PSY402 Theories of Learning Chapter 5 Theories of Pavlovian Conditioning

Contemporary Theories Nature of the CR – stimulus substitution theory, SOP and AESOP theory Nature of the conditioning process: Predictiveness of the CS – the Rescorla-Wagner associative model Miller’s Comparator theory Mackintosh’s attentional theory Retrospective processing approach

Comparison of Theories

Stimulus-Substitution Theory What is the nature of the CR – is it just the UCR or is it different? Pavlov – stimulus-substitution theory: The CS stimulates the same areas of the brain as the UCS, producing the same response. Activation of CS together with UCS establishes a neural connection between brain areas.

Connections are formed between brain regions

Conditioned Opponent Response The CR and UCR are often different: CR of fear is different than UCR of pain. Siegel – best evidence of difference: Morphine (UCS) produced analgesia, reduced pain (UCR) Light or tone (CS) produced hyperalgesia, increased pain (CR). Rats remove paws from heat quickly with CS, slowly with UCS. Insulin (glycemia) works the same way, producing hypoglycemia as a CR.

Conditioning of the Opponent Response (Tolerance) The M-P-M condition presents the CS without the UCS so the tolerance is extinguished.

Drug Tolerance Overdoses Elimination of a CS results in a stronger response to the UCS, drug. Extinction of responding to environ-mental cues strengthens drug response Changing the context in which a drug is administered increases response to the drug. Novel environment does not elicit an opponent CR. No difference between small and large doses – both elicit the same withdrawal effect (opponent CR).

SOP Theory Sometimes-Opponent-Process theory (SOP) – explains why CR varies. UCS elicits primary A1 (fast) and secondary A2 (longer) responses. A1 & A2 can be same or different. Conditioning only occurs to A2 – the CR is always an A2 response. When A1 & A2 differ, UCR & CR differ.

SOP Explains Timing Effects None of the previous models explain why the timing of CS-UCS matters. SOP model requires that both CS and UCS be in the A1 stage for learning to occur. With delay more elements of CS decay from A1, becoming A2. The CR is always the A2 response.

Activation of a memory node in SOP theory bouton-fig-04-14-1.jpg

bouton-fig-04-14-2.jpg

Two-Phase Reactions Shock – results in: Morphine – results in: A1 -- Initial agitated hyperactivity A2 -- Long-lasting hypoactivity (freezing) CER (fear) elicited by CS is A2 Morphine – results in: A1 – sedation, analgesia & hypoactivity A2 – hyperactivity two hours later & hyperalgesia (greater pain sensitivity) CR elicited by CS is A2 (hyper)

A2 Morphine Hyperactivity Environment elicits A2 hyperactivity

When A1 & A2 Are the Same Grau showed that unconditioned responding to radiant heat produced: Instant, short-duration hypoalgesia (decreased sensitivity to pain) Followed by persistent hypoalgesia, opioid based The existence of distinct A1 & A2 responses was demonstrated using naloxone, which blocks A2 (opioid) but not A1 (non-opioid).

Two Circuits in Rabbit Eyeblinks Fast-acting direct circuit (A1) to sensory trigeminal nucleus to motor nuclei Slow-acting A2 circuit through inferior olive

Affective Extension of SOP Theory Why do different A2 responses have different optimal CS-UCS intervals? Two distinct UCR sequences activate distinct A1 & A2 sequences: A1 -- Sensory A2 -- Emotive These distinct sequences can have different strengths, time scales (latencies), or eliciting CS’s.

Faster bouton-fig-04-16-0.jpg Slower

The Nature of Conditioning Theories about the nature of conditioning have difficulty explaining three observed phenomena: Preexposure effects Overshadowing Blocking

Rescorla-Wagner Theory There is a maximum associative strength between CS and UCS. UCS determines the limit Strength gained on each training trial depends on prior training – diminishing returns. More learning early, less later on Rate of conditioning varies. Conditioning of a CS depends on prior conditioning to other stimuli with that UCS.

Rates of Conditioning Vary

Rescorla Wagner Model  

UCS Preexposure Effect If the UCS is encountered without the CS prior to pairing of the two, less learning occurs. UCS becomes associated with other environmental stimuli (without CS). Since there is a limit to association strength, some is drained off by such prior associations. CS-UCS association is weakened. Rescorla-Wagner explains this fine

Problems with Rescorla-Wagner Overshadowing – salient cues have more associative strength. Sometimes a salient cue potentiates another cue instead of overshadowing. Garcia says cues are indexed as food-related. R-W says the two cues are seen as a unitary stimulus (one joint CS). Unclear which explanation is correct.

UCS Preexposure Effect +C1/C1 Preexposure and conditioning in same environment +C1/C2 Preexposure in one environment and conditioning in another -C1/C1 & -C1/C2 are control groups with no preexposure

More Problems CS preexposure effect – appearance of CS without UCS prior to learning weakens learning. Shouldn’t have any effect according to Rescorla-Wagner theory, but it does. Cue-deflation effect – extinction of a more salient cue enhances learning for the less salient cue. Should be no change according to R-W.

Comparator Theory If two CS’s are associated, extinction of one should reduce responding to the other. Sometimes true, other times not. Why? CS-UCS associations exist for many stimuli but are exhibited only for the strongest. Comparator theory says the CS’s are judged in relation to each other.

Organisms might learn about elemental or configural CS nodes Wagner & Brandon bouton-fig-04-17-0.jpg Pearce

Attentional View Mackintosh – learned irrelevance occurs during preexposure of CS. Animals exposed to a novel stimulus exhibit an orienting response. No orienting with preexposure. Habituation results in failure of conditioning – no attention is paid to a habituated stimulus. Pairing of CS/UCS in novel context results in learning.

Learned Irrelevance

Retrospective Processing Most theories assume the level of responding will be constant after learning. Baker & Mercier suggest association can change after learning. Retrospective processing – CS-UCS contingency reevaluated after learning. Backward blocking – support for theory Suggests animals have mental representations, memory for events.

Comparison of Theories