Effects of stimulus preexposure

1. Effects of stimulus preexposure

4. Stimulus preexposure affects our ability to perceive and discriminate stimuli: • Stimulus recognition memory – in humans can be by report • in animals indexed by spontanous object recognition task • AA A B • if recognise A will explore B more (A is boring) • Ennaceur & Delacour 1988 • Aim was to develop a memory task parallel to those used in humans • for e.g. studying amnesia

5. Perceptual learning -- improves discrimination between stimuli

6. How do these effects work? We need to understand exactly what stimulus exposure does Gibson & Gibson (1955) proposed: "percepts change over time by progressive elaboration of qualities, features and dimensions of variation" They assumed that effects of stimulus exposure are not associative - but no formal mechanism was proposed Were they right? Or are these phenomena the result of associative processes?

7. In lecture we will ask what are possible explanations of • 1 object recognition? • perceptual learning? • in doing so we will talk about what the general associative model says are the effects of stimulus preexposure

8. According to the associative model, stimulus preexposure can have several effects on behaviour: • it can reduce responding – habituation • this will help us understand recognition memory • - relevance to human amnesia

9. According to the associative model, stimulus preexposure can have several effects on behaviour: • 2 it can reduce learning -- latent inhibition • this will help us understand those conditions in which learning is aberrant or harmful • schizophrenia • chemotherapy ANV • phobias • drug tolerance effects

10. According to the associative model, stimulus preexposure can have several effects on behaviour: • it can produce learning among elements of the stimulus – within-compound associations • helps us understand how we learn about complex events

11. Stimulus object recognition This seems very similar to habituation task: A? large UCR A A A A A? small UCR A A A B

12. Three theories of habituation Fall within general associative model: Wagner's theory S-R theory Nonassociative (maybe!) -- Comparator theory

13. Wagner's theory Short term habituation After many trials CS elements in A2 --> reduced response A2 I A1 A2 I A1

14. Wagner's theory Long term habituation Context becomes associated with CS. Sends CS elements into A2 --> reduced response A2 I A1 A2 I A1 context

15. How can we test Wagner's theory? predicts unconditioned response will return in a different context Honey and Hall (1989) investigated this: habituated stimulus in one context, test same or different context

16. Train tone Test Sametone ucr Different tone UCR what is wrong with this design?

17. Train tone Test Sametone Different tone

18. Train tone click Test Sametone Different tone

19. Train tone click Test Sametone click Different tone click

20. rats responding for food; novel stimulus suppresses this responding low ratio--> high suppression Day 1 Day 8 Test

21. rats responding for food; novel stimulus suppresses this responding low ratio--> high suppression Day 1 Day 8 Test

22. This interpretation of Wagner's theory fails in explaining simple habituation... how about other theories? S-R theory and comparator theory say nothing about context...

23. S-R theory • Link between S and R becomes less effective with use UR UR

24. Comparator theory Stimulus compared with internal representation. Novel stimulus has no internal representation, so strong UCR is elicited Mismatch! Large UR

25. Comparator theory ...but preexposure gradually allows a mental representation of the stimulus to be established: Partial mismatch! Smaller UR

26. Comparator theory until detailed stimulus representation is formed Match! small UR

27. Which is right? The stimulus omission effect ? ? Train with a compound stimulus Test with all or part

28. S-R theory says..... UR UR UR UR Habituation maintained UR

29. Comparator theory says..... Mismatch! Match! Habituation abolished Mismatch!

30. Habituation is abolished (see Hall 91)... but is it good evidence for comparator theory? Or could S-R theory explain it…? UR UR UR UR aftereffects of tone are like a novel stimulus UR UR

31. Other evidence for comparator theory Extended exposure increases detail in stored representation After short training.... After extended training

32. Other evidence for comparator theory Stimulus now easier to discriminate from other, similar stimuli * * * * test stimulus Hard to discriminate Easy to discriminate

33. predicts extended training will reduce generalisation: A+ CR A+ A+ A+ A+ A+ A+ cr predict less generalised responding to B after more training (usually more training --> more generalisation as more responding to A) A B

34. Hoffeld 1962 cited in Hall 91 Responding to B 50 95 190 285 Training of A -->

35. Problem: comparator theory has no mechanism. …. and is it necessarily nonassociative? McLaren & Mackintosh 2000 proposed several associative mechanisms arising from stimulus preexposure that could produce such effects unitisation (sticking units together)

36. this idea is actually very similar to Wagner’s model... when elements are linked they send each other into A2, explaining habituation

37. temporal B relatively novel spatial A’ and B’ in unfamiliar place can this theory explain these stimulus recognition effects? B B A A A B A B A B A’ B’ B’ A’

38. from Good Barnes Staal McGregor & Honey 2007 Train Test can this theory explain these stimulus recognition effects? A B B B A A A A A B A B A’ B’ B’ A’ A B

39. Before Perceptual Learning --Latent inhibition (LI) Preexposing a stimulus reduces learning about it. Can’t really talk about effects of stimulus preexposure without talking about latent inhibition LI important for a number of practical reasons faulty latent inhibition indicated in schizophrenia relevant to preventing anticipatory nausea and vomiting relevant to phobias, drug addiction – determines what is learned about

40. Theories of Latent Inhibition • 1 Wagner's theory: CS predictability • 2 CS predictive ability (Pearce &Hall 1980, Mackintosh 1975) • 3 Retrieval failure

41. Wagner's account: CS predictability • context context context context • CS CS CS CS+ • If CS preexposed, association forms between context and CS • Now context puts most CS elements into A2 • CS can't easily recruit elements into A1  poor learning • Theory predicts that latent inhibition will be context specific • Honey and Hall 1989 – context specificity of habituation – went on to look at latent inhibition in same experiment:

42. TRAIN tone click TEST Same tone click Different tone click

43. TRAIN tone click TEST Same tone+ click+ Different tone+ click+

44. Day 1 Day 8 Test Conditioning

45. Wagner's account also predicts that extinguishing the context should reduce latent inhibition, because this will weaken the context-->CS association: click click+ SLOW click+ FAST click

46. Baker and Mercier (1982) tested effect of context extinction: Group no pre click+ FAST Group pre click click+ slow Group pre/extclick click+ FAST group pre should show latent inhibition, but group pre/ext should not

48. predictabilityof CS does not determine latent inhibition ....so Wagner's theory not completely right can you think of another way Wagner can explain latent inhibition?

49. CS predictive ability theories • V =  ( - V) •  refers to associability of a stimulus. Rescorla & Wagner assumed that this was a fixedproperty of a stimulus • But Mackintosh (1975) suggested that  might changewith experience -- • good predictors command attention

50. Mackintosh 1975 • VA =  ( - VA) • A >0 if I - VAI < I - VxI • if CS is betterat predicting the outcome than anything else, • then its goesUP • A <0 if I - VAI >= I - VxI • if CS isno better at predicting the outcome than anything else, • then its goes DOWN