Compensatory coarticulation, /u/-fronting, and sound change in Standard Southern British: anacoustic and perceptual study.*

Jonathan Harrington, Felicitas Kleber, Ulrich Reubold

* submitted Journal of the Acoustical Society of America

General aim of this paper

To establish to what extent a sound-change in progress, /u/-fronting in Standard Southern British (SSB) – can be linked to diminished perceptual compensation for coarticulation in Ohala's (1993) model of sound change.

Background

A. Perceptual compensation for coarticulation

B. Ohala's model of sound change

C. /u/-fronting in SSB

A. What is perceptual compensation for coarticulation?

si

su

Fre

que

ncy

of f

rica

tive

no

ise ACOUSTICS

1. Anticipatory coarticulatory lip-rounding causes spectral centre of gravity lowering in /s/

PERCEPTION

Listeners reverse the effects of coarticulation

si su

2. Listeners know this and reverse its effect (= compensation for coarticulation*)

*e.g. Fujisaki & Kunisaki, 1977; Mann & Repp, 1980;

If you synthesise a continuum from /s/ to // that can be done by spectral COG lowering and prepend it to a vowel, then listeners are more likely to perceive the SAME synthetic token as /s/ before /u/ than before /a/

Perceptual compensation for coarticulation

s

Fre

quen

cy o

f no

ise

+ /u/ + /a/

Listener compensates for coarticulation (= factors out COG lowering assumed to be attributable to /u/):

ss s s

s ss

s

s

B. Cental ideas in Ohala's model of sound change

Ohala: "Today's variability is tomorrow's sound change"

The origin of many sound changes is not always in the mouth of the speaker, but in the ear of the listener

Contra sociolinguists: sound change is not teleological = it's not done on purpose or for any reason, it happens by accident because of an unintended error on the part of the listener (and also for this reason, the origin of sound change is not cognitive nor phonological)

Hypoarticulation-induced sound change: one that arises out of the natural processes of coarticulation and in which the listener fails to compensate for coarticulation…

(the listener thinks: "the speaker meant to say /ci/")

Hypoarticulation-induced sound change in Ohala

Listener as speakerSpeaker Listener

/c/ has been phonologised because it is planned, produced and perceived, even in contexts that can't be explained by coarticulation

plans /ki/

[ci]

produces

[ci]acoustic signal

compensates for coarticulation

reconstructs /ki/

Sound change: /k/ -> /c/

plans /ci, cu/

[ci, cu]

reconstructs /ci/

C. /u/-fronting in Standard Southern BritishExtensive auditory and some acoustic evidence that SSB /u/ has fronted in the last 50 years e.g., Gimson, 1966, Wells 1982, Henton 1983, Deterding 1997, Hawkins & Midgley 2005, Roach, 1997).

([i] ‘heed’, [] ‘hoard’, [u], ‘who’d’)

/u/-fronting and possible chain-shifting in the Queen's Christmas broadcasts (Harrington, 2008)*

Harrington (2008), Laboratory Phonology IX, in press

This could be just such an example of a hypoarticulation-induced sound change. Why?

1. Taking into account word-frequency, /u/ frequently (p ≈ 0.7) occurs in a coarticulatory fronting context (e.g. 'you', 'too', 'lose', 'do', 'new').

j

u

F2-locus target distance

plans/ju/ [j]

produces

F2

Time

Speaker

2. In an analysis of the Christmas broadcasts at 20 year intervals, the Queen, Harrington (2008)* shows just such a reduction of F2 locus-target distance:

Time

F2

locus-target distance

locus-target distance

Decade* Harrington (2008), Laboratory Phonology 9 in press

Our extension of Ohala's model to these data and age-differences in SSB speakers is as follows:

/u/-fronting and speech perception

Acoustic input: [sn]

compensate for coarticulation

Perceived as: /sun/ /sn/

OLD listeners YOUNG listeners

/u/-fronting, speech perception and productionPRODUCTION PERCEPTION

/fjd//fd/[fd]

sound change

Front

Back

Young

Old

For the Old, the allophones diverge in production, but not in perception (this is the trigger for sound change)

For the Young, the allophones are aligned in perception and production and NO compensation for coarticulation

[fjd]

[fud]/fjud/

/fud/

compensate forcoarticulation

(food)

(feud)

[fjd]

[fud]

PRODUCTION PERCEPTION

/fjud//fud/

/fjd//fd/[fd]

sound change compensate for coarticulation

Front

Back

Young

Old

Predictions about age differences

1. (trivially) /u/ vowels are fronted for the Young.

