Classical Conditioning – Lecture 4

Learning Outcomes

• Define classical conditioning, higher-order conditioning, pairing rules for CS–US, and extinction of the conditioned response (CR).

• Trace the historical emergence of the field from Ivan Pavlov’s work on digestion.

• Explain how CS–US temporal relations, contingency, contiguity, stimulus features, prior experience, number of pairings, inter-trial interval, age, temperament, and stress influence learning.

• Distinguish theories that extend or refine Pavlov’s explanation (Stimulus-Substitution, Preparatory-Response, Compensatory-Response).

• Identify real-world applications: fears, prejudice, taste-aversion, advertising, drug addiction, health-care, and therapy.

The Beginnings: Ivan Petrovich Pavlov

• Born $1849$ in Ryazan, Russia; son of a poor village priest who also gardened for food.

• Mediocre early school performance, but displayed “the fire of a genius.”

• Personality traits: impatient, stubborn, eccentric; a passionate hands-on experimenter.

• Trained as a physiologist studying digestion, aiming for a Nobel Prize.

• Turning point (late $19^{\text{th}}$ century): noticed adaptability of salivary glands—amount of saliva varies with type of food.

  • Quote: “It is as if the glands possessed a kind of intelligence.”

• Critical observation: dog salivated before food touched the mouth → originally called these “psychic reflexes.”

From Digestion to Behaviour

• Method: Carefully recorded every external stimulus present when the reflex occurred and noted changes in the reflex itself.

• Findings

  • Sight or smell of food → salivation.

  • Mere sight of food vessel produced saliva.

  • Footsteps or appearance of the person delivering food also triggered saliva.

• Conclusion: Two reflex categories

  • Unconditional reflexes (innate): e.g., salivation when food contacts mouth.

  • Conditional reflexes (acquired): salivation triggered by varied, previously neutral stimuli; not present at birth and thus impermanent.

Experimental Apparatus (Classical Conditioning Setup)

• Dog was harnessed (movement restricted) to ensure measurement consistency.

• Tube surgically implanted to collect saliva from the mouth.

• Quantity of saliva captured in a calibrated receptacle for precise measurement.

Classical Conditioning: Basic Process

• Terminology

  • Unconditioned Stimulus (US or UCS): food.

  • Unconditioned Response (UR or UCR): reflexive salivation to US.

  • Neutral Stimulus (NS): tone before pairings (elicits no salivation or irrelevant response).

  • Conditioned Stimulus (CS): tone after pairings.

  • Conditioned Response (CR): salivation elicited by CS alone.

• Acquisition Phase

  • Sequence: NS (tone) presented → immediately followed by US (food).

  • After several pairings the NS transforms into a CS.

• Post-conditioning

  • CS produces CR even in absence of US.

Higher-Order (Second-Order) Conditioning

• Concept: A well-established CS can act as if it were a US to condition a new, neutral stimulus.

• Typical chain (example with pets):

  1. Electric can-opener (CS) → food (US) → salivation (CR).

  2. Squeaky cabinet door (new NS) paired with can-opener sound (first-order CS).

  3. Cabinet door alone becomes a second-order CS → salivation (CR) without food or can-opener.

• Human demonstration (Staats & Staats, $1957$)

  • Participants viewed nonsense syllables (YOF, LAJ, QUG).

  • Each syllable repeatedly paired with positive or negative words (gift, beauty vs. thief, sad).

  • Later descriptions of syllables reflected the valence of the paired words despite absence of an explicit US.

Measuring Pavlovian Learning

• Latency: time between CS onset and first droplet of saliva.

• Test trials (probe): present CS alone (e.g., every $5^{\text{th}}$ trial) to gauge learning without reinforcement.

• Intensity: total volume of saliva produced during CS.

  • First CR weak; strength escalates quickly across early trials.

• Pseudoconditioning

  • A neutral stimulus occasionally evokes the UR merely because repeated URs have heightened general responsiveness.

  • Control procedures are required to separate true conditioning from pseudoconditioning.

Variables Affecting Pavlovian Conditioning

1. Temporal Relations (CS–US Timing)

• Delayed Conditioning (Standard Pairing)

  • CS precedes and overlaps US; most effective.

