Download LT2Ch7

PSY402
Theories of Learning
Chapter 7 – Stimulus Control
For Midterm 2


As stated in class, Chapter 7 will be on
the next midterm.
The slide in the Chap 5 materials stating
that Chap 7 would not be on the midterm is
incorrect (leftover from a previous quarter).


It has now been deleted from the set of slides.
Please send me an email if you have any
questions about what the next midterm will
cover.
The Role of Environmental Stimuli

In operant conditioning, the
stimulus becomes associated with
the reinforcer or punishment.



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



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.



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.


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.



Pigeons pecking at colored lights.
Tones paired with shocks.
Words paired with pretzels or
candy:


Synonyms and homonyms produce
salivation.
Semantic similarity works best.
Flat Gradients


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.


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.




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


Important to recognize when
reinforcement is not available so
that responding can be withheld.
Discriminative stimulus:



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:




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



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

Availability of reinforcement
depends on the condition of a
stimulus.



The stimulus does not always signal the
same thing.
More difficult to learn.
Nissen’s chimpanzees:


Large, small squares, white or black.
SD = large white, small black.
Behavioral Contrast


Behavioral contrast – the increased
responding to the differential
stimulus, decreased response to SD
Contrast also occurs with changes in
the duration of reinforcement.



VI-10 to VI-3
Local contrast – emotional
Sustained contrast – related to the
differential reinforcement.
Anticipatory Contrast

Williams – sustained contrast occurs
due to anticipation of a future
reinforcement contingency.


Not due to recall of past contingency.
VI-3, VI-6, VI-3


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


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


A Pavlovian occasion-setter can
increase operant responding.
Example:



A meal elicits CR craving for cigarette.
Requesting a cigarette after a meal –
an operant behavior caused by CR.
Conditional occasion-setting:

Second stimulus modifies meaning of
first discriminative stimulus.
Conclusions



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

Conditioned stimuli influence
operant behavior through their
effect on motivational states:



Appetitive
Aversive
Emotional responses influence
operant behavior.