PSYC 2330 Chapter Notes - Chapter 4: Conditioned Taste Aversion, Latent Inhibition, Drug Tolerance

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Chapter 4 Classical Conditioning: Mechanisms
What Makes Effective Conditioned and Unconditioned Stimuli?
Initial Responses to the Stimuli
According to Pavlov, the CS does not elicit the conditioned response initially, but comes to do so as a result of becoming
associated with US. By contrast, the US is effective in eliciting the target response from the outset without any special training
Pavlov’s definitions stated in terms of the elicitation of the response to be conditioned identifying potential CS’s and US’s
requires comparing responses elicited by each stimulus before conditioning makes identification of CS’s and US’s relative
A particular event may serve as CS relative to one stimulus, and as US relative to another
o E.g. a palatable saccharin solution for thirsty rats. Taste may serve as CS in taste aversion conditioning procedure, with
illness as US. Conditioning trials consist of exposure to saccharin flavour followed by drug that induces illness, and
participant acquires aversion to saccharin solution
o Same saccharin solution also serve as US in sign-tracking experiment. Conditioning trials involve presenting a signal
light (CS) just before each presentation of small amount of saccharin in a cup (US). After number of trials, animals
would begin to approach light CS; whether saccharin solution considered US or CR depends on relation to other stimuli
in situation
Novelty of Conditioned and Unconditioned Stimuli
Latent Inhibition or CS Preexposure
o Studies show if stimulus is highly familiar, it will not be as readily associated with US as novel stimulus
o Experiments involve 2 phases, first given repeated presentations of the CS by itself (called preexposure phase, comes
from Pavlovian conditioning trials). CS preexposure makes CS highly familiar and of no particular significance because
at this point CS presented alone and without consequence. After preexposure phase, CS paired with US using classical
conditioning, Subjects slower to respond because of CS preexposure
CS preexposure inhibits or disrupts learning
o Latent inhibition and habituation both serve to limit processing and attention to stimuli that are presented by themselves
and are inconsequential
o Habituation serves to bias elicited behaviour in favour of novel stimuli; latent inhibition serves to bias learning in favour
of novel stimuli
o Latent inhibition is reduced in acute schizophrenic patients who recently started medication and is also attenuated in
normal individual who are high on schizotypal personality scale (involvement of neurotransmitter dopamine in
schizophrenia, not surprising that latent inhibition is reduced by dopamine receptor agonists and enhanced by dopamine
receptor antagonists)
The US Preexposure Effect
o Subjects given repeated exposures to US presented by itself. US then paired with CS and progress of learning
monitored. Subjects familiarized with US before pairings with CS are slower to develop conditioned responding to the
CS than participants for whom US is novel during CS-US pairings
o Analyses of this effect have emphasized an associative interference mechanism. Presentations of the US during the
preexposure-phase conditions cues related to US administrations.
o May be contextual cues of the situation in which US is presented. If US is drug, cues related to injecting drug can
become conditioned during preexposure phase
o Presence of these cues during subsequent conditioning phase disrupts subsequent learning
CS and US Intensity and Salience
Most biological and physiological effects of stimulation related to intensity of stimulus input true of Pavlovian conditioning
More vigorous conditioned responding occurs when more intense CS and US are used
Stimulus Salience corresponds to significant or noticeability
Learning will occur more rapidly with more salient stimulus by making stimulus more intense (attention-getting), can make it
more salient, also by making it more relevant to the biological needs of the organism
o E.g. animal become more attentive to taste of salt if they suffer a nutritional salt deficiency; rats with sodium deficiency
learn stronger aversions to taste of salt than nondeficient control subjects
Increase salience of CS to make it more similar to kinds of stimuli an animal is likely to encounter in its natural environment
CS-US Relevance, or Belongingness
Importance of stimulus relevance first demonstrated in classic experiment by Garcia and Koelling
o Compared learning about peripheral pain (induced by foot shock) and learning about illness (induced by irradiation or
drug injection) in study with lab rats
o In natural environment, rats likely to get sick after eating poisonous food. Likely to encounter peripheral pain after being
chased and bitten by predator they can see/hear
o Food-related cue = flavour solution of water as CS, predator-related cues = audiovisual CS
o Rats drink water from tube before admin of one of US, water tube either salty or sweet; each lick activates brief
audiovisual stimulus (click and flash of light) rats encountered both taste and audiovisual stimulus at same time, after
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received either brief shock through floor or made sick. Because US used were aversive, rats expected to learn aversion
of some kind.
