Recency vs Primacy -- an ongoing project Nov 17th 2009 Juan Gao

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Question Two successful models What is the mechanism underlying perceptual decision making in time-controlled paradigm? Two successful models Accumulation to the bound Ratcliff 1978, 1999, Kiani et.al.2008, t x I1 I2 X1 X2 Leaky competing accumulators Usher and McClelland 2001

See also a theoretical study by Zhou, Wong-Lin and Holmes 2009 How are they different In ATB earlier > later --primacy. In LCA earlier > later if inhibition> leak --primacy; later > earlier if leak>inhibition --recency. See also a theoretical study by Zhou, Wong-Lin and Holmes 2009

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 leak > inhibition inhibition > leak

Kiani, Tanks and Shadlen 2008 Random dots. Time controlled. Stimulus duration = exponential distribution. ‘go’ cue followed by 300ms response window.

Earlier pulse matters more

Earlier pulse matters more

Two monkeys? Earlier > Later for all subjects? Earlier > Later in all moving dots experiments? If Yes, ATB If no, what determines it?

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…

The experiments 0. Repeat Kiani 2008 1. Same question, different experiment setup. 2. Release the time pressure.

Experiment 1 Stimulus Duration 1) Early 2) Late 3) Constant 4) Switch

Results in Exp.1 CS 600 trials per data point. 10 sessions

Results in Exp.1 CS

Results in Exp.1 MT 1200 trials per data point. 20 sessions.

Results in Exp.1 MT

Results in Exp.1 SC 600 trials per data point. 10 sessions.

Results in Exp.1 SC 600 trials per data point. 10 sessions.

Take home message Yes, it seems earlier > later in all three subjects with this time pressure.

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.

Results in Exp.2, without time pressure MM

Results in Exp.2, without time pressure MM 25 session, 1500 trials per point

Results in Exp.2, without time pressure WW

Results in Exp.2, without time pressure WW 10 sessions.

Results in Exp.2, without time pressure DG 15 sessions, 900 trials

Results in Exp.2, without time pressure DG 15 sessions, 900 trials

Take home message Yes, it seems earlier > later in all three subjects with this time pressure. As time pressure gets released, earlier = later.

Take home message Yes, it seems earlier > later in all subjects with this time pressure. As time pressure gets released, earlier = later. Uniform distribution  only long stimulus condition: later > earlier. possible future direction

It’s all about time! Take home message Yes, it seems earlier > later in all subjects with this time pressure. As time pressure gets released, earlier = later. Uniform distribution  only long stimulus condition: later > earlier. possible future direction It’s all about time!

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 later> earlier LCA is more general. Is decision making a fixed process or does it depends on experiment setup?

Back up slides

Zhou, Wong-Lin and Holmes 2009 A theoretical study Zhou, Wong-Lin and Holmes 2009

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

Zhou, Wong-Lin and Holmes 2009 Literature 1 Drift Diffusion model: dx = A dt + noise. A is a constant Zhou, Wong-Lin and Holmes 2009

Zhou, Wong-Lin and Holmes 2009 Literature 1 OU process: dx = (bx+A) dt + noise. Stable when b<0, unstable when b>0. Zhou, Wong-Lin and Holmes 2009

Results in Exp 1. The pulse study SC

mt

Both successful models Time (ms) Usher and McClelland 2001