W9 CC.pdf PDF - Classical Conditioning Continued

Classical Conditioning Continued PSYU2236/PSYX2236 Biopsychology & Learning Lecturer: Dr Patrick Nalepka (he/him) Reminders The Research Report and Written Reflection are due by the end of this week (11:55pm Sunday, 6th September) Reminder that Tutorial 4 starts next week (Week 10) Tuto...

Classical Conditioning Continued PSYU2236/PSYX2236 Biopsychology & Learning Lecturer: Dr Patrick Nalepka (he/him) Reminders The Research Report and Written Reflection are due by the end of this week (11:55pm Sunday, 6th September) Reminder that Tutorial 4 starts next week (Week 10) Tutorials scheduled for 7 October are not running due to public holiday. Affected should attend a different session. The next lecture topic is “Operant Conditioning” (recorded due to public holiday) Reading: Mazur Textbook Chapters 5-6 titled "Basic Principles of Operant Conditioning" and "Reinforcement Schedules: Experimental Analyses and Applications“ Make use of our PSYUX2236-2024-S2 Team for unit discussions, ask questions, or help answer questions from your peers! Revision Ingredients: , , , , We learn to form an association between something that is meaningful to us, with something First-order Classical Conditioning: that has no objective meaning to us 1. + = (the bell) 2. = I don't really understand second order conditioning In 1st order, the bell= food (that's the learned association) Second-order Classical Conditioning: 1. + = 2. = *This would be called sensory pre-conditioning if this occurred first 3. = Revision Ingredients: , , , , Learning with Compound Stimuli 1. + = 2. = Overshadowing 3. = , but = Overshadowing When we present both stimuli together one stimuli is more salient or louder than the other one which overshadows the other one. Revision Ingredients: , , , , Blocking 1. + = 2. = 3. + = 4. = , but = Latent Inhibition 1. = 2. + = 3. = Outline 1. (from last lecture)Timing, Extinction and Inhibition Effect of varying the temporal relationship between unconditioned and conditioned stimuli Reduction or elimination of behaviours Inhibiting learning 2. The Rescorla-Wagner Model of Classical Conditioning Contingency and learning The 6 Rules Alternative Theories 3. Timing, Extinction and Inhibition What factors determine whether and how much classical conditioning occurs? 1. Impact of the temporal relationship between CS and US Short-Delay Simultaneous Trace Backward 2. How can we reduce or eliminate a behaviour? Extinction Spontaneous recovery Rapid Reacquisition Disinhibition 3. Inhibition phenomena Latent inhibition Conditioned inhibition External inhibition Inhibition of delay Disinhibition Determinants of Classical Conditioning 1. Intensity of Unconditioned Stimuli (US) 2. Excitatory Vs. Inhibitory Conditioned Stimuli 3. Time Relationships between Stimuli Simultaneous conditioning Delayed conditioning Aka forward conditioning Trace conditioning Backward Conditioning 4. Acquisition Extinction  spontaneous recovery Intensity of Stimuli Stimulus intensity influences the course of both appetitive and aversive classical conditioning More intense Conditioned Stimuli (CS) are more effective in accelerating the acquisition of a CR i.e. fewer trials needed  CR More intense Unconditioned Stimuli (US) are especially powerful Extremely intense aversive US can produce PTSD!  Excitatory Vs. Inhibitory Stimuli To make our environment more predictable we search for relationships between stimuli. Some stimuli are predictive of the occurrence (+) of a stimulus and some are predictive of its absence (-). Both stimuli are just as important to learn about! Maybe the presence of the bell isn't associated with food (predictive signal) but the bell could be a signal of what will not happen (inhibitory stimuli). Excitatory Conditioned Stimuli 🛎 🍔 When the CS predicts the occurrence of the US, it becomes an excitatory conditioned stimulus (CS+).😍 🛎 CS has a positive relationship with the US - CS acquires an ability to “excite” the organism - The CS activates behavioural and neural responses related to the US in the absence of the actual presentation of the US Inhibitory Conditioned Stimuli When the CS predict the absence of the US, it will become a conditioned inhibitory stimulus ( CS-) CS has a negative relationship with the US Temporal Relationships between pairings 🛎 🍔 Most easily established 🛎 🍔 Ease of conditioning depends on the length of 🛎 the trace 🍔 Very little conditioning established 🛎 🍔 No conditioning i.e. CS can’t predict US  Temporal Relationships between pairings a) Simultaneous conditioning: CS and US are presented and terminated together. b) Delayed conditioning: CS is presented alone for a while, then the US is presented and the CS & US typically terminate together. This is most effective way! c) Trace