Classical Conditioning: Theory

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Stimulus Control of Behaviour
Stimulus Control
• Differential responding and stimulus
discrimination
• Complex environment
• “Signal” from the “noise”
• What is important?
Reynolds (1961)
Train
Test
Responses per minute
• Pigeons, operant chamber, compound
key
Bird 107
triangle
Bird 105
circle
Discrimination and
Generalization
• Differential responding
– Stimulus discrimination
• Similar responding
– Stimulus generalization
Generalization Gradients
• Train on one (or more) stimulus
• Test on continuum (i.e., a “gradient”) of
other, related stimuli
• Plot on graph… Generalization Gradient
• Tricky
– Reinforcement problem
– Extinction problem
– Probe trials and extinction blocks
Responses
Gen. Grad.: Stimulus Control
Training stimulus
Stimulus Continuum (e.g., wavelength of light)
Responses
Gen. Grad: No Stimulus
Control
Training stimulus
Stimulus Continuum (e.g., wavelength of light)
Spetch & Mondloch (1993)
•
•
•
•
•
Pigeons in localization task
Touch-screen
Peck at target area of 2cm2
Target defined by landmarks
Tested to determine the landmarks that
controlled the discrimination
Training Stimuli
Quic kTime™ and a
TIFF (LZ W) dec ompress or
are needed to see this picture.
Results: Pigeon C207
Results: Pigeon 271
Factors in Stimulus Control
Sensory Capacity
• Organism’s sensory capacity
determines what stimuli can control
behaviour
• E.g., ultraviolet stimuli for honeybee, but
not for human
• Physical orientation
Overshadowing
• Competition among stimuli for access to
learning processes
• Higher intensity stimulus more easily
conditioned
• Speed of conditioning
However…
• Stimulus element approach
– Elements in a compound stimulus treated
as distinct and separate components
– Overshadowing: most salient stimulus
gains control
• Configural-cue approach
– Compound stimulus treated as an integral
whole
– Overshadowing: generaliztion decrement
Group
Training stimuli
Test stimulus
Generalization
from training to test
Overshadowing
weak-STRONG
weak
Decrement
Control
weak
weak
No decrement
• Configural-cue interpretation
– Overshadowing due to degrees of generalization
decrement from training to testing
– No generalization decrement for control group
– Overshadowing group learned weak-STRONG,
but only tested on weak, so considerable
generalization decrement
• Evidence for both stimulus element and
configural-cue approaches
Type of Reinforcement
• Biological predispositions; belongingness
• Species
• Sometimes seasonal
– E.g., stimuli associated with courtship
disregarded outside of mating season
Force & LoLordo (1973)
Tone & light
Light
Tone
– L/T … press pedal …
food
• Group 2
– L/T … press pedal …
avoid shock
• Test compound and
individual components
Pedal Presses
• Training:
• Group 1
Group1
(food reinforcer)
Group 2
(shock avoidance)
Instrumental Response Factors
• Nature of the response required for
reinforcement can affect stimulus
control
Dobrzecka, Szwejkowska &
Konorski (1966)
Learning Factors in Stimulus
Control
• Pavlov
– Inherent properties of nervous sytem
– Innate
– Due to physical similarity of stimuli
• Lashley & Wade (1946)
– Explicit discrimination training required
– Stimulus control learned
– Stimulus generalization because animals have
NOT learned the difference between stimuli
Stimulus Discrimination
Training
• In classical or instrumental conditioning
– CS+ or CS-, S+ or S-
Cummulative responses
• Stimuli explicitly associated with other stimuli
or outcomes
S+
S-
Time
Training and Stimulus Control
• Use generalization gradient to
determine degree of stimulus control
• Need to determine the feature(s) of the
discrimination procedure that controls
the gradient
Jenkins & Harrison (1962)
Range of Discriminative Stimuli
• Wide range of stimuli have been used in
discrimination studies
– Music, auditory frequencies, painting
styles, geometric shapes, etc., etc.
