexi
cal b
ias
effe
cts.
We
have
ver
ifie
d th
is in
sim
ulat
ions
pre
sent
ing
unam
bigu
ous
toke
ns o
fIp
l or
fb
i, followed either by Irgl or
IrS/
. In
thes
e si
mul
atio
ns, t
he u
nit
for
the
pres
ente
d in
itial
seg
men
t rea
ches
a v
ery
high
leve
l of
activ
atio
n,in
depe
nden
t of
the
follo
win
g co
ntex
t. W
hen
the
segm
ent c
omes
at t
heen
d of
the
wor
d, th
e co
ntex
t exe
rts
stro
nger
eff
ects
, thu
s ac
coun
ting
for
the
fact
that
spe
ech
dist
ortio
ns a
re e
asie
r to
det
ect w
hen
they
com
e ea
rlyin
a w
ord
than
whe
n th
ey c
ome
late
(M
arsl
en-W
ilson
& W
elsh
, 197
8),
How
ever
, eve
n th
ere,
it is
pos
sibl
e to
ove
rrid
e le
xica
lly b
ased
act
ivat
ions
with
cle
ar b
otto
m-u
p si
gnal
s, a
lthou
gh th
ere
may
be
som
e sl
owin
g of
the
activ
atio
n pr
oces
s w
hich
wou
ld p
roba
bly
show
up
in r
eact
ion
times
.H
sho
uld
be n
oted
that
TR
AC
E's
acc
ount
of l
exic
al e
ffect
s is
qui
tesi
mila
r to
the
acco
unt o
ffer
ed b
y th
e fe
atur
e in
tegr
atio
n th
eory
of
Mas
saro
and
Ode
n (1
980a
). I
ndee
d, M
assa
ro a
nd O
den
s m
odel
pro
vide
s qu
anti-
tativ
e fi
ts to
Gan
ong
s fi
ndin
gs. W
e w
ill m
ake
som
e m
entio
n of
the
slig
htdi
ffer
ence
s in
qua
ntita
tive
assu
mpt
ions
bet
wee
n th
e m
odel
s be
low
. For
. now
, we
note
a m
o~e
cruc
ial d
iffe
renc
e: T
RA
CE
inco
rpor
ates
spe
cifi
cas
sum
ptio
ns a
bout
the
time
cour
se o
f pr
oces
sing
whi
ch a
llow
s it
to a
c-co
unt f
or th
e co
nditi
ons
unde
r w
hich
lexi
cal e
ffect
s w
ill b
e obtained, as
wel
l as
for
the
infl
uenc
e (o
r a
lack
ther
eoO
of
lexi
cal e
ffec
ts o
n re
actio
ntimes, to which we now turn,
Ah.
H'IIn' (~(lexicaleffed
ill some reaction-time studies,
Foss
and
Bla
nk(1
980)
pre
sent
ed s
ome
resu
lts w
hich
see
med
to p
ose
a ch
alle
nge
to in
-te
ract
ive
mod
els
of p
hone
me
iden
tific
atio
n in
spe
ech
perc
eptio
n, T
hey
gave
sub
ject
s th
e ta
~k o
f lis
teni
ng to
spo
ken
sent
ence
s fo
r oc
curr
ence
sof
a p
artic
ular
pho
nem
e in
wor
d-in
itial
pos
ition
, Rea
ctio
n tim
e to
pre
ssa
resp
onse
key
fro
m th
e on
set o
f th
e ta
rget
pho
nem
e w
as th
e de
pend
ent
varia
ble.
In o
ne e
xam
ple,
the
targ
et w
as Ig
I and the sentence was,
At t
heen
d (~
"'a.~t year, the Rovemment,
, , .
The
sub
ject
's ta
sk w
as s
impl
y to
pres
s th
e re
spon
se k
ey u
pon
hear
ing
the
IgI a
t the
beg
inni
ng o
f the
wor
dR
Ol'e
rllm
ellt.
. The pr
inci
ple
find
ing
of F
oss
and
Bla
nk's
stu
dy w
as th
at it
mad
e no
diffe
renc
e w
heth
er th
e ta
rget
cam
e at
the
begi
nnin
g of
a w
ord
or a
non
-word. Later studies by Foss and Gernsbacher (1983) in
dica
te th
at o
ther
expe
rimen
ts w
hich
hav
e fo
und
lexi
cal o
r ev
en s
eman
tic a
nd s
ynta
ctic
ntex
t effe
cts
on m
onito
ring
late
ncie
s ar
e fla
wed
, and
that
mon
itorin
gtim
es fo
r w
ord-
initi
al p
hone
mes
are
pri
mar
ily in
flue
nced
by
acou
stic
fact
ors
affe
ctin
g ph
onem
e de
tect
abili
ty, r
athe
r th
an le
xica
l, se
man
tic, o
rsyntactic fact
ors,
The
con
clus
ion
that
pho
nem
e m
onito
ring
is u
naffe
cted
by
the
lexi
cal
status of the target-be
arin
g ph
onem
e st
ring
see
ms
at v
aria
nce
with
the
spir
it of
the
TR
AC
E m
odel
, sin
ce in
TR
AC
E, t
he le
xica
l lev
el is
alw
ays
invo
lved
in th
e pe
rcep
tual
pro
cess
, How
ever
. we
have
alr
eady
see
n th
atth
ere
are
cond
ition
s un
der
whi
ch th
e le
xica
l lev
el d
oes
not g
et m
uch
ofa
c~an
ce to
exe
rt a
n ef
fect
, In
the
prev
ious
sec
tion
we
saw
that
ther
e is
no le
xica
l eff
ect o
n id
entif
icat
ion
of a
mbi
guou
s w
ord-
initi
al ta
rget
s w
hen
the
subj
ect ~
s un
der
time
pres
sure
to r
espo
nd q
uick
ly; s
impl
y be
caus
e th
esu
bjec
t mus
t res
pond
bef
ore
info
rmat
ion
is e
ven
avai
labl
e th
at w
ould
allo
w th
e m
odel
-or
any
othe
r m
echa
nism
-to
prod
uce
a le
xica
l effe
ct.
In th
e Fo
ss a
nd B
lank
situ
atio
n, th
ere
is e
ven
less
rea
son
to e
xpec
t ale
xica
l effe
ct, s
ince
the
targ
et is
not
an
am
bigu
ous
segm
ent.
We
alre
ady
saw
that
act
ivat
ion
curv
es r
ise
rapi
dly
for
unam
bigu
ous
segm
ents
; in
the
present case, they can reach near-pe
ak le
vels
wel
l bef
ore
the
acou
stic
info
rmat
ion
that
indi
cate
s w
heth
er th
e ta
rget
is in
a w
ord
or n
onw
ord
has
reac
hed
the
s~bj
ect's
ear.
T
he' r
esul
ts o
f a s
imul
atio
n ru
n ill
ustr
atin
g th
ese
poin
ts a
re s
how
n in
Fig.
9. F
or th
is e
xam
ple,
we
imag
ine
that
the
targ
et is
Itl,
Not
e ho
w d
urin
gth
e in
itial
syl
labl
e of
bot
h st
ream
s, li
ttle
activ
atio
n at
the
wor
d le
vel h
asbe
en e
stab
lishe
d, E
ven
tow
ard
the
end
of th
e st
ream
, whe
re th
e in
for-
. mation is
just
com
ing
in w
hich
det
erm
ines
thai
"tr
ugus
" is
not
a w
ord,
ther
e is
littl
e di
ffer
ence
, bec
ause
in b
oth
case
s, th
ere
are
seve
ral a
ctiv
ew
ord-
leve
l can
dida
tes,
all
supp
ortin
g th
e w
ord-
initi
al I
t/. I
t is
only
aft
erth
e en
d of
the
stre
am th
at a
rea
l cha
nce
for
a di
ffere
nce
has
occu
rred
, Wel
lbe
fore
this
tim
e ar
rive
s, th
e su
bjec
t will
hav
e m
ade
a re
spon
se, s
ince
the
strength of the
It!
resp
onse
rea
ches
a le
vel s
uffi
cien
t to
guar
ante
e a
high
accu
racy
by
abou
t Cyc
le 3
0, w
ell b
efor
e th
e en
d of
the
wor
d, a
s ill
ustr
ated
:in
Fig
, 10,
E
ven
thou
gh a
ctiv
atio
ns a
re q
uite
rap
id f
or u
nam
bigu
ous
segm
ents
,th
ese
can
still
be
infl
uenc
ed b
y le
xica
l eff
ects
, pro
vide
d th
at th
e le
xica
l.in
form
atio
n is
ava
ilabl
e in
tim
e, I
n Fi
g, I
I, w
e ill
ustr
ate
this
poi
nt f
or th
eph
onem
e It
I i'n
the
stre
ams
Isik
rtl
(the
wor
d "s
ecre
t")
and
Igld
A
guld
ut,"
a n
onw
ord)
, The
fig
ure
show
s th
e st
reng
th o
f th
e It
I r
espo
nse
as a
fun
ctio
n of
pro
cess
ing
cycl
es, r
elat
ive
to a
ll ot
her
resp
onse
s ba
sed
on a
ctiv
atio
ns o
f ph
onem
e un
its a
t Cyc
le 4
2, th
e pe
ak o
f th
e in
put s
pec-
ific
atio
n fo
r th
e It
/. C
lear
ly, r
espo
nse
stre
n~' h
gro
ws
fast
er fo
r th
e It!
inIs
ikr
tl th
an f
or th
e It
! in
Ig
ldAt!
; pic
king
an
arbi
trar
y th
resh
old
of .
9 fo
rresponse initiation, we find that the
It!
in Is
ikr
tl re
ache
s cr
iteri
on a
bout
3 cy
cles
or
75 m
s so
oner
than
the
It I i
n Ig
ld"t
/.Studies showing lexical effects in reaction times.
Mar
slen
-Wils
on(1
980)
has
rep
orte
d an
exp
erim
ent t
hat d
emon
stra
tes
the
exis
tenc
e of
lexi
cal e
ffec
ts in
pho
nem
e m
onito
ring
for
pho
nem
es c
omin
g at
late
r po
i~ts
in w
ords
. For
pho
nem
es c
omin
g at
the
begi
nnin
g of
a w
ord
or a
t the
end
of th
e fi
rst s
ylla
ble,
he
foun
d no
fac
ilita
tion
for
phon
emes
in w
ords
rel
-
TR
AC
E M
OD
EL
IN.l*
,,,~
U
-1,1
II I
;.., 1.
:=:
:.0 0.
111
!:
40-
Q.. ~ 0.
MC
CLE
LLA
ND
AN
D E
LMA
N
00
12 1
6 24
30
36 4
2 48
54
Processing Cycles
FIG, 10. Time course
of growlh in Ihe probabililY
of
Ihe
III
resp
onse
bas
ed o
n ilc
livill
illns
of
phoneme unils in Slice 12, during processing
of
Ilar
gll ilnd I
I(g
s/.
The
v.:r
lical
lin.
:sin
dica
le th
e pe
aks
on Ih
e fe
alur
e pa
uern
s co
rres
pond
ing
10 !h
e su
cces
siv.
: pho
n.:m
.:s o
f Ih
epr
eseR
led
wor
d.-L
arl-
L-
-Lar
. I-L
--L
arl-
L-
ms
adva
ntag
e co
mpa
red
to c
orre
spon
ding
pos
ition
s in
non
words. This
com
pare
s qu
ite c
lose
ly w
ith th
e va
lue
of a
bout
75
ms
we
obta
ined
for
the
Isik
rt/-
ld't
l exa
mpl
e. A
t the
end
s of
eve
n lo
nger
wor
ds, t
he w
ord
ad-
vant
age
incr
ease
d in
siz
e to
185 ms. Marslen-
Wils
ons
resu
lt Ih
us c
on-
firm
s th
at th
ere
are '
inde
ed le
xica
l effe
cts
in p
hone
me
mon
ilori
ng-e
ven
for unambiguous inputs-
but u
nder
scor
es th
e ta
ct th
at th
ere
is n
o w
ord
adva
ntag
e fo
r ph
onem
es w
hose
pro
cess
ing
can
be c
ompl
eted
long
bef
ore
lexi
cal i
nflu
ence
s w
ould
ha\
:,e a
cha
nce
to s
how
up,
_d__
000 _
LJ..J
L1
12 16 24
30
36 4
2 48
54 60 66 72
Processing Cycles
FIG. t t. ProbabililY
of
the
It I
response as a funclion
of
proc
essi
ng c
ycle
s. b
ased
on
acli-
vatio
n of
pho
nem
e un
its a
t Cyc
l.:A
2. f
or th
e st
ream
Isi
k..
.1 (
"se
cre.
, and
Id'
guld
ut" )
. Ver
tical
line
s in
dica
te th
e pe
aks
of th
e in
put p
atte
rns
corr
espo
ndin
g 10
Ihe
succ
essi
ve p
hone
mes
in e
ither
slr
eam
.
IIIm
m
B I
100
.!:
.... ~
0.II
I1.
0
.... en
0.
III g 0.
III
III
020
-Lr-
s- -Lr-a-
s- -
Lr- a
-e-
FIG. 9. Stale of Ihe ltace al three di
ffer
ent p
ainl
s du
ring
the
proc
essi
ng o
f th
e w
ord
targ
el(/
targ
t/!
and
the
nonw
ord
"tru
gus "
(/tr
sf),
ativ
e to
pho
nem
es in
non
wor
ds (
in f
act t
here
was
a n
on w
ord
adva
ntag
efo
r th
ese
earl
y ta
rget
con
ditio
ns).
For
targ
ets
occu
rrin
g at
the
end
of th
ese
cond
syl
labl
e of
a tw
o-sy
llabl
e w
ord
(lik
e " s
ecre
tth
ough
the
stim
uli
in th
is p
artic
ular
exp
erim
ent w
ere
Dut
ch)
Mar
slen
- Wilson found an 85-
- -- ----
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
The
TR
AC
E m
odel
and
Mar
slen
-Wils
ons
CO
HO
RT
mod
el (
Mar
slen
-W
ilson
& T
yler
, 198
0; M
arsl
en-W
ilson
& W
elsh
, 1978) offer fairly similar
inte
rpre
tatio
ns o
f le
xica
l eff
ects
in p
hone
me
mon
itori
ng, B
oth
mod
els
acco
unt f
or th
e gr
owth
in th
e ef
fect
as
a fu
nctio
n of
pos
ition
in th
e w
ord,
As
in C
OH
OR
T, l
exie
alef
fect
s in
TR
AC
E d
epen
d on
the
poin
t at w
hich
the
patte
rn o
f act
ivat
ion
at th
e w
ord
leve
l beg
ins
to s
peci
fy th
e id
entit
ies
of the ph
onem
es, I
nC
OH
OR
T, t
here
is a
dis
cret
e m
omen
t whe
n th
isoc
curs
-whe
n th
e co
hort
of
item
s co
nsis
tent
with
the
inpu
t is
redu
ced
to a single item. In T~R
AC
E, t
hing
s ar
e no
t qui
te s
o di
scre
te, H
owev
er,
it w
ill s
till g
ener
ally
be
the
case
in T
RA
CE
that
the
size
of t
he le
xica
lef
fect
will
var
y w
ith th
e lo
catio
n of
the
"uni
que
poin
t,"
the
poin
t at w
hich
the
botto
m-u
p in
put r
emai
ns c
onsi
sten
t with
onl
y a
sing
le w
ord,
How
-ever, since Marslen-
Wils
ons
expe
rimen
ts w
ere
perf
orm
ed w
ith D
utch
wor
ds, w
e ha
ve n
ot b
een
able
to s
imul
ate
his
expe
rim
enta
l dem
onst
ratio
nof
this
eff
ect i
n de
tail.
TR
AC
E a
nd C
OH
OR
T m
ake
sim
ilar
pred
ictio
ns in
som
e si
tuat
ions
,bu
t not
in a
ll. I
n th
e ne
xt s
ectio
n, w
e co
nsid
er a
phe
nom
enon
whi
chT
RA
CE
acc
ount
s fo
r ,v
ia th
e sa
me
mec
hani
sms
it us
es to
acc
ount
for
the
lexi
cal e
ffec
ts w
e ha
ve b
een
cons
ider
ing.
Her
e, th
e gr
aded
fee
dbac
k fr
omth
e w
ord
leve
l to
the,
pho
nem
e le
vel a
llow
s T
RA
CE
to a
ccou
nt f
or a
nef
fect
that
wou
ld n
ot b
e pr
edic
ted
by C
OH
OR
T, u
nles
s ad
ditio
nal a
s-su
mpt
ions
wer
e m
ade,
A
re P
lrOllO
toct
ic R
ille
Ejfe
ct.f the Res"lt of a Co1lspiracy?
Rec
ently
, Mas
saro
;;tn
d C
ohen
(19
83)
have
rep
orte
d ev
iden
ce th
ey ta
keas
sup
port
for
the
use
of p
hono
tact
ic r
ules
in p
hone
me
iden
tific
atio
n. I
non
e ex
peri
men
t, M
assa
ro a
nd C
ohen
s st
imul
i con
sist
ed o
f pho
nolo
gica
lsegments ambiguous between
Irl
and
III
in d
iffe
rent
con
text
s. I
n on
e co
n-text (fLi/)
Irl
is permissible in English, but
III
is n
ot. I
n an
othe
r co
ntex
t(/5-i/) /11
is permissible in English but
Irl
is not. In a third context
(/L
i/)both are permissible, and in a fourth
(/v_
i/)
neith
er is
per
mis
sibl
e. M
assa
roan
d C
ohen
foun
d a
bias
to p
erce
ive
ambiguous segments as
Irl
whe
n Ir
lwas permissible or as
III
whe
n 11
/ w
as p
erm
issi
ble.
No
bias
app
eare
d in
eith
er o
f the
oth
er tw
o co
nditi
ons.
With
mos
t of
thes
e st
imul
i, ph
onot
actic
acc
epta
bilit
y is
con
foun
ded
with the actual lexica1 status of the item; thus
/nil
and
ffri
l fl
ee" and
free
) are both words, as is
Itri
l bul not
Illil
, In the
Is_i
l co
ntex
t, ho
w-
ever. neither Islil or
Isri
l ar
e w
ords
, yet
Mas
saro
and
Coh
en f
ound
a b
ias
to hear the ambiguous segment as
III,
in accordance with phonotactic
rule
s.It
turn
s ou
t tha
t TR
AC
E p
rodu
ces
the
sam
e ef
fect
, eve
n th
ough
it la
cks
phon
otac
tlc r
ules
, The
rea
son
is th
at th
e am
bigu
ous
stim
ulus
pro
duce
s
part
ial a
ctiv
atio
ns o
f a n
umbe
r of
wor
ds (
'~sl
eep" and "sleet" in the
mod
el' s
lexi
con;
it w
ould
als
o ac
tivat
e "s
leev
e,
" " sl
eek,
and
othe
rs in
a m
odel
with
a f
ulle
r le
xico
n). N
one
of th
ese
wor
d un
its g
ets
as a
ctiv
eas
it w
ould
if th
e en
tire
wor
d ha
d be
en p
rese
nted
, How
ever
, all
of th
em(i
n th
e si
mul
atio
n, th
ere
are
ony
two,
but
the
prin
cipl
e st
ill a
pplie
s) a
repa
rtia
lly a
ctiv
ated
, and
all
cons
pire
toge
ther
and
con
trib
ute
to th
e ac
ti-vation of
III.
This feedback support for the
III
allo
ws
it to
dom
inat
e th
eIr
l, just as it would if
Islil
w
ere
an a
c~ua
l wor
d, a
s sh
own
in F
ig, 1
2,
The
hyp
othe
sis
that
pho
nota
ctic
rul
e ef
fect
s ar
e re
ally
bas
ed o
n w
ord
activ
atio
ns le
ads
to a
pre
dict
ion:
that
we
shou
ld b
e ab
le to
rev
erse
thes
eef
fect
s if
we
pres
ent i
tem
s th
at a
re s
uppo
rted
str
ongl
y by
one
or
mor
ele
xica
l ite
ms
even
if th
ey v
iola
te p
hono
tact
ic r
ules
, A r
ecen
t exp
erim
ent
by E
lman
(19
83)
conf
irm
s th
is p
redi
ctio
n, I
n th
is e
xper
imen
t, am
bigu
ous
phonemes (for example, halfway between
Ibl
and
Id/)
w
ere
pres
ente
d in
thre
e di
ffere
nt ty
pes
of c
onte
xts,
In a
ll th
ree
type
s, o
ne o
f the
two
(in th
iscase, the
Id/)
was phonotactically acceptable, while the other (the
Ib/)
was
not
. How
ever
, the
con
text
s di
ffere
d in
thei
l' re
latio
n to
wor
ds. I
n on
eca
se, t
he le
gal i
tem
act
ually
occ
urre
d in
a w
ord
("bw
indl
edw
indl
eIn
a s
econ
d ca
se, n
eith
er it
em m
ade
a w
ord,
but
the
illeg
al it
em w
as v
ery
cI()
se to
a w
ord
("bw
acel
et"
dwac
elet
"). I
n a
thir
d ca
se, n
eith
er it
em
EiI
TllJ
IIT
rntil
ltil
l
9tIJ
JE
!l. 1
;..1
- 5
S J
1- -51- -81- -5
FIG
. 12.
Sta
te (
If th
e 1i
'ace
at s
ever
al p
oint
s in
pro
cess
ing
a se
gmen
t am
bigu
ous
betw
een
111
and
Irl,
in the context
Is_i
/. T
he u
nits
for
"sl
eep "
IIs
lip/)
and
"sl
eet"
(/s
lit/)
are
box
edto
geth
er s
ince
they
take
on
iden
tical
act
ivat
ion
valu
es.
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
was
par
ticul
arly
clo
se to
a w
ord
("bw
ime
dwim
eR
esul
ts
of
the
expe
rimen
t are
sho
wn
in Th
ble 4. The existence
of
a w
ord
iden
tical
toon
e of
the two alternatives or differing from one
of
the
alte
rnat
ives
by
asingle phonetic feature
of
one
phon
eme
stro
ngly
influ
ence
d th
e su
bjec
t'ch
oice
s be
twee
n th
e tw
o al
tern
ativ
es, I
ndee
d, in
the
case
whe
re th
e ph
o-notactically irregular alternative ("bw
acel
et)
was
one
fea
ture
aw
ay f
rom
a pa
rtic
ular
lexi
cal i
tem
(" b
race
let"
), s
ubje
cts
tend
ed to
hea
r th
e am
big-
uous
item
in a
ccor
d w
ith th
e si
mila
r le
xica
l ite
m (
that
is, a
s a
Ibl)
even
thou
gh it
was
pho
nota
ctic
ally
inco
rrec
t.. To determine whether the model w
ould
als
o pr
oduc
e su
ch a
reve
rsal
of
the phonotactic rule effects with the appropriate kinds
of
stim
uli,
ran a simulation using a simulated inputambiguous between
Ipl
and
It I i
nthe context I-Iuli/,
Ipl
is p
hono
tact
ical
ly a
ccep
tabl
e in
this
con
text
, but
It I i
n th
is c
onte
xt m
akes
an
item
that
is v
ery
clos
e to
the
wor
d " t
ruly
,The results
of
this
run
, at t
wo
diff
eren
t poi
nts
duri
ng p
roce
ssin
g, a
resh
own
in F
ig. 1
3, E
arly
on
in p
roce
ssin
g, th
ere
is a
slig
ht b
ias
in fa
vor
of
the
Ipl
over the
Itl,
because at first a large number
of
Ipll
wor
ds a
reslightly more activated than any words beginning with
Itl,
Lat
er, t
houg
h,th
e It
I get
s th
e up
per
hand
as
the
wor
d " t
ruly
" co
mes
to d
omin
ate
at th
eword level. Thus, by the end
of
the
wor
d or
sho
rtly
ther
eaft
er, t
he c
lose
stw
ord
has
begu
n to
pla
ya d
omin
atin
g ro
le, c
ausi
ng th
e m
odel
to p
refe
rthe phonotactically inappropriate interpretation
of
the
ambi
guou
s in
itial
segm
ent.
Of
cour
se, a
t the
sam
e tim
e th
e w
ord
" tru
ly" tends to support
Irl
rath
erth
an
III for the second segment.. Thus, even. though th
is s
egm
ent i
s no
tambiguous, and the III would suppress the
Irl
inte
rpre
tatio
n in
a m
ore
neutral context, the
Irl
stay
s qu
ite a
ctiv
e,
Tra
ding
Rel
atio
ns a
nd C
ateg
oriL
'al P
erc'
eptio
n
In th
e si
mul
atio
ns c
onsi
dere
d th
us fa
r, p
hone
me
iden
tific
atio
~ is
intlu
-enced by two different kinds
of
fact
ors,
fea
tura
l and
lexi
cal.
Whe
n on
eso
rt
of
info
rmat
ion
is la
ckin
~, th
e ot
her
can
com
pens
ate
for
it. T
he im
age
tha, emerges from these kinds
of
findings is
of
a sy
stem
that
exh
ibits
grea
t fle
xibi
lity
by b
eing
abl
e to
bas
e id
entif
icat
ion'
dec
isio
ns o
n di
ffere
ntso
urce
s of
information, It is.
of course, well established il1
at w
ithin
the
feat
ura
l dom
ain
each
pho
nem
e is
generally signaled by a number
of
dif-
ferent cues, and that human subjects can trade these cues
off
agai
nst e
ach
othe
r, T
he T
RA
CE
mod
el e
xhib
its th
i-s
sam
e fl
exib
ility
, as
we
deta
ilsh
ortly
.But there is something
of
a pa
rado
x, W
hile
the
p(:r
cept
ual m
echa
nism
sex
hibi
t gre
at f
lexi
bilit
y in
the
cues
that
they
rel
y on
for
pho
nem
e id
enti-
fica
tion,
they
als
o ap
pear
to b
e qu
ite "
cate
gori
cal"
in n
atur
e. T
hat i
sth
ey p
rodu
ce m
uch
shar
per
boun
dari
es b
etw
een
phon
etic
cat
egor
ies
than
we
mig
ht e
xpec
t bas
ed o
n th
eir
sens
itivi
ty to
mul
tiple
cues; and they
appe
ar to
trea
t aco
ustic
ally
dis
tinct
feat
ure patterns as perceptually
equi
vale
nt, a
s lo
ng a
s th
ey a
re id
entif
ied
as in
stan
ces
of
the
sam
e ph
o-ne
me.
In th
is s
ectio
n, w
e ill
ustr
ate
that
in T
RA
CE
, jus
t as
in h
uman
spe
ech
. per
cept
ion,
fle
xibi
lity
in f
eatu
re in
terp
reta
tion-
spec
ifica
lly, t
he a
bilit
yto trade one feature
of
a ph
onem
e of
f aga
inst
ano
ther
-coe
xist
s w
ith a
stro
ng te
nden
cy to
war
d ca
tego
rica
l per
cept
ion.
For
thes
e si
mul
atio
ns, t
he m
odel
was
str
ippe
d do
wn
to th
e es
sent
ial
min
imum
nec
essa
ry, s
o th
at th
e ba
sic
mec
hani
sms
prod
ucin
g cu
e tr
adc-
n:::u
u:n
JIT
!iI:
TI
!a:it
Ln
u::r
::ill
fillJ
8iam
u I
I U
I i
-f I
I I
P r
a r
iP r
,,
TA
BL
E 4
Perc
enla
ge C
hoic
e of
Pho
nola
clic
ally
Irr
egul
ar C
onso
nant
Stim
ulus
type
Leg
al w
ord/
illeg
al n
on w
ord
Leg
al n
on w
ord/
illeg
al n
onw
ord
Leg
al n
onw
ord/
illeg
al n
earw
ord
Exa
mpl
e
dwin
dle/
bwin
dle
dwim
e/bw
ime
dwac
elel
/bw
acel
el
Perc
enta
ge o
f id
enlif
iclil
ions
as "
illeg
al"
phon
eme
F(2,34) = 26.414, p
c:: .
001.
luli- _
lull- _
luli- _
luli-
FIG. 13. Slate of the Trace al several points in processing an ambiguous
Ipl-
/11
segm
enl
followed by Ilulil
TR
AC
E M
OD
EL
. MC
CLE
LLA
ND
AN
D E
LMA
N
100
150 300
seve
ral c
ateg
o~ic
al p
erce
ptio
n st
udie
s of
VO
T c
ontin
ua (u
sing
Ig
/-/k
/.
Id/-
/tl.
or
Ib/-
/pl
stim
uli)
hav
e co
vari
ed b
oth
VO
T a
nd F
IOF.
if o
nly
beca
use
FIO
F te
nds
to c
ovar
y w
ith V
OT
Whl
.ll r
ealis
tic s
timul
i are
use
d(e
.g..