conditioning: CS begins and ends before US is presented. d) Backward conditioning: CS is presented after US is terminated. Temporal Relationships: How do they compare? Simultaneous conditioning (CS and US presented at same time) Much weaker conditioning May be product of distraction of US If CS not before US, how can it serve as a signal? Trace conditioning (CS and US separated by longer time interval in which neither stimulus is present) “Memory trace”- requires memory As CS-US interval increase, so does the decline in level of conditioning Temporal Relationships between pairings Delayed conditioning is the most effective (fastest) way of producing a strong conditioned response! But the optimal delay between the onset of CS and the onset of US is very short Typically ~0.5 – 1.0 sec. As the interval increases, CR usually weakens. When this gap is more than several seconds, no learning is achieved. (taste aversions are an exception!) Temporal Relationships Between CS and US What happens when there is a long delay? Onset of CS precedes US by at least several seconds CS continues until US presented Like Trace, CS-US interval impacts conditioning, but not as severe Pavlov’s dogs - 10 second Tone (CS) – Food (US) delay - 1st salivated as soon a tone presented - Over time, dogs began to estimate delay. Salivary response only occurs after 8-9 seconds. - Compound stimulus: Onset of Tone + delay Temporal Relationships Between CS and US Backward conditioning (CS presented after US) Level of conditioning markedly lower Order is important Predictiveness principle: The onset of CS signals a time in which the US will be absent How can we reduce or eliminate a behaviour? Extinction Extinction is a method for eliminating a conditioned response Extinction paradigm: Repeatedly present the conditioned stimulus (CS) alone (without the US) With repeated exposure to the CS, it stops being a predictor of the US and the CR decreases and eventually stops Systematic Desensitisation/Exposure therapy uses an extinction-like paradigm Represents gradual way to expose CS Highly e ective treatment for phobias and PTSD  Virtual reality technology is sometimes used in exposure therapy  Virtual reality technology is sometimes used in exposure therapy Acquisition, Extinction, and Spontaneous Recovery Acquisition, Extinction, and Spontaneous Recovery Extinction: Repetition of CS without US reduces CR. Spontaneous Recovery: After extinction, if there is a delay, the CS will often produce a weak CR. What has been learnt can never be truly forgotten or broken, even in extinction and this is evident by spontaneous recovery, disinhibition and rapid re-acquisition. Extinction Occurs gradually After extinction, there is no CR. But CS-US association is not erased! Three phenomena illustrate this point: 1. Spontaneous recovery 2. Disinhibition 3. Rapid Reacquisition Relearning/Reacquisition Effect Extinguish CR Recondition with CS-US pairing Fewer trials required Rapid reacquisition! We nd that we often need less pairings to bring back the behaviour after extinction (fewer experiences and less time are required for rapid re-acquisition). Acquisition, Extinction, and Spontaneous Recovery Spontaneous Acquisition Extinction Recovery Reacquisition Strength of CR CS&US CS alone CS alone CS&US Trials/Time Rate of Extinction: Total Duration Matters Most The number of trials does not determine rate of extinction The total duration of exposure to the CS determines how fast the CR is extinguished The impact of the duration, rather than the number of times an individual is exposed to the CS, is an important consideration for exposure therapy! Shipley, R.H. (1974). Extinction of conditioned fear in rats as a function of several parameters of CS exposure. Journal of Comparative and Physiological Psychology, 87(4), 699-707. Inhibition phenomena Inhibition Phenomena Latent inhibition Pre-exposure to the CS (without the US) inhibits later learning (discussed last week) External inhibition – presence of a novel cue during conditioning inhibits the CR Conditioned Inhibition – a CS that predicts the absence of the US Inhibition of Delay – the CR is withheld until an appropriate time Disinhibition – removal of inhibition by the presentation of a novel stimulus Inhibition Phenomena Latent inhibition Pre-exposure to the CS (without the US) inhibits learning later (discussed in the previous lecture) External inhibition – presence of a novel cue during conditioning inhibits the CR Conditioned Inhibition – a CS that predicts the absence of the US Inhibition of Delay – the CR is withheld until an appropriate time Disinhibition – removal of inhibition by the presentation of a novel stimulus Pavlov’s “eureka” moment External inhibition was discovered by Pavlov in a lecture hall The dog didn't