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Effects of stimulus preexposure. Stimulus preexposure affects our ability to perceive and discriminate stimuli: Stimulus recognition memory – in humans.

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Presentation on theme: "Effects of stimulus preexposure. Stimulus preexposure affects our ability to perceive and discriminate stimuli: Stimulus recognition memory – in humans."— Presentation transcript:

1 Effects of stimulus preexposure

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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 A A 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? 2perceptual 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: 1it 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: 3it 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 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 IA1 A2 IA1 A2

14 Wagner's theory Long term habituation Context becomes associated with CS. Sends CS elements into A2 --> reduced response context IA1 A2 IA1 A2

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 Same tone ucr Different tone UCR what is wrong with this design?

17 Train tone Test Same tone Different tone

18 Train tone click Test Same tone Different tone

19 Train tone click Test Same tone click Different tone click

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

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

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

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 Habituation maintained

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

30 Habituation is abolished (see Hall 91)... but is it good evidence for comparator theory? Or could S-R theory explain it…? UR aftereffects of tone are like a novel stimulus 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 test stimulus Hard to discriminate Easy to discriminate Stimulus now easier to discriminate from other, similar stimuli * * * *

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) AB

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

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 Wagners 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 B A BA A B B A can this theory explain these stimulus recognition effects?

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

39 Before Perceptual Learning --Latent inhibition (LI) Preexposing a stimulus reduces learning about it. Cant 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 contextcontextcontextcontext CS CS CSCS+ 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

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

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48 predictability of 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 fixed property of a stimulus But Mackintosh (1975) suggested that might change with experience -- good predictors command attention

50 Mackintosh 1975 V A = ( - V A ) A >0 if I - V A I < I - V x I if CS is better at predicting the outcome than anything else, then its goes UP A = I - V x I if CS is no better at predicting the outcome than anything else, then its goes DOWN

51 Unique evidence for this comes from intradimensional/extradimensional shift tasks + + Train colour relevant (shape irrelevant) then test on a new task with different stimuli

52 + + + + Test colour relevant (shape irrelevant)

53 + + + + + + Test colour relevant (shape irrelevant) or shape relevant (colour irrelevant)

54 If colour stays relevant, test is easier. Theory is that attention to predictive colour dimension has increased, whereas attention to nonpredictive shape dimension has decreased (e.g. Mackintosh & Little, 1969) but not all the evidence is that good....

55 Pearce & Hall, 1980 Pearce and Hall (1980) also suggested that might change with experience – but they predict the opposite bad predictors command attention A novel stimulus has high because its outcome is uncertain but if stimulus is preexposed -- latent inhibition -- drops because CS is a good predictor of nothing

56 Pearce & Hall, 1980... if a stimulus is conditioned and the outcome always occurs -- drops CS+ CS+ this is because CS is a good predictor of something... but if a stimulus is conditioned and the outcome only occurs occasionally -- stays high CS+ CS- this is because CS is an unreliable predictor

57 Pearce & Hall, 1980 V = S n = I n-1 - V n-1 I suggested that related to the orienting response (OR) uncertain outcome -- High -- lots of orienting certain outcome -- low -- little orienting

58 Swan & Pearce manipulated the predictive ability of a light CS to be higher in Group Same than in Group Different: Group Same Group Different tone click light food tone click light food tone click light food

59 Predict: Group Same: light has (relatively) predictable outcomes low -- little orienting and learned about slowly.... Group Different: light had unpredictable outcomes high -- high orienting and learned about fast.... -- tested orienting to light -- paired light with food to look at learning speed light food

60 More orienting to light in Group Different

61 More conditioned responding to light in Group Different

62 One final theory Some have argued that learning is normal after latent inhibition, but that retrieval is impaired Two associations CS--> nothing (from preexposure) CS--> US (from conditioning) two associations compete, and so less CR Not much evidence for this but you should know it's a possibility

63 Latent inhibition summary 1 Mixed support for Wagner's account – whether CS is predicted matters context extinction doesnt eliminate latent inhibition but it is context specific could we adapt Wagners theory but say elements of the stimulus becoming associated with each other cause LI, not just associations with the context?