• Can use these discrimination studies to
assess the sensory capability of species
Pigeon Art
Appreciation
• Watanabe et al. (1995)
• Trained pigeons to
discriminate between
Monet and Picasso
• Achieved high degree of
accuracy
• Pigeons generalized to
other artists of the same
style (Impressionist or
Cubist)
What’s Learned
• Spence’s (1936) theory
• Learn about both S+ and S– Stimuli treated separately
• S+ represents excitation
• S- represents inhibition
• Test
– Excitatory stimulus generalization gradient
• Most response near S+
– Inhibitory stimulus generalization gradient
• Least response near S-
Honig et al. (1963)
S+/S- Interactions
• Interactions likely to occur between S+
and S• Especially likely if using
intradimensional discrimination
– Stimuli from same stimulus continuum
• Example seen in peak shift
Peak Shift
• Maximum
responding on
generalization
gradient not to
trained stimulus
• With S+/S- training
• Already seen in
Jenkins & Harrison
(1962)
Peak shift
Hanson (1959
Spence’s Interpretation
• Opponent process system
• S+ generates internal excitatory
gradient
• S- generates internal inhibitory gradient
• Actual generalization gradient (i.e.,
measured behavioural response) due to
net sum of excitatory and inhibitory
gradients
Actual
generalization
gradient (i.e.,
net sum)
excitatory
inhibitory
e.g., responses
Hypothetical
internal
gradients
S-
S- S+ S-
S-
Stimulus continuum
S-
Absolute/Relative Control
• Absolute interpretations
– Learn specifics of individual stimuli
– Spence’s theory is an absolute theory
• Relational interpretatsions
– Learn relationship between stimuli
Transposition Task
• Kohler (1939)
• Can a relational rule be transferred to a
new stimuli set?
Training
S+
S-
Testing
transfer
(relational)
absolute
Intermediate Size Problem
• Gonzales, Gentry & Bitterman (1954)
• Chimpanzees, visual display of squares
• Chimps choose intermediate size on
transfer test
Training
1
4
S+
Transfer Test
9
4
7
9
Training Technique
• Simultaneous discrimination training
– S+ and S- presented together
• Successive discrimination training
– S+ and S- presented alone on different
trials
• Relative stimulus control with
simultaneous
• Absolute stimulus control with
successive
Stimulus Equivalence Training
• Train subjects to treat dissimilar stimuli
as similar
• Training to generalize, not discriminate
• Categorization learning
Herrnstein, Loveland & Cable
(1976)
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•
•
•
•
Pigeons
Presence/absence pictures
S+: item present
S-: item absent
Various S+ stimuli: water, trees, people
Stimuli for Water as S+ Condition
S-
S+
Results
Trees
Water
People
Contextual Cues
• Context cues can exert stimulus control
• Perform behaviours appropriate to a
given context
Siegel (1975)
• Morphine tolerance
• Home room and injection room
• Same amount of morphine across 4
days
• Conditional compensatory response to
context cues of injection room
Perkins & Weyant (1958)
• Two groups of rats run through two
mazes, one white, one black; same
maze layout
• Half of each group tested in same
colour maze, half in opposite colour
maze
• Poor performance for rats tested in
opposite compared to same
Kamin (1957)
State-dependent learning
Rats; avoidance learning
Test at various retention intervals
Rats’ own internal physiology serves as
context cue
Avoidance (%)
•
•
•
•
100
50
0
12
24
36
48
60
72
Retention Interval (hr)
84
Akins (1985)
• Male quail sexual conditioning
• Arena with two compartments
– Sand floor, orange walls
– Wire-mesh floor and walls, green ceiling
• Individual subjects allowed to move back and
forth in baseline
– Less preferred compartment made CS+
• Conditioning
– Experimental group: CS+ paired with sexually
receptive female (US)
– Control group: US only in home cage, never in CS+
compartment
% time spent in
CS+ compartment
Results
Experimental
Control
1
2
Preference Tests
3
Conditional Relations
• Binary relations: between two events
(CS-US, operant-outcome)
• Modulator: a third event that determines
the nature of a binary relation
• Modulator signals a conditional relation
Modulators
• Instrumental
– S+: respond --> reinforcer
– S-: respond --> no reinforcer
• Classical
– “Facilitators” or “occasion setters”, not excitatory or
inhibitory conditional stimuli
– CS = noise, US = food, modulator = light
light
light
noise
noise
food
food
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