demonstrate the response outside of a lab setting so what is being The dog is brought in….. inhibited is a CR in response to a change in context. Pavlov decided to demonstrate his discovery of conditioned responses to the other members of his academy…. Pavlov’s “eureka” moment ….but nothing happens The dog is on the bench in the lecture theatre looking at Pavlov, the metronome tick-tocks – but no drooling Why not? Pavlov had discovered external inhibition! Pavlov’s “eureka” moment The context has changed! The presence of the audience (a novel stimulus) inhibited the dog’s conditioned response (CR) of salivating And so Pavlov makes yet another serendipitous discovery … the phenomenon of inhibition of a CR Inhibition Phenomena Latent inhibition Pre-exposure to the CS (without the US) inhibits learning later (discussed in the previous lecture) External inhibition – presence of a novel cue during conditioning inhibits the CR Conditioned Inhibition – a CS predicts the absence of the US Inhibition of Delay – the CR is withheld until an appropriate time Disinhibition – removal of inhibition by the presentation of a novel stimulus Conditioned inhibition Conditioning in which a neutral stimulus is associated with the presentation of a US is known as excitatory conditioning. The result is that the CS (now called an excitatory CS or CS+) acquires the capacity to regularly elicit a CR. Conditioning in which the neutral stimulus is associated with the absence or removal of a US is known as inhibitory conditioning. The result is that the CS (now called an inhibitory CS, conditioned inhibitor or CS-) comes to inhibit the occurrence of a CR. Conditioned inhibition Conditioned inhibition has an important prerequisite: for the absence of a US to be a significant event, the US has to occur periodically in the situation There are many signals for the absence of events in our daily lives: Signs such as ‘Closed’, ‘Out of Order’ and ‘No Entry’ are of this type. However, these signs provide meaningful information and influence what we do only if they indicate the absence of something we otherwise expect to see. Conditioned inhibition General rule: inhibitory conditioning and inhibitory control of behaviour occur only if there is an excitatory context for the US in question Pavlov recognised this and provided such a context in his standard inhibitory training procedure: 1. Stimulus A is a metronome 2. Stimulus B is a light 3. Food is the US 4. Dogs as subjects Conditioned inhibition Definition: A CS signals the absence of an otherwise expected US. Standard Method: Conditioned Inhibition Procedure A+  US follows CS CSA Excitatory conditioning AB-  No US after compound CS CSA + CSB Inhibitory conditioning Why do you think that CSB is presented with CSA in stage 2?  Pavlov’s procedure for conditioned inhibition Trial Type A On some trials (Type A), the CS+ (metronome) is paired with the US (food). Time On other trials (Type B), the CS+ (metronome) is presented with the CS- Trial Type B (light) and the US (food) is omitted. The procedure is effective in conditioning inhibitory properties to the Time CS- (light) Inhibition Phenomena Latent inhibition Pre-exposure to the CS (without the US) inhibits learning later (discussed in the previous lecture) External inhibition – presence of a novel cue during conditioning inhibits the CR Conditioned Inhibition – a CS that predicts the absence of the US Inhibition of Delay – the CR is withheld (inhibited) until an appropriate time Disinhibition – removal of inhibition by the presentation of a novel stimulus Inhibition of Delay ― Pavlov’s dogs  10 second Tone (CS) – Food (US) delay  At first, they salivated as soon a tone presented  Over time, dogs began to estimate delay. Salivary response only occurs after 8-9 seconds.  Compound stimulus: Onset of Tone + delay i.e., delay becomes part of the CS First Few Trials Later Trials CS CS US US UR CR UR CS = metronome US = food UR = salivation Time CR = salivation Inhibition Phenomena Latent inhibition Pre-exposure to the CS (without the US) inhibits learning later (discussed in the previous lecture) External inhibition – presence of a novel cue during conditioning inhibits the CR Conditioned Inhibition – a CS that predicts the absence of the US Inhibition of Delay – the CR is withheld until an appropriate time Disinhibition – removal of inhibition by the presentation of a novel stimulus I don't really understand disinhibition Disinhibition Disinhibition is the removal of inhibition the CR increases in strength Disinhibition can occur during extinction Presentation of a novel stimulus interrupts extinction E.g., disinhibition of the inhibition of delay occurred with a novel stimulus. - Kimmel (1965) CR was withheld for 4.0 secs, but only for 2.3 secs with a novel stimulus (i.e., when