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PSY402
Theories of Learning
Wednesday
November 12, 2003
Chapter 7 – Stimulus Control
The Role of Environmental Stimuli
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In operant conditioning, the
stimulus becomes associated with
the reinforcer or punishment.
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Reward or punishment is the UCS.
The stimulus signaling reward or
punishment is the CS.
The CR motivates operant behavior.

Responding can be used as a measure
of the strength of a CR.
Definitions of Terms
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Stimulus control -- Environmental
stimuli signal the opportunity for
reward or punishment.
Generalization – responding in the
same way to similar stimuli.
Discrimination – responding to
some stimuli but not to others.
Generalization Gradient

Degrees of generalization occur.
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In some situations, the same response
occurs to similar stimuli.
In other situations, the amount of
response varies with the similarity.
Generalization gradient – a graph
showing how the strength of
response changes with similarity.

Steep gradients mean narrow response
(stimuli must be very similar).
Kinds of Gradients

Excitatory conditioning (S+) – a CSUCS response to a stimulus is
learned.

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Excitatory gradient – the S+ is varied
and the CR is measured.
Inhibitory conditioning (S-) – a CS
signals absence of the UCS and thus
inhibits the CR.

Inhibitory gradient – the S- is varied
and the CR is measured.
Shapes of Gradients

Most sensory stimuli produce similar
gradients.
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Pigeons pecking at colored lights.
Tones paired with shocks.
Words paired with pretzels or
candy:
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Synonyms and homonyms produce
salivation.
Semantic similarity works best.
Flat Gradients
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A flat gradient means all stimuli are
being responded to as if they were
the same.
Responding with a gradient to a
tone occurred only when the tone
signaled reward during training.
Generalization of Inhibition

Inhibition example: fear of dating.

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A good experience leads to less fear of
dating a different person.
Inhibition gradients are similar to
excitatory gradients – the more the
stimulus varies, the less inhibition.
Explanation

Lashley-Wade theory – people and
animals generalize because they are
unable to discriminate.


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Can’t tell the difference between stimuli
A contrast is needed during training to
enable discrimination.
Discrimination training leads to
steeper generalization gradients.
Perceptual experience matters.
Discrimination Learning
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Important to recognize when
reinforcement is not available so
that responding can be withheld.
Discriminative stimulus:

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SD – reinforcement is available (S+)
SD – reinforcement is unavailable (S-)
Conditioned stimuli always produce
a response. Discriminative stimuli
signal the opportunity to respond.
Two-Choice Discrimination Tasks

The discriminative stimuli are on the
same dimension:

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Red vs green light.
Need not be presented
simultaneously.
Two-choice discrimination includes
one SD and one SD .
Other tasks can use multiple
multiple SD or multiple SD.
Three Phases
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Subjects begin by responding
equally to both stimuli –
prediscrimination phase.
Discrimination phase -- with
training, response to SD increases
and response to SD declines.
Shift back to non-differential
reinforcement to show that behavior
was caused by reinforcement.
Conditional Discrimination
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Availability of reinforcement
depends on the condition of a
stimulus.
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The stimulus does not always signal the
same thing.
More difficult to learn.
Nissen’s chimpanzees:
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Large, small squares, white or black.
SD = large white, small black.
Behavioral Contrast
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Behavioral contrast – the increased
responding to the differential
stimulus, decreased response to SD
Contrast also occurs with changes in
the duration of reinforcement.

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VI-10 to VI-3
Local contrast – emotional
Sustained contrast – related to the
differential reinforcement.
Anticipatory Contrast
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Williams – sustained contrast occurs
due to anticipation of a future
reinforcement contingency.

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Not due to recall of past contingency.
VI-3, VI-6, VI-3
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Compare the first and third VI-3
behavior.
VI-6 affected the first VI-3 more than
the last VI-3 -- a prospective effect.
Occasion Setting
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A conditioned stimulus (CS) can
create the conditions for operant
responding to a second conditioned
stimulus (CS).
Occasion setting – ability of one
stimulus to enhance the response to
another stimulus.

The facilitating stimulus does not
produce a CR by itself.
SD as an Occasion Setter
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A Pavlovian occasion-setter can
increase operant responding.
Example:
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A meal elicits CR craving for cigarette.
Requesting a cigarette after a meal –
an operant behavior caused by CR.
Conditional occasion-setting:
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Second stimulus modifies meaning of
first discriminative stimulus.
Conclusions
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An occasion-setter can increase
operant responding.
A discriminative stimulus (SD) can
increase response to a CR
(Pavlovian conditioning).
This implies interchangeability of
Pavlovian occasion-setters and
discriminative stimuli.
Central Motivational States
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Conditioned stimuli influence
operant behavior through their
effect on motivational states:
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Appetitive
Aversive
Emotional responses influence
operant behavior.