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Chapter 4

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University of Guelph
PSYC 2330
Francesco Leri

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 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 (CS 1 paired with US often enough to condition strong response to CS1. Once CS 1licited conditioned response, pairing CS1with new stimulus CS a2le to condition CS t2 also elicit conditioned response. Conditioning of CS 2ccurred in absence of US o “Higher order” implies, conditioning may be considered to operate at different levels st  1ndrder conditioning = CS 1aired with US  2 order conditioning = CS2paired with CS 1 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 - CS and CS become associated with one another (with no US) 1 2  CS 1aired with US and conditioned aversion (CR) develops to CS 1  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 Learning and Homeostasis: A Special Case of Stimulus Substitution  Homeostasis – introduced by Walter Cannon to refer to physiological mechanisms that serve to maintain stability of critical physiological functions  Achieving homeostasis requires that challenge to homeostatic level trigger compensatory reaction that will neutralize disturbance o Include peripheral vasoconstriction and shivering – operates through negative feedback loop  Dworkin (1993) pointed out challenges to homeostasis that can be corrected more effectively if those challenges are anticipated o Pavlovian conditioning provides mans for such feed-forward anticipation o Warm-blooded animals learn about cues that signal when they will get cold – enables them to make feed-forward compensatory adjustments in anticipation of cold and avoid suffering drop in body temperature  CR to physiological challenge is same as reflexive compensatory response to challenge – CR is same as UR, but UR is compensatory reaction to physiological disturbance  Drugs often cause physiological challenges to homeostasis that trigger unconditioned compensatory reactions – cues that become associated with drug-induced physiological challenge can come to activate compensatory reactions as anticipatory or feed- forward CRs  The Conditioning Model of Drug Tolerance o Tolerance to drug is said to develop when repeated administrations of the drug have progressively less effect  Increasing doses are required to produce the same drug effect o Conditioning Model of Drug Tolerance – view that drug tolerance can result from Pavlovian conditioning of homeostatic compensatory processes  Assumes that each drug-taking episode is conditioning trial and is built on idea of learned homeostasis  Administration of psychoactive drug causes physiological changes that disrupt homeostasis – changes in turn trigger unconditioned compensatory adjustments to counteract disturbance  Stimuli that accompany drug administration become conditioned to elicit these compensatory adjustments. Impact of drug is reduced, resulting in phenomenon of drug tolerance  Attributes tolerance to compensatory responses conditioned to environmental stimuli paired with drug administration  Drug tolerance will be reduced if participants receive drug under novel circumstances or in the absence of the usual drug predictive cues  Various factors (such as CS preexposure) that attenuate the development of conditioned responding will also attenuate the development of drug tolerance The CS as a Determinant of the Form of the CR  Form of CR also influenced by the nature of CS  Timberlake and Grant investigate classical conditioning in rats with food as US. Instead of conventional tone/light, CS was presentation of another rat 10 seconds before food delivery through flap door on one side of experimental chamber  Stimulus-substitution model predicts CS-US pairings will generate responses to CS that are similar to responses elicited by food US  Since food US elicited gnawing and biting, these responses were also expected to be elicited by CS  Contrary to prediction, CS did not elicit gnawing and biting; rather, as CS rat was repeatedly paired with food, it came to elicit social affiliate responses (orientation, approach, sniffing, social contacts). Responses did not develop if CS rat was not paired with food or was presented at times unrelated to food o Outcome does not support any model that explains form of CR solely in terms of US that is used o Conditioned social responses that were elicited by CS rat were no doubt determined by having another rat serve as CS Conditioned Responding and Behaviour Systems  Different systems of behaviour have evolved to enable animals to accomplish various critical tasks (e.g. eating, producing and raising offspring)  Behaviour systems theory assumes that presentation of US in Pavlovian conditioning procedure activates behaviour system relevant to that US o Food-US activates foraging and feeding system. Classical conditioning procedures involve superimposing a CS-US relationship on behavioural system activated by US o As conditioned stimulus becomes associated with US, becomes integrated into behavioural system and comes to elicit component responses of that system  Especially provocative prediction of behaviour systems theory is that form of CR will depend on CS-US interval that is used. CS- US interval assumed to determine where CS becomes incorporated into sequence of responses that makes up behaviour system  Developed most extensively by William Timberlake and is consistent with much of what we know about nature of classically conditioned behavioural responses o Theory is clearly consistent with fact that the form of CRs is determined by the nature of the US, since different USs activates different behaviour systems; also, form of CR is determined by the nature of the CS o Nature of CS is expected to determine how the CS becomes incorporated into the behaviour system S-R versus S-S Learning  Conditioned behaviour viewed as response elicited directly by CS  Conditioning establishes new stimulus-response or S-R connection between CS and CR  Alternative view is that subjects learn new stimulus-stimulus or S-S connection between CS and US  Participants respond to CS not because it elicits CR directly, but because the CS activates a representation or memory of US.
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