a novel tone was presented). Summary Numerous factors determine whether and how much conditioning is demonstrated E.g., stimulus intensity, the nature of the stimulus (excitatory/inhibitory), the presentation context (e.g., acquisition stage, during extinction etc.), and the temporal relationship between the CS and the US. Di erent temporal relationships between CS and US lead to di erences in the size and nature of conditioning E.g., Short-Delay, Simultaneous, Trace, Backward Learning is not unlearned during extinction Spontaneous recovery, rapid reacquisition, and disinhibition demonstrate the enduring and complex nature of learning Inhibition phenomena are varied and insightful and demonstrate: the importance of context and novelty on conditioning that predicting the absence or delay of something is just as important as learning/predicting the presence of something Break Break Time 2. The Rescorla-Wagner Model of Classical Conditioning Contingency Contingency refers to the predictability of the occurrence of one stimulus from the presence of another Increasing the delay between the CS and US results in the CS becoming less useful as a predictor of the US Contingency is the probabilistic relationship with the US given that a CS has occurred This probabilistic relationship between the occurrence of the US and the CS is the basis of a prominent mathematical model of classical conditioning- The Rescorla-Wagner Model Contingency Theory Contingency theory - a conditioned response (CR) develops when the conditioned stimulus (CS) is able to predict the occurrence of the unconditioned stimulus (US). After repeated CS-US pairings, the individual can begin to predict when the US is coming based on the CS being present. When the CS is presented, the individual forms an expectancy of the US. This expectancy is what drives the CR. 49 The role of expectations and surprise CS Expectations 🍔🍔 Surprise! You get You get what you Surprise! You get 🍔 more than you less than you expected 🍔🍔 expected 🍔 🍔 expected Increase: No change Decrease: Your expectations needed Your expectations Learning occurs! No Learning occurs Learning occurs! Contingency depends on reliability and uniqueness Contingency depends on: Reliability of CS-US pairing: How often is the CS followed by US? What is the probability that the US will occur given that the CS has just occurred? Uniqueness of CS-US pairing: How often does US happen without CS? What is the probability of the US occurring given that no CS has occurred? 51  Quantifying Contingency Relationships Contingency refers to the predictive relationship between stimuli (CSs and USs) The CS has to convey information about US occurrence. Rescorla used the following expression to describe these relationships: p(US/CS) > p(US/no CS) This translates to: The probability (p) of a The probability (p) of US occurring given that *** is greater than (>)*** a US given that (/) (/) a CS is present NO CS is present If this condition is met, learning (excitatory conditioning) will occur Rescorla’s Equation: +ve correlation between CS & US p (US / CS) > p (US / No CS) The left side of the equation simply notes the percentage/proportion of CSs that are temporally contiguous (paired) with a US If p = 1.0 then 100% of CSs are paired with USs If p = 0.5 then 50% CSs are paired with USs and 50% of CSs are presented alone If p = 0.0 then all the CSs are presented alone, there are no CS-US pairings Rescorla’s Equation: +ve correlation between CS & US p (US / CS) > p (US / No CS) The right side of the equation simply notes the percentage/proportion of time intervals without a CS in which a US occurs. If p = 1.0 then USs are presented on 100% of the time intervals with No CS present If p = 0.5 then USs are presented on 50% of the time intervals with No CS present If p = 0.0 then USs are never presented when No CS is present Positive contingency between CS and US This is an example of delayed conditioning If the CS is a reliable predictor of the presence of the US, then the CS and US are positively correlated It's 1 (which is 100% of the time that when you hear a bell- food will arrive. That's why it's positively correlated. CS US p(US/CS) = 1 > p(US/no CS) = 0 No contingency between CS and US If the CS is an unreliable predictor of the US, then the CS and US are not correlated In this case we say that no learning occurs because there's no reason to assume that the ringing of the bell will lead to more food. CS US p(US/CS) = 0.25 = p(US/no CS) = 0.25 Negative contingency between CS and US If the CS reliably predicts the absence of the US, then the CS and US are negatively correlated When you hear the bell in negative correlation you learn that there's no food coming. (It's predicting no food in this case). CS US p(US/CS) = 0 < p(US/no