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

2. People

3. 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

4. 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

5. 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

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

7. Earlier pulse matters more

8. Earlier pulse matters more

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

10. 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…

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

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

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

14. Results in Exp.1 CS

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

16. Results in Exp.1 MT

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

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

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

20. 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.

21. Results in Exp.2, without time pressureMM

22. Results in Exp.2, without time pressureMM
25 session, 1500 trials per point

23. Results in Exp.2, without time pressureWW

24. Results in Exp.2, without time pressureWW
10 sessions.

25. Results in Exp.2, without time pressureDG
15 sessions, 900 trials

26. Results in Exp.2, without time pressureDG
15 sessions, 900 trials

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

28. 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

29. 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!

30. 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?

31. Back up slides

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

35. 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

36. 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

37. 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

38. Results in Exp 1. The pulse studySC

39. mt

40. Both successful models
Time (ms)
Usher and McClelland 2001