Piso
ni &
Laz
arus
. 1974: Samuel. 1977), Though the simulations us
e
Ig/-
/kl
cont
inuu
m. w
e co
nsid
er s
ever
al c
ateg
oric
al p
erce
ptio
n ex
peri
-ments using
Id/-
/tl
and
Ibl-
lpl
cont
inua
. sin
ce th
e sa
me
dim
ensi
ons
can
diff
eren
tiate
the
two
mem
bers
of
both
of
thes
e ot
her
pair
s, W
e al
so c
on-
side
r da
ta o
btai
ned
in e
xper
imen
ts o
n ot
her
cont
inua
. usi
ng o
ther
cue
s,W
e co
uld
easi
ly h
ave
repe
ated
the
sim
ulat
ions
with
oth
er s
ets
of c
ontin
ua; .
how
ever
. the
gen
eral
qua
litat
ive
form
of
the
resu
lts w
ould
be
the
sam
e,W
hat w
ould
var
y fr
om c
ase
to c
ase
wou
ld b
e th
e m
agni
tude
of
the
effe
ctof
a s
tep
alon
g a
give
n di
men
sion
,T
he p
atte
rn o
f ex
cita
tory
inpu
t to
the
VO
T a
nd F
IOF
dete
ctor
s pr
o-duced by the canonical mock speech
Igl
and
Ikl
used
in th
e si
mul
atio
nsar
e ill
ustr
ated
in F
ig. 1
5,
Trad;"g relat;OIu,
TR
AC
E q
uite
nat
ural
ly te
nds
to p
rodu
ce tr
adin
gre
latio
ns b
etw
een
feat
ures
. sin
ce it
rel
ies
on th
e w
eigh
ted
sum
of
the
exci
tato
ry in
puts
to d
eter
min
e ho
w s
tron
gly
the
inpu
t will
act
ivat
e a
par-
ticul
ar p
hone
me
unit.
All
else
bei
ng e
qual
. the
pho
nem
e un
it re
ceiv
ing
the
larg
est s
um b
otto
m-u
p ex
cita
tion
will
be
mor
e st
rong
ly a
ctiv
ated
than
any
othe
r, a
nd w
ill th
eref
ore
be th
e m
ost l
ikel
y re
spon
se w
hen
a ch
oice
mus
t be
mad
e be
twee
n on
e ph
onem
e an
d an
othe
r, S
ince
the
net b
otto
m-
up input is just the sum of all of the inputs, no one input is necessarily
deci
sive
in th
is r
egar
d,G
ener
ally
, exp
erim
ents
dem
onst
ratin
g tr
adin
g re
latio
ns b
etw
een
two
or .
mor
e cu
es m
anip
ulat
e ea
ch o
f the
cue
s ov
er a
num
ber
of v
alue
s ra
ngin
gbe
twee
n a
valu
e m
ore
typi
cal o
f on
e of
two
phon
emes
and
a v
alue
mor
ety
pica
l of t
he o
ther
, Sum
mer
fiel
d an
d H
agga
rd d
id th
is f
or V
OT
and
FIO
F, a
nd f
ound
the
typi
cal r
esul
t. na
mel
y th
at th
e va
lue
of o
ne c
ue th
atgives rise to 50% choices of
Ikl
was
affe
cted
by'
the
valu
e of
the
othe
rcu
e: th
e hi
gher
the
valu
e of
FIO
F, th
e sh
orte
r th
e va
lue
of V
QT
nee
ded.
for
50%
cho
ices
of
Ik/.
Unf
ortu
nate
ly; t
hey
did
not p
rese
nt f
ull c
urve
sre
latin
g ph
onem
e id
entif
icat
ion
to th
e va
lues
use
d on
eac
h of
the
two
dim
ensi
ons,
In
lieu
of th
is, w
e pr
esen
t cur
ves
in F
ig, 1
6 fr
om a
cla
ssic
trad
ing
rela
tions
exp
erim
ent,
by D
enes
(195
5), S
imila
r pa
ttern
s of
res
ults
have
bee
n re
port
ed in
oth
er s
tudi
es, u
sing
oth
er c
ues
(e,g" Massaro.
1981
, Fig
s. 4
and
5),
thou
gh th
e tr
ansi
tions
are
oft
en s
omew
hat s
teep
er(s
ee b
elow
for
a d
iscu
ssio
n of
the
is~u
e of
ste
epne
ss).
We
have
cho
sen
to p
rese
nt th
e sh
allo
wer
cur
ves
repo
rted
by
Den
es b
ecau
se in
them
we
see
clea
rly.
that
ther
e ar
e ca
ses
in w
hich
a c
ue th
at f
avor
s on
e of
the
two
phon
emes
to a
mod
erat
e de
gree
will
giv
e ri
se to
the
perc
eptio
n of
the
othe
r ph
onem
e w
hen
pair
ed u
p w
ith a
str
ong
cue
that
fav
ors
the
othe
r
offs
and
cat
egod
cal p
erce
ptio
n co
uld
be b
roug
ht to
the
fore
. The
wor
dle
vel w
as e
limin
ated
alto
geth
er. a
nd a
t the
rho
nem
elev
el th
ere
wer
e on
lythree phonemes.
tal. Ig/.
and
Ik/,
plus silence
(I-I
).
From
thes
e fo
ur it
ems.
inputs and percepts of the form
ga-
and
ka-
coul
d be
con
stru
cted
.. T
he fo
llow
ing
addi
tiona
l con
stra
ints
wer
e im
pose
d on
the
feat
ure
spec
i-
fications of each of the phonemes: (I) the
Ial
and
I-I
had no overlap with
eith
er
Igl
or
Ik/,
so that neither
Ial
nor
I-I
wou
ld b
ias
the
activ
atio
ns o
fth
e Ig
l an
d Ik
l ph
onem
e un
its w
here
they
ove
rlap
ped
with
the
cons
onan
t:(2
) Ig
l an
d Ik
l w
ere
iden
tical
on
five
of
the
seve
n di
men
sion
s. a
nd d
iffe
red
only
on
the
rem
aini
ng tw
o di
men
sion
s,
The two dimensjons which differentiated
Igl
and
Ikl
wer
e vo
ice
onse
ttim
e (V
OT
) an
d th
e ()
nset
fre
quen
cy o
f th
e fi
tst f
orm
ant (
FIO
F), T
hese
dim
ensi
ons
repl
aced
the
voic
ing
and
burs
t am
plitu
de d
imen
sion
s us
ed in
all o
f th
e ot
her
sim
ulat
ions
, Fig
ure
14 il
lust
rate
s ho
w F
IOF
tend
s to
incr
ease
as
voic
e on
set t
ime
is d
elay
ed.
Sum
mer
fiel
d an
d H
agga
rd (
1977
) ha
ve s
how
n th
at s
ubje
cts
are
sens
itive
both
to V
aT a
nd to
FIO
F an
d th
at it
is p
ossi
ble
to tr
ade
one
of th
ese
cues off against the other. Thus. the boundary between
Igal
an
d Ik
al
shif
tsto
long
er V
OT
swhe
n FI
sta
rts
off
low
er r
athe
r th
an h
ighe
r,C
ateg
oric
al p
erce
ptio
n an
d tr
adin
g re
latio
ns a
mon
g cu
es h
ave
been
stud
ied
on a
var
iety
of d
iffer
ent c
ontin
ua b
y a
varie
ty o
f diff
eren
t inv
es-
tigat
ors,
We
have
chi
osen
to f
ocus
on
the
VO
T a
nd F
IOF
feat
ures
. as
exemplified by the
Igal
-/kal
co
ntin
uum
. bec
ause
ther
e is
dat
a on
trad
e-of
fs b
etw
een
thes
e cu
es (
Sum
mer
fiel
d &
Hag
gard
, 197
7). a
nd b
ecau
se
2000
1500
i'510
00Ii
I. 0:lL 500
TIM
E
FlU
, 14,
Sch
emat
ic d
iag~
am of a syllable that will be heard as
Igal
or
Ik
al,
depe
ndin
g on
the
poin
t in
the
sylla
ble
at w
hich
voi
cing
beg
ins,
Prio
r to
the
onse
t of v
oici
ng. F
2 '(l
OP
curv
el is
ene
rgiz
ed b
y ap
erio
dic
nois
e so
urce
s. a
nd F
I is
"cu
t bac
k" (
the
nois
e so
urce
has
liUle
or
no e
nerg
y in
this
ran
gel.
Bec
ause
of t
he fa
ct th
at F
t ris
es o
ver
time
afte
r sy
llabl
eon
set (
as th
e vo
cattr
uct m
oves
from
a s
hape
con
sist
ent w
ith th
e co
nson
ant i
nto
a. s
hape
cons
iste
nt w
ith...
he v
owel
l. its
freq
uenc
y at
the
onse
t of v
oici
ng is
hig
her
for
late
r va
lues
of V
OT
. Par
amet
ers
used
in c
onst
ruct
ing
this
sch
emat
ic s
ylla
ble
are
deri
ved
from
Kew
ley-
!'ort
's (
1982
1 an
alys
is o
f the
par
amet
ers
of fo
rman
ts. i
n na
tura
l spe
ech.
and
are
sim
ilar
toth
ose
used
in m
any
perc
eptu
al e
xper
imen
ts,
....
..5 0.
:5 0,
I.. U)
0.
....
..5 075
:5 0.
till
s..
en 025
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
Ioo
~80
I!i 4
9
, ~20
r 0
III
12345 Ikl
I .
Voi
ce O
nset
Tim
e10
0 20
0FR
ICA
TIO
N D
UR
AT
ION
(M
SEC
)
FIG
. .16
. Res
ulls
of a
n ex
perim
enl d
emon
slra
ling
Ihe
Irad
e-of
f bel
wee
n IW
O c
ues
10 Ih
eidentity of
Isl
and
Iii.
Dala from Denes, 1955
, fill
ed b
y th
e m
odel
of
Mas
saro
and
Coh
en,
1977. e. so ms; 0, 100 ms; 8, ISO ms; A
, 200
ms,
Rep
rinl
ed w
ilh p
erm
issi
on f
rom
Mas
saro
and
Coh
en (
1977
).
1.00
1&1
1234
5 Ik
l
trad
e-of
f cur
ves
as h
ave
been
gen
eral
ly r
epor
ted,
we
gene
rate
d a
set o
f25
inte
rmed
iate
pho
netic
seg
men
ts m
ade
up b
y pa
irin
g ea
ch o
f fi
ve d
if-
fere
nt in
term
edia
te p
atte
rns
on th
e V
OT
dim
ensi
on w
ith e
ach
of li
vedi
ffere
nt in
term
edia
te p
atte
rns
on th
e FI
OF
dim
ensi
on. T
he d
ilfcr
ent
feat
ure
patte
rns
used
on
each
dim
ensi
on a
re s
how
n in
Fig
. 15,
alo
ng w
iththe canonical feature patterns for
IgJ
and
Ikl
on e
ach
of th
e Iw
o di
men
-si
ons,
On
the
rem
aini
ng fi
ve d
imen
sion
s, th
e in
term
edia
te s
egm
ents
all
had the common canonical feature values for
Ig/
and
Ik/.
The
mod
el w
as te
sted
with
eac
h of
the
25 s
timul
i. pr
eced
ed b
y si
lenc
e(I
- I) and followed by
la-I.
In th
is a
nd
all s
ubse
quen
t sim
ulat
ions
we
repo
rtin
this
pap
er. t
he p
eak
of th
e in
itial
sile
nce
phon
eme
occu
rred
at T
ime
Slic
e 6
in th
e in
put.
and
the
peak
s of
suc
cess
ive
phon
eme
segm
ents
oc-
curred at six sl
ice
inte
rval
s. T
hus.
for
thes
e st
imul
i. th
e pe
ak o
n th
ein
term
edia
te p
hone
tic s
egm
ent o
ccur
red
at S
lice
12. t
he p
eak
of th
e fo
l-lo
win
g vo
wel
occ
urre
d at
Slic
e 18
. and
~he
pea
k of
the
fina
l sile
nce
oc-
curr
ed a
t Slic
e 24
. For
eac
h in
put '
pres
ente
d. th
e in
tera
ctiv
e ac
tivat
ion
proc
ess
was
allo
wed
to c
ontin
ue th
roug
h a
tota
l of 6
0 tim
e sl
ices
. wel
lpa
st th
e en
d of
the
inpu
t. T
he s
tate
of t
he T
race
at v
ario
us p
oint
s in
proc
essi
ng. f
or th
e m
ost/g
/~Ii
ke o
f th
e 25
stim
uli,
is s
how
n in
Fig
. 17.
At
the
end
of th
e 60
th ti
me
slic
e. w
e re
cord
ed th
e ac
tivat
ion
of th
e un
its f
orIg
/ an
d Ik
l in
Tim
e Sl
ice
12 a
nd th
e . probability of choosing
Igl
base
d on
thes
e ac
tivat
ions
, (It
mak
es n
o di
ffer
ence
to th
e qu
alita
tive
appe
aran
ceof
the
resu
lts if
a d
iffer
ent d
ecis
ion
time
is u
sed;
ear
lier
deci
sion
tim
esar
e as
soci
ated
with
sm
alle
r di
ffer
ence
s in
rel
ativ
e ac
tivat
ion
betw
een
the
IgI
and
Ikl
phon
eme
units
. and
late
r on
es w
ith la
rger
dif
tere
nces
. but
the
gene
ral p
atte
rn is
the
sam
e,
Ft Onset Frequency
FIG
. 15.
Can
onic
al fe
atur
e-level inpul for Ig! and I
kI,
on I
helw
o di
men
sion
s Ih
al d
islin
guis
h .
them
. and
Ihe
palle
rns
used
for
the
live
inle
rmed
iale
val
ues
used
in th
e Ir
adin
g re
lalio
nssi
mul
atio
n, A
long
Ihe
absc
issa
of e
ach
dim
ensi
on Ih
e ni
ne u
nils
for
the
nine
dil1
eren
l val
uerdnges of the dimension are armyed. The curves labeled Ig! and
Ikl
jndi
cale
Ihe
rela
live
slre
nglh
of
the
exci
tato
ry in
pullo
eac
h i,)
f Ihe
se u
nils
, pro
duce
d by
Ihe
indi
cale
d ph
onem
e.T
he c
anon
ical
cur
ves
also
indi
cale
Ihe
slr
engl
hs o
f th
e fe
atur
e-la
- pho
nem
e co
nnec
lions
for
Ig!.
an
d Ik
l on
Ihe
se d
imen
sion
s. T
hai i
s. I
he c
anon
ical
inpu
t pal
lern
for
eac
h ph
onem
eex
aclly
mal
ches
Ihe
slr
engl
hs o
f Ih
e co
rres
pond
ing
feat
ure-
phon
eme
conn
eclio
ns. N
um-
bere
d cu
rves
on
each
dim
ensi
on s
how
Ihe
feat
ure
palle
rns
used
in Ih
e Ir
adin
.: re
lalio
nssi
mul
alio
n.
phon
eme,
An
addi
tiona
l fin
ding
is th
e bo
win
g of
the
curv
es; t
hey
tend
tobe
app
roxi
mat
ely
linea
r th
roug
h th
e m
iddl
e of
thei
r ra
nge,
but
to le
vel
off a
t bot
h en
ds. w
here
' the
val
ues
on b
oth
dim
ensi
ons
agre
e in
poi
ntin
gto
one
alte
rnat
ive
or th
e ot
her,
To
see
if T
RA
CE
wou
ld s
imul
ate
the
basi
c tr
ade-
off
effe
ct o
btai
ned
bySu
mm
erfi
eld
and
Hag
gard
. and
to s
ee if
it w
ould
prd
duce
the
sam
e sh
ape
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
~ 1,
00"-
060
-..c
Ik/-
like
valu
es o
n bo
th d
imen
sion
s, In
term
s of
Sum
mer
field
and Hag-
gard
's m
easu
re. t
he v
alue
of
VaT
nee
ded
to a
chie
ve 5
0% p
roba
bilit
y of
repo
rtin
g Ik
/. w
e ca
n se
e th
at th
e V
aT n
eede
d in
crea
ses
as th
e FI
OF
decr
ease
s, ju
st a
s th
ese
inve
stig
ator
s fo
und.
C
ue tr
ade-
offs
in p
hone
me
iden
tific
atio
n ar
e ac
coun
ted
for
in d
etai
l by
the
feat
ure
inte
grat
ion
mod
el o
fOde
n an
d M
assa
ro (
1978
; Mas
saro
. 198
1;
Mas
sarQ
and
Ode
n. I
980a
. 198
0b);
Whi
le w
e ha
ve s
how
n ho
w T
RA
CE
can
acco
unt f
or th
e ba
sic
trad
e-of
f ef
fect
and
the
gene
ral f
orm
of
the
trad
e-of
f cur
ves.
we
have
not
yet
atte
mpt
ed th
e ki
nds
of d
etai
led
fits
that
Mas
saro
, Ode
n, a
nd c
olla
bora
tors
hav
e re
port
ed in
a n
umbe
r of
stu
dies
,H
owev
er. t
he m
odel
s ar
e qu
ite s
imila
r. s
o it
seem
s ra
ther
unl
ikel
y th
atcu
e tr
ade-
off
data
wou
ld b
e ab
le to
diS
crim
inat
e be
twee
n th
em, A
nd b
oth
mak
e sp
ecia
l ass
umpt
ions
abo
ut la
ck o
f in
vari
ance
of
cues
to p
hone
me
iden
tity
acro
ss c
onte
xts,
O
ne a
ppar
ent d
issi
mila
rity
bet
wee
n th
e m
odel
s de
serv
es c
omm
ent.
Whe
reas
cue
str
engt
hs a
re c
ombi
ned
mul
tiplic
ativ
ely
in th
e de
term
inat
ion
of r
espo
nse
stre
ngth
s in
the
feat
ure
inte
grat
ion
mod
el. t
hey
are
com
bine
dad
ditiv
eiy
in th
e bo
ttom
-up
inpu
ts to
the
units
in T
RA
CE
, How
ever
, in
TR
AC
E, t
wo
furt
her
com
puta
tiona
l ste
ps ta
ke p
lace
bef
ore
thes
e in
puts
result in resp
onse
str
engt
hs. F
irst
, the
inte
ract
ive-
activ
atio
n process en-
hanc
es d
iffe
renc
es b
etw
een
com
petin
g un
its, S
econ
d, th
e re
sulti
ng u
nit
activ
atio
ns a
re s
ubje
cted
to a
n ex
pone
ntia
l tra
nsfo
rmat
ion.
Jus
t thi
s. second step by its
elf
wou
ld tr
ansf
orm
infl
uenc
es th
at h
ave
addi
tive
effe
cts
on u
nit a
ctiv
atio
ns in
to in
flue
nces
that
. hav
e m
ultip
licat
ive
effe
cts
on r
e-sp
onse
str
engt
h. T
hus,
the
mod
els
wou
ld b
e m
athe
mat
ical
ly e
quiv
alen
tif
the
inte
ract
ive
activ
atio
n pr
oces
s w
ere
sim
ply
repl
aced
by
a lin
ear,
addi
tive
com
bina
tion
of in
puts
to th
e un
its. I
n qu
antit
ativ
e fo
rmul
atio
nsof
the
inte
ract
ive
activ
atio
n pr
oces
s cl
osel
y re
late
d to
the
ones
we
use
(Gro
ssbe
rg, 1
978)
, wha
t the
inte
ract
ive
activ
atio
n pr
oces
s do
es is
sim
ply
resc
ale
the
unit
activ
atio
ns, p
rese
rvin
g th
e ra
tios
of th
eir
botto
m-u
pac
tivat
ion
but k
eepi
ng th
em b
ound
ed. T
houg
h ou
r ve
rsio
n of
thes
e eq
ua-
tions
doe
s no
t do
this
exa
ctly
, the
way
s in
whi
ch it
dev
iate
s fr
om th
isw
ould
be
diff
icul
t to
use
as th
e ba
sis
for
an e
mpi
rica
l dis
tinct
ion
betw
een
the
TR
AC
E a
ppro
ach
and
the
feat
ure
inte
grat
ion
mod
el"
Thu
s, u
p to
apo
int,
we
can
see
TR
AC
E a
s (a
ppro
xim
atel
y) im
plem
entin
g th
e co
mpu
-ta
tions
spe
cifi
ed in
ade
n an
d M
assa
ros
mod
el. T
he m
odel
s di
ffer,
thou
gh, i
n th
at T
RA
CE
is d
ynam
ic a
nd in
that
it in
corp
orat
es f
eedb
ack
to th
e ph
onem
e le
vel.
Thi
s al
low
s T
RA
CE
to a
ccou
nt f
or c
ateg
oric
alpe
rcep
tion
in a
diff
eren
t way
.Categorical perception.
In s
pite
ofth
e fa
ct th
at T
RA
CE
is q
uite
flex
ible
in th
e w
ay it
com
bine
s in
form
atio
n fr
om d
iffe
rent
fea
ture
s to
det
erm
ine
the identity of a ph
onem
e, th
e m
odel
is q
uite
categorical in its overt
resp
onse
s, T
his
is il
lust
rate
d in
two
way
s: f
irst
. the
mod
el s
how
s a
muc
hsh
arpe
r tr
ansi
tion
in it
s ch
oice
s of
res
pons
es a
s w
e m
ove
from
Ig/ to
Ikl
07+
- g
II..
g 04
~ 03
5;!.
0 I
Xn"
-X
..- -
Xa-
+2
-X..- +.
1'10
. 17,
The
sta
te o
f the
'/i'ac
e at
var
ious
poi
nts
durin
g an
d af
ter
the
pres
enta
tion
of a
sylla
hle
cuns
istil
fg (
,f th
e m
ost I
gI-l
ike
ot th
e 2S
inte
rmed
iate
seg
men
ts u
sed
in th
e tr
adin
grelations experiment. represented by
I'!(/
. preceded by silence and followed by
lal,
then
anot
her
sile
nce.
Res
pons
e pr
obab
ilitie
s w
ere
com
pute
d us
ing
the
form
ulas
giv
en e
arlie
rfo
r co
nver
ting
activ
atio
ns to
res
pons
e st
reng
ths
and
stre
ngth
s in
to p
rob-
abili
ties,
The
res
ultin
g re
spon
se p
roba
bilit
ies,
for
eac
h of
the
25 c
ondi
-tio
ns o
f th
e ex
peri
men
t, ar
e sh
own
' in
Fig
, 18
. The
pat
tern
of
resu
lts is
quite
sim
ilar
to th
at o
btai
ned
in D
enes
(1955) experiment on the
1st-
cont
inuu
m. T
he c
ontr
ibut
ion
of e
ach
cue
is a
ppro
xim
atel
y lin
ear
and
addi
tive
in th
e m
iddl
e of
the
rang
e; b
ut th
e cu
rves
fla
tten
out a
t the
extr
emes
, as
in th
e D
enes
(19
55)
expe
rim
ent.
Mor
e im
port
antly
, the
mod
-el
's b
ehav
ior
exhi
bits
the
abili
ty to
trad
e on
e cu
e of
f ag
ains
t ano
ther
. For
exam
ple,
ther
e ar
e th
ree
diffe
rent
com
bina
tions
of f
eatu
re v
alue
s w
hkh
lead
to a
pro
babi
lity
betw
een
.82
and
,85 of choosing
Ik/:
(I)
the
neut
ral
valu
e of
the
VO
T d
imen
sion
cou
pled
with
the
mos
t Ik/
-lik
e va
lue
on th
e1'
101'
dim
ensi
on: (
2) th
e ne
utra
l val
ue o
n th
e F
IOF
dim
ensi
on c
oupl
edw
ith th
e m
ost I
k/-l
ike
valu
e of
the
VaT
dim
ensi
on; a
nd (
3) th
e so
mew
hat
...;' '- 060-
Yoke Olisel.Tirne
FI(L III, Simulated prob;lbility of choosing
Ik/ll
t T
ime
Slic
e 1i
0, fo
r ea
ch o
f the
25
stim
uli
used
in 'h
e tr
adin
g re
latio
ns s
imul
atio
n ex
peri
men
t. N
umbe
rs n
ext t
o ea
ch c
urve
ref
er to
the
inte
rmed
iate
p;ll
Iern
on,
the
FIO
F c
ontin
uum
use
d in
the
five
stim
uli c
ontr
ibut
ing
toea
ch c
urve
, Uig
her
num
bers
cor
resp
ond
to h
ighe
r va
lues
of F
IOF
.
:..,
::= 0
40-
020
a.. 0,
0 I
3, 4
6
7 8
\I 10 II 12
Stim
ulus
Num
ber
FIG
. 20.
Eff
ects
of
com
petit
ion
on p
hone
me
activ
iltio
ns. T
he f
irst
pan
el s
how
s re
lativ
eamounts of bollom-up excitatory input to
Igl
and
IkJ
produced by each of the II st
imul
ius
ed in
the
cate
goric
al p
erce
ptio
n si
mul
atio
n, T
he s
econ
d pa
nel s
how
s th
e ac
tivat
ions
ul"
units for Ig/ and
Ikl
at T
ime
Cyc
le 6
0, S
timul
i 3 a
nd 9
cor
resp
und
10 I
he c
anon
ical
/gl a
ndIk
/, re
spec
tivel
y.
of th
e un
its f
or /g
/ and
/k/ a
t the
end
of
60 c
ycle
s of
pro
cess
ing.
The
slig
htdi
ffer
ence
s in
net
inpu
t hav
e be
en g
reat
ly a
mpl
ified
. and
the
activ
atio
ncu
rves
exh
ibit
a m
uch
stee
per
tran
sitio
n th
an th
e re
lativ
e bo
ttom
-up
ex-
cita
tion
curv
es.
The
re a
re tw
o re
ason
s w
hy th
e ac
tivat
ion
curv
es ,a
re s
o m
uch
shar
per
than
the
initi
al b
otto
m-u
p ex
cita
tion
func
tions
. The
pri
mar
y re
ason
iscompetitive inhibition.
The
eff
ect o
f th
e co
mpe
titiv
e in
hibi
tion
at th
e ph
o-ne
me
leve
l is
to g
reat
ly m
agni
fy th
e sl
ight
diff
eren
ce in
the
exci
tato
ryin
puts
to th
e tw
o ph
onem
es. I
t is
easy
to s
ee w
hy th
is h
appe
ns. O
nce
one
phon
eme
is s
light
ly m
ore
stro
ngly
act
ivat
ed th
an th
e ot
her.
it e
xert
sa
stro
nger
inhi
bito
ry in
fluen
ce o
n th
e ot
her
than
the
othe
r ca
n ex
ert o
nit.
The
net
res
ult i
s th
at "
the
rich
get r
iche
r," This general property of
com
petit
ive
inhi
bitio
n m
echa
nism
s w
as d
iscu
ssed
by
McC
lella
nd a
nd R
u-m
elha
rt (
1981
), fo
llow
ing
earli
er o
bser
vatio
ns b
y G
ross
berg
(se
e G
ross
-berg, 1978, f
or a
dis
cuss
ion)
and
Lev
in (
1976
); it
is a
lso
wel
l kno
wn
ason
e po
ssib
le b
asis
' of e
dge
enha
ncem
ent e
ffec
ts in
low
leve
ls o
f vi
sual
TR
AC
E M
OD
EL
alon
g th
e V
aT a
nd F
IOF
dim
ensi
ons
than
we
wou
ld e
xpec
t fro
m th
esl
ight
cha
nges
in th
e re
lativ
e ex
cita
tion
of th
e /g
/ and
/kI
units
. Sec
ond,
.th
e m
odel
tend
s to
obl
itera
te d
iffer
ence
s be
twee
n di
ffere
ntin
puts
whi
chit
iden
tifie
s as
the
sam
e ph
onem
e, w
hile
sha
rpen
ing
diff
eren
ces
betw
een
inpu
ts a
ssig
ned
to d
iffe
rent
cat
egor
ies,
We
will
con
side
r ea
ch o
f th
ese
two
poin
ts in
turn
, aft
er w
e de
scrib
ethe
stim
uli u
sed
in the simulations.
Ele
ven
diff
eren
t con
sona
nt f
eatu
re p
atte
rns
wer
e us
ed, e
mbe
dded
inth
e sa
me
sim
ulat
ed /-
/ context as in the trading relations simulation,
The
stim
uli v
arie
d fr
om v
ery
low
val
ues
of b
oth
VaT
and
FIOF, more
extr
eme
than
the
cano
nica
l /g/
, thr
ough
ver
y hi
gh v
alue
s on
bot
h di
men
-sions, more extreme than the canonical
/kl.