CS) = 0.375 The effect of contingency on classical conditioning Contingency means occurrence/happening/chance For both groups there’s only a 40% chance that bells will be followed by shock. However, for Group B, shock is less likely when no bell is sounded, and, for this group, the bell becomes a fearful stimulus. Positive Contingency p(US/CS) > p(US/no CS) 40% > 20% Bell  Fear CR In this group the rat will learn that the ringing of the bell will induce shock (positive contingency) Zero Contingency p(US/CS) = p(US/no CS) 40% = 40% No learning The rat will not learn because there's an equal likelihood between the bell and the shock (no true predictive relationship) Negative Contingency The bell is negatively correlated to the freezing behaviour in this case p(US/CS) < p(US/no CS) 40% < 80% Shock is less likely to occur after CS 40% 60% 80% 20% Bell  inhibitory response Interim Summary When subjects experience CSs and USs that are positively correlated they acquire a conditioned response to the CS; this is called excitatory conditioning. When subjects experience CSs and USs that are negatively correlated responses are inhibited (not performed) when the CS is present; this is called inhibitory conditioning or conditioned inhibition. When subjects experience CSs and USs that are NOT correlated they no conditioning. It can be determined if learning is likely to occur by quantifying and comparing the probabilities of the US occurring with and without the CS. The Rescorla-Wagner Model Learning occurs when there is a prediction error i.e., discrepancy between the actual outcome of a conditioning trial and the expected outcome of that trial The Rescorla-Wagner Model allows us to quantify the size of the contingency relationship between a CS and a US. Rescorla-Wagner was the first and most influential model of learning – we will go over this model in more detail in the second part of the lecture…. Rescorla, R. A, & Wagner, AR. (1972). A theory of Pavlovian conditioning: variations in the effectiveness of reinforcement and non reinforcement. In AH. Black & W.F. Prokasy (eds.), Classical conditioning II: current research and theory (pp. 64-99) New York: Appleton-Century-Crofts. The Rescorla-Wagner Model A mathematical model designed to predict the outcome of classical conditioning procedures on a trial-by-trial basis Learning will occur only when the subject is surprised, that is, when what actually happens is different from what the subject expected to happen Always 3 possibilities in conditioning trials: 1. excitatory conditioning 2. inhibitory conditioning 3. no conditioning and all Which of these three possibilities actually occurs depends upon: 1. The strength of the subjects’ expectation of what will occur 2.The strength of the US that is actually presented  Six Rules of the Rescorla-Wagner Model 1. If the strength of the actual US is greater than the strength of the subjects’ expectation, all CSs that were paired with the US will receive excitatory conditioning. 2. If the strength of the actual US is less than the strength of the subjects’ expectation, all of the CS is that were paired with the US will receive some inhibitory conditioning. 3. If the strength of the actual US is equal to the strength of the subjects expectation, there will be no conditioning. 4. The larger the discrepancy between the strength of the expectation and the strength of the US, the greater the conditioning that occurs (either excitatory or inhibitory) 5. More salient CSs will condition faster 6. If two or more CSs are presented together, the subjects’ expectation will be equal to their total strength (with excitatory and inhibitory stimuli tending to cancel each other out) Rescorla-Wagner: Acquisition With each successive conditioning trial, the expectation of the US following the CS should get stronger, and so the di erence between the strength of the expectation and the strength of the US gets smaller Therefore, the fastest growth in excitatory conditioning occurs in the first trial, and there's less and less additional conditioning as the trials proceed When the CS elicits an expectation that is as strong as the US, the asymptote of learning is reached, and no further excitatory conditioning will occur with any additional CS-US pairings  Rescorla-Wagner: Acquisition Asymptote US fully expected 10 0 The 1st and 4th rule of the Rescorla Wagner 80 Model can help us understand learning Growth Units of Habit curves generally. Why do we see rapid 60 rate learning at the beginning which plateau's? Strength There's a mismatch between what you 4 0 expected and what you received, then we rapidly condition towards expecting food 20 but it reaches a point where there's a reduction in the US maximally surprising 0 amount of learning. I.e. Asymptote. Successive