2. C-on-/u/ coarticulation is greater in the Old (their /u/ allophones show greater divergence).

Production

3. Young and Old differ primarily on the back allophones (if sound change involves a shift of these to the front).

Perception

4. The Old but not the Young compensate perceptually for coarticulation.

Experimental analysis I: Production(Predictions 1 -3)

30 Standard Southern British speakers recruited through University of Cambridge and University College London.

YOUNG: 14 subjects aged 18-20 (11 F, 3 M)

OLD: 13 subjects aged 53-88 (7 F, 9 M)

Method: Speakers

Subjects were carefully checked to ensure that they were SSB speakers.

only 1 subject took part in the production study only

MaterialsIsolated word production of words each produced 10 times

/u/C(C)

Word

j used 269

fj feud 266

hj hewed 266

kj queued 270

f food 269

s soup 270

k cooed 264

h who'd 270

sw swoop 268

2412

/i/C(C)

Word

j yeast 269

f feed 267

h heed 270

k keyed 270

s seep 269

sw sweep 269

1614

//C(C)

Word

h hard 270

Recordings made in U.K. with SpeechRecorder (Draxler & Jänsch, 2004)

Acoustic parameters

Formants calculated and F2 was checked and manually corrected.

Each F2-trajectory was reduced to a single point in a three-dimensional space formed from the first three coefficients of the discrete-cosine-transformation (Watson & Harrington, 1999; Harrington, 2006; Zahorian, and Jagharghi, 1993)

We did this because we wanted to assess vowel fronting in the entire F2-trajectory (from onset to offset) rather than just at the vowel's temporal midpoint (which encodes no dynamic information).

Also with the DCT, we avoid having to make an often arbitrary decision about the location of the vowel target.

Discrete-cosine-transformationdecomposes any signal into a set of ½ cycle cosine waves which, if summed, reconstruct entirely the original signal.

The amplitudes of these cosine waves are the DCT coefficients. Moreover, the cosine waves at the lowest frequencies encode important properties of the trajectory's shape…

…at frequency (rad/sample)…

…is proportional to the trajectory's:DCT-coeff

DCT-0 average

mean linear slope

curvature

0

DCT-1 1

DCT-2 2

so you can use this technique to smooth formants…

620 660 700 740

1400

1600

1800

Raw

Time (ms)

F2

(Hz)

620 660 700 740

1400

1600

1800

DCT-smoothed

Time (ms)

A n a l y s i s

DCTcoeffs

But the important point for this paper is that each F2 trajectory is reduced to a single point in a 3D-space which encodes a smoothed trajectory, like the one on the right.

F2

(Hz)

620 660 700 74014

0016

0018

00

Raw

Time (ms)

F2

(Hz)

620 660 700 740

1400

1600

1800

DCT-smoothed

Time (ms)

S y n t h e s i s

F2

(Hz)

For each speaker separately, we quantified the extent of /u/-fronting in this DCT space by calculating each [u] token's relative distance to the front and back /i/ and // vowel centroids

Quantification of /u/-fronting

du = log(E1/E2) = log(E1) – log(E2)

Log Euclidean distance ratio

du = 0, [u] equidistant bet. /i/ and // du < 0, [u] nearer // (back)

du > 0, [u] nearer /i/ (front)

So if following hypothesis 1 /u/ is phonetically more back in the Old, then du should be lower for the Old compared with the Young

2. Quantification of C-on-/u/ perseverative coarticulationWe measured separately for each speaker the Inter-Euclidean distance in the DCT space between 'swoop' and 'used'

swoop

ju

ju

ju

juju

ju

ju

ju

ju

ju

used

wu

wu

wu

wu

wuwu wuwu

wu

wu

DC

T-0

DCT-1

swoop tokens to used centroid used tokens to swoop centroid

If the coarticulatory influences of C-on-/u/ are greater in Older speakers (= hypothesis 2), then 'swoop' (/w/ has a backing influence) and 'used' (/j/ has a fronting influence) will be further apart i.e., the distances between them will be greater than for the Young.

Hypothesis 3: the age-difference is context-specific

i.e., if sound change involves a shift of back allophones towards the front, then Young and Old should differ more on words with a non-front allophone ('food') than those with a front allophone ('feud')

We calculated the distance in the DCT-space between Old and Young speakers together separately for each word.

Thus the prediction is that the distance between e.g. Old/Young 'food' is expected to be greater than between Old/Young 'feud'.