o Measured response to animals to taste and audiovisual CSs presented individually after conditioning. During tests of
taste CS, water flavoured as before, but now licks not activate audiovisual cue. During tests of audiovisual CS, water
unflavoured, but audiovisual cue briefly turned on each time animal licked spout
o Degree of conditioned aversion to taste or audiovisual CS inferred from suppression of drinking
Animals conditioned with shock subsequently suppressed drinking much more when tested with audiovisual
stimulus than when tested with taste CS. Opposite occurred for animals that have been conditioned with
sickness. Rats suppressed drinking much more when taste CS was presented than when drinking produced
audiovisual stimulus
Demonstrates principle of CS-US relevance, or belongingness
o Selective-Association effect extensive experience with tastes and sickness (or audiovisual cues and peripheral pain) is
not necessary for stimulus-relevance effect. Reflects genetic predisposition for selective learning of certain combos of
CS and US
o Stimulus-relevance effects prominent in acquisition of fear in primates
Learning Without an Unconditioned Stimulus
Higher-Order Conditioning
o Irrational fears often develop through H-OC
E.g. Fear of crowds. Being in crowd is CS that elicited conditioned fear. Perhaps you were pushed in crowd
(CS) and suffered an injury (US). Only go to movies during the day, but if theatre gets busy could associate
theatres with crowds. Thus, one CS had conditioned fear to another (theatre) that previously elicited no fear
o Occurs in 2 phases
Phase 1 cue (CS1) paired with US often enough to condition strong response to CS1. Once CS1 elicited
conditioned response, pairing CS1 with new stimulus CS2 able to condition CS2 to also elicit conditioned
response. Conditioning of CS2 occurred in absence of US
o “Higher order” implies, conditioning may be considered to operate at different levels
1st order conditioning = CS1 paired with US
2nd order conditioning = CS2 paired with CS1, and so on.
Sensory Preconditioning
o Associations can also be learned between 2 stimulus, each of which elicits only mild orienting response before
conditioning
o 2-stage process - CS1 and CS2 become associated with one another (with no US)
CS1 paired with US and conditioned aversion (CR) develops to CS1
Help us make sense of things we seem to like or dislike for no apparent reason
What Determines the Nature of the Conditioned Response?
The Stimulus-Substitution Model
Association of CS and US turns CS into surrogate US. CS comes to function much like US did previously. Thus, CS assumed to
activate neural circuits previously activated only by US and elicit responses similar to US
Pavlov suggested that conditioning results in establishment of new functional neural pathways
o During course of repeated pairings of CS and US, ne connection develops between neural circuits previously activated
by CS and circuits previously activated only by US. Once new connection been established, presentation of CS results in
activation of US circuits, which in turn generate behaviour similar to UR
o According to Pavlov, conditioning makes CS a substitute for US
The US as Determining Factor for CS
o Different US elicit different URs. Food elicits salivation and approach, while shock elicits aversion and withdrawal
o If conditioning turns CS into surrogate US, CSs conditioned with different USs should elicit different types of CRs
o Jenkins and Moore compared Pavlovian conditioning in pigeons with food vs. water as US
Pigeon eating grain makes rapid, hard pecking movements directed at the grain with its beak open just before
contact with piece of grain
Pigeon drinks by lowering its beak into water with beak mostly closed, then once under water, beak opens and
shuts periodically
URs of eating and drinking differ in both speed and form
Interested in whether responses conditioned with food and water would differ in corresponding
fashion
CS was illumination of pecking key for 8 seconds. CS was paired with either presentation of grain or access to
water. Conditioning resulted in pecking of key light in both cases
Form of CR differed depending on US
When food = US, pigeons pecked key light a if eating (rapid and with beak open a moment of contact)
When water = US, pecking movements slower with beak closed and often accompanied by
swallowing
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