1. Introduction By Elisabeth Rounis and Louise Whiteley

2. What affects a decision? OR?

3. What affects a decision? OR ?

4. What affects a decision? You have: What would you rather… OR ?

5. What affects a decision? OR

6. What affects a decision? OR Healthy? Or not?

7. What affects a decision? Vs. WartimePeacetime

8. Big decisions…

9. Forming a decision Decision Information

10. Behaviour

11. Decision

13. Behaviour

14. Neuronal recording

15. The Start: Building a perceptual decision http://monkeybiz.stanford.edu/movies/0coh_circle.qt

16. LIP.. Are the dots moving left or right?

18. So what happens when we actually see something?

19. Representation of sensory evidence

20. Value B A Compute V(A) and V(B) Choose

21. Value B=£500 A=£1000 V(A) > V(B), so choose A

22. Discounting B A Compute V(A) and V(B) Choose Time Value Now! 3 weeks…

23. Discounting B = £500 A = £1000 V(B t=now ) > V(A t=3 weeks ) so choose B 3 weeks… Now!

24. Relative wealth B A Compute V(A) and V(B) relative to your wealth now and in 3 weeks Choose Time Value Now! 3 weeks… Utility Value

25. Relative wealth B = £500 A = £1000 Now, V(B t=now, W t=now ) < V(A t=3 weeks, W t=3 weeks ) so choose A Plus pension of £1000 in 3 weeks!!

26. Probability B A Weight V(A) and V(B) by the probability they will occur Choose U = p * V x p(A) x p(B)

27. Probability B = £500 A = £1000 In other words… U(B t=now, W t=now ) > U(A t=3 weeks, W t=3 weeks ) so choose B U = p * V Risky bet Safer bet p = 0.1 p = 0.9 Now, V(B t=now, W t=now )*0.9 > V(A t=3 weeks, W t=3 weeks )*0.1 so choose B

28. Deciding what we’re seeing A B p = 0.9 p = 0.1 On balance, we think we saw B Choose

29. Deciding what we’re seeing Tumour Healthy p = 0.7 p = 0.3 p(healthy|x-ray) > p(tumour|x-ray), so thought to be healthy… Training a medical student…

30. Priors A B p = 0.7 x prior p = 0.3 x prior Now we are not so sure… Choose B is only rarely seen, small prior belief

31. Priors Tumour Healthy Smokes 40 a day p = 0.3 p = 0.7 Now, p(healthy|x-ray) * p(healthy) < p(tumour|x-ray) * p(tumour), so more likely a tumour Training a medical student…

32. Value (again…) A B p = 0.7 x prior x value p = 0.3 x prior x value Better be safe than sorry – decide on “A” Choose Detecting A is very important, detecting B is less so

33. Value (again…) Tumour Healthy Smokes 40 a day p = 0.3 p = 0.7 Treat All clear Treat All clear V = 100 V = -500 V = -20 V= 0 In the real world… 1) U(“tumour”|tumour) = p(tumour) * p(tumour|x-ray) * V(treat, tumour) 2) U(“healthy”|tumour) = p(healthy) * p(healthy|x-ray) * V(all clear, tumour) Then, U(“tumour”) = 1+3, U(“healthy”) = 2+4… choose which is bigger! 3) U(“tumour”|healthy) = p(healthy) * p(healthy|x-ray) * V(treat, healthy) 4) U(“healthy”|healthy) = p(healthy) * p(healthy|x-ray) * V(all clear, healthy)

34. Putting it all together Decision Value Discounting Relative wealth Risk Perceptual uncertainty Priors

35. Decision Value Discounting Relative wealth Risk Perceptual uncertainty Priors ?

36. Behaviour

37. Neuronal recording

39. Functional Imaging

40. Functional vs Structural Task-related activityStructure ?Pathology

41. Need good hypotheses!

42. So… how is decision made in the brain???

43. An appropriate behavioural paradigm