Post on 22-Jul-2020
Reaction time
Roozbeh Kiani
Center for Neural Science and Department of Psychology, NYU
How I learned to stop worrying and love the reaction time
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.
Roitman & Shadlen, 2002 Kiani et al, 2011
Motion direction discrimination task
Reward for correct choice
Roitman & Shadlen, 2002 Kiani et al, 2011
Motion direction discrimination task
Psychometric funcBon: Accuracy
Chronometric funcBon: Speed
Rea
ctio
n tim
e [m
s]
Hubel, 1988
Sensory “Evidence”
From: Hubel & Wiesel
From: Celebrini & Newsome
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
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
Roitman & Shadlen, 2002
saccade
motion onset
select Tin
select Topp
Roitman & Shadlen, 2002
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
Choose right
Accumulated evidence for rightward target
– +
Momentary evidence (Δr)
Accumulated evidence for leSward target
Choose leS
Time
μ= kC
accumulaBon-‐to-‐bound model
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
Best fi]ng chronometric funcBon
t(C) = BkCtanh(BkC)+ tnd
Predicted psychometric funcBon
P =1
1+ e−2k C B
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
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
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.
Viewing duration varies from 80ms to 1500ms
Tin Tout
Kiani et al, 2008
Correct response probability improves with stimulus duration
Probability correct
Stimulus duration (ms)
coherence
Kiani et al, 2008
Discrimination threshold (%coh)
Stimulus duration (ms)
data Perfect accumulation
Failure to integrate all the information for longer stimuli
Kiani et al, 2008
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
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
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
Time
Bound
The pulse effect is expected to depend on both the pulse time and the strength of primary motion
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
What are the implicaBons?
Visualstimulus
Neuronalresponse
Behavioraljudgement
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
Barlow, Levick and Yoon, 1971
Britten, Shadlen, Newsome & Movshon, 1992
Britten, Shadlen, Newsome & Movshon, 1992
Coherence (%)
Pro
port
ion
corr
ect
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
When measured correctly!
Cohen & Newsome, 2009
Saccade
Motion
Targets
Fixation
Time
]
ReactionTime
Hanks, Kiani & Shadlen, 2014
Speed-Accuracy Tradeoff
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
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
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
−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
−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
Saccade
Motion
Targets
Fixation
Time
]
ReactionTime
Hanks, Kiani & Shadlen, 2011
Integration of priors in the decision-making process
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
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
−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
−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