Classical
Conditioning II
Generalization/Discrimination
Temporal Parameters
Generalization and
Discrimination
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Generalization: Responding to a new
stimulus, based on its similarity to the CS
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Example: child fears a dog because the child was
once bitten by another dog.
Discrimination: Responding differently to a
new stimulus, despite its similarity to the CS
Generalization and discrimination are two
ends of the same dimension.
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More generalization = less discrimination
More discrimination = less generalization
Procedure for Assessing
Generalization/Discrimination
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Pair CS with UCS repeatedly, until the CS
evokes a strong CR (e.g., pair a tone with
food).
In extinction, test a variety of stimuli that
differ from the CS to varying degrees along
some dimension. Record the strength of CR
to each (e.g., test tones of various pitches).
Plot a generalization gradient based on these
data.
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Generalization Gradient
CS
Drops of Saliva
30
25
20
Less responding due
to discrimination
15
10
Responding due to
generalization
5
0
900
950
1000
1050
1100
Tone Frequency (Hz)
Example of Complete
Generalization
CS
Drops of Saliva
30
25
20
15
Other stimuli responded to as
strongly as the original CS
10
5
0
900
950
1000
1050
1100
Tone Frequency (Hz)
Example of Complete
Discrimination
Maximum response
to CS
Drops of Saliva
30
25
20
No response to
other stimuli
15
10
5
0
900
950
1000
1050
1100
Tone Frequency (Hz)
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Importance of Generalization
and Discrimination
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Generalization allows us to respond
adaptively when we encounter situations
similar to those we have experienced before.
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“If one dog bit us, maybe this one will, too. Better
be careful!”
Discrimination allows us to respond
differently after we have had experience with
the new situation.
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“Hey, this dog is friendly. No need to worry!”
Temporal Parameters:
Effect of Order and Timing of Stimuli
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Classical conditioning procedures differ in the
order and timing of CS and UCS, and in their
effects. Procedures include:
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Forward conditioning
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Delay conditioning
Trace conditioning
Simultaneous conditioning
Backward conditioning
Temporal conditioning
Delay Conditioning
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The CS begins, continues for some time,
then ends with the delivery of the UCS.
This is the most effective procedure, if the
delay between the start of the CS and the
delivery of the UCS is optimal (5-10 seconds
for salivary conditioning).
Making the delay longer or shorter than the
optimal reduces effectiveness.
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Trace Conditioning
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CS appears briefly (e.g., 1 second), followed
by a trace interval (during which the CS and
UCS are both absent), ending with delivery of
the UCS.
Effective, but less so than delay conditioning
with the same interval between the start of
the CS and delivery of the UCS.
Pavlov thought that association between CS
and UCS was weakened because the CS
was not present when the UCS occurred.
Simultaneous Conditioning
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The CS and UCS are presented together, as
a unit (i.e., simultaneously).
This procedure maximizes the temporal
contiguity between CS and UCS, so one
might expect it to be highly effective.
However, it is almost completely ineffective.
Thus, it appears that, to be effective, the CS
must act as a signal for the UCS.
Backward Conditioning
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The UCS is presented first, then the CS.
(This reverses the usual order, thus the name
backward conditioning.)
Pavlov thought that this procedure was
ineffective. However, Pavlov was wrong.
This procedure transforms the CS into an
inhibitory stimulus. An inhibitory CS has to
power to suppress a response rather than
evoke one.
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Temporal Conditioning
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This procedure is unusual in that there is no explicit
CS being presented by the experimenter.
The UCS is presented at regular intervals (e.g.,
once every 30 seconds).
After many UCS deliveries, the subject begins to
produce a CR just before each UCS delivery.
Internal, time-correlated stimuli can function as an
implicit CS.
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