Chapter 3

Classical Conditioning

Ivan Petrovich Pavlov (1849-1936)

• Classical (Pavlovian) conditioning

• Medical physiologist• Digestion• Human/animal

differences• Conditioned reflexes

en.wikipedia.org/wiki/File:Ivan_Pavlov_(Nobel).pngen.wikipedia.org/wiki/File:One_of_Pavlov%27s_dogs.jpg

Terminology• Unconditional stimulus (US)

– Stimulus that elicits the innate reflex (e.g., food)

• Unconditional response (UR)– Reflex action that occurs in response to US (e.g.,

salivation)

• Conditional stimulus (CS)– Any stimulus that doesn’t originally elicit the UR

(e.g., bell)

• Conditional response (CR)– The action elicited by the CS (e.g., salivation)

Conditioning and Awareness

• Awareness of conditioning not required for learning

Innate

• US-UR is an innate stimulus-behaviour

• “Reflex”

• Hardwired

• Stereotypic pattern of behaviour

Example: Bell and Food

CS

US

URCR

Later Trials

CS

US

UR

First Few Trials

Time

CS = bellUS = foodUR = salivation

CR = salivation

Processes

• Acquisition– Acquiring a CR– E.g., pair CS with US

• Extinction– Reduce/eliminate a CR– E.g., present CS without US

Measuring Conditioning

• Sometimes difficult to measure CR– e.g., if CS & US close together, CR & UR can

overlap

• Test trial (probe trial)– Give CS alone

• Intensity– Does CR intensity increase with experience?

Example: Eyeblink Conditioning

• Airpuff on eye

• Blink

• UR vs. CR eyeblinks– UR blink faster than CR blink

CS (tone) US (airpuff)

CR (blink) UR (blink)

Example: Taste Aversion

• Very strong• Very persistent• Usually conditioned after one presentation• Experiment

– Rats fed novel food (CS)– Injected with lithium chloride (US)– Choice: novel food or regular food– Chose regular food

Higher-Order Conditioning

• CSs and USs can be associated (First-order)

• CSs can be associated with other CSs

• Second-order conditioning

First-Order Conditioning

salivation (CR)

first-order

tone (CS1) food (US)

Second-Order Conditioning

light (CS2) tone (CS1)

second-order

salivation (CR)

Risk of extinction?

salivation (CR)

tone (CS1) food (US)

CS+ and CS-

• CS+ (excitatory CS)– CS predicts occurrence of US– Activates behaviour related to US

• CS- (inhibitory CS)– CS predicts non-occurrence of US– Suppresses behaviour related to US

• Randomize trial type presentation

CS+

CS-

US

Trial Type A Trial Type B

• Context cues serve as CS+

CS-

US

NEGATIVE CONTINGENCY PROTOCOL

PAVLOV’S PROCEDURE

Testing for CS-

• CS- produces absence of CR

• No CR– You’ve produced CS-

– Haven’t learned anything

• How to measure nothing…

• Summation test– Measure CR with CS+– Compound stimulus of CS+

& CS-; measure CR

• Retardation of acquisition– Trained CS- and novel

stimulus; pair both with novel US for same number of trials

– Measure CR for both– Prior learning of CS-

inhibits learning new association

Short Delay Conditioning

• Strongest and most rapid

• Simple autonomic responses: 5-30 seconds

• Quick skeletal responses: 0.5 seconds

CSUS

or

Long Delay Conditioning

• Other distracting stimuli?

• Timing estimation required

CSUS

or

Trace Conditioning

• From “memory trace”

• Must remember CS

• Other stimuli interfere

CSUS

trace interval

Simultaneous Conditioning

• Weaker than short delay

• CS can’t signal onset of US– Not predictive

CSUS

Backward Conditioning

• Ignores order; US comes first

• CS has no predictiveness

• Might become CS-

CSUS

Influences in Classical Conditioning

CS-US Contiguity

• Closeness together in time and/or space

• Usually, more learning if greater contiguity between CS & US

• Type of conditioning may influence this

• e.g., eyeblink vs. taste aversion

CS-US Contingency

• If-then situation

• X iff Y

• Consistency of pairing CS and US

• Greater contingency, greater learning

Stimulus Features

• Nature of stimulus affects its conditioning ability

• Intensity

• Novelty

Compound Stimuli

• Two+ simple CSs presented at the same time

• Paired with US

Overshadowing

• Salience

• Exclusive regulation of CR by most salient CS in compound stimuli

Latent Inhibition

• Repeatedly present neutral stimulus (N)

• Pair N with US

• Harder to condition N as CS

• CS- or habituation

Blocking

• CS1 -- US

• CS1 and novel stimulus (CS2) with US

• CS1 --> CR

• CS2 --> no or very weak CR

Textbook Error: p. 77

• “But suppose we eat two foods, one spicy and the other bland. If we then become sick, thanks to blocking we are likely to develop an aversion to the spicy food -- even though it may have been the bland food that caused our illness.”