Results 1: Young speakers have a fronter /u/

F1 x F2 plots at vowel midpoint

(When du = 0, /u/ is equidistant between /i/ and //)

Log Euclidean distance ratio, du

Front

Back

Results 1: Young speakers have a fronter /u/

Results 2: a greater C-on-/u/ influence for the Old

Averaged, linearly time-normalised F2 trajectories in used and swoop

Euclidean distance between 'used' and 'swoop'

Results 2: a greater C-on-/u/ influence for the Old

Results 3: smaller age difference for words where /u/ is in a fronting context

C has a fronting effect on /u/?

No Yes

Euclidean distance between Young and Old separately per word

(i.e., the sound change involves a shift of back allophones to the front)

Part II: Speech Perception

Method: synthetic continua

We used HLSYN to create two 13 step synthetic /i-u/ continua at equal Bark intervals by varying F2 in two sets of minimal pairs :(a) /jist/ --- /just/ YEAST---USED (p. tense)(b) /swip/ --- /swup/ SWEEP---SWOOP

A separate group of listeners verified that the endpoints of the continua could be correctly identified.

Stimuli randomised and both continua presented in one session 5 times (5 x 13 x 2 = 130 randomised stimuli).

Forced-choice identification task: Subjects responded with one of ''used'', ''yeast'', ''swoop'', ''sweep'' to each stimulus.

Speech perception predictions

F2 high F2 lowui

F2 high F2 lowui

F2 high F2 lowui

OLD

left-shift relative to Old because they have a fronter /u/

and no (or much less) compensation for coarticulation

YOUNG

yeast-used boundary

sweep-swoop boundary

so the different predicted responses are:

F2 high F2 low

ui

ui

1. WORD: yeast-used boundary left-shifted relative to sweep-swoop (red vs blue)

2. AGE: Young left-shifted relative to Old (dash vs. straight)

3. AGE x WORD Small difference between Young vs. Old on yeast-used (red dash vs. red straight), big difference between Young vs. Old on sweep-swoop (blue dash vs. blue straight).

Results 1: WORD

Significantly greater proportion of /u/ responses (across both age groups) in YEAST-USED relative to SWEEP-SWOOP (compatibly with Mann & Repp, 1980).

Results (2): AGE

The /i-u/ boundary is significantly left-shifted (greater proportion of /u/ responses) in YOUNG compared with OLD speakers.

Prediction 3. Small difference between YOUNG vs. OLD on yeast-used … big difference between YOUNG vs. OLD on sweep-swoop

YOUNG OLD

Results (3): WORD x AGE

In the 1950-60s. The large phonetic separation between allophones of /u/ in production required coarticulatory compensation to realign them as the same category in perception.

For whatever reason, young listeners give up on compensating for coarticulation. They do not attribute

[] to context but presume that // (not /u/) was

intended by the speaker. Thus, // becomes phonologised...

…leading to [] in their own productions even in contexts like 'food', 'move' where it has no coarticulatory explanation.

Discussion I: /u/-fronting and sound-change in terms of Ohala's model.

But which comes first?

Ohala: first give up on compensating for coarticulation, then there is a realignment in speech production (= sound change): loss of coarticulatory compensation in perception results in sound change in production.

Or perhaps: first there is sound change and then there is a loss of perceptual compensation for coarticulation? This story would be compatible with exemplar theory (Pierrehumbert, 2003) as follows:

1. /u/ in Standard British English occurs most often (about 70% of the time) after consonants with a high F2 locus ('you', 'too', 'lose', 'do', 'new')

2. According to exemplar theory, this imbalance in lexical and phonological frequency is the trigger for sound change – i.e., the infrequently occurring back [u] in low F2-locus contexts (e.g., 'move', 'swoop') is perceptually unstable and so will be inclined to shift towards the more frequently occurring front allophone [].

3. As this shift occurs in production, there will be less need to compensate for coarticulation in perception, because the allophones will be in progressively closer alignment. So this story has: sound change first, then loss of perceptual compensation.

/u/-fronting, sound change, exemplar theory

A way forward may be to investigate compensatory coarticulation in young children. Perhaps children learn to compensate for coarticulation relatively late (Ohala, 1993) – perhaps they are more inclined than adults to perceive (incorrectly) an allophone as intended by the speaker.

We might then have an alternative explanation for why sound change is so often led by the young.

According to the sociolinguistics, this is intentional: the young lead sound change because they want to sound different from their parents/elder generation.

From the Queen to language acquisition

But in terms of Ohala (1993) it would be unintentional and come about because children are just not as good at compensating for coarticulation perceptually…

So as usual we need another experiment…

Thank you for listening!