64 Latent inhibition summary 2 Mackintosh and Pearce Hall – whether CS is predictive matters Mackintosh says predictive stimuli command attention: evidence -- intradimensional/extradimensional shifts Pearce & Hall say predictive stimuli ignored: evidence -- expected effects on orienting and on conditionability see Le Pelley (2004) for discussion of paradox... evidence for Pearce-Hall comes from studies with one CS evidence for Mackintosh looks at stimuli in compounds...

65 Perceptual Learning Gibson & Walk (1956) exposed animals to stimuli in their home cages Then tested them to discriminate between the stimuli in a jumping stand

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68 Standard procedure AX --> LiCl BX ? 5ml (low) Rats are conditioned to a compound flavour AX, and then tested with a similar flavour BX (A and B are sucrose and saline, X is lemon) Distinguish between the common elements (X) and the unique elements (A and B) Animals reject BX because the common element X was paired with LiCl

69 preexpose condition test water AX --> LiCl BX ? AX AX --> LiCl BX ? BX AX --> LiCl BX ? AX BX AX --> LiCl BX ? preexposing both stimuli seems to help discrimination Redrawn from Symonds & Hall 1995

70 Whats the explanation? Clue is in common elements: water AX --> LiCl BX ? AX AX --> LiCl BX ? BX AX --> LiCl BX ? AX BX AX --> LiCl BX ? remember animals reject BX because the common element X was paired with LiCl so the less X conditions the less animals reject BX

71 water AX --> LiCl BX ? AX AX --> LiCl BX ? BX AX --> LiCl BX ? AX BX AX --> LiCl BX ? In Group W X is novel and conditions well – BX very nasty

72 water AX --> LiCl BX ? AX AX --> LiCl BX ? BX AX --> LiCl BX ? AX BX AX --> LiCl BX ? In Group W X is novel and conditions well – BX very nasty In Group AX X is latently inhibited and conditions less well – BX less nasty

73 water AX --> LiCl BX ? AX AX --> LiCl BX ? BX AX --> LiCl BX ? AX BX AX --> LiCl BX ? In Group W X is novel and conditions well – BX very nasty In Group AX X is latently inhibited and conditions less well – BX less nasty In Group BX X is latently inhibited and conditions less well – BX less nasty

74 water AX --> LiCl BX ? AX AX --> LiCl BX ? BX AX --> LiCl BX ? AX BX AX --> LiCl BX ? In Group AX/BX X elements are exposed twice as much as in Group AX or BX -- so conditions twice as badly – BX not very nasty at all

75 Latent inhibition of common elements is one mechanism of perceptual learning - McLaren & Mackintosh 2000... but it is not all: preexpose condition test AX AX AX AX BX BX BX BX AX --> LiCl BX ? AX BX AX BX AX BX AX BXAX --> LiCl BX ? Redrawn from Symonds & Hall 1995

76 Intermixed and blocked schedules of exposure to AX and BX should produce identical latent inhibition to X... but it is not all: what about this experiment: preexpose condition test AX AX AX AX BX BX BX BX AX --> LiCl BX ? AX BX AX BX AX BX AX BXAX --> LiCl BX ? so what is going on?!

77 Learning about elements of a stimulus McLaren & Mackintosh 2000 proposed several associative mechanisms arising from stimulus preexposure that involve learning about elements of a stimulus, and that could produce perceptual learning 1 unitisation (sticking units together) – see above 2 latent inhibition of common elements 3 mutual inhibition between unique elements

78 AX BX AX --> LiCl BX ? Rats fear BX because X has been conditioned… but there is another reason: -- X is associated with A, which has also been conditioned … so if you can stop X making the animals think of A, they will drink more BX A LiCl BXBX

79 Intermixed preexposure could stop X making you think of A… Remember conditioned inhibition... tone --> food tone+light --> nothing makes light an inhibitor for food, because tone makes you think about food which doesn't happen... food

80 this could happen in AX and BX preexposure: X A B X X B A X A B on BX trials X makes you think of A, but no A happens..; so B comes to inhibit A same on AX trials