All
the
stim
uli w
ere
spac
edeq
ual d
ista
nces
apa
rt o
n th
e V
aT a
nd F
IOF
dim
ensi
ons,
The
loca
tions
of th
e pe
ak a
ctiv
atio
n va
lues
on
each
of
thes
e tw
o co
ntin
ua a
re s
how
nin
Fig
, 19,
F
igur
e 20
indi
cate
s th
e re
lativ
e in
itial
bot
tom
-up
activ
atio
n of
the
/g/
, and
/k/ p
hone
me
units
for
eac
h of
the
II stimuli used in the simulation.
The
firs
t thi
ng to
not
e is
that
the
rela
tive
botto
m-u
p ex
cita
tion
of th
e tw
oph
onem
e un
its d
iffe
r on
ly s
light
ly, F
or e
xam
ple,
the
cano
nica
l fea
tl,Jr
epa
ttern
for
/g/ s
ends
75%
as
muc
h ex
cita
tion
(0 /g
/ as
it se
nds
to /k
/, T
hefe
atur
e pa
ttern
two
step
s to
war
d/g/
from
/k/ (
Stim
ulus
5),
sen
ds 8
8% a
sm
uch
activ
atio
n to
/g/ a
s to
/k/.
The
fig
ure
also
indi
cate
s, in
the
seco
nd p
anel
, the
res
ultin
g ac
tivat
ions
r:: 0 1.
::;.... 0
0.c.
J
iii 0.
::;
026
r::
!:! 1.
....
::; 0. 0:
10
5 0.
.r:: Il.
/s/
/k/
1 2 3 4 5 6 7 8 91011
Voi
ce O
nsel
Tim
e
/s/
/k/
1 2
3 4
5 6
7 8
9 10
11
0 2
Ft Onsel Frequency
FtG
. t9.
Loc
atio
ns o
f pe
ak a
ctiv
atio
ns a
long
Ihe
VaT
and
FtO
F di
men
sion
s. lo
r ea
ch o
fth
e II
stim
uli u
sed
in th
e ca
tego
rica
l per
cept
ion
sim
ulat
ion.
MC
CLE
LLA
ND
AN
D E
LMA
N
/8/
/k/
...
1'2
Stim
ulus
Num
ber
/s/
/k/
TR
AC
E M
OD
EL
:46
MC
CLE
LLA
ND
AN
D E
LMA
N
/81
Ikl
Thi
s ob
viou
sly
brin
gs o
ut th
e fa
ct th
at th
e ap
pare
nt s
teep
ness
of
the
iden
tific
atio
n fu
nctio
n de
pend
s on
the
grai
n of
the
sam
plin
g of
diff
eren
tpo
ints
alo
ng th
e co
ntin
uum
bet
wee
n tw
o st
imul
i, as
wel
l as
a ho
st
othe
r fa
ctor
s (L
ane,
196
5), W
heth
er a
n em
piri
cal o
r si
mul
ated
iden
tifi-
catio
n fu
nctio
n lo
oks
stee
p or
not
dep
ends
on
the
sele
ctio
n of
stim
uli b
yth
e ex
peri
men
ter
or m
odel
er, H
owev
er, i
t is
wor
th n
otin
g th
at th
e st
eep-
ness
of
the
iden
tific
atio
n fu
nctio
n is
inde
pend
ent o
f th
e pr
esen
ce o
ftr
adin
g re
latio
ns, a
t lea
st in
the
sim
ulat
ion
mod
el, T
hat i
s, if
we
had
used
mor
e w
idel
y se
para
ted
step
s al
ong
the
VO
T a
nd F
IOF
dim
ensi
on, w
e
wou
ld h
ave
obta
ined
muc
h st
eepe
r id
entif
icat
ion funct1Qns. The additivity
of e
xcita
tory
inpu
ts w
ould
stil
l app
ly, a
nd th
us it
wou
ld s
till b
e po
ssib
leto trade cues off against e~ch other,
In T
RA
CE
, the
cat
egor
ical
out
put o
f th
e m
odel
com
es a
bout
onl
y af
ter
an interactive competition process that greatly sharpens the differences
in the activation of the detectors for the relevant units, This interactive
proc
ess
take
s tim
e. I
n th
e si
mul
atio
n re
sults
rep
orte
d he
re, w
e as
sum
edth
at s
ubje
cts
wai
ted
a fi
xed
time
befo
re r
espo
ndin
g. B
ut, i
f w
e as
sum
e, t
hat s
ubje
cts
are
able
to r
espo
nd a
s so
on a
s th
e re
spon
se st
reng
th r
atio
reac
hes
som
e cr
iteri
alle
vel,
we
wou
ld f
ind
that
sub
ject
s w
ould
be
able
to r
espo
nd m
ore
quic
kly
to s
timul
i nea
r th
e pr
otot
ype
of e
ach
cate
gory
than
they
can
to s
timul
i nea
r th
e bo
unda
ry, T
his
is e
xact
ly w
hat w
as
foun
d by
Pis
o~i a
nd T
ash
(197
4).
The
sha
rpen
ing
the
mod
el im
pose
s on
the
iden
tific
atio
n fu
nctio
n,
conj
unct
ion
with
the
faC
t tha
t it c
an tr
ade
one
feat
ure
off
agai
nst a
noth
er,
show
s ho
w th
e m
odel
, lik
e hu
man
per
ceiv
ers
of s
peec
h, c
an b
e bo
th
flex
ible
and
dec
isiv
e at
the
sam
e tim
e, T
hese
asp
ects
of T
RA
CE
are
shar
ed w
ith th
e fe
atur
e in
tegr
atio
n m
odel
(M
assa
ro, 1
981)
,. How
ever
, the
TR
AC
E m
odel
's d
ecis
iven
ess
exte
nds
eve.
1 fu
rthe
r th
an w
e ha
veob
-
serv
ed th
us f
ar: f
eedb
ack
from
the
phon
eme
to th
e fe
atur
e le
vel t
ends
to.
caus
e th
e m
odel
to o
blite
rate
the
diffe
renc
es b
etw
een
inpu
t fea
ture
pat
-te
rns
that
res
ult i
n th
e id
entif
icat
ion
of th
e sa
me
phon
eme,
thus
allo
win
gth
e m
odel
to p
rovi
de a
n ac
coun
t not
onl
y fo
r sh
arp
iden
tific
atio
n fu
nc-
tions
, but
als
o fo
r th
e fa
ct th
at d
iscr
imin
abili
ty o
f spee
ch s
ound
s is
far
poor
er w
ithin
cat
egor
ies
than
it is
bet
wee
n ca
tego
ries
.S
tric
tly s
peak
ing,
at l
east
as
defin
ed b
y Liberman, Cooper, Shank-
wei
ler,
and
Stu
dder
t-K
enne
dy (
1967
), tr
ue c
ateg
oric
al p
erce
ptio
n is
onl
yex
hibi
ted
whe
n th
e ab
ility
to d
iscr
imin
ate
diff
eren
t sou
nds
is n
o be
tter
than
. cou
ld b
e ex
pect
ed '
base
d on
the
assu
mpt
ion
that
the
only
bas
is a
liste
ner
has
for
disc
rim
inat
ion
is th
e ca
tego
rica
l ass
ignm
ent o
f th
e st
im-
ulus
to a
par
ticul
ar p
hone
tic c
ateg
ory,
How
ever
, it i
s co
nced
ed th
attr
ue"
cate
gori
cal p
erce
ptio
n in
this
sem
o: is
nev
er in
fac
t obs
erve
d(S
tudd
ert-
Ken
nedy
, Lib
erm
an, H
arri
s, &
Coo
per,
197
0), W
hile
it is
true
that
the
disc
rimin
atio
n o
f so
unds
is m
uch
bette
r fo
r so
unds
whi
ch p
er-
info
rmat
ion
proc
essi
ng, A
sec
ond
caus
e of
the
shar
peni
ng o
f th
e ac
tiva-
tion
curv
es is
the
phon
eme-
to-f
eatu
re fe
edba
ck, w
hich
we
cons
ider
in
deta
il in
a m
omen
t. T
he id
entif
icat
ion
func
tions
that
res
ult f
rom
app
lyin
g th
e L
uce
choi
ceru
le to
the
activ
atio
n va
lues
sho
wn
in th
e se
cond
pan
el o
f Fi
g, 2
0 ar
e
show
n in
Fig
. 21 along with the
lBX
di
scri
min
atio
n fu
nctio
n, w
hich
is
disc
usse
d be
low
. The
iden
tific
atio
n fu
nctio
ns a
re e
ven
shar
per
than
the
activ
atio
n cu
rves
; the
re is
onl
y a
4% c
hanc
e th
at th
e m
odel
will
choo
se
/k/ i
nste
ad o
f /g
/ for
Stim
ulus
5, f
or w
hich
/k/ r
ecei
ves
88%
as
muc
h
botto
m-u
p su
ppor
t as
/g/,
The
in~r
ease
d sh
arpn
ess
is d
ue to
th~
prop
ertie
s
of th
e re
spon
se s
tren
gth
assu
mpt
ions
. The
se a
ssum
ptio
ns e
ssen
tially
im-
plem
ent t
he n
otio
n th
at th
e se
nsiti
vity
of
the
deci
sion
mec
hani
sm, i
n
terms of
d'
for
choo
sing
the
mos
t str
ongl
y. a
ctiv
ated
of
two
units
, is
a
linea
r fu
nctio
n of
the
diff
eren
ce in
act
ivat
ion
of th
e tw
o un
its, W
hen
the
activations are far enough apart,
d'
)Viii
be
suffi
cien
t to
ensu
re n
ear-
lOO
%
corr
ect p
elfo
rman
ce, e
ven
thou
gh b
oth
units
hav
e gr
eate
r th
an 0
act
iva-
tion,
Of
cour
se, t
he .
amou
nt o
f se
para
tion
in th
e ac
tivat
ions
that
is n
ec-
essa
ry f
or a
ny g
iven
leve
l of
perf
orm
ance
is a
mat
ter
of p
aram
eter
s; th
ere
leva
nt p
aram
eter
her
e is
the
scal
e fa
ctor
use
d in
the
expo
nent
ial t
rans
-fo
rmat
ion
of a
ctiv
atio
ns. T
he v
alue
use
d fo
r th
is p
aram
eter
in th
e pr
esen
tsi
mul
atio
ns (
10)
was
the
sam
e as
that
use
d in
all
othe
r ca
ses
whe
re w
etr
ansl
ate
activ
atio
n in
to r
espo
nse
prob
abili
ty, i
nclu
ding
the
trad
ing:
rela
-tio
ns s
imul
atio
n.
Som
e re
ader
s m
ay b
e pu
zzle
d as
to w
hy T
RA
CE
II
exhi
bits
a s
harp
iden
tific
atio
n fu
nctio
n in
the
cate
gori
cal p
erce
ptio
n ex
peri
men
t, bu
tsh
ows
a m
uch
mor
e gr
adua
l tra
nsiti
on b
etw
een
/g/ a
nd /k
/ in
the
trad
ing
rela
tions
sim
ulat
ion,
The
rea
son
is s
impl
y th
at f
iner
ste
ps a
long
the
VO
Tan
d FI
OF
cont
inua
wer
e us
ed in
the
trad
ing
rela
tions
sim
ulat
ion,
All
of
the stimuli for the tl1ading relations si
mul
atio
n lie
bet
wee
n St
imul
i 6 a
nd4
in th
e ca
tego
rica
l per
cept
ion
sim
ulat
ion.
~ 1. 10
0
~ o~-
~ 0.
'-.. 0.
.. 6: 0. 00
0
020
10 II
Stim
ulus
F"L 21. Simulated identilicalion functions and forced-choice accuracy in the
AB
X
task
.
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
ceiv
ers
assi
gn to
dif
fere
nt c
ateg
orie
s th
an f
or s
ound
s th
ey a
ssig
n to
the
sam
e ca
tego
ry, t
here
is a
lso
at le
ast a
tend
ency
for
disc
rimin
atio
n to
be
som
ewha
t bet
ter
than
pre
dict
ed b
y th
e id
entif
icat
ion
func
tion,
eve
n be
-tw
een
stim
uli w
hich
are
alw
ays
assi
gned
to th
e. s
ame
cate
gory
. TR
AC
EII
pro
duce
s th
is k
ind
of a
ppro
xim
ate
cate
gori
cal p
erce
ptio
n.T
he w
ay it
wor
ks is
this
, Whe
n a
feat
ure
patte
rn c
omes
in, i
t sen
dsm
ore
exci
tatio
n to
som
e ph
onem
e un
its th
an o
ther
s; a
s th
ey b
ecom
eac
tive,
they
beg
in to
com
pete
, and
one
gra
dual
ly c
omes
to d
omin
ate
the
othe
rs, T
his
muc
h w
e ha
ve. a
lread
y ob
serv
ed, B
ut a
s th
is c
ompe
titio
npr
oces
s is
goi
ng o
n, th
ere
is a
lso
feed
bpck
from
the
phon
eme
leve
l to
the
feat
ure
leve
l. T
hus,
as
a pa
rtic
ular
pho
nem
e be
com
es a
ctiv
e, it
tend
s to
impo
se it
s ca
noni
cal p
atte
rn o
f act
ivat
ion
on th
e fe
atur
e le
vel,
The
effe
ctof
the
feed
back
bec
omes
par
ticul
arly
str
ong
as ti
me
goes
on,
sin
ce th
efe
atur
e in
put o
nly
exci
tes
the
feat
ure
units
ver
y br
iefly
; the
orig
inal
pat
-te
rn o
f ac
tivat
ion
prod
uced
by
the
phon
eme
units
is, t
here
fore
, gra
dual
lyre
plac
ed b
y th
e ca
noni
cal p
atte
rn im
pose
d by
the
feed
back
from
the
pho-
" ne
me
leve
l, T
he r
esul
t is
tha~
the
patte
rn o
f ac
tivat
ion
rem
aini
ng a
t the
feat
ure
leve
l aft
er 6
0 cy
cles
of
proc
essi
ng h
as b
ecom
e as
sim
ilate
d to
the
prot
otyp
e, I
n th
is w
ay, f
eatu
re p
atte
rns
for
diff
eren
t inp
uts
assi
gned
toth
e sa
me
cate
gory
are
ren
dere
d ne
arly
indi
stin
guis
habl
e,A
n im
pres
sion
of
the
mag
nitu
de o
f th
is e
ffec
t is
illus
trat
ed in
Fig
, 22,
whi
ch s
how
s ho
w d
iffe
rent
the
feat
ure
patte
rns
of a
djac
ent s
timul
i are
at
the
end
of 6
0 cy
cles
of
proc
essi
ng. T
he m
easu
re o
f di
ffere
nce
is s
impl
yI -
"b'
whe
re
"b
stan
ds f
or th
e co
rrel
atio
n of
the
patte
rns
prod
uced
by
stim
uli
and
b,
Onl
y th
e tw
o di
men
sion
s w
hich
act
ually
dif
fer
betw
een
the canonical
IgI
and
Ikl
are
cons
ider
ed in
the
diffe
renc
e m
easu
re, F
ur-
ther
mor
e, th
e co
rrel
atio
n co
nsid
ers
only
the
feat
ure
patte
rn o
n th
e fe
atur
e
units
in T
ime
Slic
e 12
, rig
ht a
t the
cen
ter
of th
e in
put s
peci
fica
tion.
If
all
dim
ensi
ons
are
cons
ider
ed, t
he v
alue
s of
the
diff
eren
ce m
easu
re a
re r
e-du
ced
over
all,
but t
he p
atte
rn is
the
sam
e, In
clus
ion
of ft
!'dtu
re p
atte
rns
from
sur
roun
ding
slic
es li
kew
ise
mak
es li
ttle
diffe
renc
e.T
o re
late
the
diffe
renc
e be
twee
n tw
o st
imul
i ~o
prob
abili
ty c
orre
ctchoice performance in the
AB
X
task
gen
eral
ly u
sed
in c
ateg
oric
al p
er-
cept
ion
expe
rimen
ts, w
e on
ce a
gain
use
the
Luce
(19
59) choice model.
The
pro
babi
lity
of id
entif
ying
stim
ulus
with alternative
in is given
by
Ix=
,,)
II.(
w
here
Sax is the "st
reng
th"
of th
e si
mila
rity
between (/ and
x.
Thi
s is
given simply by the exponential of the correlation of
and
"x = e
k,r"
x
g 0.
is 0.
and similarly for
Sbx'
(T
he e
xpon
entia
l tra
nsfo
rmat
ion
is r
equi
red
to tr
ans-
late
cor
rela
tions
, ran
ging
fro
m +
Ito
- I,
into
pos
itive
val
ues,
so
that
Luc
es
ratio
rul
e ca
n be
use
d. T
he s
ame
tran
sfor
mat
ion
is u
sed
for
tran
s-la
ting
activ
atio
ns in
to r
espo
nse
stre
ngth
s in
iden
tific
atio
n ta
sks.
) Here
is th
e pa
ram
eter
that
sca
les
the
rela
tion
betw
een
corr
elat
ions
and
stre
ngth
s, T
hese
ass
umpt
ions
are
con
sist
ent w
ith th
e ch
oice
ass
umpt
ions
mad
e fo
r id
entif
icat
ion
resp
onse
s, T
he r
esul
ting
resp
onse
pro
babi
litie
s,for one choice of the parameter
,.
(5)
are
show
n in
Fig
; 21
(the
exp
onen
-
tiation parameter
,.
is different than the parameter
used
in g
ener
atin
g
iden
tific
atio
n pr
obab
ilitie
s fr
om a
ctiv
atio
ns b
ecau
se c
orre
latio
ns a
nd a
c-tivations are not on equivalent scales),
Bas
ical
ly, t
he f
igur
e sh
ows
that
the
effe
ct o
f fe
edba
ck is
to m
ake
the
feat
ure
patte
rns
for
inpu
ts w
ell w
ithin
eac
h ca
tego
ry m
ore
sim
ilar
than
thos
e fo
r in
puts
nea
r th
e bo
unda
ry b
et~e
en categories. Differences be-
twee
n st
imul
i nea
r th
e pr
otot
ype
of th
e' s
ame
phon
eme
are
alm
ost o
bli-
tera
ted.
Whe
n tw
o st
imul
i str
addl
e th
e bo
unda
ry, t
he fe
atur
e-level pat-
tern
s ar
e m
uch
mor
e di
stin
ct. A
s a
resu
lt, th
e pr
obab
ility
of c
orre
clly
disc
rim
inat
ing
stim
uli w
ithin
a p
hone
me
cate
gory
is m
uch
low
er I
han
Ihe
prob
abili
ty o
f di
scri
min
atin
g st
imul
i in
diff
eren
t cat
egor
ies.
The
pro
cess
of
"can
onic
aliz
atio
n" of the representation of a speech
soun
d vi
a th
e fe
edba
ck m
echa
nism
take
s tim
e. O
urin
g Ih
is li
me,
Iw
oth
ings
are
hap
peni
ng: o
ne is
that
the
activ
atio
ns in
itial
ly p
rodu
ced
by th
esp
eech
inpu
t are
dec
ayin
g; a
noth
er is
that
the
feed
back
, whi
ch d
rive
s th
ere
pres
enta
tion
tow
ard
the
prot
otyp
e, is
bui
ldin
g up
. In
the
sim
ulat
ions
,
we
allo
wed
a c
onsi
dera
ble
amou
nt o
f tim
e fo
r th
ese
proc
esse
s be
fore
r:::
030
I 2
7 8
8 10. II 12
Stim
ulus
Num
ber
FIG
. 22.
Diff
eren
ces
betw
een
palle
rns
of a
ctiv
atio
n at
the
feat
ure
leve
l at C
ycle
60.
I()r
pairs of stimuli one step apart along the
Ir/-
iki
cont
inuu
m u
sed
for
prod
ucin
g th
e id
entif
i-ca
tion
func
tions
sho
wn
prev
ious
ly in
Fig
. 21.
The
dif
fere
nce
mea
sure
is th
e co
rrel
atio
n of
the
two
patte
rns,
sub
trac
ted
from
1.0
; thu
s, if
the
two
patte
rns
corr
elat
ed p
erfe
ctly
, the
irdifference would be O.
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
L~ '
com
putin
g si
mila
ritie
s of
dif
fere
nt a
ctiv
atio
n pa
ttern
s to
eac
h ot
her,
Ob-
viou
sly.
if w
e ha
d le
ft le
ss ti
me.
ther
e w
ould
not
hav
e be
en a
s m
uch
ofan
opp
ortu
nity
for
thes
e fo
rces
to o
pera
te. T
hus,
TR
AC
E is
in a
gree
men
twith the finding that there tends to be an increase in within-category
disc
rimin
atio
n w
hen
n ta
sk is
use
d w
hich
allo
ws
subj
ects
to b
ase
thei
r
resp
onse
s on
judg
m~n
ts o
f th
e si
mila
rity
of
stim
uli s
pace
d cl
osel
y to
-ge
ther
in ti
me
(Pis
onl&
Laz
arus
, 197
4).
It s
houl
d be
not
ed th
at it
wou
ld b
e po
ssib
le to
acc
ount
for
cat
egor
ical
perc
eptio
n in
TR
AC
E w
ithou
t inv
okin
g fe
edba
ck f
rom
the
phon
eme
leve
lto
the
feat
ure
leve
l, A
ll w
e w
ould
nee
d to
~o
is a
ssum
e th
at th
e fe
atur
ein
form
atio
n th
at g
ives
ris
e to
pho
nem
e id
entif
icat
ion
is in
acce
ssib
le, a
s. p
ropo
sed
by th
e m
otor
theo
ry o
f sp
eech
per
cept
ion
(Lib
erm
an e
t ai"
1967
). o
r is
rap
idly
lost
as
prop
osed
by
the
"dua
l-co
de"
mod
el (
Fujis
aki
& K
awas
him
a, 1
968;
Mas
saro
. 1975, 1981; Pisoni, 1973, 1975,)
The
dua
l-
code
mod
el, w
hich
has
had
con
side
rabl
e su
cces
s ac
coun
ting
for
cate
gor-
ical
per
cept
ion
data
, ass
umes
that
pho
nem
e id
entif
icat
ion
can
be b
ased
eith
er o
n pr
ecat
egor
ical
info
rmat
ion
or o
n th
e re
sults
of t
he p
hone
me
iden
tific
atio
n pr
oces
s, S
ince
it is
ass
umed
that
fea
ture
info
rmat
ion
deca
ysra
pidl
y (e
spec
ially
for
cons
onan
t fea
ture
s-se
e be
low
), r
espo
nses
mus
t
ofte
n be
bas
ed s
olel
y on
the
outp
ut o
f th
e ph
onem
e id
entif
icat
ion
proc
ess,
whi
ch is
ass
umed
to "
rovi
de a
dis
cret
e co
de o
fthe
seq
uenc
e of
pho
nem
es.
Thi
s in
terp
reta
tion
acco
unts
for
muc
h of
the
data
on
cate
gori
cal p
erce
p-tio
n qu
ite w
ell.
Inde
ed, i
t is
fairl
y di
fficu
lt to
find
way
s of
dis
tingu
ishi
ngbe
twee
n a
feed
back
f!1o
del a
nd o
ne th
at a
ttrib
utes
cat
egor
ical
per
Cep
tion
to a
loss
of
info
rmat
ion
from
the
feat
ure
leve
l cou
pled
with
a r
elia
nce
ona
mor
e ab
stra
ct c
ode,
Bot
h fe
edba
ck m
odel
s an
d du
al c
ode
mod
els
can
acco
mm
odat
e th
e fa
ct th
at v
owel
s sh
ow le
ss o
f a
tend
ency
tow
ard
cat-
egor
ical
per
cept
ion
than
con
sona
nts
(Fry
, Abr
amso
n, E
imas
, & L
ib-
erm
an, 1
962;
Pis
oni,
1973
). It
is s
impl
y ne
cess
ary
to a
ssum
e th
at v
owel
feat
ures
are
mor
e pe
rsis
tent
than
con
sona
nt f
eatu
res
(Cro
wde
r, 1
978,
1981
; Fuj
isak
i & K
awas
him
a, 1
968;
Pis
oni,
1973
, 197
5), H
owev
er, t
hetw
o cl
asse
s of
inte
rprt
etat
ions
do
diff
er in
one
way
, The
fee
dbac
k ac
coun
tse
ems
to d
iffe
r m
ost c
lear
ly f
rom
a li
mite
d fe
atur
e ac
cess
acc
Qun
t in
itspr
edic
tions
of p
erfo
rman
ce in
dis
crim
inat
ing
two
stim
uli,
both
aw
ay fr
omth
e ce
nter
of
a ca
tego
ry, b
ut s
till w
ithin
it H
ere,
TR
AC
E te
nds
to s
how
grea
ter
disc
rim
inat
ion
than
it s
how
s be
twee
n st
imul
i squ
arel
y in
the
mid
dle
of a
cat
egor
y,
Sta
ndar
d in
terp
reta
tions
of c
ateg
oric
al p
erce
ptio
n ca
n ac
coun
t for
in-
crea
ses
in ~
lo;c
rimin
abili
ty n
ear
the
boun
dary
bet
wee
n tw
o ca
tego
ries
(whe
re id
entif
icat
ion
.may
in fa
ct b
e so
mew
hat v
aria
ble)
, sim
ply
in te
rms
of th
e fa
ct th
at m
argi
nal s
timul
i are
mor
e lik
ely
to g
ive
rise
to d
iffer
ent
cate
gory
labe
ls, B
ut T
RA
CE
can
acc
ount
for
incr
ease
s in
dis
crim
inab
ility
at e
xtre
me
valu
es o
f fea
ture
con
tinua
whi
ch w
ould
not
giv
e ris
e to
dif-
fere
nt c
ateg
ory
labe
ls. I
n T
RA
CE
, the
rea
son
for
this
incr
ease
in d
iscr
im-
inab
ility
is th
at th
e ac
tivat
ion
of th
e ap
prop
riate
item
at t
he p
hone
me
leve
l is
,wea
ker,
and
ther
efor
e th
e fe
edba
ck s
igna
l is
wea
ker,
than
it is
whe
n th
e in
put o
ccur
s ne
ar th
e ce
nter
of
the category. For example,
Stim
ulus
I in
our
sim
ulat
ions
fal
ls b
elow
the
cano
nica
l/g/ s
timul
us, a
ndth
eref
ore
activ
ates
the
Ig/ p
hone
me
dete
ctor
less
str
ongl
y th
an s
timul
icloser to the canonical
Ig/,
A similar thing happens with the
Ik/.
Thi
s
resu
lts in
less
"ca
noni
caliz
atio
n"
of th
e ex
trem
e st
imul
i, an
d pr
oduc
es a
-sha
ped
disc
rim
inat
ion
func
tion,
as
show
n in
Fig
. 22,
The
re is
som
e ev
iden
ce b
eari
ng o
n th
is a
spec
t of
TR
AC
E's
acc
ount
of
cate
gori
cal p
erce
ptio
n, S
amue
l (1977) has reported
AB
X
disc
rim
inat
ion
data
that
sho
w n
otic
eabl
e m
inim
a in
the
disc
: im
inat
ion
func
tion
near
the
canonical stim~1i within each category on a
Id/-
/tl
cont
inuu
m, I
ndee
d,
Sam
uel's
acc
ount
of
this
eff
ect,
thou
gh n
ot c
ouch
ed in
term
s of
inte
rac-
tive
activ
atio
n pr
oces
ses,
has
a g
reat
dea
l of
sim
ilari
ty to
wha
t we
see
inT
RA
CE
; he
sugg
ests
that
nea
r-ca
noni
cal i
tem
s ar
e m
ore
stro
ngly
ass
im-
ilate
d to
the
cano
nica
l pat
tern
, Unf
ortu
nate
ly th
e ef
fect
we
seek
is fa
irly
subt
le, a
nd s
o it
will
be
diff
icul
t to
sepa
rate
fro
m n
oise
. In
Sam
uel'
expe
rim
ent.,
the
effe
ct is
fai
rly
clea
r-cu
t at b
oth
extr
emes
of t
he V
OT
cont
inuu
m in
thre
e ob
serv
ers
at th
e en
d of
ext
ensi
ve tr
aini
ng, a
s sh
own
in F
ig, 2
3, a
nd e
ven
unpr
actic
ed s
ubje
cts
tend
to s
how
the
effe
ct to
war
dthe high end of the VOT continuum, well past the prototype for
It/.
In s
umm
ary,
TR
AC
E a
ppea
rs to
pro
vide
a f
airl
y ac
cura
te a
ccou
nt o
fth
e ph
enom
ena
of c
ue tr
ade-
offs
and
cat
egor
ical
per
cept
ion
of s
peec
hso
unds
, It a
ccou
nts
for
cate
goric
al p
erce
ptio
n w
ithou
t rel
ying
on
the
no-
tion
that
the
phen
omen
on d
epen
ds o
n re
adou
t fro
m a
n ab
stra
ct le
vel o
fpr
oces
sing
; it a
ssum
es in
stea
d th
at th
e fe
atur
e le
vel,
like
othe
r le
vels
of
the
syst
em, i
s su
bjec
t to
feed
back
from
hig
her
leve
ls w
hich
act
ually
chan
ges
the
repr
esen
tatio
n as
it is
bei
ng r
etai
ned
in m
emor
y, p
ushi
ng
tow
ard
a ca
noni
cal r
epre
sent
atio
n of
the
phon
eme
mos
t str
ongl
y ac
tivat
edby
the
inpu
t.
Oth
er P
heno
men
a at
the
Pho
nem
e Le
vel
The
lite
ratu
re o
n ph
onem
e pe
rcep
tion
incl
udes
sev
eral
furt
her
findi
ngs
we
have
not
yet
bee
n ab
le to
con
side
r in
det
ail.
The
nex
t few
. par
agra
phs
cons
ider
one
of
thes
e fi
ndin
gs a
nd h
ow it
mig
ht b
e ac
com
mod
ated
in th
eTRACE model.
Effects of global and local context on phoneme identification.
In o
ur
sim
ulat
ions
of
trad
ing
rela
tions
, we
have
sho
wn
that
the
crite
rial
val
uene
eded
on
one
dim
ensi
on o
f st
imul
us v
aria
tion
can
be a
ffec
ted
by o
t~er
dim
ensi
ons.
Thu
s, w
hen
the
onse
t of
FI is
rel
ativ
ely
high
, sho
rter
voi
cing
late
ncie
s ar
e ne
eded
to p
erce
ive
a so
und
as u
nvoi
ced,
Oth
er f
acto
rs a
lso
innu
ence
the
phon
eme
perc
eive
d as
a r
esul
t of
a pa
rtic
ular
fea
tura
l inp
ut.
TR
AC
E M
OD
EL
TRAINED SUBJECTS
100
LZ
:un
.
. '
.0 "
/ -
20 '
AG
S
.....
I&J
..J ..J I&J
III
..J ... 100
c( 0
I&J
......
MD
S
100
....
80 ..
.40
\.20
MCB01
0205
0405
0101
010
'"'
MC
CLE
LLA
ND
AN
D E
LMA
N
CONTROL GROUP
spea
ker
para
met
ers,
Our
mai
n po
int h
ere
is th
at c
onne
ctio
n m
odul
atio
nis
qui
te a
diff
eren
t mec
hani
sm th
an th
e si
mpl
e a
dditi
ve ,
com
bina
tion
ofex
cita
tory
influ
ence
s th
at u
nder
lies
the
way
TR
AC
E a
ccoO
'nts for trade-
offs
am
ong
the
cues
to a
sin
gle
phon
eme
or f
or th
e ef
fect
s of
top-
dow
nin
flue
nces
on
the
phon
eme
boun
dary
,
Sum
mar
y of
Pho
nem
e Id
entif
icat
ion
Sim
ulat
iolls
We
have
con
side
red
a nu
mbe
r of
phe
nom
ena
conc
erni
ng th
e id
entit
i-ca
tion
and
perc
eptio
n of
pho
nem
es, T
hese
incl
ude
lexi
cal i
nflu
ence
s on
phpn
eme
iden
tific
atio
n, a
nd th
e la
ck th
ereo
f, b
oth
in r
eact
ion
time
and
in r
espo
nse
choi
ce m
easu
res;
"ph
onot
actic
rul
e" effects on ph
onem
eid
entif
icat
ion
and
the
role
of s
peci
fic
lexi
cal i
tem
s in
infl
uenc
ing
thes
eef
fect
s; th
e in
tegr
atio
n of
mul
tiple
cue
s to
pho
nem
e id
entit
y an
d th
e ca
t-eg
oric
al n
atur
e of
the
perc
ept t
hat r
esul
ts fr
om th
is in
tegr
atio
n. T
RA
CE
inte
grat
es a
ll of
thes
e ph
enom
ena
into
a s
ingl
e ac
coun
t tha
t inc
orpo
rate
sas
pect
s of
the
acco
unts
off
ered
for
par
ticul
ar a
spec
ts o
f th
ese
resu
lts b
yot
her
mod
els,
In th
e ne
xt s
ectio
n, w
e sh
ow h
ow T
RA
CE
can
also en-
com
pass
a n
umbe
r of
phe
nom
ena
conc
erni
ng th
e re
cogn
ition
of s
poke
nw
ords
,
. ,""
."
\.
CG
I
/ "
, ,..' "
. .. "
CG
2
CG
3
0 10 20 50 40 50 IiO
10
.0
TH
E T
IME
CO
UR
SE
OF
WO
RD
RE
CO
GN
ITIO
N
The
stu
dy o
f sp
oken
wor
d re
cogn
ition
has
a lo
ng h
isto
ry, a
nd m
any
mod
els
have
bee
n pr
opos
ed, M
orto
ns
now
-cla
ssic
logo
gen
mod
el(M
orto
n, 1
969)
was
the
first
to p
rovi
de a
n ex
plic
it ac
coun
t of t
he in
te-
grat
ion
of c
onte
xtua
l and
sen
sory
info
rmat
ion
in w
ord
reco
gniti
on. O
ther
mod
els
of th
is p
erio
d (e
,g.,
Bro
adbe
nt, 1
967) concentrated primarily on
effe
cts
of w
ord
freq
uenc
y, U
ntil
the
mid
197
0s, h
owev
er, t
here
was
littl
eex
plic
it co
nsid
erat
ion
of th
e tim
e co
urse
of s
poke
n w
ord
reco
gniti
on.
Sev
eral
stu
dies
by
Mar
slen
-Wils
on a
nd h
is c
olla
bora
tors
(M
arsl
en-
Wilson, 1973; Marslen-W
ilson
& T
yler
, 1975) and by Cole and hiscollab-
orat
ors
(Col
e, 1
973;
Col
e &
Jak
imik
, 1978, 1980) pioneered the in
vest
i-ga
tion
of th
is p
robl
em,
Mar
slen
-Wils
ons
CO
HO
RT
mod
el (
Mar
slen
~W
ilson
& T
yler
, 198
0;
M!i
rsle
n-W
ilson
& W
elsh
, 197
8) o
f spe
ech
perc
eptio
n w
as b
ased
on
this
earl
y w
ork
on th
e tim
e co
urse
of
spok
en w
ord
reco
gniti
on. T
he C
OH
OR
Tm
odel
was
one
of
the
sour
ces
of in
spir
atio
n fo
r T
RA
CE
, for
two
mai
nre
ason
s" F
irst
, it p
rovi
ded
an e
xplic
it ac
coun
t of
the
way
top-
dow
n an
dbo
ttom
-up
info
rmat
ion
coul
d be
com
bine
d to
pro
duce
a w
ord
reco
gniti
onm
echa
nism
that
act
ually
wor
ked
in r
eal t
ime.
Sec
ond,
it a
ccou
nted
for
the
findi
ngs
of a
num
ber
of im
port
ant e
xper
imen
ts d
emon
stra
ting
the
" on
-
line"
character of the speech recognition process. H
owev
er, s
ever
al d
e-fi
cien
cies
of
the
CO
HO
RT
mod
el h
ave
been
poi
nted
out
, as
we
shal
l see
,B
ecau
se T
RA
CE
was
mot
ivat
ed in
larg
e pa
rt b
y a
desi
re to
kee
p w
hat
is g
ood
abou
t CO
HO
RT
and
impr
ove
upon
its
wea
knes
ses,
we
begi
n th
is
VO
ICE
ON
SET
TIM
E (
mile
)FIG, 23. Identification (solid curves) and
AB
X
disc
rim
inat
ion
data
(da
shed
cur
ves)
fro
mIh
ree
prac
ticed
and
thre
e na
ive
subj
ects
. Sim
plifi
ed a
nd r
eprin
ted,
with
per
mis
sion
, fro
mSa
mue
l(
1977
).
The
iden
tity
of p
hone
mes
sur
roun
ding
a ta
rget
pho
nem
e, th
e ra
te o
fsp
eech
of
a, s
ylla
ble
in w
hich
a p
artic
ular
feat
ure
valu
e oc
curs
, as
wel
l as
char
acte
rist
ics
of th
e sp
eake
r an
d th
e la
ngua
ge b
eing
spo
ken
all i
nflu
ence
the
inte
rpre
tatio
ns o
f fe
atur
es. S
ee R
epp
and
Lib
erm
an (1984) for a dis-
cuss
ion
of a
ll of
thes
e so
rts
of in
flue
nces
on
the boundaries between
phon
emes
, It
has
bee
n su
gges
ted
by M
iller
, Gre
en, a
nd S
cher
mer
(198
4) a
nd b
yR
epp
and
Libe
rman
(19
84)
that
thes
e di
ffere
nt e
ffect
s m
ay h
ave
diffe
rent
sour
ces,
In
part
icul
ar, M
iller
et a
l. (1
984)
sug
gest
that
lexi
cal e
ffec
ts a
nd, s
eman
tic a
nd s
ynta
ctic
influ
ence
s on
the
one
hand
may
be
due
to a
dif-
fere
nt m
echa
nis~
than
infl
uenc
es s
uch
as s
peec
h ra
te a
nd c
oart
icul
ator
yin
flue
nces
due
to lo
cal p
hone
tic c
onte
xt.
The
ass
umpt
ions
we
have
inco
rpor
ated
into
TR
AC
E m
ake
a si
mila
rdi
stin
ctio
n, I
n T
RA
CE
I, w
e ha
ve a
ccou
nted
for
eff
ects
of
phon
etic
con
-te
xt b
y al
low
ing
activ
atio
ns o
f un
its to
infl
uenc
e th
e fe
atur
e-to
- pho
nem
eco
nnec
tions
in a
djac
ent t
ime
slic
es (
see
Elm
an &
McC
lella
nd, i
n pr
ess,
for
deta
ils).
In
the
disc
ussi
on,
we
' con
side
r w
ays
of e
xten
ding
the
con-
nect
ion
mod
ulat
ion
idea
to a
ccom
mod
ate
effe
cts
of v
aria
tions
in r
ate
and
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
sect
ion
by c
onsi
derin
g th
e C
OH
OR
T m
odel
in s
ome
deta
il. F
irst w
e re
-vi
ew th
e ba
sic
assu
mpt
ions
of
the
mod
el, t
hen
cons
ider
its
stre
ngth
s an
dw
eakn
esse
s. T
here
app
ear
to b
e fo
ur b
asic
ass
umpt
ions
of t
he C
OH
OR
Tm
odel
.
J. T
he m
odel
use
s th
e fir
st s
ound
(in
Mar
slen
-Wils
on &
Tyl
er, 1
980,
the
initi
al c
onso
nant
clu
ster
-plu
s-vo
wel
) of
the
wor
d to
det
erm
ine
whi
chw
ords
will
be
in a
n in
itial
coh
ort o
r ca
ndid
ate
set,
2. O
nce
the
cand
idat
e se
t is
esta
blis
hed,
the
mod
el e
limin
ates
wor
ds
from
the
coho
rt im
med
iate
ly, a
s"ea
ch s
ucce
ssiv
e ph
onem
e ar
rive
s, if
the
new
pho
nem
e fa
ils to
mat
ch th
e ne
xt p
hone
me
in th
e w
ord,
Wor
ds c
anal
so b
e el
imin
ated
on
the
basi
s of
sem
antic
con
stra
ints
, alth
ough
the
initi
alco
hoI'I
is a
ssum
ed to
'be determined by acoustic input alone.
3. W
ord
recognition occurs immediately, as
. soo
n as
the cohort has
been
red
uced
to a
sin
gle
mem
ber;
in a
n au
dito
ry le
xica
l dec
isio
n ta
sk,
the
deci
sion
that
an
item
is a
non
wor
d ca
n be
mad
e as
soo
n as
ther
e ar
eno
rem
aini
ng m
embe
rs in
the
coho
rt,
4. W
ord
reco
gniti
on c
an in
fluen
ce th
e id
entif
icat
ion
of ph
onem
es in
a
wor
d on
ly a
fter
the
wor
d ha
s be
en r
ecog
nize
d,
The
re is
a c
onsi
de~a
ble
body
of
data
that
sup
port
s va
riou
s pr
edic
tions
of th
e C
OH
OR
T m
odel
, It h
as b
een
obse
rved
in a
var
iety
of
para
digm
s
thai
lexi
cal i
nflu
ence
s on
pho
nem
e id
entif
icat
ion
resp
onse
s ar
e m
uch
grea
ler
lale
r in
wor
ds th
an a
t the
ir b
egin
ning
s (B
agle
y, 1
900;
Col
e an
d
Jakimik, 1978, 1980; Marslen-Wilson, 1980; Marslen-Wilson and Welsh,
1978
). W
e co
nsid
ered
som
e of
this
evi
denc
e in
earlier section~.. A
noth
er
impo
rtan
t fin
ding
suJ
i)po
rtin
g C
OH
OR
T is
the
fact
that
the
reat
tion
time
to d
ecid
e th
at a
n ite
m is
a n
on w
ord
is c
onst
ant,
whe
n m
easu
red
from
the
occu
rren
ce o
f the
firs
t pho
nem
e th
at r
ules
out
the
last
rem
aini
ng w
ord
inth
e co
hort
(M
arsl
en-W
ilson
, 198
0),
Perh
aps
the
mos
t dir
ect s
uppo
rt f
or th
e ba
sic
wor
d re
cogn
ition
as-
sum
ptio
ns o
f C
OH
OR
T c
omes
fro
m th
e ga
ting
para
digm
, int
rodu
ced
firs
tby
Gro
sjea
n (1
980)
, In
this
par
adig
m, s
ubje
cts
are
requ
ired
to g
uess
the
iden
t it y
of a
wor
d af
ter
hear
ing
succ
essi
ve p
rese
ntat
ions
of
the
wor
d, T
hefir
st p
rese
ntat
ion
is c
ut o
fT so
that the subject hears only the first
(N
= 3
0 to
50
in d
iffe
rent
stu
dies
). L
ater
pre
sent
atio
ns a
re s
ucce
ssiv
ely
leng
then
ed in
N-m
s in
crem
ents
unt
il ev
entu
ally
the
who
le w
ord
is p
re-
sent
ed. T
he d
urat
ion
at w
hich
hal
fthe
sub
ject
s co
rrec
tly id
entif
y th
e w
ord
is c
alle
d th
e "i
sola
tiQn
poin
t. "
Con
side
rabl
y m
ore
inpu
t is
requ
ired
befo
resubjects are. reason~bly sure of the identity of the w
ord;
that
poi
nt is
tenn
ed th
e "a
ccep
tanc
e po
int." Grosjean
s in
itial
stu
dy c
onfi
rmed
man
y
basi
c pr
edic
tions
of
CO
HO
RT
, tho
ugh
it al
so r
aise
d a
few
dif
ficu
lties
for
it (s
ee b
elow
). I
n a
mor
e re
cent
stu
dy u
sing
the
sam
e m
etho
d, T
yler
and
Wes
sels
(19
83)
carr
ied
out a
ver
y cl
ose
anal
ysis
of
the
rela
tion
betw
een
the
empi
rica
lly d
eter
min
ed is
olat
ion
poin
t and
the
poin
t at w
hich
the
inpu
t
the
subj
ect h
as r
ecei
ved
is c
onsi
sten
t with
one
and
onl
y on
e re
mai
ning
item
, the
poi
nt a
t whi
ch r
ecog
nitio
n w
ould
be
exep
ecte
d to
occ
ur in
the
CO
HO
RT
mod
el. T
hey
repo
rt th
at th
e is
olat
ion
poin
t fal
ls v
ery
clos
e to
this
theo
retic
ally
der
ived
rec
ogni
tion
poin
t, st
rong
ly s
uppo
rtin
g th
e ba
sic
immediacy assumptions of the COHORT model,
It s
houl
d be
not
ed th
at th
e ga
ting
task
is n
ot a
tim
ed ta
sk, a
nd s
o it
does
not
. pro
vide
a d
irec
t measure of what the su
bjec
t kno
ws
as th
e
spee
ch in
put i
s un
fold
ing,
How
ever
, it i
s no
w in
fair
ly w
ide
use,
and
Cotton and Grosjean (1984) have established that the basic patterns of
resu
lts o
btai
ned
in G
rosj
ean
s (1
980)
pio
neer
ing
gatin
g ex
peri
men
t do
not
depe
nd o
n th
e pr
esen
tatio
n of
suc
cess
ivel
y lo
nger
and
long
erpr
esen
ta-
tions
of
the
sam
e st
imul
us.
A dilemma for COHORT,
Tho
ugh
the
CO
HO
RT
mod
el a
ccou
nts
for
ala
rge
body
of d
ata,
ther
e ar
e se
vera
l diff
icul
t:"s
with
it. W
e co
nsid
er f
irst
the
one
that
see
ms
the
mos
t ser
ious
: as
stat
ed, C
OH
OR
T r
equi
res
ac-
cura
te, u
ndis
tort
ed in
form
atio
n ab
out t
he id
entit
y of
the
phon
emes
in a
wor
d up
to th
e is
olat
ion
poin
t. W
ords
can
not e
nter
into
cons
ider
atio
n
unle
ss th
e in
itial
con
sona
nt c
lust
er p
lus
vow
el is
hea
rd. a
nd th
ey a
r~discarded from it as soon as a ph
onem
e co
mes
alo
ng th
at th
ey f
ail t
om
atch
. No
expl
icit
proc
edur
e is
des
crib
ed f
or r
ecov
erin
g w
ords
into
the
coho
rt o
nce
they
hav
e be
en e
xclu
ded
from
it, o
r w
hen
the beginning of
the
wor
d is
not
acc
urat
ely
perc
eive
d du
e to
noi
se o
r el
isio
n,T
hese
asp
ects
of
CO
HO
RT
mak
e it
very
diff
icul
t for
the
mod
el to
explain recognition of words with distorted be
ginn
ings
. suc
h as
dwib
ble"
(Norris, 1982), or w
ords
who
se b
egin
ning
s ha
ve b
een
repl
aced
by n
oise
(Sa
Jass
o &
Pis
oni,
1985
). F
rom
a c
ompu
tatio
nal p
oint
of
view
,th
is m
akes
the
mod
el a
n ex
trem
ely
britt
le o
ne; i
n pa
rtic
ular
it f
ails
to d
eal
with
the
prob
lem
of
nois
e an
d un
ders
peci
fica
tion
whi
ch is
so
cruc
ialf
orre
cogn
ition
of r
eal s
peec
h (T
hom
pson
. 1984
),
The
rec
ogni
zabi
lity
of d
isto
rted
item
s lik
e "dw
ibbl
e" might be taken
as s
ugge
stin
g th
at w
hat w
e ne
ed to
do
is lib
eral
ize
the
crite
rion
for
en-
teri
ng a
nd r
etai
ning
wor
ds in
the
coho
rt. T
hus,
the
coho
rt c
ould
be
de-
fined
as
the
set o
f wor
ds c
onsi
sten
t with
wha
t has
bee
n he
ard
or m
ild(e
,g" one or two fe
atur
es)
devi
atio
ns f
rom
wha
t has
bee
n he
ard.
Thi
swould allow mild distortions like replacing
Irl
with
Iw
l not to disqualify
a w
ord
from
the
coho
rt. I
t wou
ld a
lso
allo
w th
e m
odel
to c
ope
with
cas
esw
here
the
begi
nnin
g of
the
wor
d is
und
ersp
ecifi
ed; i
n- th
ese
case
s. th
e
initi
al c
ohor
t wou
ld s
impl
y be
larg
er th
an in
the
case
whe
re th
e in
put
dear
ly s
peci
fied
the
initi
al p
hone
mes
.H
owev
er. t
here
is s
till a
pro
blem
. Som
etim
es w
e ne
ed to
be
able
toru
le o
ut it
ems
whi
ch m
ism
atch
the
inpu
t on
one
or tw
o di
men
sion
s an
d
som
etim
es w
e do
not
. Con
side
r th
e ite
ms
"plea
sant" and "
blac
elet
." In
the
firs
t cas
e. w
e ne
ed to
exclude "
pres
ent" from the cohort, so the
TR
AC
E M
OD
EL
MC CLELLAND AND ELMAN
slig
ht d
iffe
renc
e be
twee
n II
I an
d Ir
l mus
t be
suff
icie
nt to
rul
e it
out;
in th
ese
cond
cas
e, w
e do
not
wan
t to
lose
the
wor
d " b
race
let,
" si
nce
it pr
o-vides the best fit overall to the input. Thus, in this case, the difference
betw
een
III a
nd Ir
l mus
t not
be
allo
wed
to r
ule
a w
ord
cand
idat
e ou
t.T
hus
the
dile
mm
a: o
n th
e on
e ha
nd, w
e w
ant a
mec
hani
sm th
at w
ill b
eab
le to
sel
ect t
he c
orre
ct w
ord
as s
oon
as a
n un
dist
orte
d in
put s
peci
fies
it un
ique
ly, t
o ac
coun
t for
the
Tyl
er a
nd W
esse
ls r
esul
ts. O
n th
e ot
her
hand
, we
do n
ot w
ant t
he m
odel
to c
ompl
etel
y el
imin
ate
poss
ibili
ties
whi
ch m
ight
late
r tu
rn o
ut to
. be
corr
ect,
We
shal
l sho
rtly
see
that
TR
AC
Epr
ovid
es...
way
out
of
this
dile
mm
a.
Another problem for COHORT.
Gro
sjea
n (1
985)
has
rec
ently
poi
nted
out a
noth
er p
robl
em f
or C
OH
OR
T, n
amel
y, th
e po
ssib
ility
that
the
sub-
ject
may
be
unce
rtai
n ab
out t
he location of the beginning of each suc-
cess
ive
wor
d, A
taci
t ass
umpt
ion
of th
e m
odel
is th
at th
e su
bjec
t goe
sin
to th
e be
ginn
ing
of e
ach
wor
d kn
owin
g th
at it
is' t
he b
egin
ning
. In
the
rela
ted
mod
el' o
f Col
e an
d Ja
kim
ik (
1980) this as
sum
ptio
n is
mad
e ex
plic
it.U
nfor
tuna
tely
, it i
s no
t alw
ays
poss
ible
to k
now
in a
dvan
ce w
here
one
wor
d st
arts
and
the
next
wor
d en
ds. A
s w
e di
scus
sed
in th
e in
trod
uctio
n,ac
oust
ic c
ues
to ju
nctu
re a
re n
ot a
lway
s re
liabl
e,' a
nd in
the
abse
nce
ofac
oust
ic c
ues,
eve
n an
opt
imal
ly e
ffic
ient
mec
hani
sm ~
anno
t alw
ays
, know th
at it
has
hea
rd th
e en
d of
one
wor
d un
til it
hea
rs e
noug
h of
the
next
to r
ule
out t
he p
ossi
ble
cont
inua
tions
of t
he fi
rst w
ord.
Wha
t is
need
ed, t
hen.
is a
mod
el th
at c
an a
ccou
nt fo
r C
OH
OR
T'
succ
esse
s, a
nd o
verc
ome
thes
e tw
o im
port
ant d
efic
ienc
ies,
The
nex
t tw
ose
ctio
ns s
how
that
TR
AC
E d
oes
quite
wel
l on
both
cou
nts.
The
fir
st o
fth
ese
sect
ions
exa
min
es T
RA
CE
' s b
ehav
ior
in p
roce
ssin
g w
ords
who
sebe
ginn
ings
and
end
ings
are
cle
arly
del
inia
ted
for
it by
the
pres
ence
of
sile
nce,
The
sec
ond
cons
ider
s th
e pr
oces
sing
of
mul
tiwor
d in
puts
, whi
chth
e m
odel
mus
t par
se fo
r its
elf.
One
Wor
d tit
(t T
ime
In th
is s
ectio
n w
e se
e ho
w T
RA
CE
res
olve
s th
e di
lem
ma
faci
ng C
O-
HO
RT
, in
that
it is
imm
edia
tely
sen
sitiv
e to
new
info
rmat
ion
but i
s st
illab
le to
cop
e w
ith u
nder
spec
ifie
d or
dis
tort
ed w
ord
begi
nnin
gs, W
e al
soco
nsid
er h
ow th
e m
odel
acc
ount
s fo
r th
e pr
efer
ence
for
sho
rt-w
ord
re-
spon
ses
earl
y in
pro
cess
ing
a lo
ng w
ord,
The
sec
tion
conc
lude
s w
ith a
disc
ussi
on o
f w
ays
the
mod
el c
ould
be
exte
nded
to a
ccou
nt fo
r w
ord
freq
uenc
y an
d co
ntex
tual
influ
ence
s,C
ompe
titio
n ~'
S bottom-lip inhibition.
TR
AC
E d
eals
with
CO
HO
Rrs
dile
mm
a by
usi
ng c
ompe
titio
n. r
athe
r th
an p
hone
me-
to-w
ord
inhi
bitio
n.T
he e
ssen
ce o
f th
e id
ea is
sim
ply
this
, Pho
nem
e un
its h
ave
exci
tato
ryco
nnec
tions
to a
ll th
e w
ord
units
they
are
con
sist
ent w
ith. T
hus,
whe
n-ev
er a
pho
nem
e be
com
es a
ctiv
e in
a p
artic
ular
slic
e of
the
Tra
ce, i
t sen
ds.
exci
tatio
n to
all
the
wor
d un
its c
onsi
sten
t with
that
pho
nem
e in
that
slic
e.T
he w
ord
units
then
com
pete
with
eac
h ot
her;
item
s th
at c
onta
in e
ach
succ
essi
ve p
hone
me
dom
inat
e al
l oth
ers,
but
if n
o w
ord
"mat
ches
per
-fe
ctly
, a w
ord
that
pro
vide
s a
clos
e tit
to th
e phoneme sequence can
even
taul
ly w
in o
ut o
ver
wor
ds th
at p
rovi
de le
ss a
dequ
ate
mat
ches
. The
exac
t met
ric
of "
clos
enes
s of
fit
" de
pend
s. o
f co
urse
. on
a la
rge
num
ber
of d
etai
ls, I
n th
e ab
senc
e of
suc
h a
met
ric,
a s
impl
e co
unt o
f th
e nu
mbe
rof
aco
ustic
feat
ures
diff
erin
g be
twee
n a
lexi
cal i
tem
.an
d a
pres
ente
d st
im-
ulus
can
pro
vide
a u
sefu
l fir
st a
ppro
xim
atio
n. b
ut o
ther
fac
tors
suc
h as
stre
ss, l
ocat
ion
of d
iffer
ence
s w
ithin
the
wor
d, a
nd d
iscr
imin
abili
ty o
f the
diffe
ring
feat
ure~
. will
of c
ours
e co
me
into play.
Con
side
r, f
rom
this
poi
nt o
f vi
ew, o
ur tw
o ite
ms
" ple
asan
t" a
nd "
blac
e-le
t" a
gain
, In
the
firs
t ins
tanc
e. "
plea
sant
" w
ill r
ecei
ve m
ore
botto
m-u
pex
cita
tion
than
"pr
esen
t," and so w
ill w
in o
ut in
the
com
petit
ion.
We
have
alre
ady
seen
, in
our
anal
ysis
of c
ateg
oric
al p
erce
ptio
n at
the
pho-
nem
elev
el, h
ow e
ven
slig
ht d
iffer
ence
s in
initi
al b
otto
m-u
p ex
cita
tion
can
be m
agni
fied
by
the
join
t eff
ects
of
com
petit
ion
and
feed
back
. But
the
real
bea
uty
of th
e co
mpe
titio
n m
echa
nism
is th
at th
is a
ctio
n is
con
tinge
nton
the
activ
atio
n of
oth
er w
ord
cand
idat
es, T
hus,
in th
e ca
se o
f " b
lace
-le
t", s
ince
ther
e is
no
wor
d "b
lace
let
" "
brac
el~t
" w
ill n
ot b
e Sl
Ip-
pres
sed,
Ini
tially
, it i
s tr
ue, w
ords
like
"bl
ame "
and "
blat
ant"
will tend
t~ d
omin
ate
"bra
cele
t," but since the input matches "
brac
elet
" be
tter
than
any
oth
er w
ord,
"br
acel
et" wjll eventually co
me
to d
omin
ate
the
other possibilities,
Thi
s be
havi
or o
f th
e m
odel
is .
illus
trat
ed u
sing
~xa
mpl
es f
rom
its
re-
stri
cted
lexi
con
in F
ig. 2
4. I
n on
e ca
se. t
he in
put i
s " l
egal
," a
nd th
e w
ord
rega
l" is
com
plet
ely
dom
inat
ed b
y "l
egal
." In the other case. the input
is "
lugg
ed, "
and
the
wor
d "r
ugge
d" e
vent
ually
dom
inat
es, b
ecau
se th
ere
is n
o w
ord
" lug
ged"
(pr
onou
nced
to r
hym
e w
ith "
rugg
ed"
the
wor
dlu
g"
is n
ot in
the
mod
el' s
lexi
con)
, Her
e "r
ugge
d~' m
ust c
ompe
te w
ithot
her
part
ial m
atch
es o
f " l
ugge
d,"
of c
ours
e, a
nd it
is le
ss e
ffect
ive
inth
is r
egar
d th
an it
wou
ld b
e if
the
inpu
t ,ex
actly
mat
ched
it, b
ut it
doe
sw
in o
ut in
the
end.
