View
244
Download
11
Category
Preview:
Citation preview
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)
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
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
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
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
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
• 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
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
Recommended