Sensory Preconditioing

• Pair two neutral stimuli repeatedly

• Pair one with US repeatedly until CR produced

• Test other stimulus

• CR produced

Number of CS-US Pairings

• Acquisition curve

• Non-linear

• Asymptote

Conditioning Trials

CR

Str

engt

h

asymptote

Intertrial Interval

• ITI

• Time between each CS-US pairing (i.e., between trials)

• Generally, around 30 seconds effective

Extinction of CR

Extinction

• CS without US --> Extinction

• Weakening and stopping of CR

• Not forgetting

• A type of conditioning

• CS paired with absence of US

Spontaneous Recovery

• After extinction, let time pass

• Present CS again (no US)

• Temporary, small return of CR

• Shows extinction is not forgetting

Relearning/Reacquisition Effect

• Extinguish CR

• Recondition with CS-US pairing

• Fewer trials required

Putting it Together

Trials/Time

Str

engt

h of

CR

Acquisition ExtinctionSpontaneous Recovery Reacquisition

CS&US CS alone CS alone CS&US

Theories of Classical Conditioning

Associationism, Stimulus Substitution, Preparedness, Rescorla-Wagner

Associationism

• Linking together of:– Events– Memories– Actions and consequences

• Contiguity, similarity, contrast

• Central to study of learning and behaviour

Ebbinghaus’ Memory Experiments

• 1880s• Nonsense syllables

– E.g., ZOG, PAF, TOB

• One subject• Recite from memory• Savings

– E.g., if 10 trials initially, then after a delay 3 more trials, savings = (10-3)/10 = 7/10 = 70%

Major Findings

• List length

• Effects of repetition– Overlearning

• Effects of time

• Role of contiguity

• Backwards associationsTime between study and relearning

20min 1hr 8.8hr 1day 2days 6days 31days

100

75

50

25Per

cent

Sav

ings

Forgetting Curve

Classical Conditioning

• Innate US-UR reflex pathway

• CS is associated with the US

• Through the associative process, CR is produced

Stimulus Substitution Theory

• Pavlov

• CR and UR produced by same neural region

• CS takes on properties of US

• Substitution

• CR should be the same as UR

Example: Sign Tracking

• Response not required• US often food• Stimulus (CS) indicates

US availability• Subject “tracks” the

sign more and more• CS takes on properties

of US• Pigeon autoshaping• Longbox autoshaping

F

F= CS = US

Biological Predispositions

Timberlake & Grant (1975)

Burns & Domjan (2000)

Problems with SST

• CS not a complete substitute for US– e.g., eyeblink differences– Magnitudes

• CSs produce different responses– Omissions and additions

• Compensatory conditional responses

Preparatory Response Theory

• Learn responses that prepare organism for US occurrence

• Sometimes CR same as UR, sometimes different

Example: Drug Tolerance

• Neurophysiological dependencies

• Siegel (1975)

• Contextual stimuli act as CSs

• Compensatory CR

• Morphine

Contextual Stimuli Theory

• Rats on hotplate

• Between-groups study

• Independent variables:– Morphine or placebo– Location of injection (Home or Injection room)

• Dependent variable: time to lift feet

Results

• Control (placebo): 13 sec.

• Exp. Gr. 1 (morphine): 24 sec. (day 1) to 13 sec. (day 4)– Injection room gives contextual cues– Compensatory CR

• Exp. Gr. 2 (morphine): – Day 1-3 injection room: 24 --> 13 sec. latency– Day 4 home room: 28 sec. latency

Interpretation

• US: Morphine

• UR: Pain reduction

• CS: Injection room

• CR: Pain sensitivity

• CS prepares rats for morphine injection

• Body homeostasis

Rescorla-Wagner Theory

• Contiguity account

• Associative strength

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

Three Factors in Theory

• Maximum associative strength

• Difference between current and maximum strength

• Number of additional CSs

Rescorla-Wagner Equation

Vn: change in associative strength for CS on one trial

Vn = c( - Vn-1)

c: represents salience of CS and US; a constant (0.0-1.0)

: maximum associative strength (magnitude of UR)

Vn-1: associative strength already accrued by CS

Acquisition Phase

• Example: set c = 0.25, = 10.0• Vn-1 starts at 0.0

– For the first trial Vn-1 = V1-1 = V0

– For the second trial Vn-1 = V2-1 = V1

• First CS-US pairing:

Vn = c( - Vn-1)

V1 = 0.25(10.0 - 0.0)

= 2.5• Second CS-US pairing:

V2 = 0.25(10.0 - 2.5)

= 1.88

• Total associative strength Vn (or “VTotal”) after two trials:V1 + V2 = 2.5 + 1.88 = 4.38

• Third CS-US pairing:V3 = 0.25(10.0 - 4.38)

= 1.41

Acquisition PhaseTrial Vn Vn (VTotal)

0 0.00 0.001 2.50 2.502 1.88 4.383 1.41 5.794 1.05 6.845 0.79 7.636 0.59 8.227 0.45 8.678 0.33 9.009 0.25 9.2510 0.19 9.44

Trials

Ass

ocia

tive

Str

engt

h (V

n)

V1

V2

V3

Extinction

• Example:

– Set c = 0.25, = 0.0

• After first extinction trial:

Vn = c ( - Vn-1)

= 0.25(0.0 - 10.0)

= -2.5

Extinction

Trials

Ass

ocia

tive

Str

engt

h (V

i)

= 0.0

V1

V2

V3

Blocking

• Learned CS blocks subsequent CSs• Example

– CS = tone, novel CS = light

– c = 0.25, = 10.0– Completed 8 trials with just tone, V8 = 9.0 Vn = 0.25(10.0 - 9.0)

• Only 1 unit of associative strength left to split between the tone and the light

• Ultimately, Vtone=9.5 and Vlight=0.5