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NROC61H3 (42)


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Rutsuko Ito

Laws of associability 1. Many factors affect the strength of conditioning that occurs between CS and US a. Temporal contiguity i. For an association to form between two stimuli, they must occur close together in time ii. Types of temporal conditioning 1. Delay a. Conditioning works best when CS occurs before the US i. Signaling that a US is about to happen 2. Trace a. CS and US presentations are separated by a big interval b. Neural trace of the CS (rather than CS itself) is paired with US c. Limitation i. US conditioning to the context rather than CS itself 3. Simultaneous a. CS and US presented simultaneously 4. Backward a. US presented before the CS b. Least effective b. Novelty i. Novel stimuli facilitate learning ii. Prior exposure interferes with formation of new learning 1. Latent inhibition a. Harder to form new associations with familiar stimuli compared to novel stimuli i. E.g. less likely to associate familiar stimuli with aversive experiences 2. CS pre-exposure effect a. Causes habituation of the attentional response to the stimulus b. Pre-exposure to the US can also retard subsequent conditioning c. Salience (intensity) of CS and US i. More intense stimuli are more biologically relevant 1. E.g. lion roar right beside you compared to lion roar in the distance d. Frequency i. The more frequently stimuli are presented together, the more strongly they are associated e. Similarity i. Particular associations are easier to form due to the structure of sensory systems within the brain 1. Things that are internal are easier to associate together a. Taste / odor / illness 2. Things that are external are easier to associate together a. Light / tone / shock f. Causal relevance i. Strength of association depends on the informational value of the CS-US association ii. Organisms tend to attribute a particular effect (illness / fear) to its most probable cause 1. Perhaps as a result of evolutionary history iii. DOMJAN and WILSON study 1. 2 groups of rats received saccharin solution a. 1 group received electrical shock b. 1 group received LiCl to induce illness 2. When both groups given a choice between water and saccharin solution a. Only the second group (LiCl) avoided the saccharin b. Pairing of internal associations between food and illness iv. OHMAN study 1. 2 groups of humans a. 1 group shown pictures of phobic stimuli (snake) b. 1 group shown pictures of neutral stimuli (houses) 2. Both groups received electric shock 3. Test period showing both phobic and neutral stimuli to both groups a. Phobic stimuli induced more CR (sweating measured by GSR) than neutral stimuli when tested in extinction g. Contingency i. RESCORLA study 1. Coincidence of CS and US (contiguity) is not sufficient for associations to form a. Things that add to ability to predict a biologically important event will be learned b. Things that do not add, will not be learned i. Or they learn that it predicts nothing 2. CS must predict the US (contingent relationship) a. The probability of CS predicting US must be greater than the probability of the US presented alone (without the CS) i. This is a positive contingency ii. RESCORLA study 1. Conditioned suppression a. Lever press for food b. CS paired with shock (US) under 4 conditions of varying probabilities of US presented without CS c. Results i. When probability of CS  US was the highest  lowest conditioned suppression ratio occurred (i.e. strongest learning) RESCORLA and WAGNER theory 1. Mathematical learning theory to account for phenomenon of pavlovian learning 2. Central assumption that learning occurs on a given conditioning trial only if the US is surprising (or to the extent that the outcome US was unpredicted) 3. Therefore learning occurs the most at the beginning until an asymptotic level of learning is reached (i.e. CS becomes perfect predictor of US) 4. Equation represented by Δ V = α(λ – Σ V) a. Δ V = change in associative strength / predictive value of stimuli b. α = constant representing the salience of the CS c. (λ – ΣV) = predictability of the US i. Where λ is dependent on magnitude of the US ii. Where Σ V is the cumulative associative strength (i.e. the summed V values of all stimuli present on a given trial) Blocking 1. KAMIN study a. Stimulus A initially paired with food b. Stimulus A + Stimulus B paired with food i. However, no learning occurs for stimulus B because the Stimulus A  Food association blocks an association from forming between B and food (Stimulus A already fully predicts the Food) 1. This is known as blocking a. One element of a compound CS blocks the conditioning of the other CS 2. RW model explanation of the KAMIN study a. Stimulus A = maximum associative strength such that V =λ=1 A b. Stimulus B = no associative strength, VB=0 c. No condition happens to B since (λ – ΣV) is equal to (1-(1+0))=0 i. i.e. no surprise occurs  no learning occurs for stimulus B 3. Unblocking a. How do we overcome blocking according to the RW model? i. Increase intensity of the US, giving λ a larger value Conditioned inhibition 1. Stimulus A paired with US 2. Stimulus A paired with Stimulus B (without occurrence of US) 3. λ = 0 since there is no US 4. Associative strength of stimulus B will decrease since it predicts the absence of US 5. Stimulus B defined as an inhibitor since the associative strength of stimulus B is negative a. Δ V = 0.3(0 – 1) B b. Δ V =B-0.3 Shortcomings of the RW model 1. Failure to explain the phenomenon of latent inhibition a. If a subject is pre-exposed to a CS before conditioning begins, subsequent conditioning between that CS and a US is slowed down b. Since there is no US presentation during the pre-exposure phase, there is no reason why this phase should affect the conditioning phase (according to the RW model) 2. Does not address how much attention is paid to the CS (assumes
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