Reaction time How I learned to stop worrying and love the ... · Reaction time Roozbeh’Kiani ......
Transcript of Reaction time How I learned to stop worrying and love the ... · Reaction time Roozbeh’Kiani ......
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Reaction time
Roozbeh Kiani
Center for Neural Science and Department of Psychology, NYU
How I learned to stop worrying and love the reaction time
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What is a decision?
• A commitment to a proposition or plan of action based on evidence, prior knowledge, payoff, and urgency.
• Decisions often involve interpretation and contingency.
• The study of decision-making offers insight into how higher brain areas read out or interpret information acquired through the senses.
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Roitman & Shadlen, 2002 Kiani et al, 2011
Motion direction discrimination task
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Reward for correct choice
Roitman & Shadlen, 2002 Kiani et al, 2011
Motion direction discrimination task
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Psychometric funcBon: Accuracy
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Chronometric funcBon: Speed
Rea
ctio
n tim
e [m
s]
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Hubel, 1988
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Sensory “Evidence”
From: Hubel & Wiesel
From: Celebrini & Newsome
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Responses of MT neurons
Britten et al., 1993
Rightward Leftward
Trivial
Easy
Difficult
100 ms
50 s
pike
s/s
– 0 +
Momentary evidence (Δr)
µ= kC
6.4%
99.9%
25.6%
Coherence
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Adapted from Caret Van Essen, 2002 URL: http://www.nitrc.org/projects/caret/
Lateral intra-parietal cortex (LIP)
V1 V4
7a 7b
V2d
V2v
Posterior Anterior
MT/MST
Frontal eye field
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Roitman & Shadlen, 2002
saccade
motion onset
select Tin
select Topp
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Roitman & Shadlen, 2002
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High motion strength!
Low motion strength!
Time"Stimulus
on!Stimulus
off!
Spikes/s"
Time"Stimulus
on!Stimulus
off!
Low motion strength!
accumulaBon-‐to-‐bound model
MT: Sensory Evidence
MoBon energy
“step”
LIP: Decision FormaBon
AccumulaBon of evidence “ramp”
Bound
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Choose right
Accumulated evidence for rightward target
– +
Momentary evidence (Δr)
Accumulated evidence for leSward target
Choose leS
Time
μ= kC
accumulaBon-‐to-‐bound model
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Momentary evidence e.g.,
∆Spike rate: MTRight– MTLeft
Decision variable (v)
Link 1992 Ratcliff & Smith, 2004 Palmer et al, 2005 Laming, 1968 Luce, 1986
Choose left
Time
– +
Momentary evidence (Δr)
μ= kC
Choose right
3 degrees of freedom: B, k, t0
accumulaBon-‐to-‐bound model
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Best fi]ng chronometric funcBon
t(C) = BkCtanh(BkC)+ tnd
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Predicted psychometric funcBon
P =1
1+ e−2k C B
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tnd = 200, 300, 400msB= 0.55, 0.71, 0.83 1/k = 0.03, 0.06, 0.12ms
Gaining intuiBon about the model
Palmer et al, 2005
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Gaining intuiBon about the model
t(C) = Bk C
2Pcor C( )−1⎡⎣ ⎤⎦ + tnd Luce 1986, Link 1992
Coupling response Bme and accuracy
(halfway Bme threshold) / (halfway accuracy threshold) ~ 3.5
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Why should you care about decision Bme?
Why it isn’t enough to say “I always have fixed sBmulus duraBons in my experiments”? Because the same decision-‐making process applies, curtailing the effect of the sBmulus.
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Viewing duration varies from 80ms to 1500ms
Tin Tout
Kiani et al, 2008
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Correct response probability improves with stimulus duration
Probability correct
Stimulus duration (ms)
coherence
Kiani et al, 2008
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Discrimination threshold (%coh)
Stimulus duration (ms)
data Perfect accumulation
Failure to integrate all the information for longer stimuli
Kiani et al, 2008
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Effect of motion pulses on the choice
• Do early motion pulses have stronger effect on the behavior? • Does the monkey ignore late motion pulses?
Fixation Targets on
Motion Go
Eye movement Motion pulse: 3.2%, 200 ms
Kiani et al, 2008
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Motion pulses bias the monkey’s behavior
-50 -25 0 25 50
Motion strength (%coh)
1
0.75
0.5
0.25
0
Proportion of rightward choices
Kiani et al, 2008
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The effect of the motion pulse diminishes by pulse time
Pulse time (ms) 0 400 800
1
0
Shi
ft (%
coh)
Motion strength (%coh)
Pro
porti
on o
f rig
htw
ard
choi
ce
-20 0 20 -20 0 20
1
0.5
0
1
0.5
0
Pulse time < 175 ms 362-563 ms
175-362 ms > 563 ms
Kiani et al, 2008
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Time
Bound
The pulse effect is expected to depend on both the pulse time and the strength of primary motion
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0 200 400 600 800
0.3 0.2 0.1 0 -0.1
Pulse time (ms)
Change of rightward choice proportion
The effect of the motion pulse depends on the primary motion strength
0%
12.8%
Kiani et al, 2008
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What are the implicaBons?
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Visualstimulus
Neuronalresponse
Behavioraljudgement
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Britten, Shadlen, Newsome & Movshon, 1993
MT responses depend on motion coherence
0 25 50 75 1000
50
100
150
200
0 10 20 30 40 500
50
100
0 25 50 75 1000
10
20
30
40
50
0 10 20 30 400
25
50
75
100
Firi
ng r
ate
(impu
lses
/tria
l)
Coherence (%)
Preferred directionNull direction
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Barlow, Levick and Yoon, 1971
Britten, Shadlen, Newsome & Movshon, 1992
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Britten, Shadlen, Newsome & Movshon, 1992
Coherence (%)
Pro
port
ion
corr
ect
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Britten, Shadlen, Newsome & Movshon, 1992
Coherence (%)
Pro
port
ion
corr
ect
0
20
40
60
Num
ber
of c
ells
0.1 1 10Threshold ratio (neuron/behavior)
MT cells are as sensitive as monkeys to visual motion
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When measured correctly!