It
sho
uld
be n
oted
that
the
deta
ils o
f w
hat w
ord
will
be
mos
t str
ongl
yac
tivat
ed in
suc
h ca
ses
depe
nd o
n a
num
ber
of f
acto
rs, i
nclu
ding
, in
part
icul
ar, t
he d
istin
ctiv
enes
s of
mis
mat
chin
g ph
onem
es. A
lso,
it is
pos
-si
ble
to f
ind
case
s in
whi
ch a
wor
d th
at c
orre
ctly
spa
ns a
par
t of
a lo
nger
strin
g do
min
ates
a lo
nger
wor
d th
at s
pans
the
who
le s
trin
g bu
t mis
ses
out o
n a
phon
eme
in o
ne p
lace
or
anot
her.
An
item
like
"vi
gore
tte" may
or m
ay n
ot b
e a
case
in p
oint
. In
such
cas
es, t
houg
h, th
e m
ost i
mpo
rtan
tth
ing
mig
ht n
ot tu
rn o
ut to
be
win
ning
and
losi
ng, b
ut r
athe
r th
e fa
ct th
atbo
th te
nd to
sta
y in
the
gam
e, S
uch
neol
ogis
ms
can
sugg
est a
poe
tic
...
TR
AC
E M
OD
EL
MC
CLE
LI,-
AN
D A
ND
ELM
AN
~Jj
fIT
ClJ
tEH
'.=-f
1
tIT
iI
q;-
EliT
Ia:
:w
- Ji
g ~
I- I
i g
I' a
. . I i g - 1-
- I
I g
- I
-llg~l- +2
phon
emes
, In
this
sec
tion,
we
exam
ine
how
wel
l TR
AC
E e
mul
ates
the
CO
HO
RT
mod
el, i
n ca
ses
whe
re th
e in
put i
s an
und
isto
rted
rep
rese
nta-
tion
of s
ome
part
icul
ar w
ord.
In
part
icul
ar, w
e w
ante
d to
see
how
clo
se.
TR
AC
E w
ould
com
e to
beh
avin
g in
acc
ord
with
CO
HO
RT
's a
ssum
ptio
nth
at in
corr
ect w
ords
are
dro
pped
fro
m th
e co
hort
of
activ
e ca
ndid
ates
as
soon
as
the
inpu
t div
erge
s fr
om th
em,
To
exam
ine
this
pro
cess
, we
cons
ider
ed th
e pr
oces
sing
of
the
wor
d "p
rodu
ct"
(/pr
ad"c
t/). F
igur
e 25
sho
ws
the
stat
e of
the
Tha
ce a
tva
riou
s po
ints
in p
roce
ssin
g th
is' w
ord,
and
Fig
. 26
show
s th
e re
spon
sest
reng
ths
of s
ever
al u
nits
rel
ativ
e to
the
stre
ngth
of
the
wor
d "p
rodu
ct"
itsel
f, a
s a
func
tion
of ti
me
rela
tive
to th
e ar
riva
l of
the
succ
essi
ve p
ho-
nem
es in
the
inpu
t. In
this
fig
ure,
the
resp
onse
str
engt
h of
"pr
oduc
t" is
sim
ply
set t
o 1,
0 at
eac
h tim
esl
ice
and
the
resp
onse
str
engt
hs o
f uni
tsfo
r ot
her
wor
ds a
re p
lotte
d in
term
s of
the
ratio
of
thei
r st
reng
th. d
ivid
edby
the
stre
ngth
of
"pro
duct
." T
he c
urve
s sh
own
are
for
the
wor
ds !'
trot
,po
ssib
le," priest,
" "
prog
ress
," and "
prod
uce
; the
se w
ords
diff
erfr
om th
e w
ord
"pro
duct
" (a
ccor
ding
to th
e si
mul
atio
n pr
ogra
ms
stre
ss-
less
enc
odin
g of
them
!) ir
, the
1st
, 2nd
, 3d,
4th
, and
5th
pho
nem
es, r
e-sp
ectiv
ely,
Fig
ure
26 s
how
s th
at th
ese
item
s be
gin
to d
rop
out o
f "c
on-
tent
ion
" ju
st a
fter
eac
h su
cces
sive
pho
nem
e co
mes
in, O
f co
urse
, the
reis
not
hing
har
d an
d fa
st o
r ab
solu
te a
bout
dro
ppin
g a
cand
idat
e in
TR
AC
E. W
hat w
e se
e in
stea
d is
that
mis
mat
chin
g ca
ndid
ates
sim
ply
begi
n to
fad
e as
the
inpu
t div
erge
s fr
om th
em in
fav
or o
f so
me
othe
rca
ndid
ate.
Thi
s is
just
the
kind
of
beha
vior
the
CO
HO
RT
mod
el w
ould
fi' -
j! "
...!!
;
G (E!J
If-;
;-'
(E!J
S - r I
lit I
.,;:!
d" If
tE.i.
.!t
~ d
- I -
g ~
d -
- I
'to
I..
ra
k II
i..u"
l8l8
tIl8
111
tr ~
~I u 91
- p
r ad
- k
r a
ull
I II u
DfI
g-d-
-g-
d- -
,;-d- +2
FIG, 24, SIBle of Ihe lrace al
lwo
poin
ls during processing of "'e
ga'"
and
"'u
gged
.
conj
unct
ion
of m
eani
ngs,
if u
sed
just
rig
ht: "
He
wal
ked
bris
kly
dow
n th
est
reet
, puf
fing
his
vigo
rette
.T
ime
CO
llr.fe of w(ird recognition in
TR
AC
E.
So
far
we
have
sho
wn
how
TR
AC
E o
verc
omes
a d
ific
ulty
with
the
CO
HO
RT
mod
el in
cas
esw
here
the
begi
nnin
g of
a w
ord
has
been
dis
tort
ed. I
n ea
rlie
r se
ctio
ns o
nph
onem
e pr
oces
sing
,so
me
of th
e si
mul
atio
ns il
lust
rate
that
the
mod
el is
capa
ble
of r
ecog
nizi
ng w
ords
with
und
ersp
ecif
ied
(i, e
" am
bigu
ous)
initi
al
prad
~kl
- -p
rad-
kl-
-pra
d~kl
- -p
rad-
kl-
FIG, 25. State of th
elhl
ce a
t var
ious
poi
nts
in p
roce
ssin
g th
e w
ord
"pro
duct
" (/prad'kt
/'.
12 1
8 24
30
38 4
2 48
!i4
80 8
8 Pr
oces
sing
Cyc
les
FIG
. 26.
Res
pons
e st
reng
ths
of tt
~ u
nits
for
seve
ral w
ords
rel
ativ
e to
the
resp
onse
str
engt
hof
the
unit
for
" pro
duct
" (/
prad
- kt/)
. as
a fu
nctio
n of
tim
e re
lativ
e to
the
peak
of
the
firs
tph
onem
e th
at fa
ils to
mat
ch th
e w
ord,
The
suc
cess
ive
curv
es c
omin
g of
f of t
he h
oriz
onta
llin
e re
pres
entin
g th
e no
rmal
ized
res
pons
e st
reng
th o
f " p
rodu
ct"
are
for
the
wor
ds "
Irot
." ,
poss
ible
," "
prie
sl," "
prog
ress
, " and "
prod
uce." respectively. In our lexicon they are
, rendered as
Itni
l/,
Ipas
I/, I
pris
t/, I
prag
rs/
, and
Ipra
dus/
, res
pect
ivel
y.
.... ~
2.~
1.
.... VJ
1.80
~ 1.
S 1
. 100
Q)
,D::: 0.
Q)
0.~
0.'ii
' 0.
D::: 0.
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
We
wer
e at
fir
st s
omew
hat d
istu
rbed
by
this
asp
ect o
f th
e m
odel
'sbe
havi
or, b
ut it
turn
s ou
t to
corr
espo
nd q
uite
clo
sely
with
res
ults
obt
aine
din
exp
erim
ents
by
Gro
sjea
n (1
980)
and
Cot
ton
and
Gro
sjea
n (l9
H4)
usi
ngth
e ga
ting
para
digm
, Bot
h pa
pers
fou
nd th
at s
ubje
cts
hear
ing
the
begi
n-ni
ngs
of w
ords
like
"ca
ptai
n" tended to report shorter words consistent
with
wha
t the
y ha
d he
ard
(e.g.
, "
cap
). H
owev
er, w
e sh
ould
obs
erve
that
in th
e ga
ting
para
digm
, whe
n th
e w
ord
" cap
tain
" is truncated just
after the
Ipl,
it w
ill s
ound
qui
te a
bit
like
" cap
" followed by silence, In
TR
AC
E, t
his
sile
nce
wou
ld a
ctiv
ate
sile
nce
units
at t
he p
hone
me
and
wor
d le
vels
, and
the
wor
d-le
vel s
ilenc
e un
its w
ould
com
pete
with
uni
tsfo
r w
ords
that
ext
end
into
the
sile
nce.
It w
ill r
einf
orce
the
pref
eren
ce o
fth
e m
odel
for
sho
rt-w
ord
inte
rpre
tatio
ns, b
ecau
se th
e de
tect
ion
of th
esi
lenc
e w
ill in
hibi
t the
det
ecto
r fo
r th
e lo
nger
wor
d, T
hus,
ther
e ar
e ac
-tu
ally
two
reas
ons
why
TR
AC
E m
ight
fav
or s
hort
-wor
d in
terp
reta
tions
over
long
-wor
d in
terp
reta
tions
in a
gat
ing
expe
rim
ent.
Whe
ther
hum
ansu
bjec
ts s
how
a r
esid
ual p
refe
renc
e fo
r sh
orte
r in
terp
reta
tions
ove
r lo
nger
ones
in th
e ab
senc
e of
a fo
llow
ing
sile
nce
durin
g th
e co
urse
of p
roce
ssin
gis
not
yet
cle
ar f
rom
ava
ilabl
e da
ta,
We
shou
ld p
oint
out
that
the
expe
rim
enta
l lite
ratu
re in
dica
tes
that
the
adva
ntag
e of
sho
rter
wor
ds o
ver
long
er o
nes
hold
s on
ly u
nder
the
spec
ial
circ
umst
ance
s of
gat
ed p
rese
ntat
ion
and
then
onl
y w
ith e
arly
gat
es, w
hen
shor
ter
wor
ds a
re r
elat
ivel
y m
ore
com
plet
e th
an lo
nger
one
s w
ould
be.
It h
as b
een
wel
l kno
wn
for
a lo
ng ti
me
that
long
er w
ords
are
gen
eral
lym
ore
read
ily r
ecog
nize
d th
an s
hort
er o
nes
whe
n th
e w
hole
wor
d is
pre
-se
nted
for
iden
tific
atio
n ag
ains
t a b
ackg
roun
d of
noi
se (
Lic
klid
er &
Mill
er, 1
951)
, Pre
sum
ably
, the
rea
son
for
this
is s
impl
y th
at lo
nger
wor
dsge
nera
lly p
rovi
de a
larg
er n
umbe
r of
cue
s th
an s
hort
er w
ords
do
and
henc
e ar
e si
mpl
y le
ss c
onfu
sabl
e.Frequency a"d context effects,
The
re ,ar
e, o
f co
urse
, oth
er fa
ctor
sw
hich
infl
uenc
e w
hen
wor
d re
cogn
ition
will
occ
ur b
eyon
d th
ose
we
have
cons
ider
ed th
us f
ar, T
wo
very
impo
rtan
t one
s ar
e w
ord
freq
uenc
y an
dco
ntex
tual
pre
dict
abili
ty, T
he li
tera
ture
on
thes
e t)
oVo
fact
ors
goes
bac
kto the turn of the century (Bagley, 1900).\ M
orto
ns
(196
9) lo
goge
n m
odel
effe
ctiv
ely
deal
s w
ith s
ever
al im
port
ant a
spec
ts o
f th
is h
uge
liter
atur
ethough not with the time course of these effects,
We
have
not
yet
incl
uded
eith
er w
ord
freq
uenc
y or
hig
her
leve
l con
-te
xtua
l inf
luen
ces
in T
RA
CE
, tho
ugh
of c
ours
e w
e be
lieve
they
are
im-
port
ant.W
ord
freq
uenc
y ef
fect
s co
uld
be a
ccom
mod
ated
, as
they
wer
ein
the
inte
ract
ive-
activ
atio
n m
odel
of w
ord
reco
gniti
on, i
n te
rms
of v
arat
ion
in th
e re
stin
g ac
tivat
ion
leve
l of
wor
d un
its, o
r in
term
s of
var
iatio
nin
the
stre
ngth
of
phon
eme-
to-w
ord
conn
ectio
ns. C
onte
xtua
l inf
luen
ces
can
be th
ough
t of
as s
uppl
ying
act
ivat
ion
to w
ord
units
fro
m e
ven
high
erle
vels
of
proc
essi
ng th
an th
e w
ord
leve
l. In
this
way
, bas
ic a
spec
ts o
f
prod
uce
in th
is c
ase,
thou
gh o
f cou
rse
the
drop
-off
wou
ld b
e as
sum
ed to
be a
n ab
rupt
, dis
cret
e ev
ent,
The
re is
one
asp
ect o
f TR
AC
E' s
beh
avio
r w
hich
dif
fers
fro
m th
aI o
fC
OH
OR
T: a
mon
g th
ose
wor
ds th
at a
re c
onsi
st~n
t with
the
inpu
t up
to a
part
icul
ar p
oint
in ti
me.
TR
AC
E s
how
s a
bias
in f
avor
of
shor
ter
wor
dsov
er lo
nger
wor
ds, T
hus,
"pr
iest
" ha
s a
slight advantage before the
Ial
com
es in
, and
"pr
oduc
e" is well ahead of "pr
oduc
t" u
ntil
the
tlcom
esin
(in
pho
nem
es, "
prod
uce.
" is
one
sho
rter
than
"pr
oduc
t"T
his
adva
ntag
e fo
r sh
orte
r w
ords
is d
ue to
the
com
petit
ion
mec
hani
sm,
Rec
all t
hat w
ord
units
com
pete
with
eac
h ot
her
in p
ropo
rtio
n to
the
over
lap
of th
e se
ts o
f tim
e sl
ices
spa
nned
by
each
of
the
wor
ds, O
verl
apis
, of
cour
se, s
ymm
etri
cal,
so lo
ng a
nd s
hort
wor
ds in
hibi
t eac
h ot
her
toan
equ
al e
xten
t. B
ut lo
nger
wor
ds s
uffe
r m
ore
inhi
bitio
n fr
om o
ther
long
wor
ds th
an s
hort
wor
ds d
o. F
or e
xam
ple,
"pr
ogre
ss" and "
prob
able
inhi
bit "
prod
uct "
mor
e th
an th
ey in
hibi
t "pr
iest
" an
d " p
rodu
ce. "
Thu
sun
its f
or lo
nger
wor
ds a
re g
ener
ally
sub
ject
ed to
ext
ra in
hibi
tion,
par
tic-
ular
ly e
arly
on
whe
n m
any
cand
idat
es a
re a
ctiv
e, a
nd s
o th
ey te
nd to
suff
er in
com
pari
son
to s
hort
wor
ds a
s a
resu
lt.3
The
dat
a re
port
ed b
y T
yler
and
Wes
sels
act
ually
app
ears
to in
dica
te a
n e,ven more
imm
edia
te d
rop-
off
than
is s
een
in th
is s
imul
atio
n. H
owev
er, i
l sho
uld
be r
emem
bere
d t h
atth
e cu
rves
sho
wn
in F
ig. 2
6 ar
e on
- lin
e re
spon
se s
tren
gth
curv
es, a
nd th
us r
enec
t the lags
inherent in the percolation of input from the feature to the word level. The gating task, on
the other hand, does not require subjects 10 respond on,lin
e. "
If th
e i n
put i
s' s
impl
y tu
rned
off
at th
e pe
ak o
f ea
ch p
hone
me
s in
put s
peci
fica
tion,
and
then
allo
wed
to r
un f
ree
for
afe
w c
ycle
s, th
e dr
opou
t poi
nt s
hift
s ev
en e
arlie
r.
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
thes
e tw
o ki
nds
of in
nuen
ces
can
be c
aptu
red.
We
leav
e it
to fu
ture
rese
arch
. how
ever
. to
dete
rmin
e to
wha
t ext
ent t
hese
ela
bora
tions
of
TR
AC
E w
ould
pro
vide
a d
etai
led
acco
unt o
f the
dat
a on
the
role
s of
thes
e fa
ctor
s, F
or n
ow. w
e tu
rn to
the
prob
lem
of d
eter
min
ing
whe
re o
new
ord
ends
and
the
next
one
beg
ins,
we
can
say
eith
er it
em in
a w
ay th
at m
akes
it s
ound
like
a s
ingl
e w
ord
or li
ke tw
o w
ords
, the
re is
an
inte
rmed
iate
way
of
sayi
ng th
em s
o th
atth
e fi
rst s
eem
s to
be
two
wor
ds a
nd th
e se
cond
see
ms
like
only
one
.T
o se
e w
hat T
RA
CE
II
wou
ld d
o w
ith s
ingl
e- a
nd m
ultip
le-w
ord
inpu
ts,
we
ran
sim
ulat
ion
expe
rim
ents
with
eac
h in
divi
dual
wor
d in
the
mai
n 2
I 1-
wor
d le
xico
n pr
eced
ed a
nd fo
llow
ed b
y si
lenc
e, a
nd th
en w
ith 2
I I p
airs
of w
ords
, with
a s
ilenc
e at
the
begi
nnin
g an
d at
the
end
of th
e en
tire
stre
am. T
he p
airs
wer
e m
ade
by s
impl
y pe
rmut
ing
the
lexi
con
twic
e an
dth
en a
butti
ng th
e tw
o pe
rmut
atio
ns s
o th
at e
ach'
wor
d oc
curr
ed o
nce
asth
e fi
rst w
ord
and
once
as
the
seco
nd w
ord
in th
e en
tire
set o
f 21
1 pa
irs,
We
stre
ss, o
f co
urse
, tha
t rea
l spe
ech
wou
ld te
nd to
con
tain
cue
s th
atw
ould
mar
k w
ord
boun
dari
es in
man
y ca
ses;
the
expe
rim
ent i
s si
mpl
yde
sign
ed. t
o sh
ow w
hat T
RA
CE
wou
ld d
o in
cas
es w
here
thes
e cu
es a
rela
ckin
g,W
ith th
e in
divi
dual
wor
ds, T
RA
CE
mad
e no
mis
take
s-th
at is
, by
afe
w s
lices
aft
er th
e en
d of
the
wor
d, th
e w
ord
that
spa
nned
the
entir
ein
put w
as m
ore
stro
ngly
act
ivat
ed th
an a
ny o
ther
wor
d, A
n ex
ampl
e of
this is shown using the item
Ipar
til
in Fig. 27. The stream
Ipar
til
mig
ht b
eei
ther
one
wor
d ("
part
y)
or tw
o ("
par tea" or "par tee
the
mod
elknows of only one word pronounced
Iti/)
. A
t ear
ly p
oint
s in
'pr
oces
sing
the
wor
d, "
par" dominates over "
part
y" and other longer words, for
reas
ons
disc
usse
d in
the
prev
ious
sec
tion,
By
the
time
the
mod
el h
as h
ada
chan
ce to
pro
cess
the
end
of th
e w
ord,
however, "
part
y" comes to
dominate. .
Why
doe
s a
sing
le lo
nger
wor
d ev
entu
ally
win
out
ove
r tw
o sh
orte
r
Lex
ical
Bas
;. ~ (
~r W
OI:
d Se
gmen
tatio
n
How
do
we
know
whe
n on
e w
ord
ends
and
the
next
wor
d be
gins
? T
his
is b
y no
mea
ns a
n ea
sy ta
sk. a
s w
e no
ted
in th
e in
trod
uctio
n, T
o re
cap
our
earl
ier
argu
men
t. th
ere
are
som
e cu
es in
the
spee
ch s
trea
m. b
ut a
sse
vera
l inv
estig
ator
s ha
ve p
oint
ed o
ut (
Col
e &
Jak
imik
. 198
0; G
rosj
ean
& Gee. 19
84: T
hom
pson
. 198
4), t
hey
are
not a
lway
s su
ffic
ient
. par
ticu-
larl
y in
flu
ent s
peec
h, I
t wou
ld th
us a
ppea
r th
at th
ere
is a
n im
port
ant r
ole
for
lexi
cal k
now
ledg
e to
pla
y in
det
erm
inin
g w
here
one
wor
d en
ds a
ndth
e ne
xt w
ord
begi
ns; a
s w
ell a
s in
iden
tifyi
ng th
e ob
ject
s th
at r
esul
t fro
mthe process of segmentation. Indeed. as R
eddy
(19
76)
has
sugg
este
d,se
gmen
tatio
n an
d id
entif
icat
ion
may
be
join
t res
ults
of
the
mec
hani
sms
of word recognition.
Col
e an
d Ja
kim
ik (
1980
) di
scus
s th
ese
poin
ts a
nd p
rese
nt e
vide
nce
that
sem
antic
and
syn
tact
ic c
onte
xt c
an g
uide
seg
men
tatio
n in
cas
es w
here
the
lexi
con
is c
onsi
s~en
t with
two
read
ings
("c
ar g
o" vs "
carg
o).
Our
pres
ent m
odel
lack
s ~y
ntac
tic a
nd s
eman
tic le
vels
. so
it ca
nnot
mak
e us
eof
thes
e hi
gher
leve
r co
nstr
aint
s; b
ut it
can
mak
e us
e of
its
know
ledg
eabout words, not only to identify individual w
ords
in is
olat
ion,
but
topi
ck o
ut a
seq
uenc
e of
wor
ds in
con
tinuo
us s
trea
ms
of p
hone
mes
. Wor
did
entif
icat
ion
and
se~m
enta
tione
mer
ge to
geth
er f
rom
the
i"te
riJc
tive~
ac-
tivat
ion
proc
ess,
as
part
and
par
cel o
f the
pro
cess
of w
ord
activ
atio
n,T
his
sect
ion
cons
ider
s se
vera
l asp
ects
of
the
way
in w
hich
wor
d se
g-
men
tatio
n em
erge
s f~
om th
e in
tera
ctiv
e-ac
tivat
ion
proc
ess,
as
obse
rved
in s
imul
atio
ns w
ith T
RA
CE
II,
Bef
ore
'we
cons
ider
thes
e, it
is w
orth
reca
lling
the
deta
ils e
lf so
me
of th
e as
sum
ptio
ns m
ade
abou
t the
bot
tom
-up
act
ivat
ion
of w
ord'
uni
ts a
nd a
bout
com
petit
ive
inhi
bitio
n be
twee
n w
ord
units
. Fir
st, t
he e
xten
t to
whi
ch a
par
ticul
ar p
hone
me
exci
tes
a pa
rtic
ular
wor
d un
it is
inde
pen
dent
of
the
leng
th o
f th
e w
ord,
Sec
ond,
the
exte
ntto
whi
ch a
par
ticul
ar w
ord
unit
inhi
bits
ano
ther
wor
d un
it is
pro
port
iona
lto
the
tem
pora
l ove
rlap
of th
e tw
o w
ord
units
. Thi
s m
eans
that
wor
dsw
hich
do
not o
verl
ap in
tim
e w
ill n
ot in
hibi
t eac
h ot
her,
but
will
gan
g up
on o
ther
wor
ds th
at p
artia
lly o
verla
p ea
ch o
f th
em. T
hese
two
assu
mp-
tions
for
m m
ost o
f th
~ ba
sis
of th
e ef
fect
s w
e ob
serv
e in
the
sim
ulat
ions
,
..,.
11/e bollndary
~ ill th
e ea
r of
the
"beh
eOl'
eI",
Firs
t, w
e co
nsid
er th
eba
sic
fact
that
the
num
ber
of w
ords
we
hear
in a
seq
uenc
e of
pho
nem
esca
n de
pend
on
our
know
ledg
e of
the
num
ber
of w
ords
the
sequ
ence
mak
es. C
onsi
der
the
two
utte
ranc
es, "
she
can
t" a
nd "
seca
nt".
Tho
ugh
ili:I
TI:
nili
:IT
I:n
m.u
II r
af
t II
tP~
ITJJ
iIJI
DiI
JID
II r
tII
ri -
u I
P
u I
pllrti- -pB
rti-
-pB
rl'
- -
pBrl
i-F
lo. 2
7. T
he s
tate
of t
he 'l
htce
at v
ario
us p
oint
s du
ring
proc
essi
ng o
f Ip
arti/
,
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
m:I
Trn
ffi:W
ilJJ
imB
m::!
LD
a r l
m::u
:rn
i!!I
IDilJ
Ju:
:nliJ
l
l -
l . -
b r
l i- P
r i
- P
- a
and
"tea
do n
ot o
verla
p. T
hus,
"ar
t " receives in
hibi
tion
from
hot
hba
r " and "
tea," while "
bar " and "
tea "
each receive in
hibi
tion
only
from "
art." Thus two words th
at d
o no
t ove
rlap
with
eac
h ot
her
can
gang
up
on a
third
eac
h ov
erla
ps w
ith p
artly
, and
dri
ve it
oul
.T
hese
rem
arka
bly
sim
ple
mec
hani
sms
of a
ctiv
atio
n an
d co
mpe
titio
n do
a ve
ry g
ood
job
of w
ord
segm
enta
tion,
with
out t
he a
id o
f an
y sy
llabi
fi-
catio
n, s
tres
s, p
hone
tic w
ord
boun
dary
cue
s, o
r se
man
tic a
nd s
ynta
ctic
constraints. In 189 of the 211 w
ord
pairs
test
ed in
the
sim
ulat
ion
expe
r-im
ent,
the
mod
el c
ame
up w
ith th
e co
rrec
t par
se, i
n th
e se
nse
that
no
othe
r w
ord
was
mor
e ac
tive
than
eith
er o
f th
e tw
o w
ords
that
had
bee
npr
esen
ted,
Som
e of
the
failu
res
of th
e m
odel
occ
urre
d in
cas
es w
here
the
inpu
t was
act
ually
con
sist
ent w
ith tw
o pa
rses
, eith
er a
long
er s
pann
ing
wor
d ra
ther
than
a s
ingl
e w
ord
(as
in "
part
y)
or a
dif
fere
nt p
arse
into
two
wor
ds, a
s in
"part rust"
for
"par trusl." In such cases T
RA
CE
tend
sto
pre
fer
pars
es in
whi
ch th
e lo
nger
wor
d co
mes
firs
t. T
here
wer
e, h
ow-
ever
, som
e ca
ses
in w
hich
the
mod
el d
id n
ot c
ome
up w
ith a
val
id p
arse
,th
at is
, a p
atte
rn th
at r
epre
sent
s co
mpl
ete
cove
rage
of
the
inpu
t hy
a se
tof
non
over
lapp
ing
wor
ds. F
or e
xam
ple,
con
side
r th
e in
put I
park
i/.Though this makes the
two
wor
ds "
par " and "
key," the word "
park
"has a stronger activation than either "
par" or "
key." as illustrated in
Fig. 28,
Thi
s as
pect
of
TR
AC
E I
I's
beha
vior
indi
cate
s th
at th
e pr
esen
t vcr
sion
of th
e m
odel
is f
ar f
rom
the
fina
l wor
d on
wor
d se
gmen
tatio
n. A
com
plet
em
odel
wou
ld a
lso
expl
oit s
ylla
bifi
catio
n, s
tres
s, a
nd o
ther
cue
s to
wor
did
entit
y to
hel
p el
imin
ate
som
e of
the
poss
ible
inte
rpre
tatio
ns o
f T
RA
CE
II's
sim
ple
phon
eme
stre
ams,
The
' act
ivat
ion
and
com
petit
ion
mec
ha-
nism
s in
TR
AC
E I
I ar
e su
ffici
ent t
o do
qui
te a
bit
of th
e w
ord
segm
en-
tatio
n w
ork,
but
we
do n
ot e
xpec
t the
m to
do
this
per
fect
ly in
all
case
sw
ithou
t the
aid
'of other cues.
