Rescorla-Wagner Model  US-processing model  Can account for some Pavlovian Conditioning phenomena: acquisition blocking unblocking with an upshift conditioned inhibition US-pre-exposure effect  Cannot account for some Pavlovian Conditioning phenomena: extinction (i.e., spontaneous recovery) unblocking with a downshift latent inhibition temporal factors (i.e., CS-US interval)

Pearce-Hall Model  attention model of conditioning  a CS-processing model  according to the model, it is highly adaptive to pay pay attention to, or process, CSs that could become valid predictors of important outcomes (i.e., USs)  it is also adaptive not to pay attention to, or process, CSs when the important event is already predicted by something else

Pearce-Hall Model  also based on the concept of surprise  when the subject is surprised, attention to, or processing of the CS occurs  as the US becomes predicted by a CS, and is less surprising, processing of the CS declines  The amount of processing, that is associability of a CS, changes on each trial depending on whether the US was predicted (on the previous trial)  If the US was predicted, then attention to the CS declines  If the US was not predicted, then attention to the CS increases

Pearce-Hall Model Recall from the RW Model, ΔV A = k(λ – V T ) k = constant; salience or associability of the CS With the PH Model, k changes across trials (CS processing model, not a US processing model)

Pearce-Hall Model k A N = λ N-1 – V A N-1 k A N = associative strength or associability of CS A on trial N λ N-1 = strength of the US on previous trial V A N-1 = strength of CS A on previous trial (could become V T if more than one CS) Important point: k depends on what happened on the previous trial; on first exposure, novelty causes some attention

Pearce-Hall Model k A N = λ N-1 – V A N-1 Early in training, when the strength of the CS is low (i.e., λ – V is high) see high k value and thus, more attention to the CS When the CS is strong in later trials (i.e., λ – V is small) attention to the CS is low The important point is that attention to the CS changes across trials

Pearce-Hall Model Attention to, or processing of, the CS can be measured in terms of an OR (i.e., looking at a L) This is different than the CR Support for the PH Model comes from the finding that subjects orient towards novel stimuli and maintain their orientation, provided the stimulus is a poor predictor of the US

Kaye & Pearce compared the OR in 3 groups of rats Group 1: L alone Group 2:Lcondensed milk Group 3:Lmilk/no milk (inconsistent/random) Looked at OR to L Attention (OR) was high on the first trial since the L is novel

Group 1: L alone k A N = λ N-1 – V A N-1 k stays low (decrease attention) Group 2: L milk V A gets bigger over time which makes the total term smaller (this means small k and decrease in attention) Group 3: L milk/no milk Attention remains high since V A is low

When the CS is not a good predictor, rats maintained their attention to the cue If the CS is a good predictor (of the US or no US), then attention decreases

Pearce-Hall Model and Blocking  like the RW Model, all CSs combine to predict the US  if one CS already predicts the US, then pay less attention to all CSs on that trial  when a new CS is added, should pay attention to it because it is novel  therefore, should see some conditioning to the new cue on the first trial based on the salience of the CS

Pearce-Hall Model and Blocking  only after first trial is over would the animal know that nothing new had happened  according to the model, should see blocking from trial 2 and onwards  however, in most cases see blocking right from the start

Pearce-Hall Model and Unblocking  when subjects encounter a US that is not well predicted, or is surprising (either bigger or smaller), then subjects should pay attention to all CSs on that trial and get unblocking k A N = λ N-1 – V A N-1  because the formula includes the absolute value of λ N-1 – V A N-1 it doesn’t matter if the US is bigger or smaller  if the US changes we’ll see increase in attention and thus, learning

Pearce-Hall Model and latent inhibition When the CS is given by itself, see decrease in attention to the CS over trials (λ = 0) However, a problem with the model is that it cannot explain the context-specificity of LI If CS pre-exposures are given in one context, and conditioning occurs in a second context, there is no retardation of learning According to the model, k should be low regardless of context

The Comparator Hypothesis  developed by Ralph Miller  this is a model of performance, not learning  according to Miller, all CSs have excitatory power; there is no separate inhibitory process  the strength of performance (or CR) depends on the relative strength of the various excitatory associations  a subject compares the excitatory strength of the explicit CS to the strength of other cues present in the situation, such as apparatus cues

The Comparator Hypothesis  when the strength of a CS is relatively greater than the background cues, get a measurable CR  when the strength of a CS is weaker than the background cues, get weakened level of excitation (what others might call inhibition)  according to the theory, the competition between two excitatory reactions controls performance

The Comparator Hypothesis  during normal excitatory, get CS-US pairings – but the US is also paired with background cues and these background cues are the comparator stimuli  because these background cues are also present during the ‘no-US’ condition, they are typically weaker than the explicit CS  so, under normal conditioning procedures, the CS has stronger excitatory strength than the comparator cues

The Comparator Hypothesis  during inhibitory conditioning, the CS is weak relative to the background cues  during inhibitory conditioning, have CS – no US pairings; but the background cues are paired with the US and the absence of the US  thus, the CS is weaker than the background cues and see little CR to the CS

Prediction – After training one can manipulate the excitatory value of the context and this will affect the excitatory value of the CS E.g. – After conditioning, give repeated exposure to the context alone followed by exposure to CS One will see greater responding to CS The Comparator Hypothesis

Temporal Factor Models  designed to explain the effects of time in conditioning  effects of time not considered in US-processing models like the RW model nor in CS-processing models like the PH model  CS-US interval is one important temporal variable  a more critical temporal variable appears to be the ratio of the ISI to ITI

Midterm Exam Thursday, Feb. 17, covers everything up to and including today’s lecture -in the case of a storm, the exam will take place during the very next class