Chapter 5

Theories and Research on Classical Conditioning

Compound Stimuli

• Two or more simple conditioned stimuli that are presented at the same time

Overshadowing

• Salience of stimuli
• Exclusive regulation of CR by most salient of compound stimuli

Blocking

• CS associated with US prevents subsequent CS-US associations

• Test

Sensory Preconditioning

• Preconditioning phase
• Two stimuli presented together without US
• Pair one stimuli with US

• Test other stimuli

Rescorla-Wagner Model of Conditioning

• Contiguity account
• Associative strength
• CS acquires limited amount of associative strength on any one trial

Three Factors in Model

• Maximum associative strength
• Difference between current and maximum strength
• Number of additional CSs

Rescorla-Wagner Equation

Si: represents salience of CS; a constant (0.0-1.0)

Vmax: maximum associative strength (magnitude of UR)

Vi: associative strength already accrued by CS1

Vsum: associative strength already accrued by other stimuli

Acquisition Phase

• Example: set Si = 0.25, Vmax = 10.0, Vsum = 0.0
• Vi starts at 0.0

• First CS-US pairing:

Acquisition Phase

(Figures 1 and 2)

Blocking

• Learned CS blocks subsequent CSs
• Example
• CS = tone, novel CS = light
• Si = 0.25, Vmax = 10.0
• Completed 8 trials, V8 = 9.0

Extinction

• Example:
• Set Si = 0.25, Vmax = 0.0, Vsum = 0.0
• After first extinction trial:

Extinction

(Figure 3)

Conditioned Inhibition

• Excitatory CS paired with inhibitory CS
• Mazur (1990)
• Example: tone = CS+, light = CS-
• Start values:

• We define

• And

(Figures 4 and 5)

Overexpectation Effect

• Predicted by Rescorla-Wagner model before being empirically demonstrated

(Figure 6)

CS Preexposure Effect

• Preexposure group: give CS alone
• Control group: pair CS with US
• Test: how long to get CR in both groups
• "Habituation" in preexposure group

CS Preexposure Effect

• Not explained by Rescorla-Wagner model
• First preexposure trial
• No prior conditioning

• But, something is learned
• Salience variable, not constant

Text Version of Rescorla-Wagner Equation

• Text version

• Full version

Biological Constraints in Classical Conditioning

• Contiguity
• Important Associationist concept
• Temporal link between
• Stimuli
• Stimuli and reinforcement

Taste-aversion

• Long-delay or trace-conditioning
• US = poison
• CS = novel taste
• Delay between taste and nausea

• Does this violate contiguity?

Explanations?

• Sensitization
• Aftertaste
• Biological preparedness

Equipotentiality Premise

• Pavlov
• Doesn’t matter what you use as CS

• Problems?

Biological Preparedness in
Taste-Aversion

• Garcia & Koelling (1966)

(Figure 7)

Explanation

• Biological predisposition
• Taste and nausea
• Audiovisual and shock
• Must know about CS-US relationship before predicting nature of CR

Form of Conditioned Response: Drug Tolerance

• Neurophysiological dependencies
• Opponent-process theory
• Contextual stimuli theory

• Morphine

Contextual Stimuli Theory

• Rats on hotplate
• Control (placebo): 13 sec. latency (control)
• Group 1 (morphine): 24 sec. latency (day 1) to 13 sec. latency (day 4)

• Group 2 (morphine):

• Extinguish response
• CS (contextual cues) without US (morphine)
• 3 morphine trials in experimental room
• 9 placebo trials in experimental room
• Test with morphine injection

Stimulus Substitution Revisited

• Pavlov’s theory: CS takes on attributes of US
• Supporters of theory say:
• Compensatory CRs cases of mismeasured CR or UR
• True URs initiated by CNS
• Glucose example
• Give low dose of insulin…initial drop in blood glucose
• Is this decrease a UR? No. Blood glucose not CNS controlled. But, CNS monitors blood glucose; if low, causes increase.
• Real UR to insulin is increase
• CS (tone) - US (insulin) --> increase in blood glucose
• Non-pharmacological examples?

Conditioned Opponent Theories

• Schull (1979)
• a-process followed by b-process
• b-process not automatically strengthened/weakened with use/disuse
• Stimuli paired with emotional experience becomes CS that elicits b-process
• Increase in b-process leads to CR elicited by CS(s)

Other Conditioned Opponent Theories

• Wagner et. al.
• Sometimes opponent process (SOP) theory
• Sometimes CR same as UR, sometimes opposite
• CR same when UR monophasic
• CR opposite when UR biphasic

• Affective extension of SOP (AESOP) theory
• Single US has two centres
• Sensory properties
• Emotional properties
• US centres activate two different types of URs
• Hard to say which US centre CS will form strongest association

Classical Conditioning: Aplysia

• Temporal arrangement important
• Shock to tail (US) --> full gill retraction (UR)
• Touch siphon (CS) --> partial gill retraction
• Pair CS with US
• Now siphon touch --> full gill retraction (CR)
• Short-delay conditioning; 0.5 sec. optimal
• Increased Ca²⁺ --> increased NT release

Classical Conditioning: Higher Animals

• Eyeblink in rabbit
• Different neural pathways for UR and CR

• Difficult to understand in higher vertebrates
• Many brain regions involved
• Different CRs involve separate brain regions
• Different conditioning phenomena involve different brain regions
• UR and CR can follow different pathways