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PSY 402
Theories of Learning
Chapter 3 – Nuts and Bolts of Conditioning
(Mechanisms of Classical Conditioning)
Classical vs. Instrumental

The modern view is that these two types of learning
involve similar learning processes, but differ in the
following ways.
1.
2.
In Classical conditioning, two stimuli are associated with
each other but in Instrumental conditioning, a stimulus
and a response are associated.
In Classical conditioning, the response is a reflex or
involuntary action but in Instrumental conditioning, the
response is a voluntary, freely emitted behavior.
Pavlov’s Conditioned Reflex


Conditioning -- a stimulus that initially
produces no response can acquire the ability
to produce one.
Learning occurs through pairing in time and
place of one stimulus with another stimulus
that produces an involuntary response.
Political Classical Conditioning
Terminology of Conditioning

Unconditioned stimulus (US or UCS)


Elicits a reflexive response without learning.
Unconditioned response (UR or UCR)


The response that occurs with a US, typically a
reflex, emotion or drug state
Involuntary and automatic.
More Terminology

Neutral stimulus


Conditioned stimulus (CS)


A stimulus not capable of producing an
unconditioned response (before learning).
A previously neutral stimulus that has acquired
the ability to evoke a response.
Conditioned response (CR)

The learned response, often similar to the UCR,
an involuntary reflex, emotion or drug state.
Prior to conditioning
Neutral stimulus
(tone)
(Orientation to sound
but no response)
UCS
(food powder in mouth)
UCR
(salivation)
During Conditioning
Neutral stimulus
CS (tone)
+
UCS
(food powder)
CR
(salivation)
After conditioning
CS
(tone)
CR
(salivation)
Conditioning Processes



Stimulus generalization – stimuli like the CS
become able to evoke the conditioned
response.
Extinction – if the UCS and CS are not paired,
the CS loses its ability to produce a
conditioned response.
Spontaneous recovery – an extinguished CS
briefly returns but quickly goes away again.
What is Learned?

Pavlov believed the association was between
the two stimuli (tone and meat powder), not
between the tone and salivation.
Either is
possible
Stimulus substitution
Conditioning Situations

Sign-tracking (autoshaping) – animals must
recognize signs of food (UCS) and respond
(UCR).

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
Pigeons pecking at key.
UCR, not an operant response, because behavior
is specific to the stimulus.
Eyeblink conditioning


UCR is rapid, CR is slow.
Many trials are needed (100 pairings)
3.7 Autoshaping in pigeons (Part 1)
3.7 Results of autoshaping tests in pigeons (Part 2)
3.5 Design of eyeblink conditioning experiment in rabbits (Part 1)
3.5 Results of eyeblink conditioning experiment in rabbits (Part 2)
Conditioned Emotional Responses



Fear is an anticipatory pain response based on
past experience.
Fear is conditioned (becomes a CR) whenever
a CS is associated with an aversive (painful or
undesirable) event.
Fear motivates two responses:


Escape (when pain is present)
Avoidance (when pain is imminent)
Fear conditioning


Avoidance is not a good measure of fear.
Suppression of an operant behavior occurs
with a feared stimulus.


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First – an operant behavior is learned.
Second – a CS is paired with an aversive UCS.
Third – the CS is presented in the operant
chamber and the effect on operant responding is
measured.
3.6 Conditioned suppression in rats (Part 1)
Suppression Ratio
During CS
Suppression Ratio =


During CS + Without CS
The amount of time during and without the CS is
equal.
The more fear, the lower the suppression ratio.


Ratios typically fall between 0 and .5
This will be on the midterm
3.6 Conditioned suppression in rats (Part 2)
Flavor Aversion Learning

Garcia – rats will not drink water with
saccharin if they get ill after drinking.


Significant avoidance occurs after just one trial.
Human food aversions are related to illness
(89%).

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Even if illness occurs hours later it is linked to the
previous meal.
Not cognitive – you can know the food is not to
blame and still feel an aversion to it.
Acquired Changes in Response


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Habituation – response to a repeated stimulus
decreases with non-threat experience.
Sensitization – response to a variety of stimuli
increases with a single threat experience.
Examples:

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Ingestional neophobia, fear of new food
Rats orient less toward light, startle decreases
Chicks are less frightened by shadows flying
overhead with repeated exposure.
Factors Affecting Conditioning

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Timing – how closely in time are the CS and
UCS, and which occurs first.
Novelty of the CS and UCS.
Intensity (strength) of the CS and UCS.
Consistency of the pairing between the CS
and UCS.

If one or the other appears alone then
conditioning is weakened.
Stimulus Presentation Paradigms
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Delayed conditioning – the CS onset precedes
the UCS onset.
Trace conditioning – the CS starts and ends
before the UCS onset.
Simultaneous conditioning – the CS and UCS
occur together.
Backward conditioning – the UCS starts and
ends before the CS onset.
These paradigms will be on the midterm
3.8 Different ways to present CS and US in time
This works best
The longer the gap (trace interval) the worse this works
This isn’t as good as delayed
This doesn’t work at all
Massed vs Spaced Trials


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Better learning occurs when trials are spaced
out over time (spaced), rather than bunched
together (massed).
Memory consolidation or rehearsal may be
needed between trials.
The ratio between the exposure to the CS and
the time in-between is the important factor.

If both are the same duration, learning is weaker.
3.9 Trial spacing in Pavlovian conditioning
This works best
This doesn’t work as well
Importance of Novelty

Preexposure to the CS (before it is paired with
the UCS) reduces learning.


The same thing happens with preexposure to
the US (before it is paired with the CS).


Called latent inhibition because it inhibits
learning of the CS-UCS association.
Called the US preexposure effect
Other, more novel stimuli are more likely to
become associated with the UCS.
Stimulus Intensity (Strength)


The stronger the US (UCS), the faster the
learning and the stronger the association.
The stronger the CS, the better the learning.

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Salience – how attention-getting the stimulus is in
relation to other stimuli in the environment.
The most salient CS becomes associated with the
UCS.
An overpowering CS may elicit a response of
its own, preventing learning.
Pseudo-conditioning

Responses to the CS may occur due to the
strength of the UCS, not learning.

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Once air has been puffed at the eye, blinking may
occur in response to any stimulus that comes
next, without any learning.
Sensitization resulting from an intense UCS may
cause the response to a CS to be increased, even
when there is not greater learning.
A control group lets you tell the difference.
3.10 Bernstein’s experiment on taste aversion learning