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What makes effective Conditioned and Unconditioned Stimuli?
• Classical conditioning procedures do not always result in learning
• Just pairing two stimuli together does not necessarily result in
information being stored in the brain, depends on:
– timing of stimuli
– characteristics of the CS
– characteristics of the US
Initial responses to the stimuli
• Based on Pavlov’s definitions
– CS – does not elicit the CR initially (usually biologically weak)
– US – elicits the target response without any special training (usually biologically
strong)
– Need to evaluate responses to determine biological strength
• However, a particular stimulus “food” can be a CS or as a US
– Food is a special case because
• it has several sensory cues, visual, odor, taste
• as well as biological consequences, nutrition, toxins and so on
– Sucrose food pellets – a tasty treat that rats like
• Sucrose food pellets can serve as the CS in a taste-aversion experiment where
illness is the US
• The same sucrose food pellets could serve as the US in sign tracking
– light ---> Sucrose food pellets pairings in a sign tracking procedure
– The animal would approach the light
The Novelty of Conditioned and Unconditioned Stimuli
• The behavioral impact of a stimulus depends on its novelty
• Familiar stimuli do not elicit as vigorous a response as do novel
stimuli (i.e., Habituation)
• Stimulus novelty is also important for classical conditioning
• If the CS and/or the US are familiar, conditioning proceeds more
slowly than if they were novel (note: can still get conditioning)
• Testing the role of stimulus novelty involves 2 phases:
– (1) preexposure of the stimulus only
– (2) conditioning of CS – US
CS-Preexposure effect or Latent Inhibition
• Phase 1: Preexposure - Subjects are given repeated presentations
of the CS alone
– is similar to habituation because the repeated preexposure to the CS limits
the processing of, or attention to the stimulus
– is due to a stimulus-specific decline of attention
– more processing of new inputs and less processing of older unimportant
ones
– helps preserve limited attentional resources
• Phase 2: Conditioning - Subjects are given pairings of the CS with
the US
– Preexposore of the CS retards learning called “Latent Inhibition”
• Recent models of latent inhibition are based on retrieval
competition concepts
CS-preexposure effect “Latent Inhibition”
• Evidence That latent inhibition Is Modulated by Attentional
Processes
• modulation of latent inhibition by attentional processes that are
governed by attentional variables
• latent inhibition is reduced by manipulations that maintain or
restore attention
– a second, neutral, stimulus is paired with the target stimulus on each of its
preexposure presentations (masking task)
– salience of the stimulus
Latent Inhibition Models of Schizophrenia
• Latent inhibition measures for Schizophrenia
– latent inhibition effects on attentional processes
– selective attention disorder, as represented by high distractibility, is central to
schizophrenia
– nonmedicated acute schizophrenia patients show reduced latent inhibition
compared to normal subjects
• Nature of Attentional Dysfunction in Schizophrenia
– healthy subjects show latent inhibition during the early stages of
conditioning
– schizophrenics have perseveration of latent inhibition
– due to a failure to shift from controlled to automatic processing
US-preexposure effect
• Experiments on the importance of US novelty are designed in a
similar way to CS novelty
• Phase 1: Preexposure - Subjects are given repeated presentations
of the US alone
• Phase 2: Conditioning - Subjects are given pairings of the CS with
the US
• The initial preexposure to the US usually retards subsequent
Conditioning
• This may be due to conditioning of background cues during the
preexposure phase
• Pre-exposure effects have two explanations
– Associative Interference - stimuli are less able to form associations
– Memory Interference - memory of preexposure interferes with memory of
conditioning
The Principles of Learning and Behavior, 7e by Michael Domjan
Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved.
CS and US Intensity and Salience
• Stimulus salience
– refers to the significance or noticeability of the stimulus
– Within limits Learning occurs more rapidly with more salient, or more
noticeable stimuli
– Intensity increases salience due to greater noticeability
– Stimuli relevant to the biological needs of the animal
• can increase the salience of a salt taste by depriving the animal of salt
• CS Salience
– A more intense CS also results in better conditioning
• This makes sense from an ecological point of view
• a more intense CS will be more salient than the background and will command
more attention
• With CTA, a stronger concentration of flavor results in bigger taste aversions
– using a CS similar to stimuli animals might encounter in the natural
environment such as realistic quail models,
• see figure 4.2
The Principles of Learning and Behavior, 7e by Michael Domjan
Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved.
CS-US Relevance, or Belongingness
• Rate of Classical Conditioning is also affected by the extent to which
the CS is relevant to or belongs with the US
– The importance of stimulus relevance was demonstrated in an experiment by
Garcia & Koelling (1966) see figure 4.3 and figure 4.4
• They compared learning about peripheral pain (footshock) and learning about
nausea type of illness
• In nature, rats are likely to get sick after eating poisonous food, but experience
peripheral pain after an encounter with a predator
• Rats that got poisoned decreased saccharin consumption
• Rats that got shocked decreased consumption of the ‘bright and noisy’ water
• This experiment suggests that tastes are more readily associated with sickness
than with shock (peripheral pain) and that audiovisual cues (LN) are more readily
associated with pain/shock than with sickness
• We see evidence of this selectivity of association in other species
– For example
• certain birds locate food by its visual characteristics, rather than by its taste
• rats find food mostly by odor
• foxes use auditory information
The Principles of Learning and Behavior, 7e by Michael Domjan
Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved.
The Principles of Learning and Behavior, 7e by Michael Domjan
Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved.
Learning without an Unconditioned Stimulus
• In the early research on classical conditioning the US - UR
relationship was seen as essential for learning
– Some sort of physiological reflex or response system that could be
conditioned with a sensory cue the CS
– This is OK for many basic examples such as salivary reflex, eyeblink or even
nausea from eating bad food
• However there are applied situations that are more complex then
this where identifying a US - UR relationship may not be possible
– Cues in the environment, such as sounds, odors or visual stimuli can be
associated with each other.
– Wolves may detect an odor, hear a sound and see some movement while
searching for food before actually getting contact with the food.
Higher-order Conditioning
• Historical background
– Initially, the CS is weaker than the US
– But after conditioning, the CS is strong and elicits a vigorous response
– Could the strong CS now serve as a US?
• Procedure : See figure 4.5
– A stimulus (CS) that has become strongly conditioned may serve as a US
– CS1(tone) - US(food); CS1(tone) -> CR (first-order)
– CS2(light) - CS1(tone); CS2(light) -> CR (second-order)
– CS3(buzzer) - CS2(light); CS3(buzzer) -> CR (third-order)
• Examples
– Money is a powerful CS for humans although money is not always closely
paired with a US
• buy some food and then eat the food later
– Crowds can be a powerful fear stimulus (CS) for some people without ever
being paired with an aversive US.
The Principles of Learning and Behavior, 7e by Michael Domjan
Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved.
Sensory Preconditioning
• Both stimuli elicit weak biological responses before conditioning
See figure 4.6
–
–
–
–
1. CS2(light) -> CS1(tone) sequential pairing
2. CS1(tone) -> US(food) -> CR
Test: CS2(light) -> CR
Note: the Domjan book example of vanilla - cinnamon in food is a confusing
example because food can be a US and the flavors are presented
simultaneously.
• This challenges the concept of differential biological strength
• Biological Strength as a facilitator of performance rather than
learning
• In sensory preconditioning, the initial CS2->CS1 association is
“mute” does not produce a response
• Making the CS1 biologically strong, allows expression of the
association with CS2
• Not all associations are directly evident in behavior
CS2
The Principles of Learning and Behavior, 7e by Michael Domjan
Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved.