Recency vs Primacy -- an ongoing project

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

2. People

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

4. 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. inhibition > leak leak > inhibition 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

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. If Yes, ATB Two monkeys? Earlier > Later for all subjects? Earlier > Later in all moving dots experiments? 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. 1) Early 2) Late 3) Constant 4) Switch Experiment 1 Stimulus Duration

13. Results in Exp.1 CS

14. Results in Exp.1 CS

15. Results in Exp.1 MT

16. Results in Exp.1 MT

17. Results in Exp.1 SC

18. Results in Exp.1 SC

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 pressure MM

22. Results in Exp.2, without time pressure MM

23. Results in Exp.2, without time pressure WW

24. Results in Exp.2, without time pressure WW

25. Results in Exp.2, without time pressure DG

26. Results in Exp.2, without time pressure DG

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

37. 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 study SC

39. mt

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