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Chapter 4

Chapter 4. Classical Conditioning: Mechanisms What makes effective conditioned and unconditioned stimuli? What determines the nature of the conditioned response? How do conditioned and unconditioned stimuli become associated?. What determines the nature of the CR?.

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Chapter 4

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  1. Chapter 4 • Classical Conditioning: Mechanisms • What makes effective conditioned and unconditioned stimuli? • What determines the nature of the conditioned response? • How do conditioned and unconditioned stimuli become associated?

  2. What determines the nature of the CR? Classical conditioning is defined by the development of a CR to a previously neutral CS Look at why particular responses become conditioned The first explanation for the nature of the CR is the Stimulus Substitution model

  3. The Stimulus Substitution Model • developed by Pavlov • the association of the CS with the US turns the CS • into a ‘surrogate’ US • the CS activates neural circuits previously activated • only by the US and elicits responses similar to the US • with pairings of the CS and US, a new connection • develops between the neural circuits previously • activated by the CS and the neural circuits previously • activated only by the US

  4. Diagram of Pavlov’s Stimulus Substitution Model • Conditioning enables the CS to elicit the UR • The CS substitutes for the US

  5. The US as a determining factor for the CR • The quality or nature of the US affects the type of CR • Different USs elicit different URs • L Food; elicits salivation • L Shock; elicits fear response • More subtle differences in CRs depending on the US • KL Food • KL water • Pigeons peck at the KL in both cases but the pecking • response is different • Thus, the form of the CR resembles the form of the UR

  6. Learning & Homeostasis • The concept of Homeostasis was introduced by • Water Cannon • certain physiological responses are maintained at • acceptable levels (temp., HR, BP) • change in one direction must be accompanied by an • opposite response to return the system to a baseline or • optimal level • operates through a negative feedback loop • i.e., a drop in temp. is detected and serves as a • stimulus to activate compensatory responses

  7. Learning & Homeostasis • Homeostatic mechanisms operate by a negative • feedback process that counteracts a challenge after • the disturbance has already caused a deviation from • homeostatic level • Pavlovian conditioning can be beneficial to anticipate • the challenges to homeostasis and start compensatory • mechanisms earlier

  8. Learning & Homeostasis • For ex., exposure to cold • Feedback processes require a drop in temp. before • compensatory responses (shivering, vasoconstriction) • occur to counteract the cold • If subjects learn which cues signal when they will get • cold, they can make feed-forward compensatory • adjustments in anticipation of the cold and avoid the • actual drop in temp.

  9. Conditioned Homeostatic Responses • examined most extensively with psychoactive drugs • Conditioning model of drug tolerance • tolerance = repeated presentations of the drug have • progressively less effect • administration of a psychoactive drug causes • physiological changes that disrupt homeostasis = US • these physiological changes caused by the drug trigger • unconditioned compensatory changes to counteract the • drug = UR

  10. Conditioned Homeostatic Responses • stimuli that accompany drug administration become • associated with the drug (syringe, context cues, etc…) • these cues associated with drug administration trigger • the compensatory response, so the drug has less effect • the CR then counteracts the drug effect

  11. The CS as a determinant of the form of the CR The quality or nature of the CS affects CR, even though the CS is supposed to be innocuous or neutral Experiment by Holland with rat subjects Tone Food T elicits headjerk behavior (rapid back and forth movements of the head) Light Food L elicits rearing and investigation of the food cup

  12. The CS as a determinant of the form of the CR Timberlake and Grant (1975) – described in textbook Investigated classical conditioning in rats with food as the US The CS was a presentation of another rat Instead of gnawing and biting (as stimulus substitution model might predict), the CR was orientation, approach, sniffing and social contact

  13. Conditioned Behavior and Behavior Systems Presentation of a US activates the behavior system relevant to that US - food activates foraging/feeding system - mate activates sexual behavior system As a CS becomes associated with the US, it becomes integrated into that behavior system The form of the CR will depend on the CS-US interval that is used The CS-US interval determines where the CS becomes incorporated into the sequence of responses that makes up the behavior system

  14. Sexual Behavior System General search behavior Focal search behavior Consummatory behavior (copulation) CS US CS US • Atkins (2000) • Light  Female quail • 60 sec CS-US interval (male searched in area of light) • 20 min CS-US interval (male searched all of chamber)