Som
e re
ader
s m
ay b
e tr
oubl
ed b
y a
mec
hani
srr
that
doe
s no
t ins
ist
upon
a p
arse
in w
hich
eac
h ph
onem
e is
cov
ered
by
one
and
only
one
wor
d, A
ctua
lly, t
houg
h, th
is c
hara
cter
istic
of
the
mod
el is
oft
en a
vir
tuc,
sinc
e in
man
y ca
ses
the
last
pho
nem
e of
h w
ord
mus
t do
doub
le d
uty
asth
e fi
rst p
hone
me
of th
e ne
xt, a
s in
"ho
und
dog"
or "
brush shop," Whilc
spea
kers
tend
to s
igna
l the
dou
blin
g in
car
eful
spe
ech,
the
cues
to s
ingl
evs
dou
ble
cons
onan
ts a
re n
ot a
lway
s su
ffici
ent f
or d
isam
bigu
atio
n, a
s is
clea
r w
hen
stri
ngs
with
mul
tiple
inte
rpre
tatio
ns a
re u
sed
as s
timul
i. Fo
rex
ampl
e, a
n ut
tera
nce
inte
nded
as
'no
not
ion
" w
ill s
omet
imes
be
hear
das
"kn
own
notio
n"
(Nak
atan
i & D
ukes
, 197
7). T
he m
odel
is n
ot in
clin
edto
sup
pres
s ac
tivat
ions
of
part
ially
ove
rlap
ping
wor
ds, e
ven
whe
n a
non-
over
lapp
ing
pars
e is
ava
ilabl
e. T
his
beha
vior
of
TR
AC
E is
illu
stra
ted
with
IbA
stap
l ("b
us top" or "
bus
stop
) in
Fig
. 29.
In
this
cas
e, h
ighe
r le
vels
coul
d pr
ovid
e an
add
ition
al s
ourc
e of
info
rmat
ion
that
wou
ld h
elp
the
mod
el c
hoos
e be
twee
n ov
erla
ppin
g an
d no
nove
rlapp
ing
inte
rpre
tatio
ns.
ones
in T
RA
CE
? T
here
are
two
mai
n re
ason
s, F
irst o
f all,
a lo
nger
wor
dev
entu
ally
rec
eive
s m
ore
botto
m-u
p su
ppor
t tha
n ei
ther
sho
rter
wor
d,si
mpl
y be
caus
e th
ere
are
mor
e ph
onem
es a
ctiv
atin
g th
e lo
nger
wor
d th
anth
e sh
orte
r w
ord.
The
sec
ond
reas
on h
as to
do
with
the
sequ
entia
l nat
ure
of th
e in
put,
In th
e ca
se o
f Ipa
rtil,
by
the
time
the
Itil i
s co
min
g in
, the
word "
part
y"
is w
ell e
noug
h es
tabl
ishe
d th
at it
kee
ps I
til f
rom
get
ting
asst
rong
ly a
ctiv
ated
as
it w
ould
oth
erw
ise,
as
illus
trat
ed in
Fig
. 27.
Thi
sbe
havi
or o
f the
mod
el le
ads
to th
e pr
edic
tion
that
sho
rt w
ords
em
bedd
edin
the
ends
of
long
er w
ords
sho
uld
not g
et a
s st
rong
ly a
ctiv
ated
as
shor
ter
wor
ds c
omin
g ea
rlie
r in
the
long
er w
ord.
Thi
s pr
edic
tion
coul
d be
test
edus
ing
the
gatin
g pa
radi
gm, o
r a
cros
s-m
odal
pri
min
g pa
radi
gm s
uch
asth
e on
e us
ed b
y Sw
inne
y (1
982)
.H
owev
er, i
t. sh
ould
be
note
d th
at th
is a
spec
t of t
he b
ehav
ior
of th
em
odel
can
be
over
ridde
n if
ther
e is
bot
tom
-up
info
rmat
ion
favo
rine
the
two-
wor
d in
terp
reta
tion,
Cur
rent
ly, t
his
can
only
hap
p~n
in T
RA
CE
thro
ugh
the
inse
rtio
n of
a b
rief
sile
nce
betw
een
the
"par
" and the "te
a.A
s sh
own
in F
ig, 2
8, th
is r
esul
ts in
"pa
r" a
nd "
tea"
dom
inat
ing
all o
ther
word candidates,
Wha
t hap
pens
whe
n th
ere
is n
o lo
ng w
ord
that
spa
ns th
e en
tire
stre
am,
as in
Iba
rtil?
In
this
cas
e, th
e m
odel
set
tles
on th
e tw
o-w
ord
inte
rpre
tatio
nba
r te
a,"
as s
how
n in
Fig
, 28.
Not
e th
at o
ther
wor
ds, s
uch
as "
art,
that
spa
n ap
ortio
n of
the
inpu
t, ar
e le
ss successful than either "
bar " or
tea.
" T
he r
easo
n is
that
the
inte
rpre
tatio
ns "
bar" and "
art" overlap
with
eac
h ot
her,
and
"ar
t" a
nd "
tea"
ove
rlap
with
eac
h ot
her,
but
"ba
r
part
i- '+
3 -p
ar-t
1-+
3 -b
arf
j- +
3 -p
ark i- +3
FIG
. 28,
Sla
le o
f th
e 'lt
ace
afte
r pr
oces
sina
the
stre
ams
/par
liJ,
/par
-tiJ
,/b
arliJ
, uni
t Ipa
rki/.
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
~!'
fl~
P -
- b
esta
blis
h w
here
a w
ord
will
end
eve
n be
fore
i. a
ctua
lly d
oes
end,
par
tic-
ular
ly in
the
case
of l
onge
r w
ords
or
whe
n ac
tivat
ions
at t
he w
ord
leve
lar
e ai
ded
by s
ynta
ctic
and
sem
antic
con
stra
ints
, How
ever
, it i
s m
uch
hard
er to
est
ablis
h th
e en
d of
a n
onw
ord,
sin
ce th
e fa
ct th
at it
is a
non
-w
()rd
mea
ns th
at w
e ca
nnot
exp
loit
any
know
ledg
e of
whe
re it
sho
uld
end
to d
oso
,T
his
fact
may
acc
ount
for
the
find
ing
of Foss and Blank (1
980)
that
subj
ects
are
muc
h sl
ower
to r
espo
nd to
targ
et p
hone
mes
at t
he b
egin
ning
of a word preceded by a non w
ord
than
at t
he b
egin
ning
of a
wor
dpreceded by a word. For example, responses to detect word initial
Idl
wer
e fa
ster
in s
timul
i lik
e th
e fo
llow
ing:
At t
he e
nd o
f las
t yea
r, th
e go
vern
men
t dec
ided
. . .
b-sl
ap-
-br-
Sap.
FIG. 29. State of the Trace at the end of the streams Ibustapl ("bus stop"
or "bus top
and
Ibru
Sapl
("b
rush
sho
p
than
they
wer
e w
hen
the
wor
d pr
eced
ing
the
targ
et (
in th
is c
ase
gove
rn-
men
t) w
as r
epla
ced
by a
non
wor
d su
ch a
s "g
atabont." It should be noted
that
the
targ
ets
wer
e sp
ecifi
ed a
s w
ord-
initi
al s
egm
ents
, The
refo
re, t
hesu
bjec
ts h
ad n
ot o
nly
to id
entif
y th
e ta
rget
pho
nem
e, th
ey h
ad to
det
er-
min
e th
at it
fel
l at t
he b
egin
ning
of
a w
ord,
as,
wel
l, T
he f
aef
that
rea
ctio
ntim
es w
ere
fast
er w
hen
the
targ
et w
as p
rece
ded
by a
wor
d su
gges
ts th
atsu
bjec
ts w
ere
able
to u
se th
eir
know
ledg
e of
whe
re th
e w
ord
"gov
ern-
men
t" e
nds
to h
elp
them
det
erm
ine
whe
re th
e ne
xt w
ord
begi
ns,
An
exam
ple
of h
ow T
RA
CE
allo
ws
one
wor
d to
hel
p es
tabl
ish
whe
reits
suc
cess
or b
egin
s is
illu
stra
ted
in F
ig, 3
0; I
n th
e ex
ampl
e, th
e. m
odel
rece
ives
the
stre
am "
possible target" or "
pagu
sle
targ
et." and we
imag
ine
that
the
targ
et is
wor
d-in
itial
/t/. I
n th
e fi
rst c
ase.
the
wor
d "p
os-
, sib
leis
cle
arly
est
ablis
hed
and
com
petit
ors
unde
rnea
tIJ
it ha
ve b
een
completely crushed by the time the initial
It I
in
"ta
rget
" be
com
es a
ctiv
eat
the
phon
eme
leve
l (se
cond
pan
el in
the
uppe
r pa
rt o
f th
e fi
gure
). s
othere is no ambiguity about the fact that this
It I
is
at t
he b
egin
ning
of t
hene
xt w
ord,
(T
he d
ecis
ion
mec
hani
sm w
ould
. of
cour
se. b
e re
quir
ed to
note
that
the
mod
el h
ad established the location of the end of the
prec
edin
g w
ord,
We
have
not
yet
inco
rpor
ated
exp
licit
assu
mpt
ions
abo
utho
w th
is w
ould
be
done
.) In
the
seco
nd c
ase.
wor
ds b
egin
ning
and
end
ing
at a
num
ber
of. d
iffer
ent p
lace
s. in
clud
ing
som
e th
at o
verl
ap w
ith th
elocation of the
Itl,
are
part
ly a
ctiv
ated
, Thu
s. th
e su
bjec
t wou
ld h
ave
tow
ait u
ntil
he is
wel
l int
o th
e w
ord
"tar
get"
bef
ore
it be
com
es c
lear
that
the first
It I
in
targ
et is
in fa
ct a
wor
d-in
itial
It
/.
In r
ealit
y, th
e si
tuat
ion
is p
roba
bly
not a
s bl
eak
for
the
perc
eive
r as
itap
pear
s in
this
exa
mpl
e, b
ecau
se in
man
y ca
ses
ther
e w
ill b
e cu
es in
the
man
ner
of p
ronu
ncia
tion
and
the
sylla
bifi
catio
n of
the
inpu
t tha
t will
hel
pto
indi
cate
the
loca
tion
of th
e w
ord
boun
dary
. How
ever
. giv
en '
the
im-
prec
isio
n an
d fr
eque
nt a
bsen
ce o
f su
ch c
ues.
it is
not
sur
pris
ing
that
the
The
sim
ulat
ions
we
have
rep
orte
d sh
ow th
at th
e w
ord
activ
atio
n/co
m-
petit
ion
mec
hani
sm c
an g
o a
long
way
tow
ard
prov
idin
g a
com
plet
e in
-terpretation of the input stream as a seq,ue
nce
of w
ords
, As
a w
ord
isbe
ginn
ing
to c
ome
in. t
he m
odel
tend
s to
pre
fer
shor
ter
wor
ds c
onsi
sten
tw
ith th
e in
put s
trea
m o
ver
long
er o
nes.
As
the input unfolds through
time.
how
ever
. the
mod
el te
nds
to p
refe
r to
inte
rpre
t streams of pho-
nem
es a
s si
ngle
long
er w
ords
rat
her
than
as
a se
quen
ce o
f sh
ort w
ords
;an
d it
tend
s to
fin
d pa
rses
that
acc
ount
for
eac
h ph
onem
e on
ce. B
ut it
does
not
insi
st u
pon
this
. and
will
occ
asio
nally
pro
duce
an
inte
rpre
tatio
nth
at le
aves
par
t of
the
stre
am o
f ph
onem
es u
nacc
ount
ed f
or o
r w
hich
acco
unts
for
part
of t
he s
trea
m o
f pho
nem
es tw
ice,
Ofte
n en
ough
, it w
illal
so le
ave
an a
ltern
ativ
e to
its
"pre
ferr
ed p
aise
" in a strong position. so
that both the preferred parse and the al
tern
ativ
e w
ould
be
avai
labl
e to
high
er le
vels
and
sub
ject
to p
ossi
ble
rein
forc
emen
t by
them
.T
hus
far
in th
is s
ectio
n, w
e ha
ve c
onsi
dere
d th
e ge
nera
l pro
pert
ies
ofth
e w
ay in
whi
ch T
RA
CE
use
s le
xica
l inf
orm
atio
n to
seg
men
t a s
peec
hst
ream
into
wor
ds. b
ut w
e ha
ve n
ot c
onsi
dere
d m
uch
in th
e w
ay o
f em
-pi
rica
l dat
a th
at th
ese
aspe
cts
of th
e m
odel
she
d lig
ht o
n, H
owev
er. t
here
are
two
find
ings
in th
e lit
erat
ure
whi
ch c
an b
e in
terp
rete
d in
acc
orda
nce
with
TR
AC
E' s
han
dlin
g of
mul
tiwor
d sp
eech
str
eam
s,W
here
doe
s 1I 1I00lword elld?
A n
umbe
r of
inve
stig
ator
s (e
,g,.
Col
e &
Jaki
mik
. 198
0) h
ave
sugg
este
d th
at w
hen
one
wor
d is
iden
tifie
d. it
s id
en-
tity
can
be u
sed
to d
eter
min
e w
here
it e
nds
and
ther
efor
e w
here
the
next
wor
d be
gins
. In
TR
AC
E. t
he in
tera
ctiv
e ac
tivat
ion
proc
ess
can
ofte
n
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
a s -
as-
a s -
ElD
as-b
lif
a . '
tl!.!
!J!.
.:tgi
iII2
ili 8
H,j,
.. -
II
- p
- b
u I
r -'I
:0 ~
r 8
or "
tarn
ishe
d" o
r on
e of
sev
eral
oth
er p
ossi
bilit
ies,
It i
s on
ly a
fter
mor
ctim
e ha
s pa
ssed
. and
we
have
per
ceiv
ed e
ither
a s
ilenc
e or
eno
ugh
of th
ene
xt w
ord
to r
ule
out a
ny o
f th
e co
ntin
uatio
ns o
f It
arl,
that
we
can
deci
dew
e ha
ve h
eard
the
wor
d "t
ar, "
Thi
s si
tuat
ion.
as
it ar
ises
in T
RA
CE
with
the
sim
ple
utte
ranc
e It
arba
ksl (
" tar
box
) is illustrated in Fig. 31.
Though "
tar"
is s
omew
hat m
ore
activ
e th
an th
e lo
nger
wor
d " t
arge
twhen the
Irl
is c
omin
g in
. it i
s on
ly w
hen
the
wor
d "b
ox" emerges as
the
inte
rpre
tatio
n of
the
phon
emes
fol
low
ing
" tar
" th
at th
e ri
val "
targ
et"
fina
lly f
ades
as
a se
riou
s co
nten
der,
With
long
er w
ords
the
situ
atio
n is
dif
fere
nt. A
s w
e ha
ve a
lrea
dy s
een
in a
noth
er e
xam
ple.
by
the
time
the
end
of a
long
er w
ord
is r
each
ed it
is
pas'
b-Il
arl-
~-pa
s-b-
Ilar
l-l-
pas-
b-Il
arl-
l-II
TD
...-r
!i;-
~IC
OI
ar:w
!i:I
!:D
!!J!
Dj
s a
iE!!
llllI
a rb
. ra
k
Pili
Pil
II I
u I !
!~
III
I
- p' .
Elii
.'!E
bEn
lli!!
i!::i
EE
TIl
W!i
.!-
s t:-
. -
fii.i
4P:~
=:.
'-II
- . . 1111
i2ili
9L__
_.C
iLl1
- s
- P
a
. -
r d
ja
S a
-lar
baka
--I
arb,
ka-
-Iar
b,",
--I
,rba
k,-
pal-s
-llar
,-I-
-P"
I-s-
Ilarg
-t-
-pal
-s-
llsrl
-l-
FIG
. 30,
Sta
te o
f th
e T
race
at s
ever
al p
oint
s du
ring
Ihe
pro
cess
ing
of "
poss
ible
targ
et"
and
pagu
sle
targ
et.
rjb-
;' .,
S)
fCIT
iI
u::L
fi
11m
iIT
IDI,
~ili
liE
!!I
a k
a r
s -
a k
u I
u I
PII
I.ia
d -
. lex
ical
sta
tus
of o
ne p
art o
f a
spee
ch s
trea
m p
lays
an
impo
rtan
t rol
e in
dete
rmin
ing
whe
re th
e be
ginn
ing
of th
e ne
xt w
ord
mus
t be.
The
lollg
tlllJ
~'horl of lI'ort! ideillifi('tllioll,
One
pro
blem
atic
fea
ture
of
spee
ch is
the
fact
that
it is
not
alw
ays
poss
ible
to id
entifya word un-
ambi
guou
sly
until
one
has
hea
rd th
e w
ord
afte
r it.
Con
side
r. f
or e
xam
ple.
the
wor
d "t
ar,"
If w
e ar
e lis
teni
ng to
an
utte
ranc
e an
d ha
ve g
otte
n ju
stto the
Irl
in "
The
man
saw
the
tar
box." though "
tar" will tend to be
the
pref
erre
d hy
poth
esis
at t
his
poin
t. w
e do
not
hav
e en
ough
info
rmat
ion
to s
ay u
nequ
ivoc
ally
that
the
wor
d " t
ar"
will
not
turn
out
to b
e " t
arge
t
,-Ia
rbak
,-I-
Iarb
,",-
I-I,
rb,k
.-I-
Iarb
aks-
FtG
. 31.
Sia
le o
f Ihe
Tra
ce a
l sev
eral
poi
nts
in p
roce
ssin
g "t
ar b
ox" and "
guita
r bo
x,
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
muc
h m
ore
likel
y th
at o
nly
one
wor
d ca
ndid
ate
will
rem
ain,
Inde
ed, w
ithlo
nger
wor
ds it
is o
ften
pos
sibl
e to
hav
e en
ough
info
rmat
ion
to id
entif
yth
e w
ord
unam
bigu
ousl
y w
ell b
efor
e th
e en
d of
the
wor
d. A
n ill
ustr
atio
nof
this
situ
atio
n is
pro
vide
d by
a simulation using the utterance "
guita
rbo
x" Ig
tarb
aks/
, By
the
time
the
Irl h
as r
egis
tere
d, "
guita
r " is clearly
dom
inan
t at t
he w
ord
leve
l. an
d ca
n be
unai11biguously identified without
furt
her
ado.
Rec
ently
, an
expe
rim
ent b
y G
rosj
ean
(198
5) h
as d
emon
stra
ted
thes
esa
me
effe
cts
empi
rica
lly, G
rosj
ean
pres
ente
d su
bjec
ts w
ith lo
ng o
r sh
ort
wor
ds f
ollo
wed
by
ase
cond
w()
rd a
nd m
easu
red
how
muc
h of
the
wor
dan
d its
suc
cess
or th
e su
bjec
t nee
ded
to h
ear
to id
entif
y th
e ta
rget
. With
long
er w
ords
, sub
ject
s co
uld
usua
lly g
uess
the
wor
d co
rrec
tly w
ell b
efor
eth
e en
d of
the
wor
d, ;
and
by th
e en
d of
the
wor
d th
ey w
ere
quite
sur
e of
the
wor
d's
iden
tity,
With
mon
osyl
labi
c w
ords
, on
the
othe
r ha
nd, m
any
of th
e w
ords
cou
ld n
ot b
e id
entif
ied
corr
~ctly
unt
il w
ell i
nto
the
next
wor
d, O
n th
e av
erag
e, s
ubje
cts
wer
e no
t sur
e of
the
wor
d's
iden
tity
until
abou
t the
end
of t
he n
ext w
ord,
or
the
begi
nnin
g of
the
one
afte
r, A
sGrosjean (1985) points out, a m
~or
reas
on f
or th
is is
sim
ply
that
the
spok
en in
put o
ften
does
not
uni
quel
y sp
ecify
the
iden
tity
of a
sho
rt w
ord.
In s
uch
case
s, th
e pe
rcep
tual
sys
tem
is o
ften
forc
ed to
pro
cess
the
shor
tw
ord,
and
its
succ
esso
r, a
t the
sam
e tim
e.RecoRllizilll: the words
ill
a short selltellce,
One
last
exa
mpl
e of
TR
AC
E I
I's p
erfo
rman
ce in
seg
men
ting
wor
ds is
illu
stra
ted
in F
ig, 3
2,T
he fi
gure
sho
ws
the
stat
e of
the
lrace
at s
ever
al p
oint
s du
ring
the
pro-
cessing of the stream ISiS"
t"ba
ks/.
By
the
end,
the
wor
ds o
f th
e ph
rase
She
shu
t a b
ox, "
whi
ch f
ils th
e in
put p
erfe
ctly
with
no
over
lap,
dom
i-na
te a
ll ot
hers
. .T
his
exam
ple
illus
trat
es h
ow f
ar it
is s
omet
imes
pos
sibl
e to
go
inpa
rsin
g a
stre
am o
f pho
nem
es in
to w
ords
, with
out e
ven
cons
ider
ing
syn-
tacl
ic a
nd s
eman
tic '(
onst
rain
ts, o
r st
ress
, syl
labi
ficat
ion,
and
junc
ture
cues
to w
ord
iden
tific
atio
n. T
he e
xam
ple
also
illu
stra
tes
the
diff
icul
ty th
em
odel
has
in p
erce
ivin
g sh
ort,
unst
ress
ed w
ords
like
". T
his
is, o
fco
urse
, jus
t an
extr
eme
vers
ion
of th
e di
ffic
ulty
the
mod
el h
as in
pro
-ce
ssin
g m
ol1o
sylla
bic
wor
ds li
ke "
tar,
" an
d is
con
sist
ent w
ith G
rosj
ean
data
on
the
diff
icul
ty s
ubje
cts
have
with
iden
tifyi
ng s
hort
wor
ds. I
n fa
ct,
Gro
sjea
n an
d G
ee (
1984
) re
port
pilo
t dat
a in
dica
ting
that
thes
e di
ffic
ultie
sar
e ev
en m
ore
seve
re w
ith f
unct
ion
wor
ds li
ke "
" and "
of. " It should
be n
oted
that
TR
AC
E m
akes
no
spec
ial d
istin
ctio
n be
twee
n co
nten
t and
func
tion
wor
ds, p
er s
e, a
nd n
eith
er d
o G
rosj
ean
and
Gee
, How
ever
, fun
c-tio
n w
ords
are
usu
ally
uns
tres
sed
and
cons
ider
ably
sho
rter
than
con
tent
wor
ds. T
hus,
it is
not
nec
essa
ry to
poi
nt to
any
spe
cial
mec
hani
sms
for
clos
ed v
ersu
s op
en c
lass
mor
phem
es to
acc
ount
for
Gro
sjea
n an
d G
eere
sults
.
m:n
IDJ
IH&
fnJi
JE
EJJ
5 I
s -
p u
s u
II i
S \I
-SIS
-l-b
aks-
SiS-
t-ba
ks-
SiS-
l-ba
ks-
tE:D
1~~
J3l~
Iru s
-
~ , 1t
-lt:: ~~
- 1- b
b.,;
s I S
s
I Silk
S I
pug S
SIS"
'I-ba
ks-
SIS-
l-ba
ks-
SiS-
l-bl
lks-
FIG
. 32.
The
sta
te o
f the
Tra
ce a
t sev
erat
poi
nts
durin
g th
e pr
oces
sing
of t
he s
trea
mIS
is
Tba
ksl (
" She
shu
t 8 b
ox
,.
Sum
mar
y of
Wor
d Id
emiji
catio
n Si
mul
atio
ns
Whi
le p
hone
me
iden
tific
atio
n ha
s be
en s
tudi
ed fo
r m
any
year
s, d
ata
from on-lin
e st
udie
s of
wor
d re
cogn
ition
is ju
st b
egin
ning
to a
ccum
ulat
e;T
here
is a
n ol
der
liter
atur
e on
acc
urac
y of
wor
d id
entif
icat
ion
in n
oise
.bu
t it h
as o
nly
been
qui
te r
ecen
tly th
at u
sefu
l tec
hniq
ues
have
bee
n de
-ve
lope
d fo
r st
udyi
ng w
ord
reco
gniti
on in
rea
l tim
e.W
hat e
vide
nce
ther
e is
. tho
ugh
indi
cate
s th
e co
mpl
exity
of
the
wor
d
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
iden
tific
atio
n pr
oces
s, W
hile
the
wor
d id
entif
icat
ion
mec
hani
sm is
sen
-si
tive
to e
ach
new
inco
min
g ph
onem
e as
it a
rriv
es, i
t is nevertheless
robu
st e
noug
h to
rec
over
fro
m u
nder
spec
ific
atio
n or
dis
tort
ion
of w
ord
begi
nnin
gs. A
nd it
app
ears
h..
be c
apab
le o
f so
me
sim
ulta
neou
s pr
oces
sing
of s
ucce
ssiv
e w
ords
in th
e in
put s
trea
m, T
RA
CE
app
ears
to c
aptu
re th
ese
aspe
cts
of th
e tim
e co
urse
of
wor
d re
cogn
ition
. In
thes
e re
spec
ts, i
t im
-pr
oves
upo
n th
e C
OH
OR
T m
odel
, the
onl
y pr
evio
usly
ext
ant m
odel
that
prov
ides
an
expl
icit
acco
unt o
f th
e on
- lin
e pr
oces
s of
wor
d re
cogn
ition
,A
nd th
e m
echa
nism
s it
uses
. to
acco
mpl
ish
this
are
the
sam
e on
es th
at it
used
for
the
sim
ulat
ions
of
the
proc
ess
of p
hone
me
iden
tific
atio
n de
-scribed in the preceding section,
lene
e,th
e m
odel
exh
ibits
imm
edia
te s
ensi
tivity
to in
form
atio
n fa
vorin
gon
e w
ord
inte
rpre
tatio
n ov
er a
noth
er. I
t sho
ws
an in
itial
pre
fere
nce
for
shor
ter
wor
ds r
elat
ive
to lo
nger
wor
ds, b
ut e
vent
ually
a s
eque
nce
ofph
onem
es th
at m
atch
es a
long
wor
d pe
rfec
tly w
ill b
e id
entif
ied
as th
atw
ord,
ove
rtur
ning
the
initi
al p
refe
renc
e fo
r th
e sh
ort-
wor
d in
terp
reta
tion.
The
se a
spec
ts o
f the
mod
el, a
re c
onsi
sten
t with
hum
an d
ata
from
gat
ing
expe
rim
ents
.7,
Tho
ugh
the
mod
el is
hea
vily
influ
ence
d by
wor
d be
ginn
ings
, it c
anre
cove
r fr
om u
nder
spec
ifica
tion
or d
isto
rtio
n of
a w
ord'
s be
ginn
ing.
S, T
he m
odel
can
use
its
know
ledg
e of
the
lexi
con
to p
arse
seq
uenc
esof
pho
nem
es in
to w
ords
, and
to e
stab
lish
whe
re o
ne w
ord
ends
and
the
next
one
beg
ins
whe
n cu
es to
wor
d bo
unda
ries
are
lack
ing.
9, L
ike
hum
an s
ubje
cts,
the
mod
el s
omet
imes
can
not i
dent
ify
a w
ord
until
it h
as h
eard
par
t of
the
next
wor
d, A
lso
like
hum
an s
ubje
cts.
it c
anbe
tter
dete
rmin
e w
here
a w
ord
will
beg
in w
hen
it is
pre
cede
d by
a w
ord
rath
er th
an a
non
wor
d,10
. The
mod
el d
oes
not d
eman
d a
pars
e of
a p
hone
me
sequ
ence
that
incl
udes
eac
h ph
onem
e in
one
and
onl
y on
e w
ord,
Thi
s al
low
s it
to c
ope
grac
eful
ly w
ith e
lisio
n. o
f ph
onem
~s a
t wor
d bo
unda
ries
. It w
ill o
ften
perm
it se
vera
l alte
rnat
ive
pars
es to
rem
ain
avai
labl
e lo
r hi
gher
leve
l in-
flue
nces
to c
hoos
e am
ong,
In a
dditi
on to
thes
e ch
arac
teri
stic
s ob
serv
ed in
the
pres
ent p
aper
, our
sim
ulat
ions
with
TR
AC
E I
sho
w s
ever
al f
urth
er c
orre
spon
denc
es b
e-tw
een
the
mod
el a
nd h
uman
spe
ech.
per
cept
ion,
Mos
t im
port
ant o
f th
ese
is th
e fa
ct th
at th
e m
odel
is a
ble
to u
se a
ctiv
atio
ns o
f pho
nem
e un
its in
one
part
of
the
Tra
ce to
adj
ust t
he c
onne
ctio
n st
reng
ths
dete
rmin
ing
whi
chfe
atur
es w
ill a
ctiv
ate
whi
ch p
hone
mes
in a
djac
ent p
arts
of
the
Tra
ce. I
nthis WaY, the m
odel
can
adj
ust a
s hu
man
sub
ject
s do
to c
oart
icuh
.itor
yin
flue
nces
on
the
acou
stic
pro
pert
ies
of p
hone
mes
(Fo
wle
r. 1
984;
Man
n&
Rep
p, 1
980)
. T
here
is, o
f cou
rse.
mor
e da
ta o
n so
me
of th
ese
poin
ts th
an o
ther
s. II
will
be
very
inte
rest
ing
to s
ee h
ow w
ell r
RA
CE
will
hol
d up
aga
inst
the
data
as
furt
her
empi
rica
l stu
dies
are
car
ried
oul
.