Cohen & Newsome, 2009
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Saccade
Motion
Targets
Fixation
Time
]
ReactionTime
Hanks, Kiani & Shadlen, 2014
Speed-Accuracy Tradeoff
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a b
cBound for Tin
0
A Bound for Tout
0
A
Tin accumulator Tout accumulator
0 20 40 600.5
0.6
0.7
0.8
0.9
1
Motion strength (% coh)
Prop
ortio
n co
rrect
0 20 40 60
0.4
0.5
0.6
0.7
Motion strength (% coh)R
eact
ion
time
(s)
Wednesday, November 6, 2013
Speed-Accuracy Tradeoff
Hanks, Kiani & Shadlen, 2014
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a b
cBound for Tin
0
A Bound for Tout
0
A
Tin accumulator Tout accumulator
0 20 40 600.5
0.6
0.7
0.8
0.9
1
Motion strength (% coh)
Prop
ortio
n co
rrect
0 20 40 60
0.4
0.5
0.6
0.7
Motion strength (% coh)
Rea
ctio
n tim
e (s
)
Wednesday, November 6, 2013
Speed-Accuracy Tradeoff
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0 200 400
0.40.60.8
Time from dots onset (ms)
Nor
mal
ized
firin
g ra
te Accuracy condition
0 200 400
0.40.60.8
Time from dots onset (ms)
Speed condition
−50 0 500123
Motion strength (% coh
Build
up ra
te(N
orm
aliz
ed F
R /
s)
StrongTin
StrongTout
Weak
a b cStrong Tin
Strong Tout
Weak
Wednesday, November 6, 2013
Speed-Accuracy Tradeoff
Hanks, Kiani & Shadlen, 2014
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−400 −200 0
0.5
1
Time from saccade (ms)Nor
mal
ized
firin
g ra
te Accuracy condition
−400 −200 0
0.5
1
Time from saccade (ms)
Speed condition
0 20 40 60
0.8
1
1.2
Motion strength (% coh)
Nor
mal
ized
FR
befo
re s
acca
de
Faster
Slower
Faster
Slower
a b c
Wednesday, November 6, 2013
Speed-Accuracy Tradeoff
Hanks, Kiani & Shadlen, 2014
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−100 0 100 200 300
0.4
0.6
0.8
1
1.2
Time from motion onset (ms)
Nor
mal
ized
firin
g ra
te
−300 −200 −100 0 100Time from saccade (ms)
0 20 40 600.50.60.70.80.9
Motion strength (% coh)
Prop
ortio
n co
rrect
0 20 40 60
0.4
0.5
0.6
0.7
Motion strength (% coh)
Rea
ctio
n tim
e (s
)
Speed vs. Accuracya b
c
0 0.05 0.1 0.150
0.2
0.4
0.6
0.8
Decision time (s)
Urg
ency
sig
nal (
Frac
tion
boun
d)
Wednesday, November 6, 2013
Speed-Accuracy Tradeoff
Hanks, Kiani & Shadlen, 2014
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Saccade
Motion
Targets
Fixation
Time
]
ReactionTime
Hanks, Kiani & Shadlen, 2011
Integration of priors in the decision-making process
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0
0.2
0.4
0.6
0.8
1
Proportion positive choice
−50 −25 0 25 500
500
1000
1500
2000
Motion strength (%coh)
Reaction time (ms)
0
0.2
0.4
0.6
0.8
1
−50 −25 0 25 500
500
1000
1500
2000
Motion strength (%coh)
0
0.2
0.4
0.6
0.8
1
−50 −25 0 25 50200
400
600
800
Motion strength (%coh)
Subject SK Subject LH Monkeys B, I, N, and S
50:50 prior80:20 prior
Integration of priors in the decision-making process
Hanks, Kiani & Shadlen, 2011
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dt
Accumulatedevidence
A
-A
time
a
b
time
Decision variable
dt
Accumulatedevidence Bias signal
+
(Decision variable)
Momentaryevidence
Momentaryevidence
A
-A
Integration of priors in the decision-making process
Hanks, Kiani & Shadlen, 2011
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−30 −20 −10 0 10 20 30−100
0
100
200
300
Motion Strength (% coh)−30 −20 −10 0 10 20 30
−100
0
100
200
300
Motion Strength (% coh)
Time from motion onset (ms) Time from motion onset (ms)
250 300 350 400 450 500 550−10
01020304050
Time from motion onset (ms)250 300 350 400 450 500 550
−60−40−20
020
Time from motion onset (ms)
Buildup rate (sp/s )
Time−dependent bias signal (sp/s)
Difference in buildup rate (sp/s )
a b
dc
2
2
300 400 500 600 7000
10
20
30
300 400 500 600 700−20
−15
−10
−5
0e f
50:50 prior80:20 prior
50:50 prior20:80 prior
Tim
e-de
pend
ent
Bia
s sig
nal (
sp/s
) Integration of priors in the decision-making process
Hanks, Kiani & Shadlen, 2011
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−50 −25 0 25 500
0.2
0.4
0.6
0.8
1
−50 −25 0 25 50200
400
600
800
Motion strength (%coh)
Proportion positive choice
Reaction time (ms)
a
b
50:50 prior80:20 prior
Integration of priors in the decision-making process
Hanks, Kiani & Shadlen, 2011