  15. How does a CS produce responding? Some Different Views as to What is Learned in Classical Conditioning a. S-S Learning b. S-R Learning

  16. S-S Learning Interpretation States that the CS enters into an association with the US (or US representation) The CS triggers a memory of the US which in turn elicits a response

  17. Early Learning Trial CS US CS US U R An association begins to develop between? The CS center and the US center UR

  18. CS-Only Test Trial CS US CS U R CR

  19. S-R Learning Interpretation States that because the CS occurs close in time to the UR, it comes to trigger the response directly An association forms between the CS and the response

  20. Early Learning Trial CS CS US US U R An association begins to develop between? The CS center and the response UR UR

  21. CS-Only Test Trial CS CS U R CR

  22. S-S versus S-R Learning S-R Learning Support: studies where CR is identical to UR Problem: sensory preconditioning S-S Learning Support: US-devaluation experiments Problem: does not specify the nature of the CR

  23. US-Devaluation Procedure Phase Experimental Group Control Group US Conditioning CS CS US US Devaluation e.g., CTA to chocolate e.g., no exposure to US Decreased CR Test/Result CS CS CR i.e., Devaluation of US in Experimental Group results in decreased CR relative to Control Group

  24. Support for S-S theory comes from study by Holland He showed that the memory of an event could substitute for the event itself in the formation of a new association Phase 1: T Wintergreen/sucrose L Nothing Phase 2: ½ got T LiCl ½ got L LiCl Phase 3: Measured consumption of wintergreen Results: Rats that had T - LiCl pairings consumed significantly less than rats that had L – LiCl pairings

  25. Explanation According to Holland, the T in phase 2 calls up a representation or memory of the flavor and this memory gets associated with the LiCl. Even though the flavor was never paired with LiCl, we see an aversion because the T was paired with LiCl The 2 stimuli essentially substitute for each other Evidence for S-S theory

  26. How do Conditioned and Unconditioned Stimuli Become Associated? Contiguity Two stimuli become associated if they occur close together in time While contiguity is important, it is not sufficient for conditioning to occur Contingency Refers to the predictive relationship between stimuli The CS has to convey information about US occurrence p(US/CS) > p(US/no CS)

  27. Rescorla’s (1968) Classic Experiment on Contingency Method Used the CER procedure with rats: First phase, operant conditioning to establish steady bar pressing. Second phase, CER training: classical conditioning to establish CER.

  28. Method (continued) CER training (daily for 5 days): • All rats exposed to 12 tones (the CS). • The tones were 2-min long and the mean inter-tone interval was 8 min. • The probability of shock (the US) during the tone was .40 for all rats. • Groups differed in the probability of shock during the inter-tone interval.

  29. Method (continued) During the Inter-tone interval: • Group 0 : no shocks • Group .1: shocked with a probability of .1 • Group .2: shocked with a probability of .2 • Group .4: shocked with a probability of .4

  30. ToneCS US for Group: 0 .1 .2 .4 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 Time = 2 minutes of Tone CS = Shock US in presence of Tone CS = Shock US in absence of Tone CS

  31. Method (continued) Third phase, after CER training, the rats were returned to bar pressing for food. While the rats were bar pressing, the tones were presented as before, but no shocks were given (what procedure is this?) Conditioning was assessed by a suppression ratio (the lower the ratio, the greater the suppression, the stronger the conditioning).

  32. Rats that experienced as many shocks in the absence of the tone as they did in its presence showed no suppression. Rats that only experienced shock with the tone, showed total suppression.

  33. These results suggest that contiguity is not the only associative principle necessary to produce learning. • All rats experienced the same degree of contiguity between tone and shock, they differed in the extent to which the shock was contingent on the tone.

  34. Problem for notion of contiguity and contingency Blocking • one of the more important phenomena in classical • conditioning • shows that simple contiguity between the CS and US • is not sufficient for conditioning • blocking experiments are typically done in 3 phases

  35. Blocking Group Phase 1 Phase 2 Phase 3 Experimental Group (blocking) A US US AB Test B Control Group AB Nothing US Test B Same # trials Contiguity Contingency

  36. Blocking In Control group, should get equal conditioning to both A and B - both are equally contiguous with the US - same predictive relationship What happens in the Blocking group? - if during phase 1, A perfectly predicts the US then should see little conditioning to B in phase 2 - B adds no new information since the US is already predicted by A B should evoke a stronger CR in the control group on test This is called Blocking

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