81 this could happen in AX and BX preexposure: X A B X X B A X... so B becomes an inhibitor of A (and vice versa) A B

82 Mutual Inhibition of Unique Elements So now when tested with BX, even though X tries to make you think of A… A LiClBX

83 Mutual Inhibition of Unique Elements So now when tested with BX, even though X tries to make you think of A… … B will stop you thinking of A, which stops you thinking of LiCl A LiClBX

84 So how does all this help explain this result? AX AX AX AX BX BX BX BX AX --> LiCl BX ? AX BX AX BX AX BX AX BXAX --> LiCl BX ?

85 AX AX AX AX BX BX BX BX AX --> LiCl BX ? AX BX AX BX AX BX AX BXAX --> LiCl BX ? AAAA AAAA This mechanism requires a strong X A association... and the association is weaker in the blocked case

86 Perceptual learning summary Several types of learning could result from stimulus exposure, that could contribute to perceptual learning Unitisation (see habituation) Latent inhibition of common elements Mutual inhibition of unique elements So is there any no associative component, as the Gibsons proposed? No one has found one yet...

87 References Baker, A.G., & Mercier, P. (1982). Extinction of the context and latent inhibition. Learning and Motivation, 13, 391- 416. Dickinson (1980) Contemporary associative learning theory. Cambridge University Press. Ch. 4 discusses Pearce & Hall and Mackintosh models mathematically Ennaceur, A., & Delacour, J., (1988). A newone-trial test for neurobiological studies of memory in rats 1: Behavioral data. Behavioural Brain Research, 31, 47-59. Object recognition task Gibson, E.J., & Walk, R.D. (1956). The effect of prolonged preexposure to visually presented patterns on learning to discriminate them. Journal of Comparative and Physiological Psychology, 49, 239-242. Good, M.A., Barnes, P., Staal, V., McGregor, A., & Honey, R.C. (2007). Context- but not familiarity-dependent forms of object recognition are impaired following excitotoxic hippocampal lesions in rats. Behavioural Neuroscience, 121, 218-223. Talks about object recognition from an associative perspective Hall, G. (1991) Perceptual and Associative learning. Oxford University Press. Chapters on habituation, latent inhibition and perceptual learning Hall, G., & Honey. R.C. (1989). Contextual effects in conditioning, latent inhibition and habituation: Associative and retrieval functions of contextual cues. Journal of Experimental Psychology: Animal Behavior Processes, 15, 232-241. Discusses Wagners acount of habituation and latent inhibition

88 References Hoffield, D.R. (1962). Primary stimulus generalisation and secondary extinction as a function of strength of conditioning. Journal of Comparative and Physiological Psychology, 55, 27-31. Le Pelley, M.E. (2004). The role of associative history in models of associative learning: A selective review and a hybrid model. Quarterly Journal of Experimental Psychology, 57B, 193-243. discusses discrepancy between Pearce Hall and Mackintosh theories McLaren, I.P.L., & Mackintosh, N.J. (2000). An elemental model of associative learning: 1. Latent inhibition and perceptual learning. Animal Learning and Behavior, 26, 211-246. (be selective, it's quite dense; they obviously like their theory) Mackintosh, N.J. (1975). A theory of attention: variation in the associability of stimuli with reinforcement. Psychological Review, 82, 276-298. Mackintosh, N.J., & Little, L. (1969). Intradimensional and extradimensional shift learning by pigeons. Psychonomic Science, 14, 5-6. Pearce, J.M., & Hall, G. (1980). A model for Pavlovian learning: Variations in the effectiveness of conditioned but not of unconditioned stimuli. Psychological Review, 87, 532-552. Swan, J.A., & Pearce, J.M. (1988). The orienting response as an index of stimulus associability in rats. Journal of Experimental Psychology: Animal Behavior Processes, 14, 292-301. Symonds, M., & Hall, G. (1995). Perceptual learning in flavor aversion conditioning: Roles of stimulus comparison and latent inhibition of common elements. Learning and Motivation, 26, 203-219. Discusses several associative mechanisms of perceptual learning


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