Reinforcements The R-W model explains Hull’s Theoretical Learning Curve: The increases in height in the curve  smaller across trials. The most learning occurs when surprise is greatest and expectation least As the CS comes to be expected little further learning occurs Figure from Hull, C.L. (1943). Principles of Behavior (p. 1116) NY: Appleton Century Crofts Rescorla-Wagner: Blocking How the Rescorla-Wagner Model explains blocking: When two CSs are presented, the subject's expectation is based on the total expectations of both. No conditioning occurs to the added CS because there is no surprise – the strength of the subject's expectation matches the strength of the US Increasing the size/strength of the US when presenting the compound CS may prevent blocking effects The shaking of the box on it's own becomes predictive 100% of the time that there will be food. Rescorla-Wagner: Extinction & Conditioned Inhibition How the Rescorla-Wagner Model explains Extinction & Conditioned Inhibition : The strength of the expected US is greater than that of the actual US, leading to a decrease in the association between the CS and the US. Following acquisition: CS  No-US This leads any CS or compound CS to acquire some inhibitory conditioning CS  No-US learning occurs until the absence of the US is no longer surprising CS conditioned inhibitor! Rescorla-Wagner: Combining CSs The Rescorla-Wagner makes predictions about when CSs are combined: When two CSs that elicit CRs on their own are combined, the expected US of the compound CS is roughly equal to their total strength. E.g. a CS+ and a CS- conditioned separately are presented as a compound CS: 🛎 means food + ✨ shining a light means no food= they cancel each other out + = O set each other CSExcitatoryCSInhibitory CR Rescorla-Wagner: The Overexpectation E ect The animal will end up reducing its response to both of those stimuli after the over-expectation e ect The Rescorla-Wagner predicted the overexpectation effect: There is a decline in responding to a pair of well established conditioned stimuli (CSs) when they are presented as a compound. Over-Expectation Effect: If two CSs are conditioned separately and then together, the animal has an over-expectation about the size of the US, and both CSs will experience some inhibitory conditioning The animal expects twice the US, so if only the same US follows the compound CS as did each CS alone, this does not meet the animals expectations Over-expectation e ect + = US x 2 + CS1 CS2 Individual CSs lose excitatory strength and gain Inhibitory Same US Moderate CR strength Interim Summary: Rescorla-Wagner Model The Rescorla-Wagner model can be thought of as a model of US e ectiveness Unpredicted (surprising) US is e ective in promoting learning to the CS Well-predicted US is ine ective in promoting learning Alternatives to the Rescorla-Wagner Model Rescorla-Wagner’s model focuses on US side of the association Unpredicted (surprising) US is e ective in promoting learning Well-predicted US is ine ective in promoting learning Alternative theories focus on attention to the CS instead A common feature of these theories is the assumption that the learner will pay attention to informative CSs but not to uninformative CSs These theories might also be called theories of CS e ectiveness, because they assume that the conditionability of a CS, not the e ectiveness of the US, changes from one situation to another Rescorla-Wagner cannot explain latent inhibition The Rescorla-Wagner Model cannot explain latent inhibition! But when you present the bell/metronome on itself it doesn't produce a response The RWM is assuming that there are equal amounts of attention in each phase here as well Recap on latent inhibition/pre-exposure e ect: Classical conditioning proceeds more slowly if a CS is repeatedly presented by itself before it is paired with the US  Rescorla-Wagner cannot explain latent inhibition The Rescorla-Wagner model does not predict this CS pre-exposure effect! When the (to-be-CS) stimulus is presented by itself before the training, the expected US is zero, and the actual US is zero According to the Rescorla-Wagner model, since the actual US = expected US, there should be no learning of any kind during the pre-exposure However, subjects evidently do learn something during the pre-exposure trials, which reduces their ability to later develop a CSUS association Attention-based theories are able to explain the pre-exposure effect Because the CS predicts nothing during the pre-exposure, attention to the CS decreases, and so conditioning is slower when the CS is first paired with the US at the beginning of the conditioning phase Mackintosh, N.J. (1975) A Theory of Attention: Variations in the Associability of Stimuli with Reinforcement. Psychological Review , 82, 276-98. Pearce J.M. & Hall G. (1980) A model for Pavlovian learning: Variations in the e ectiveness of conditioned but not of unconditioned stimuli. Psychological Review, 87, 532-552. Alternatives to the Rescorla-Wagner Model: Comparator Theories of Conditioning Comparator theories assume that the animal compares two likelihoods: The likelihood that the US will occur in the presence of the CS The likelihood that the US will occur in the absence of the CS  Comparator theories of learning Comparator theories are similar in many ways to Rescorla-Wagner and Attentional theories, but di er in two ways: They do not make predictions on a trial-by-trial basis 1. They assume what is important is not the events of individual trials but rather the overall long-term correlation between a CS and the US 2. They propose that the correlation between CS and US does not a ect the learning of a CR but rather its performance e.g. Subjects may learn an association between a CS and a US that cannot initially be seen in their performance, but this learning can be unmasked if the strength of a competing CS is weakened Miller, R. R., & Schachtman, T. R. (1985). Conditioning context as an associative baseline: Implications for response generation and the nature of conditioned inhibition. In R. R. Miller & N. E. Spear (Eds.), Information processing in animals: Conditioned inhibition (pp. 51–88). Hillsdale, NJ: Erlbaum. Stout, S. C., & Miller, R. R. (2007). Sometimes-competing retrieval (SOCR): A formalization of the comparator hypothesis. Psychological Review, 114(3), 759-783. How might we unmask learning in blocking? Comparator theories suggest that learning still occurs to a blocked stimulus, it is just masked…. What if you extinguish the blocking CS? Would any conditioning to the blocked CS be revealed?  Blocking Revisited Comparator theories explain blocking well Phase 1: Train Light CS Phase 2: Train Light CS in compound with neutral (but equally salient) Metronome CS When you extinguish the association between the light and the food the dog will start salivating at the sight of the metronome. The association of the light it stronger which is why it initially takes over. Phase 3: Revaluation of US Extinguish CR to Light and unblock metronome Phase 4: Test metronome: conditioning to Metronome is revealed Blocking is a performance issue rather than a learning one! Comparator theories of learning Comparator theories di er from R-W’s model in two ways: 1) Unlike R-W, comparator theories assume that both the CS and contextual stimuli can acquire equal excitatory strengths, because both have been paired with the US. 2) Comparator theories also assume that a CS will not elicit a CR unless it has greater excitatory strength than the contextual stimuli. The animal has learned something about the CS: that the US sometimes occurs in its presence, but the animal will not respond to the CS unless it is a better predictor of the US than the context Context plays a critical role in determining the response Rescorla-Wagner, Attentional and Comparator Theories: Common Themes The predictiveness or informativeness of the stimulus is a critical determinant of whether a CR will occur The predictiveness or informativeness of a stimulus cannot be judged in isolation It must be compared to the predictiveness of other stimuli also present in the learner's environment. In reality, contextual cues are present when the US is absent as well as present  reduces the uniqueness of the relationship with the US and therefore limits learning Summary Unblocking doesn’t sit well with the Rescorla-Wagner model – but there are other theories that offer alternative accounts of the learning process Theories of attention – Mackintosh (1975) Pearce and Hall (1980) focus on how much attention the CS is able to attract, as opposed to how much associative strength a US can support (Rescorla-Wagner, 1972). Comparator theories take contextual cues into account But R-W model is important, and still influential, because it still has a lot of explanatory power and was first in terms of developing a cognitive explanation of classical conditioning processes Next Time The Research Report and Written Reflection are due by the end of this week (11:55pm Sunday, 6th September) Reminder that Tutorial 4 starts next week (Week 10) Tutorials scheduled for 7 October are not running due to public holiday. A ected should attend a di erent session. The next lecture topic is “Operant Conditioning” (recorded due to public holiday) Reading: Mazur Textbook Chapters 5-6 titled "Basic Principles of Operant Conditioning" and "Reinforcement Schedules: Experimental Analyses and Applications“ Make use of our PSYUX2236-2024-S2 Team for unit discussions, ask questions, or help answer questions from your peers! Have a good day!