EN
ER
AL
DIS
CU
SSIO
N
Sum
ma,
.y o
f T
RA
CE
' ~' S
ucce
sses
In th
is a
rtic
le, w
e ha
ve s
een
that
TR
AC
E c
an a
ccou
nt f
or a
num
ber
ofdi
ffer
ent a
spec
ts o
f hu
man
spe
ech
perc
eptio
n. W
e be
gin
by li
stin
g th
em
ajor
cor
resp
onde
nces
bet
wee
n T
RA
CE
and
wha
t we
know
abo
ut th
ehu
man
spe
ech
unde
rsta
ndin
g pr
oces
s.
I, T
RA
CE
, lik
e hu
man
s, u
ses
info
rmat
ion
from
ove
rlap
ping
por
tions
of th
e sp
eech
wav
e to
iden
tify
succ
essi
ve p
hone
mes
,2,
The
mod
el s
how
s a
tend
ency
tow
ard
cate
goric
al p
erce
ptio
n of
pho
-ne
mes
, as
do h
uman
sub
ject
s. T
he m
odel
' s te
nden
cy to
war
d ca
tego
rical
perc
eptio
n is
aff
ecte
d by
man
y of
the
sam
e pa
ram
eter
s w
hich
aff
ect t
hede
gree
of
cate
gori
cal p
erce
ptio
n sh
own
by h
uman
sub
ject
s; in
par
ticul
ar.
the
exte
nt to
whi
ch p
erce
ptio
n w
ill b
e ca
tego
rical
incr
ease
s w
ith ti
me
betw
een
stim
uli t
hat m
ust b
e co
mpa
red,
3,
The
mod
el c
ombi
nes
feat
ure
info
rmat
ion
from
a n
umbe
r of
dift
eren
tdi
men
sion
s, a
nd e
xhib
its c
ue tr
ade-
offs
in p
hone
me
iden
tific
atio
n. T
hese
char
acte
rist
ics
of h
uman
spe
ech
perc
eptio
n ha
ve b
een
dem
onst
rate
d in
ave
ry h
irge
num
ber
of s
tudi
es,
4, T
he m
odel
aug
men
ts in
form
atio
n fr
om th
e sp
eech
str
eam
with
fced
-ba
ck f
rom
the
lexi
cal l
evel
in r
each
ing
deci
sion
s ab
out t
he id
entit
y of
phon
emes
, The
se le
xica
l int
luen
ces
on p
hone
me
iden
tific
atio
n oc
cur
inco
nditi
ons
sim
ilar
to th
ose
in w
hich
lexi
cal e
ffect
s ha
ve b
een
repo
rted
,bu
t do
not o
ccur
in c
ondi
tions
in w
hich
thes
e ef
fect
s ha
ve n
ot b
een
ob-
~~. .
5, L
ike
hum
an s
ubje
cts
the
mod
el e
xhib
its a
ppar
ent p
hono
tact
ic r
ule
effe
cts
on p
hone
me
iden
tific
atio
n. th
ough
it h
as n
o ex
plic
it re
pres
enta
tion
of th
e ph
onot
actic
rul
es, T
he te
nden
cy to
pre
fer
phon
otac
tical
ly r
egul
arin
terp
reta
tions
of
ambi
guou
s ph
onem
es c
an b
e ov
erri
dden
by
part
icul
arle
xica
l ite
ms,
just
as
it ca
n in
the
hum
an p
erce
iver
,6. In processing un
ambi
guou
s ph
onem
e se
quen
ces
prec
eded
by
si-
Som
e of
Ihe
Rea
solU
' fo,
. Ihe
Suc
ces~
'es
of T
RA
CE
To
wha
t doe
s th
e T
RA
CE
mod
el o
we
its s
ucce
s~ in
sim
ulat
ing
hum
ansp
eech
per
cept
ion'
! So
me
of T
RA
CE
's
succ
esse
s si
mpl
y de
pend
on
itsab
ility
to m
ake
use
of th
e in
form
atio
n as
it c
omes
il. F
or e
xam
ple.
it f
ails
to s
how
con
text
eff
ects
onl
y w
hen
a re
spon
se m
ust b
e m
ade.
or
can
bem
ade
with
hig
h ac
cura
cy. b
efor
e co
ntex
tual
info
rmat
ion
is a
vaila
ble.
The
re a
re s
ever
al o
ther
rea
sons
for
TR
AC
E's
suc
cess
, One
, we
thin
k.is
the
use
of c
ontin
uous
act
ivat
ion
and
com
petit
ion
proc
esse
s in
pla
ce o
f
/'"
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
disc
rete
dec
isiv
e pr
oces
ses
such
as
segm
enta
tion
and
labe
ling,
Act
ivat
ion
and
com
petit
ion
are
mat
ters
of
degr
ee a
nd p
rote
ct T
RA
CE
fr~m
cat
a-st
roph
ic c
omm
itmen
t in
mar
gina
l cas
es. a
nd th
ey p
rovi
de a
nat
uriif
mea
nsfo
r co
mbi
ning
man
y ~i
ffer
ent s
ourc
es: o
f in
form
atio
n, O
f co
urse
. thi
s fe
a-tu
re o
f th
e m
odel
is s
hare
d w
ith s
ever
al o
ther
mod
els
(e,g
.. M
orto
n. 1
969;
Ode
n &
Mas
saro
. 197
8). t
houg
h on
ly N
usba
um a
nd S
iow
iacz
ek (1
982)
have
pre
viou
sly
inco
rpor
ated
thes
e ki
nds
of a
ssum
ptio
ns in
a m
odel
of.
the
time
cour
se o
f wor
d re
cogn
ition
.Pa
rt o
f th
e su
cces
s of
TR
AC
E is
spe
cifi
cally
due
to th
e us
e of
com
-pe
titiv
e in
hibi
tory
inte
ract
ions
inst
ead
of b
otto
m-u
p (o
r to
p-do
wn)
inhi
-bi
tion.
Com
petit
ion
allo
ws
the
mod
el to
sel
ect t
he b
est i
nter
pret
atio
nav
aila
ble.
sel
l lin
g fo
r an
impe
rfec
t one
whe
n no
bel
ler
one
is a
vaila
ble.
but o
verr
idin
g po
or o
nes
whe
n a
' goo
d on
e is
at h
and,
The
se a
nd o
ther
virt
ues
of c
ompe
titiv
e in
hibi
tion
have
bee
n no
ted
befo
re (
e,g.
. Fel
dman
& Ballard. 1982: G
ro~s
berg
. 197
3; L
evin
. 197
6: R
atlif
f. 1
965;
von
Bek
esy.
1967) in other co
ntex
ts. T
heir
use
fuln
ess
here
atte
sts
to th
e ge
nera
l util
ityof
the
com
petit
ive
inhi
bitio
n m
echa
nism
.T
he e
limin
atio
n of
bet
wee
n-le
vel i
nhib
ition
fro
m th
e in
tera
ctiv
e ac
ti-va
tion
mec
hani
sm p
uts
us in
a v
ery
nice
pos
ition
with
res
pect
to o
nege
nera
l cri
tique
of
inte
ract
ive-
activ
atio
n m
odel
s. I
t is
ofte
n sa
id th
at a
c-tiv
atio
n m
odel
s ar
e ~
oo u
ncon
stra
ined
and
too
flexi
ble
to b
e an
ythi
ngm
ore
than
a la
ngua
ge f
or c
onve
nien
tly d
escr
ibin
g in
form
atio
n pr
oces
sing
,W
e ar
e no
w in
a p
ositi
on to
sug
gest
that
a r
estr
icte
d ve
rsio
n of
the
fram
e-w
ork
is n
ot o
nly
suffi
cien
t but
sup
erio
r. In
tera
ctiv
e-ac
tivat
ion
mod
els
coul
d ex
ploi
t bot
h ex
cita
tory
and
inhi
bito
ry c
onne
ctio
ns b
oth
betw
een
and
with
in le
vels
, bu~
in th
e or
igin
al in
tera
ctiv
e-ac
tivat
ion
mod
el o
f le
tter
perc
eptio
n. o
nly
inhi
bito
ry in
tera
ctio
ns w
ere
allo
wed
with
in a
leve
l. In
mor
e re
cent
ver
sion
s of
the
visu
al m
odel
(M
cCle
lland
. 1985, 1986),
and
in T
RA
CE
, we
have
gon
e ev
en fu
rthe
r, a
llow
ing
only
exc
itato
ryco
nnec
tions
bet
wee
n le
vels
and
onl
y in
hibi
tory
con
nect
ions
with
in le
vels
.F
rom
our
exp
erie
nce,
it a
ppea
rs th
at m
odel
s w
hich
adh
ere
to th
ese
con-
stra
ints
wor
k as
wel
l as
or b
ette
r th
an m
embe
rs o
f th
e m
ore
gene
ral c
lass
that
do
not.
We
hast
e n to
add
that
we
have
no
proo
f tha
t thi
s is
true
, We
have
, how
ever
. no
reas
on to
feel
that
we
coul
d im
prov
e th
e pe
rfor
man
ceof
our
mod
el b
y al
low
ing
eith
er b
etw
een-
leve
l inh
ibito
ry in
tera
ctio
ns o
rw
ithin
- leve
l exc
itatio
n,
Oth
er a
spec
ts o
f th
e su
cces
ses
of T
RA
CE
dep
end
on it
s us
e of
feed
back
from
hig
her
to lo
wer
rev
els,
Fee
dbac
k pl
ays
a ce
ntra
l rol
e in
the
acco
unts
of c
ateg
oric
al p
erce
ptio
n. le
xica
l eff
ects
on
phon
eme
iden
tific
atio
n, a
ndph
onot
actie
rule"
effe
cts,
W
e do
not
cla
im th
at a
ny o
f th
ese
phen
omen
a, ta
ken
indi
vidu
ally
, re-
quir
e th
e as
sum
ptio
n; o
f a fe
edba
ck m
echa
nism
, For
exa
mpl
e, c
onsi
der
the
phen
omen
on o
f ta
tego
rica
l per
cept
ion.
We
use
feed
back
fro
m th
e
phon
eme
to th
e fe
atur
e le
vel t
o dr
ive
feat
ure
patte
rns
clos
er to
the
pro-
totype of the ph
onem
e th
ey m
ost s
tron
gly
activ
ate,
Thi
!! m
echa
nism
.co
uple
d w
ith th
e co
mpe
titio
n m
echa
nism
at t
he p
hone
me
leve
l, ac
coun
tsfo
r be
tter
disc
rim
inat
ion
betw
een
than
with
in c
ateg
orie
s, H
owev
er, w
eco
uld
acco
unt f
or c
ateg
oric
al p
erce
ptio
n by
sug
gest
ing
that
sub
ject
s do
not h
ave
acce
ss to
the
acou
stic
leve
l at a
ll, b
ut o
nly
to th
e re
sults
of
the
phon
eme
iden
tific
atio
n pr
oces
s. S
imila
rly,
lexi
cal e
ffec
ts o
n ph
onem
eid
entif
icat
ion
can
be a
ccou
nted
for
by
assu
min
g th
at s
ubje
cts
(som
etim
es)
read
out
fro
m th
e w
ord
leve
l and
infe
r th
e id
entit
y of
pho
nem
es f
rom
the
lexi
cal c
ode
(Mar
slen
-Wilson, 1980: Marslen-
Wils
on &
Wel
sh, 1
978;
Mor
ton.
1979), In the case of "ph
onot
actic
rul
e" effects, other interpre-
tatio
ns a
re o
f cou
rse
avai
labl
e as
wel
l, O
ne c
ould
. for
exa
mpl
e, s
impl
ysu
ppos
e th
at s
ubje
cts
use
know
ledg
e of
the
phon
otac
tic c
onst
rain
ts. p
er-
haps
cap
ture
d in
uni
ts s
tand
ing
for
lega
l pho
nem
e pa
irs.
and
that
it is
the
outp
ut o
f suc
h un
its th
at a
ccou
nts
for
the
influ
ence
of p
hono
tact
ic r
eg-
ularity on phoneme identification.
We
know
of
no s
ingl
e co
nvin
cing
em
piri
cal r
easo
n to
pre
fer
feed
back
acco
unts
to o
ther
pos
sibi
litie
s, H
owev
er, w
e ha
ve tw
o th
eore
tical
rea
sons
for
pref
erri
ng to
ret
ain
top-
dow
n as
wel
l as
botto
m-u
p in
tera
ctio
ns in
our
activ
atio
n m
odel
s, O
ne r
easo
n ha
s to
do
with
the simplicity of the re-
sulti
ng d
ecis
ion
mec
hani
sms,
Fee
dbac
k al
low
s hi
gher
leve
l con
side
ratio
nsto
infl
uenc
e th
e ou
tcom
e of
pro
cess
ing
at lo
wer
leve
ls in
just
the
sam
ew
ay th
at lo
wer
leve
l con
side
ratio
ns in
flue
nce
the
outc
ome
of p
roce
ssin
gat
hig
her
leve
ls, T
he in
fluen
ces
of le
xica
l and
oth
er c
onst
rain
ts o
n ph
o-ne
me
iden
tific
atio
n ne
ed n
ot b
e pu
shed
out
of
the
theo
ry o
f sp
eech
per
-ce
ptio
n its
elf
into
dec
isio
n pr
oces
ses,
but
are
inte
grat
ed d
irec
tly in
to th
epe
rcep
tual
pro
cess
in a
uni
fied
way
, Giv
en to
p-do
wn
as w
ell a
s bo
ttom
-up
pro
cess
ing,
the
deci
sion
mec
hani
sms
requ
ired
for
gen
erat
ing
' ove
rtre
spon
ses
that
ref
lectlexical and other contextual influences are gr
eatly
sim
plif
ied;
no
spec
ial p
rovi
sion
nee
ds to
be
m.,d
e fo
r co
mbi
ning
lexi
cal
and
phon
etic
out
puts
in th
e de
cisi
on m
echa
nism
,A
sec
ond
reas
on f
or r
etai
ning
feed
back
com
es u
p w
hen
we
cons
ider
the
prob
lem
of
lear
ning
. Alth
ough
we
have
not
dis
cuss
ed h
ow le
arni
ngm
ight
occ
ur in
TR
AC
E, w
e ha
ve a
ssum
ed th
at th
e m
echa
nism
s of
spe
ech
perc
eptio
n ar
e ac
quire
d th
roug
h m
odifi
catio
n of
con
nect
ion
stre
ngth
s.V
ery
roug
hly,
in m
any
lear
ning
sch
emes
, con
nect
ions
bet
wee
n un
its a
rest
reng
then
ed w
hen
two
units
tend
to b
e ac
tivat
ed s
imul
tane
ousl
y, a
t the
expe
nse
of c
onne
ctio
ns b
etw
een
units
that
tend
not
to b
e ac
tivat
ed a
t the
sam
e tim
e (c
f, G
ross
berg
, 197
8; R
osen
blat
t. 19
62: R
umel
hart
& Z
ipse
r,19
85).
In s
uch
sche
mes
. how
ever
. the
re is
a s
erio
us p
robl
em if
act
ivat
ion
is e
ntire
ly b
otto
m-u
p: fo
r in
that
cas
e. o
nce
a pa
rtic
ular
uni
t has
bee
ntu
ned"
to r
espo
nd to
a p
artic
ular
pat
tern
. it i
s di
ffic
ult t
o re
tune
it: i
tfi
res
whe
n its
"ex
pect
ed"
patte
rn is
pre
sent
ed. a
nd w
hen
it fi
res.
its
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
tend
ency
to r
espo
nd to
that
pat
tern
onl
y in
crea
ses.
Fee
dbac
k pr
ovid
es a
way
to b
reak
this
vic
ious
cyc
le, I
f hi
gher
leve
ls in
sist
that
a p
artic
ular
phon
eme
is p
rese
nt. t
hen
the
unit
for
that
pho
nem
e ca
n be
com
e ac
tivat
edev
en if
the
botto
l11-
up in
put w
ould
nor
mal
ly a
ctiv
ate
som
e ot
her
phon
eme
inst
ead;
then
the
lear
ning
mec
hani
sm c
an "
retu
ne" the detector for the
phon
eme
so th
at it
will
nee
d to
dep
end
less
on
the
top-
dow
n in
put t
hene
xt ti
me
arou
nd,
In general. the use offeedback appears to place more
of
the
inte
llige
nce
requ
ired
for
per
cept
ion
and
perc
eptu
al le
arni
ng in
to th
e ac
tual
per
cept
ual
mec
hani
sm it
self
. and
to m
ake
the
mec
hani
sms
whi
ch e
xhib
it th
is in
tel-
ligen
ce e
xplic
it. A
s fo
rmul
ated
her
e. th
ese
mec
hani
sms
are
incr
edib
lysi
mpl
e; y
et th
ey a
ppea
r to
buy
qui
te a
lot w
hich
ofte
n ge
ts p
ushe
d in
toun
spec
ifie
d "d
ecis
ion" and "postperceptual guessing"
proc
esse
s (e
.Forster. 1976),
Fina
lly. t
h~ .
succ
ess
of
TR
AC
E a
lso
depe
nds
upon
its
arch
itect
ure,
rath
er th
an th
e fu
ndam
enta
l com
puta
tiona
l prin
cipl
es' o
f ac
tivat
ion
and
competition. or the decision to include feedback, B
y ar
chite
ctur
e, w
emean the organization
of
the Trace structure into layers consisting
of
units
corr
espo
ndin
g to
item
s oc
curr
ing
at p
artic
ular
tim
es w
ithin
the
utte
ranc
e,A
s w
e no
ted
in th
e in
trod
ucL
ion.
this
arc
hite
ctur
e is
one
we
deci
ded
upon
only after several other kinds
of
arch
itect
ure
had
faile
d,T
here
are
thre
e pr
inci
ple
posi
tive
cons
eque
nces
of
th
e T
RA
CE
arc
hi-
tect
ure.
Fir
st, i
t kee
ps s
trai
ght w
hat o
ccur
red
whe
n in
the
spee
ch s
trea
m,
Com
petit
ion
occu
rs o
nly
betw
een
units
com
petin
g to
rep
rese
nt th
e sa
me
portion of the input stream, Multiple copies of the same phoneme and
wor
d un
its c
an b
e ac
tive
at th
e sa
me
time
with
out p
rodu
cing
con
fusi
on,
Furt
herm
ore.
the
arch
itect
ure
perm
its th
e sa
me
com
petit
ion
mec
hani
smthat chooses among alternative word interpretations
of
a si
ngle
-wor
d ut
-te
ranc
e to
seg
men
t lon
ger
utte
ranc
es in
to w
ords
, No
sepa
rate
con
trol
structure. resetting the mechanism at the beginning
of
each
new
wor
d, is
requ
ired
, S
econ
d, th
e ar
chite
ctur
e pe
rmits
bot
h fo
rwar
d an
d ba
ckw
ard
inte
rac-
tions
. Bac
kwar
d in
tera
ctio
ns a
re a
bsol
utel
y es
sent
ial i
f th
e m
odel
is to
account for the fact that the identity
of
a ph
onem
e (o
r a
wor
d; W
arre
n &
Sher
man
, 1974) can be influenced by w
hat c
omes
afte
r it
as w
ell a
s w
hat
comes beforeiL Some kind
of
reco
rd
of
the
past
is n
eces
sary
to c
aptu
rethese kinds
of
influences. as well as to provide a clear picture
of
the
sour
ces
of
the more conventional effects
of preceding context, and the
Trace construct lays this out in a way that is both comprehensible' an
def
fici
enL
Thi
rd, t
he T
race
str
uctu
re p
rovi
des
an e
xplic
it m
echa
nism
whi
ch in
-st
antia
tes
the
idea
that
ther
e m
ay b
e no
dis
tinct
ion
betw
een
the
mec
ha-
nism
s w
hich
car
ry o
ut p
erce
ptua
l pro
cess
ing
and
thos
e w
hich
pro
vide
a
wor
king
mem
ory
for
the
resu
lts o
f th
e pe
rcep
tual
pro
cess
. At o
ne a
ndth
e sa
me
time.
the
Tra
ce is
a p
erce
ptua
l pro
cess
ing
syst
em a
nd a
mem
ory
syst
em, A
s a
resu
lt. th
e m
odel
aut
omat
ical
ly a
ccou
nts
fori
he f
act t
hat
cohe
rent
mem
ory
trac
es p
ersi
st lo
nger
than
inco
here
nt o
nes.
The
co-
here
nt o
nes
reso
nate
thro
ugh
inte
ract
ive
(tha
t is,
bot
tom
-up
and
top-
dow
n) a
ctiv
atio
n. w
hile
inco
here
nt o
nes
fail
to e
stab
lish
a re
sona
nce
and
ther
efor
e di
e aw
ay m
ore
rapi
dly,
Seve
ral
of
thes
e as
pect
s of
TR
AC
E o
verl
ap w
ith a
ssum
ptio
ns m
ade
inot
her
mod
els,
as
men
tione
d in
pre
viou
s se
ctio
ns; c
ontin
uity
bet
wee
nw
orki
ng m
emor
y an
d th
e pe
rcep
tual
pro
cess
ing
stru
ctur
es h
as b
een
sug-
gest
ed b
y a
num
ber
of o
ther
aut
hors
(e.
g,. C
onra
d,19
62),
and
the
notio
nth
at w
orki
ng m
emor
y is
a d
ynam
ic p
roce
ssin
g st
ruct
ure
rath
er th
an a
pass
ive
data
str
uctu
re h
as p
revi
ousl
y be
en a
dvoc
ated
by
Cro
wde
r (1
978,
1981) and Grossberg (1978), Indeed, G
ross
berg
has
not
ed th
at r
eson
atin
gac
tivat
ion/
com
petit
ion
proc
esse
s ca
n bo
th e
nhan
ce a
per
cept
ual r
epre
-se
ntat
ion
and
incr
ease
the
rete
ntio
n of
a r
epre
sent
atio
n; h
is a
naly
sis
ofin
tera
ctiv
e-ac
tivat
ion
proc
esse
s in
per
cept
ion
and
apem
ory
capt
ures
the
cont
inui
ty o
f pe
rcep
tion
and
mem
ory
as w
ell a
s m
any
othe
r de
sira
ble
prop
ertie
s of
in
tera
ctiv
e-ac
tivat
ion
mec
hani
sms,
Som
e D
efic
ienc
ies
of T
RA
CE
. Alth
ough
TR
AC
E h
as h
ad a
num
ber
of im
port
ant s
ucce
sses
, it a
lso
has
a number of equally important deficiencies. A number
of these deficien-
cies
rel
ate
to s
impl
ifyin
g as
sum
ptio
ns o
f th
e si
mul
atio
n m
odel
. It i
s im
-portant to be clear that such deficiencies are not in
trin
sic
to th
e ba
sic
stru
ctur
e of
the
mod
el b
ut to
the
sim
plifi
catio
ns w
e ha
ve im
pose
d up
onit
to in
crea
se o
ur a
bilit
y to
und
erst
and
its b
asic
pro
pert
ies.
Cer
tain
de-
ficiencies-such as the assumption th
at a
ll ph
onem
es a
re th
e sa
me
leng
th, t
hat a
ll fe
atur
es a
re e
qual
ly s
alie
nt a
nd u
sefu
l, a
nd o
verl
ap a
n eq
ual
amount from one phoneme to another-are no
t pre
sent
in T
RA
CE
I.O
bvio
usly
a f
ully
rea
listic
mod
el w
ould
take
acc
ount
of
such
din
eren
ces.
Oth
er fa
ctor
s th
at s
houl
d be
inco
rpor
ated
in a
mor
e co
mpl
ete
mod
el in
-clude some provision for effects
of
wor
ll fr
eque
ncy,
and
som
e m
echa
-ni
sms
for
expl
oitin
g av
aila
ble
cues
to w
ord
boun
dari
es,
Another deficiency
of
the
mod
el is
that
the
deci
sion
mec
hani
sms
have
not b
een
fully
eno
ugh
elab
orat
ed. F
or e
xam
ple,
as
it st
ands
the
mod
eldo
es n
ot p
rovi
de a
mec
hani
sm f
or ,d
ecid
ing
whe
n a
nonw
ord
has
been
pres
ente
d. N
or h
ave
we
spec
ified
how
dec
isio
n pr
oces
ses
wou
ld a
ctua
llyus
e th
e in
form
atio
n av
aila
ble
at th
e w
ord
leve
l to
loca
te w
ord-
initi
al p
ho-
nem
es, A
rel
ated
pro
blem
is th
e la
ck o
f an
exp
licit
prov
isio
n for vari-
abili
ty in
the
activ
atio
n an
d/or
rea
dout
pro
cess
es. I
ncor
pora
ting
vari
-ab
ility
dir
ectly
into
a s
imul
atio
n m
odel
wou
ld g
reat
ly in
crea
se th
e co
m-
plex
ity
of the simulation process, but would also increase the model's
TR
AC
E M
OD
EL
abili
ty to
cap
ture
the
deta
iled
prop
ertie
s of
rea
ctio
n tim
e di
strib
utio
nsan
d er
rors
(R
atcl
iff.
197
8).
So far we have considered de
fici
enci
es w
hich
we
wou
ld a
ttrib
ute
tosi
mpl
ifyin
g as
sum
ptio
ns a
dopt
ed to
kee
p T
RA
CE
as
sim
ple
and
tran
s-pa
rent
in it
s be
havi
or a
s po
ssib
le. H
owev
er. t
here
are
som
e pr
oble
ms
that
are
intr
insi
c to
the
basi
c st
ruct
ure
of th
e m
odel
,O
ne f
unda
men
tal d
efic
ienc
y of
TR
AC
E is
that
fac
t tha
t it requires
mas
sive
dup
licat
ion
of u
nits
and
con
nect
ions
. cop
ying
ove
r an
d ov
erag
ain
the
conn
ectio
n pa
ttern
s th
aI' d
eter
min
e w
hich
fea
ture
s ac
tivat
ew
hich
pho
nem
es a
nd w
hich
pho
nem
es a
ctiv
ate
whi
ch w
ords
. As
w~
al-
read
y no
ted.
lear
ning
in a
ctiv
atio
n m
odel
s (e
,g" Ackley, Hinton. &
Sejn
owsk
i. 19
85: G
ross
berg
. 197
6: R
umel
hart
& Z
ipse
r, 1985) usually
invo
lves
the
retu
ning
of
conn
ectio
ns b
etw
een
units
dep
endi
ng o
n th
eir
sim
ulta
neou
s ac
tivat
ion,
Giv
en T
RA
CE
's a
rchi
tect
ure.
suc
h le
arni
ngw
ould
not
gen
eral
ize
from
one
par
t of
the
Tra
ce to
ano
ther
and
so
wou
ldno
t be
acce
ssib
le f
or in
puts
ari
sing
at d
iffe
rent
loca
tions
in th
e T
race
, Ase
cond
pro
blem
is th
at th
e m
odel
. as
is. i
s in
sens
itive
to v
aria
tion
in g
loba
lpa
ram
eter
s, s
uch
as s
peak
ing
rate
, spe
aker
cha
ract
eris
tics
and
acce
nt,
and
ambi
ent a
cous
tic c
hara
cter
istic
s, A
thir
d de
fici
ency
is th
at it
fai
ls to
acco
unt f
or th
e fa
ct th
at o
ne p
rese
ntat
ion
of a
wor
d ha
s an
eff
ect o
n th
epe
rcep
tion
of it
a v
ery
shor
t tim
e la
ter
(Nus
baum
& S
iow
iacz
ek, 1
982)
,
These two pr
esen
tatio
ns. i
n th
e cu
rren
t ver
sion
of
the
mod
el. s
impl
yex
cite
sep
arat
e to
kens
for
the
sam
e w
ord
in d
iffer
ent p
arts
of t
he T
race
,A
ll th
ese
defi
cien
cies
ref
lect
the
fact
, tha
t the
TR
AC
E c
onsi
sts
of a
larg
e se
t of
inde
pend
ent t
oken
s of
eac
h fe
atur
e. p
hone
me,
and
wor
d un
it,W
hat a
ppea
rs to
be
calle
d fo
r in
stea
d is
a m
odel
in w
hich
ther
e is
a s
ingl
est
ored
rep
rese
ntat
ion
of e
ach
phon
eme
and
each
wor
d in
som
e ce
ntra
lrt
;pre
sent
atio
nal s
truc
ture
, If
this
str
uctu
re is
acc
esse
d ev
ery
time
the
wor
d is
pre
sent
ed, t
hen
we
coul
d ac
coun
t for
rep
etiti
on p
rimin
g ef
fect
s,L
ikew
ise.
if th
ere
wer
e a
sing
le c
entr
al s
truc
ture
. lea
rnin
g co
uld
occu
r in
just
one
set
of u
nits
, 'as could dynamic returning offeature-
phon
eme
and
phon
eme-
wor
d co
nnec
tions
to ta
ke a
ccou
nt o
f ch
ange
s in
glo
bal p
aram
~et
ers
or s
peak
er c
hara
cter
istic
s,H
owev
er. i
t rem
ains
nec
essa
ry to
kee
p st
raig
ht th
e re
lativ
e ,t
empo
ral
loca
tion
of d
iffer
ent f
eatu
re. p
hone
me.
and
wor
d ac
tivat
ions
. Thu
s it
will
not do to simply abandon the Trace in favor of a single set of units
cons
istin
g of
just
one
cop
y of
eac
h ph
onem
e an
d on
e co
py o
f ea
ch w
ord,
It s
eem
s th
at w
e ne
ed to
hav
e th
ings
bot
h w
ays:
we
need
a c
entr
alre
pres
enta
tion
that
pla
ys a
rol
e in
pro
cess
ing
ever
y ph
onem
e an
d ev
ery
wor
d an
d th
iit is
sub
ject
to le
arni
ng, r
etun
ing.
and
pri
min
g, W
e al
so n
eed
to k
eep
a dy
nam
ic tr
ace
of th
e un
fold
ing
repr
esen
tatio
n of
the
spee
chst
ream
. so
that
we
can
cont
inue
to a
ccom
mod
ate
both
left
and
right
con
"te
xtua
l eff
ects
.
