Recency vs Primacy -- an ongoing project

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Recency vs Primacy-- an ongoing project

• Nov 17th 2009
• Juan Gao

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People
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Question

• What is the mechanism underlying perceptual
  decision making in time-controlled paradigm?

Two successful models
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How are they different

• In ATB
• earlier gt later --primacy.
• In LCA
• earlier gt later if inhibitiongt leak --primacy
• later gt earlier if leakgtinhibition --recency.

See also a theoretical study by Zhou, Wong-Lin
and Holmes 2009
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Usher McClelland 2001
A sequence of 16 H and S letters flashing one by
one. Are their more Hs or Ss?
H S H H H S H S H H S H S S S S
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Kiani, Tanks and Shadlen 2008
Random dots. Time controlled. Stimulus duration
exponential distribution. go cue followed
by 300ms response window.
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Earlier pulse matters more
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Earlier pulse matters more
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Two monkeys? Earlier gt Later for all subjects?
Earlier gt Later in all moving dots experiments?
If no, what determines it?
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Ongoing Experiment

• Random dot motion stimuli, following the
  procedure in Kiani et.al.
• Multiple coherences, 6.4, 12.8, 25,6, 51.2. But
  for figures in this talk, we collapse data across
  coherence levels.
• Three participants per experiment, each run for
  up to 25 sessions
• Ongoing recruitment, Ongoing analysis

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The experiments

• 0. Repeat Kiani 2008

1. Same question, different experiment setup.
2. Release the time pressure.
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Experiment 1
Stimulus Duration
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Results in Exp.1
CS
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Results in Exp.1
CS
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Results in Exp.1
MT
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Results in Exp.1
MT
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Results in Exp.1
SC
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Results in Exp.1
SC
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Take home message

• Yes, it seems earlier gt later in all three
  subjects with this time pressure.

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The experiments

• 0. Repeat Kiani 2008

1. Same question, different experiment setup.

• 2. Release the time pressure.
• Stimulus duration exponential ? uniform
• Response Window 300ms ? 1 s.

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Results in Exp.2, without time pressure
MM
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Results in Exp.2, without time pressure
MM
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Results in Exp.2, without time pressure
WW
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Results in Exp.2, without time pressure
WW
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Results in Exp.2, without time pressure
DG
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Results in Exp.2, without time pressure
DG
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Take home message

• Yes, it seems earlier gt later in all three
  subjects with this time pressure.
• As time pressure gets released, earlier later.

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Take home message

• Yes, it seems earlier gt later in all subjects
  with this time pressure.
• As time pressure gets released, earlier later.
• Uniform distribution ? only long stimulus
  condition later gt earlier.
  
• possible future direction

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Take home message

• Yes, it seems earlier gt later in all subjects
  with this time pressure.
• As time pressure gets released, earlier later.
• Uniform distribution ? only long stimulus
  condition later gt earlier.
  
• possible future direction

Its all about time!
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What this means to the models

• So far
• LCA can account for the observations by
  decreasing the inhibition.
• ATB can do the same by raising the bound.
• When future is now, If latergt earlier
• LCA is more general.
• Is decision making a fixed process or does it
  depends on experiment setup?

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Back up slides
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A theoretical study
Zhou, Wong-Lin and Holmes 2009
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Usher McClelland 2001
A sequence of 16 H and S letters flashing one by
one. Are their more Hs or Ss?
H S H H H S H S H H S H S S S S
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Literature 1
Drift Diffusion model dx A dt noise. A is a
constant
Zhou, Wong-Lin and Holmes 2009
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Literature 1
OU process dx (bxA) dt noise. Stable when
blt0, unstable when bgt0.
Zhou, Wong-Lin and Holmes 2009
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Results in Exp 1. The pulse study
SC
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mt
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Both successful models
Time (ms)
Usher and McClelland 2001
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