Transposition:
Spence’s Behavioral Solution
Transposition seems to support the cognitive view that
organisms learn by discovering how things are related,
like, “the darker of the two objects leads to food.”
This implies that subjects compare the objects through
some kind of mental process rather than look at each
object separately.
The traditional behavioral view is that an association is
formed between a response and a specific stimulus;
there is no comparison between stimuli.
Transposition:
Spence’s Behavioral Solution
?
How can the apparent
transposition (transfer) of a
relationship be explained without
assuming that the subject sees a
relationship?
Transposition:
Spence’s Behavioral Solution
Kenneth W. Spence developed a general theory of
discrimination learning that not only explained
transposition but revealed a shortcoming in
cognitive theory.
The theory used existing behavioral concepts:
reinforcement, extinction, excitation, inhibition,
and stimulus generalization.
Transposition:
Spence’s Behavioral Solution
Reinforcement
Reinforcing a response to a stimulus increases the
tendency to respond to that stimulus again. This
tendency is called excitation.
Extinction
Not reinforcing a response to a stimulus decreases
the tendency to respond to that stimulus again.
This reduced tendency to respond is called
inhibition.
Transposition:
Spence’s Behavioral Solution
Excitatory Stimulus Generalization
After reinforcing a response to a stimulus, that
response will tend to occur to similar stimuli. The
greater the similarity, the stronger the response
will be.
Transposition:
Spence’s Behavioral Solution
Inhibitory Stimulus Generalization
After extinguishing (not reinforcing) a response to
a stimulus, that response will tend to be
suppressed in the presence of similar stimuli. The
greater the similarity, the strong the suppression
will be.
Transposition:
Spence’s Behavioral Solution
Excitatory Stimulus Generalization
Let’s illustrate this process using a pigeon
responding for food in an operant chamber:
Pecks on the disk (or
“key”) are reinforced
on a VI schedule. The
key is lit green.
Transposition:
Spence’s Behavioral Solution
Excitatory Stimulus Generalization
We then put the pigeon on extinction (no food for
pecking). Every minute, we change the color of
the key.
The bird will peck thousands of times without food.
We count how many responses are made to each
color.
Transposition:
Spence’s Behavioral Solution
Excitatory Stimulus Generalization
Here is a graph that shows typical results:
Number of
Responses
Wavelength
Transposition:
Spence’s Behavioral Solution
Inhibitory Stimulus Generalization
The pigeon receives discrimination training using
the following stimuli:
Discriminative Stimulus: White
Triangle on Gray Background; VI
reinforcement schedule.
Delta Stimulus: White Triangle on
Blue Background; no food
(extinction).
Transposition:
Spence’s Behavioral Solution
Inhibitory Stimulus Generalization
We keep switching back and forth:
The pigeons forms a discrimination, pecking a lot
when the background is gray but pecking very
little when the background is blue. Basically,
“blue” means STOP.
Transposition:
Spence’s Behavioral Solution
Inhibitory Stimulus Generalization
Next, we put the pigeon on extinction—no food.
The white triangle is projected on the key and we
change the color of the background every minute.
We count the number of pecks to the key in the
presence of each color.
Transposition:
Spence’s Behavioral Solution
Inhibitory Stimulus Generalization
Here is a graph that shows typical results:
Number of
Responses
Wavelength
Transposition:
Spence’s Behavioral Solution
Application to Transposition
Through stimulus generalization, the same
stimulus may produce both excitation and
inhibition. Will the subject respond or not respond
to that stimulus? Spence assumed that the
likelihood of responding could be estimated as
follows: Excitation - Inhibition
Here are some examples. Suppose that we have
measured the amount of excitation and inhibition
produced by each stimulus. Which stimulus is
more likely to produce a response?
Transposition:
Spence’s Behavioral Solution
Which Stimulus is More Likely
to Produce a Response?
Excitation = 7
Inhibition = 6
Excitation = 10
Inhibition = 4
Transposition:
Spence’s Behavioral Solution
Which Stimulus is More Likely
to Produce a Response?
Excitation = 10
Inhibition = 4
Excitation = 8
Inhibition = 1
Transposition:
Spence’s Behavioral Solution
Which Stimulus is More Likely
to Produce a Response?
Excitation = 8
Inhibition =
1
Excitation = 5
Inhibition = 0
Transposition:
Spence’s Behavioral Solution
The Transposition Experiment:
Training Phase
Excitation
or
Inhibition
VS
Brightness Dimension
Which
stimulus is
more
likely to
produce a
response?
Transposition:
Spence’s Behavioral Solution
The Transposition Experiment:
Test Phase
Excitation
or
Inhibition
VS
Brightness Dimension
Which
stimulus is
more
likely to
produce a
response?
Transposition:
Spence’s Behavioral Solution
The Transposition Experiment:
New Test Phase
Excitation
or
Inhibition
VS
Brightness Dimension
Which
stimulus is
more
likely to
produce a
response?
Transposition:
Spence’s Behavioral Solution
Surprising Prediction
Spence’s theory predicts that if the test stimuli are
far away from the training stimuli, transposition
will break down. The subject will choose the
lighter of the two stimuli.
Cognitive theory predicts that the subject will
continue to choose the darker of the two stimuli.
Spence’s prediction is confirmed! Transposition
breaks down. A big boost for the behaviorists!