• Trace Conditioning

  • CS ends before US begins; relies on memory “trace;” efficacy declines as trace interval increases.

• Simultaneous Conditioning

  • CS and US onset together; typically weak learning because CS does not predict US.

• Backward Conditioning

  • US precedes CS; usually ineffective or produces inhibitory learning.

2. CS–US Contingency (If-Then Relationship)

• Higher contingency (CS reliably predicts US) → stronger learning.

• Rescorla (1968): Rats received varying proportions of “shock-without-CS” trials.

  • Shock alone in $10\%$ of extra trials: strong conditioning.

  • Shock alone in $40\%$: weak conditioning.

• Real-world implication: Environmental noise reduces contingency and hence learning precision.

3. CS–US Contiguity (Inter-Stimulus Interval, ISI)

• $\text{ISI} = t<em>{US} - t</em>{CS\;onset}$.

• Generally, shorter ISIs promote faster conditioning up to an optimal point; zero interval (simultaneous) is sub-optimal.

• Optimal ISI length varies with response system (e.g., salivary vs. eyelid responses).

4. Stimulus Features

• Salient, intense, or biologically relevant CSs condition faster (e.g., pictures of snakes vs. neutral objects before shock).

• Compound Stimuli: presenting two or more CSs together.

  • Overshadowing: the more salient element gains associative strength; weaker component elicits little CR.

  • Example: Cold + tactile cue followed by weak acid; cold failed to elicit CR by itself.

5. Prior Experience

• Latent Inhibition: pre-exposure to CS alone retards later conditioning because contingency appears lower.

• Blocking (Kamin): an established CS prevents a novel stimulus from acquiring associative strength when both are paired with US simultaneously.

  • Adaptive—organism ignores redundant cues.

• Sensory Preconditioning (Brogden, 1939): Two neutral stimuli paired together first; later, one is conditioned with US → the other also evokes CR despite never being paired with US.

6. Number of CS–US Pairings

• More pairings generally → stronger conditioning, but first few pairings contribute disproportionately to associative strength (negatively accelerated curve).

7. Inter-Trial Interval (ITI)

• Longer ITIs often allow recovery from habituation and produce stronger conditioning; optimal ITI depends on species and response.

8. Other Influences

• Age: very young and very old animals may learn more slowly.

• Temperament: excitable animals can show faster conditioning.

• Stress: moderate stress can enhance learning; extreme stress impairs it.

Extinction and Spontaneous Recovery

• Extinction: repeated presentation of CS without US → CR diminishes.

  • Not equivalent to forgetting; original association is inhibited, not erased.

• Spontaneous Recovery: after a rest period following extinction, CS can again evoke CR, although typically weaker.

Contemporary Theoretical Extensions

• Stimulus-Substitution Theory

  • CS becomes neural substitute for US; CS → same UR circuitry.

• Preparatory-Response Theory (Kimble, 1967)

  • CR prepares organism for US (e.g., salivation lubricates digestion); CR may differ in topography from UR.

• Compensatory-Response Theory (Siegel, 1972)

  • CR counters the physiological impact of US (important in drug tolerance & overdose risk).

Tutorial Activity & Applications of Classical Conditioning

1. Fear acquisition (e.g., Little Albert).

2. Prejudice formation via evaluative conditioning.

3. Taste aversion learning (single-trial conditioning to nausea).

4. Advertising: pairing brands with positive imagery/music.

5. Drug addiction: environmental cues elicit craving or compensatory responses.

6. Health-care: conditioned immunosuppression, anticipatory nausea in chemotherapy.

7. Psychological disorders & therapy: systematic desensitization, exposure therapy.

Ethical, Philosophical & Practical Implications

• Ethical treatment of animal subjects—surgical procedures, restraint, and shock raise welfare issues.

• Conditioning underscores how environments sculpt behaviour, challenging notions of free will.

• Clinical relevance: manipulating learned associations aids treatment of phobias, addictions, and psychosomatic conditions.

• Advertising/propaganda: raises questions about informed consent and exploitation of unconscious learning processes.