MC
CLE
LLA
ND
AN
D E
LMA
N
We
are
curr
ently
beg
inni
ng to
dev
elop
a m
odel
that
has
thes
e pr
oper
-tie
s, b
ased
on
a sc
hem
e fo
r us
ing
a ce
ntra
l net
wor
k of
uni
ts to
tune
the
conn
ectio
ns b
etw
een
the
units
in th
e T
race
in th
e co
urse
of
proc
essi
ng.
ther
eby
effe
ctiv
ely
prog
ram
ing
it "o
n th
e fly
," S
imila
r id
eas
have
alr
eady
been
app
lied
to v
isua
l wor
d re
cogn
ition
(M
cCle
lland
, 198
5, 1
986)
. Our
hope
is th
at a
new
ver
sifJ
nof
the
mod
el b
ased
on
thes
e id
eas
will
pre
serv
eth
e po
sitiv
e fe
atur
es o
f T
RA
CE
I a
nd T
RA
CE
II.
whi
le o
verc
omin
g th
eir
principle deficiencies,
Som
e G
ener
al I
ssue
s in
Spe
ech
and
Lan
guag
e Pe
rcep
tion
The
re a
re a
num
ber
of g
en~r
al is
sues
in s
peec
h an
d la
ngua
ge' p
erce
p-
tion,
Fou
r qu
estio
ns in
par
ticul
ar a
ppea
r to
lie
clos
e to
the
hear
t of
our
conc
eptio
n of
wha
t spe
ech
perc
eptio
n is
all
abou
t. Fi
rst.
wha
t are
the
basi
c un
its in
spe
ech
perc
eptio
n? S
econ
d. w
hat i
s th
e pe
rcep
t. an
d w
hich
aspe
cts
of th
e pr
oces
sing
of
spok
en la
ngua
ge s
houl
d be
cal
led
perc
eptu
al?
Thi
rd. w
hat i
s th
e re
pres
enta
tion
of li
ngui
stic
rul
es?
Four
th. i
s th
ere
any-
thin
g un
ique
or
spec
ial a
bout
spe
ech
perc
eptio
n? W
e co
nclu
de th
is a
rtic
leby
con
side
ring
eac
h is
sue
from
the
pers
pect
ive
we
have
dev
elop
edth
roug
h th
e co
urse
of
our
~xpl
orat
ions
of
TR
AC
E.
What is the perceptual "nit?
Thr
ough
out t
his
artic
le. w
e ha
ve c
onsi
d-er
ed th
ree
leve
ls o
f pr
oces
sing
-fea
ture
, pho
nem
e, a
nd w
ord.
At e
ach
leve
l, in
divi
dual
pro
cess
ing
units
sta
nd f
or h
ypot
hese
s ab
out t
he f
eatu
res,
phon
emes
. and
wor
ds th
at m
ight
be
pres
ent a
t dif
fere
nt p
oint
s in
the
inpu
tst
ream
, It i
s w
orth
not
ing
that
mos
t asp
ects
of
the
mod
el's
per
form
ance
, are
inde
pend
ent o
f th
e sp
ecif
ic a
ssum
ptio
ns th
at w
e ha
ve m
ade
abou
t the
units
, or
even
the
leve
ls. T
hus.
if w
e re
plac
ed th
e ph
onem
e le
vel w
ithdemisyllables (Fujimura & Lovins, 1978) or
pho
nem
e tr
iple
s (W
icke
lgre
n.19
69),
ver
y lit
tle o
f th
e be
havi
or o
f th
e m
odel
wou
ld c
hang
e. T
hese
uni
tsca
n ca
ptur
e so
me
of th
e co
artic
ulat
ory
infl
uenc
es o
n ph
onem
e id
~nt
ity.
and
they
wou
ld r
educ
e so
me
of th
e w
ord-
boun
dary
am
bigu
ities
face
d by
the
curr
ent v
ersi
on o
f th
e m
odel
, but
nei
ther
coarticulatory influences
nor
wor
d bo
unda
ry a
mbi
guiti
es w
ould
dis
appe
ar a
ltoge
ther
(se
e E
lman
& M
cCle
lland
. in
pres
s, fo
r fu
rthe
r di
scus
sion
),
In f
act,
inte
ract
ive
activ
atio
n m
odel
s lik
e T
RA
CE
can
be
form
ulat
edin
whi
ch e
ach
perc
eptu
al o
bjec
t is
repr
esen
ted.
not
by
a si
ngle
uni
t. bu
tby
a p
atte
rn o
f act
ivat
ion
over
a c
olle
ctio
n of
uni
ts, F
or e
xam
ple.
the
phon
eme
units
in e
ach
time
slic
e of
TR
AC
E m
ight
be
repl
aced
by
adi
ffer
ent s
et o
f un
its w
hich
did
not
hav
e a
one-
to-o
ne c
orre
spon
denc
e to
phon
emes
. A p
hone
me
wou
ld b
e re
pres
ente
d by
a p
artic
ular
pat
tern
of
activ
atio
n ov
er th
e se
t of
units
(ea
ch r
epre
sent
ing,
per
haps
. to
som
e co
n-ju
nctio
n of
low
er le
vel f
eatu
res)
rat
her
than
by
a si
ngle
uni
t in
the
set.
The
re a
re s
ome
com
puta
tiona
l adv
anta
ges
of d
istr
ibut
ed r
epre
sent
atio
nco
mpa
red
to o
ur "
one
unit
one
conc
ept" assumption (Hinton, Mc-
""'
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
LMA
N
Cle
lland
, & R
umel
hart
, in
pres
s), b
ut it
is v
ery
diffi
cult
to fi
nd p
rinci
pled
way
s of
dis
tingu
ishi
ng b
etw
een
loca
l and
dis
trib
uted
rep
rese
ntat
iona
lsc
hem
es e
mpi
rica
lly, I
ndee
d, in
cer
tain
cas
es th
ere
is a
n ex
act m
appi
ngan
d, in
gen
eral
, it i
s po
ssib
le to
app
roxi
mat
e m
ost a
spec
ts o
f th
e be
havi
orof
a lo
cal s
chem
e w
ith a
dis
trib
uted
one
and
vic
e ve
rsa
(Sm
olen
sky,
1986). In light of this, our us
e of
loca
l as
oppo
sed
to d
istr
ibut
ed r
epre
-se
ntat
ions
is n
ot p
erha
ps a
s si
gnifi
cant
as
it m
ight
app
ear
at fi
rst g
lanc
e.W
hat i
s es
sent
ial i
s th
e in
form
atio
n th
at th
e re
pres
enta
tion
capt
ures
,ra
ther
than
whe
ther
it d
oes
so v
ia d
istr
ibut
ed o
r lo
cal r
epre
sent
atio
n, T
heus
e of
loca
l rep
rese
ntat
ior.
.., w
ith e
ach
unit
(at t
he p
hone
me
and
wor
dle
vels
, any
way
) re
pres
entin
g a
mut
ually
exc
lusi
ve a
ltern
ativ
e m
akes
itm
uch
easi
er to
rel
ate
the
stat
es o
f th
e pr
oces
sing
sys
tem
to o
vert
res
pons
eca
tego
ries
but
is n
ot o
ther
wis
e a
fund
amen
tal f
eatu
re o
f th
e st
ruct
ure
ofth
e m
odel
.What is the percept?
At a
num
ber
of p
oint
s in
this
art
icle
, we
have
allu
ded
to w
ays
in w
hich
our
con
cept
ion
of p
erce
ptio
n di
ffer
s fr
om th
eus
age
of o
ther
aut
hors
, Suc
h co
ncep
ts a
s pe
rcep
tion
are
inhe
rent
ly ti
edto
theo
ry, a
nd o
nly
deri
ve th
eir
mea
ning
with
res
pect
to p
artic
ular
theo
-re
tical
con
stru
cts,
Whe
re d
oes
the
TR
AC
E m
odel
pla
ce u
s, th
en, w
ithre
spec
t to
the
ques
tion,
wha
t is
spee
ch p
erce
ptio
n?F
or o
ne th
ing,
TR
AC
E b
lurs
the
dist
inct
ion
betw
een
perc
eptio
n an
dother aspects of cognitive processing, T
here
is r
eally
no
clea
r w
ay in
TR
AC
E to
say
whe
re p
erce
ptua
l pro
cess
ing
ends
and
con
cept
ual p
ro-
cess
es o
r m
emor
y be
gin,
How
ever
, fol
low
ing
Mar
rs
(198
2) d
efin
ition
of
visu
al p
erce
pt.io
n, w
e co
uld
say
that
spe
ech
perc
eptio
n is
the
proc
ess
offo
rmin
g re
pres
enta
tions
of
the
stim
ulus
-the
spe
aker
s ut
tera
nce-
atse
vera
l lev
els
of d
escr
iptio
n, T
RA
CE
pro
vide
s su
ch a
set
of
repr
esen
ta-
tions
, as
wel
l as
proc
esse
s to
con
stru
ct th
em. O
n th
is v
iew
, the
n, th
eT
race
is th
e pe
rcep
t, an
d in
tera
ctiv
e ac
tivat
ion
is th
e pr
oces
s of
per
cep-
tion, A
spec
ts o
f th
is d
efin
ition
are
app
ealin
g. F
or e
xam
ple,
on
this
vie
w, t
hepe
rcep
t is
a ve
ry r
ich
obje
ct, o
ne th
at r
efer
s bo
th to
abs
trac
t, co
ncep
tual
entit
ies
like
wor
ds a
nd p
erha
ps a
t hig
her
leve
ls e
ven
mea
ning
s, a
s w
ell
as to
mor
e co
ncre
te e
ntiti
es li
ke a
cous
tic s
igna
ls a
nd f
eatu
res,
Per
cept
ion
is n
ot r
estr
icte
d to
one
or
a su
bset
of
leve
ls, a
s it
is in
cer
tain
mod
els
(e.g
., M
arsl
en-W
ilson
, 198
0; M
orto
n, 1
979)
.O
n th
e ot
her
hand
, the
def
initi
on s
eem
s ov
erly
libe
ral,
for
ther
e is
evid
ence
sug
gest
ing
that
per
cept
ual e
xper
ienc
e an
d ac
cess
to th
e re
sults
of perceptual processing for the purposes of overt responding ,m
ay n
otbe
com
plet
ely
unco
nstn
tined
, A n
umbe
r of
exp
erim
ents
, bot
h in
spe
ech
(e.g
., Fo
ss &
Sw
inne
y, 1
973;
McN
eil &
Lin
dig,
1973) and reading (D
rew
-no
wsk
i & H
ealy
, 1977; Healy, 1976) suggest that under certain conditions
low
er le
vels
of p
roce
ssin
g ar
e in
acce
ssib
le, o
r ar
e ' a
t bes
t acc
esse
d on
ly
with
ext
ra ti
me
or e
ffor
t. O
n th
is e
vide
nce,
if p
erce
ptio
n is
to f
orm
rep
-re
sent
atio
ns, a
nd if
the
repr
esen
tatio
ns. a
re a
nyth
il18
like
thos
e po
stul
ated
in T
RA
CE
, the
n pe
rcep
tion
is q
uite
inde
pend
ent o
f th
e ex
peri
ence
of
the
perc
eive
r an
d of
acc
ess
to th
e pe
rcep
t. P
ut a
noth
er w
ay, w
e m
ay c
hoos
eto
def
ine
the
'Irac
e as
the
perc
ept,
but i
t is
not t
he p
erce
ptua
l"ex
peri
cnce
.T
his
does
not
see
m to
be
a ve
ry s
atis
fact
ory
stat
e of
affa
irs.
One
coh
eren
t 're
spon
se to
thes
e ar
gum
ents
wou
ld b
e to
say
that the
'Irac
e is
not
the
expe
rienc
e its
elf,
but t
hat s
ome
part
or
part
s of
it m
aybe the
obje
ct
of perceptual experience, It seems sensible
, for
exa
mpl
e,to
sup
pose
that
the
perc
ept i
tsel
f con
sist
s of
that
par
t of t
he T
race
und
ersc
rutin
y by
the
deci
sion
mec
hani
sms,
On
this
vie
w, i
t wou
ld n
ot b
e in
-co
here
nt to
sup
pose
that
rep
rese
ntat
ions
mig
ht b
e fo
rmed
whi
ch w
ould
nevertheless be inaccessible either to experience or to overt re
spon
sepr
oces
ses.
It w
ould
be
a m
atte
r se
para
te f
rom
the
anal
ysis
of
the
inte
r-ac
tive-
activ
atio
n pr
oces
s its
elf t
o sp
ecify
the
scop
e an
d co
nditi
ons
ofac
cess
to th
e T
race
. In
our
sim
ulat
ions
, we
have
ass
umed
that
the
deci
-si
on m
echa
nism
cou
ld b
e di
rect
ed w
ith e
qual
fac
ility
to a
ll le
vels
. but
this
may
turn
out
to b
e an
ass
umpt
ion
that
doe
s no
t app
ly in
all
case
s.HolY are rules represe~ted?
It is
com
mon
in th
eori
es o
f la
ngua
ge to
assu
me
with
out d
iscu
ssio
n th
at li
ngui
stic
rul
es a
re r
epre
sent
ed ".
..' S
lIch
in the mind of the perceiver, and that perception is guided primarily by
cons
ulta
tion
of s
uch
rule
s, H
owev
er, t
here
are
a nu
mbe
r of
dift
icul
ties
asso
ciat
ed w
ith th
is v
iew
, Fir
st, i
t :do
es n
ot e
xpla
in h
ow e
xcep
tions
are
hand
led;
it w
ould
see
m th
at f
or e
very
exc
eptio
n, th
ere
wou
ld h
ave
to b
ea
spec
ial r
ule
that
take
s pr
eced
ence
ove
r th
e m
ore general formulation.
Sec
ond,
it d
oes
not e
xpla
in a
spec
ts o
f rul
e ac
quis
ition
by
child
ren
leai
'nin
gla
ngua
ge, p
artic
ular
ly th
e fa
ct th
at"
rule
s ap
pear
to b
e ac
quire
d, a
t lea
stto
a la
rge
exte
nt, o
n a
wor
d by
wor
d ba
sis;
acq
uisi
tion
is m
arke
d by
agr
adua
l spr
ead
of th
e ru
le f
rom
one
lexi
cal i
tem
or
set o
f le
xica
l ite
ms
toot
hers
. Thi
rd, i
t doe
s no
t exp
lain
how
rul
es c
ome
,into
exi
sten
ce h
isto
ri-
cally
; as
with
acq
uisi
tion,
it a
ppea
rs th
at r
ules
spr
ead
grad
ually
ove
r th
ele
xico
n, I
t is
diff
icul
t to
reco
ncile
sev
eral
ofth
ese
findi
ngs
with
trad
ition
alru
le-b
ased
acc
ount
s of
lang
uage
kno
wle
dge
and
lang
uage
pro
cess
ing.
Mod
els
like
TR
AC
E a
nd th
e in
tera
ctiv
e-ac
tivat
ion
mod
el o
f w
ord
rec-
ogni
tion
take
a v
ery
diff
eren
t per
spec
tive
on th
e is
sue
of li
ngui
stic
rul
es,
The
y ar
e no
t rep
rese
nted
as
such
, but
rat
her
they
are
bui
lt in
to th
e pe
r-ce
ptua
l sys
tem
via
the
exci
tato
ry a
nd in
hibi
tory
con
nect
ions
nee
ded
for
proc
essi
ng th
e pa
rtic
ular
item
s w
hich
em
body
thes
e ru
les.
Suc
h a
mec
h-an
ism
app
ears
to a
void
the
prob
lem
of
exce
ptio
ns w
ithou
t dif
ticul
ty, a
ndto
hol
d ou
t the
hop
e of
acc
ount
ing
for
the
obse
rvat
ion
that
rul
e ac
quis
ition
and
rule
cha
nge
are
stro
ngly
tied
to p
artic
ular
item
s w
hich
em
body
the
ru~.
W
hat i
s sp
edt,!
abo
llt ..
.'pee
ch?
We dose by ra
isin
g a
qucs
tion
that
oft
en
TR
AC
E M
OD
EL
MC
CLE
LLA
ND
AN
D E
l ".'I
AN
RE
FER
EN
CE
S
Bag
ley,
W. C
. (I~), The apperception or
the
:spo
ken
sent
ence
: A s
tudy
in th
e ps
ycho
logy
of language,
Am
eric
an J
ollr
ncII
of
P,fy
dlol
oR."
, 12
, 80-
130.
Ballard. D. H.. Hinton, G. E,. &: Sejnowski, T. J. (1983). l'arallel visual computation.
Na-
Illre (LmIJOII).
306.
21-2
6.B
arro
w, H
. G..
&: T
enen
baum
. J. M
. (19
78).
In
A. R
. Han
son
&: E
. M. R
isem
an (
Eds
.C
ompl
ller
";,f;
C1/
l .V
Slem
s (p
p. 3
-26)
. New
Yor
k: A
cade
mic
Pre
ss.
von Bekesy, G. (1967).
Senmry ;nlrib;l;ml.
Prin
ceto
n,.N
J: P
rinc
eton
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v. P
ress
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ond,
Z. S
., &
: Gar
nes,
S. (
1980
). M
ispe
rcep
tions
of
l1ue
nt s
peec
h. I
n R
. Col
e (E
d,
),
Per-
cep;
;t1/l and pmJllcl;on of/11lenl
fpe'
e'dr
, Hill
sdal
e, N
J: E
rlbau
m.
Broadbent, D. E, (1967), Word frequency effect and response bias.
vdw
loR
kal
Rel
';ell'
74, 1-
15.
Col
e, R
. A. (
1973
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iste
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mis
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unci
atio
ns: A
mea
sure
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t we
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ch.
Pe'ru
pl;o
n &
P.fy
dlC
lpII
Y,fi
l".f,
13,
153
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Col
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akim
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, (19
78),
Und
erst
andi
ng s
peec
h: H
ow w
ords
are
hea
rd. I
n G
.U
nder
woo
d (E
d.
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Ole
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,f af
;nfim
llC/l;
cJ/I
pmce
,u;II
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Yor
k: A
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mic
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ss.
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akim
ik. J
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80).
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odel
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peec
h pe
rcep
tion.
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e (E
d,
),
Per-
cepl;an and proJllcl;on offllle'nl speech.
Hill
sdal
e, N
J: E
rlba
um.
Col
e, R
. A.,
&: R
udni
cky,
A. (
1983
). W
hat
s ne
w in
spe
ech
perc
eptio
n? T
he r
esea
rch
and
idea
s of
Will
iam
Cha
ndle
r B
agle
y. 1
874-
1946
. fy
dwla
Ric
cII
Re'
,';el
\', 9
0, 9
4-10
1.
Con
rad,
R. (
1962
). A
n as
soci
atio
n be
twee
n m
emor
y er
rors
and
err
ors
due
to a
cous
ticm
aski
ngof
spe~
ch.
Nal
llre'
(Lon
JOII
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6,
1314
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15.
Cotton. Soo &: Grosjean, F. (1
984)
. The
gad
ng p
arad
igm
: A c
ompa
riso
n of
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ive
and
individual presentation formats,
Pe',,
'ep'
;an
f.\:c
llopl
l.\'f
ics,
35
. 41-48
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row
der,
R, G
. (19
78).
Mec
hani
sms
of a
udito
ry b
ackw
ard
mas
king
in th
e st
imul
us s
uffi
xef
fect
. Ps
ycho
loR
ical
R
e"~;
e'I\
'85
. 502
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.C
row
der,
R. G
. (l9
8\),
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rol
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itory
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ory
in s
peec
h pe
rcep
tion
and
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rimi-
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And
erso
n (E
ds.).
TIle ('O
RII
;I;,'e repre.fe
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;ml o
fsp
udl
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\19)
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Yor
k: N
orth
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land
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Jour
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II.f
I;('Q
1
Soc;ely of Amer;ca,
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IIle
\ln
d C
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vide
nce
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Me'
",ol
)' C
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I;m
l, 63
6-64
7.
Elman, J, L. (1983). Unpublished results.
Elm
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cCle
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, J. L
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The
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atio
n m
odel
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spee
ch p
er-
cept
ion.
In
Nor
man
Las
s (E
d.
),
LanR
llaR
e' a
nJfp
eed,
(p
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37-3
74).
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k: A
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Elm
an, J
. L..
&: M
cCle
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, J. L
. (in
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ss).
Exp
loiti
ng th
e la
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l var
iabi
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e sp
eech
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e. I
n J.
S. P
erke
ll. &
: D. H
. Kla
tt (E
ds.
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/r;a
nce
and
I'Or;
abili
lof
,fpe
ech
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esse
s.
Hill
sdal
e. N
J: E
rlba
um.
Erm
an. L
. D..
&: L
esse
r, U
, R. (
1980
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he H
ears
ay-I
I sp
eech
und
erst
andi
ng s
yste
m: A
, tutorial. In W. A. Lea,
Tre
'nJs
;n s
peec
h re
coR
II;I
;c1/
I (p
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61...
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ngle
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d C
liffs
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Hal
l.Fe
ldm
an, J
. A.,
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alla
rd, D
. H. (
1982
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onne
ctio
nist
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els
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thei
r 'p
rope
rtie
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CoR
-
n;I;,'e Science', 6
, 205
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,F
orst
er. K
. I. .
(1976), Accessing the mental lexicon. In R. J, Wales &: E. W
alke
r (E
ds.
New
app
roac
hes
10 lanRuaRe mechanisms.
Am
ster
dam
: Nor
th-H
olla
nd..
Fos
s, D
. J..
&: B
lank
. M. A
. (19
80).
Identifying the speech codes.
CoR
n;I;
,'e P,fy
dwlo
R.\
12, 1
-31.
Fos
s, D
, J,.
&: G
erns
bach
er. M
. A. (
1983
), C
rack
ing
the
dual
cod
e: T
owar
d a
unita
ry m
odel
of phoneme identification.
Jollr
nal o
f V
erba
l Lea
rn;n
R a
nd V
erba
l Bel
la,';
or,
22. 6
09-
633.
com
es u
p in
dis
cuss
ions
of
the
mec
hani
sms
of s
peec
h pe
rcep
tion.
Is
spee
ch s
peci
al?
If s
o. in
wha
t way
s? I
t has
bee
n ar
gued
that
spe
ech
issp
ecia
l bec
ause
of
the
dist
inct
ive
phen
omen
on o
f ca
tego
rica
l per
cept
ion;
beca
use
of th
e en
code
dnes
s of
info
rmat
ion
abou
t one
pho
nem
e in
thos
epo
rtio
ns o
flhe
spe
ech
stre
am th
at a
re g
ener
ally
thou
ght t
o re
pres
ent o
ther
phon
emes
; bec
ause
the
info
rmat
ion
' in
the
spee
ch s
trea
m th
at in
dica
tes
the
pres
ence
of
a pa
rtic
ular
pho
nem
e ap
pear
s no
t to
be in
vari
ant a
t any
obvi
ous
phys
ical
leve
l; be
caus
e Q
f th
e la
ck o
f se
gmen
t bou
ndar
ies.
and
for
a va
riet
y of
oth
er r
easo
ns.
Ove
r th
e la
st s
ever
al y
ears
, a n
umbe
r of
em
piri
cal a
rgum
ents
hav
e be
enpu
t for
war
d th
at s
ugge
st th
at p
erha
ps s
peec
h m
ay n
ot b
e so
spe
cial
, or
at le
ast,
not u
niqu
e, C
ue tr
ade-
offs
and
con
text
ual i
nfluences are. of
cour
se, p
rese
nt in
man
y ot
her
dom
ains
(M
edin
& B
arsa
lou,
in p
ress
).an
d a
larg
e nu
mbe
r of
stu
dies
hav
e re
port
ed c
ateg
oric
al p
erce
ptio
n in
othe
r m
odal
ities
(se
e R
epp.
198
4. fo
r a
disc
ussi
on),
Com
puta
tiona
l wor
kon
pro
blem
s in
vis
ion
have
mad
e cl
ear
that
info
rmat
ion
that
mus
t be
extr
acte
d fr
om v
isua
l dis
play
s is
-of
ten
com
plex
ly e
ncod
ed w
ith o
ther
info
rmat
ion
(Bar
row
& T
enen
baum
; 197
8; M
arl'.
198
2), a
nd th
e la
ck
clea
r bo
unda
ries
bet;w
een
perc
ept m
il un
its in
vis
ion
is n
otor
ious
(B
alla
rdet a!.. 1983: M
arr.
198
2), T
hus,
the
psyc
holo
gica
l phe
nom
ena
that
cha
r-ac
teriz
e hu
man
spe
ech
perc
eptio
n, a
nd th
e co
mpu
tatio
nal p
robl
ems
that
mus
t be
met
by
any
mec
hani
sm o
f spe
ech
perc
eptio
n, a
re n
ot, i
n ge
nera
l,un
ique
to s
peec
h. T
o' b
e su
re. t
he p
artic
ular
con
stel
latio
n of
pro
blem
s th
atm
ust b
e so
lved
in s
peec
h pe
rcep
tion
is d
iffe
rent
than
the
cons
tella
tion
ofpr
oble
ms
face
d in
any
oth
er p
artic
ular
cas
e. b
ut m
ost o
f the
indi
vidu
alpr
oble
ms
them
selv
es d
o ap
pear
to h
ave
anal
ogs
in o
ther
dom
ains
.W
e th
eref
ore
pref
er to
vie
w s
peec
h as
an
exce
llent
test
bed
for
the
deve
lopm
ent o
f an
und
erst
andi
ng o
f m
echa
nism
s w
hich
mig
ht tu
rn o
utto
hav
e co
nsid
erab
ly b
road
er a
pplic
atio
n, S
peec
h is
spe
cial
to u
s, s
ince
it so
ric
hly
capt
ures
the
mul
tiplic
ity o
f th
e so
urce
s of
con
stra
int w
hich
mus
t be
expl
oite
d in
per
cept
ual p
roce
ssin
g, a
nd b
ecau
se it
so
clea
rly
indi
cate
s th
e po
wer
ful i
nflu
ence
s of
the
mec
hani
sms
of p
erce
ptio
n on
the
cons
truc
ted
perc
eptu
al r
epre
sent
atio
n. W
e se
e th
e T
RA
CE
mod
el a
s an
exam
ple
of a
larg
e cl
ass
of m
assi
vely
par
alle
l. in
tera
ctiv
e m
odel
s th
atho
lds
grea
t pro
mis
e to
pro
vide
a d
eepe
r un
ders
tand
ing
of th
e m
echa
nism
sge
nera
lly u
sed
in p
erce
ptio
n,
Ackley, D.. Hinton. Goo & Sejnowski, T. (l9
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