Comparator hypothesis

Abstract: According to theories of selective attention, learning about a stimulus depends on attending to that stimulus; this is represented in two-stage models by saying that subjects switch in analyzers as well as learning stimulusresponse associations This assumption, however, is equally well represented in a formal model by the incorporation of a stimulus-specific learning-rate parameter, a, into the equations describing changes in the associative strength of stimuli Theories of selective attention have also assumed (a) that subjects learn to attend to and ignore relevant and irrelevant stimuli (ie, that a may increase or decrease depending on the correlation of a stimulus with reinforcement) and (b) that there is an inverse relationship between the probabilities of attending to different stimuli (ie, that an increase in a to one stimulus is accompanied by a decrease in a to others) The first assumption is used to explain the phenomena of acquired distinctiveness and dimensional transfer, the second those of overshadowing and blocking Although the first assumption is justified by the data, the second is not: Overshadowing and blocking are better explained by the choice of an appropriate rule for changing a, such that a decreases to stimuli that signal no change from the probability of reinforcement predicted by other stimuli

Abstract: A selective review of experiments that can be said to demonstrate the effects of generalization decrement in Pavlovian condition is presented, and it is argued that an adequate theoretical explanation for them is currently not available. This article then develops a theoretical account for the processes of generalization and generalization decrement in Pavlovian conditioning. It assumes that animals represent their environment by a stimulus array in a buffer and that this array in its entirety constitutes the conditioned stimulus. Generalization is then held to occur whenever at least some of the stimuli represented in the array on a test trial are the same as at least some of those represented in the array during training. Specifically, the magnitude of generalization is determined by the proportion of the array occupied by these common stimuli during training compared to the proportion of the array they occupy during testing. By adding to this principle rules concerning excitatory and inhibitory learning, it is proposed, the model can explain all the results that were difficult for its predecessors to account for. A fundamental property of conditioned responding is that it may occur in circumstances that differ from those prevailing during acquisition. This phenomenon is referred to as generalization, and the term generalization decrement is used when this transfer is less than complete. These effects have been revealed with both Pavlovian and instrumental conditioning, using a variety of species and a wide range of conditioned stimuli (CS) and unconditioned stimuli (US). As iar as instrumental conditioning is concerned, a considerable number of studies have been directed at examining the factors that influence the magnitude of generalization from one situation to another (for reviews see Honig & Urcuioli, 1981; Mackintosh, 1974). These results also have been the focus of considerable theoretical analysis. In contrast, much less attention has been paid to the role of generalization in Pavlovian conditioning. Only a few studies have been concerned specifically with demonstrating the generalization decrement of a Pavlovian conditioned response (CR) as a result of modifying the properties of the CS (Hofiman & Fleshier, 1961; Hovland, 1937; Moore, 1972; Pavlov, 1927; Siegel, Hearst, George, & O'Neal, 1968). Furthermore, only a few theorists have been specifically concerned with the analysis of these and related effects (Hull, 1943; Pavlov, 1927). An alternative approach has been to show how a particular theoretical analysis of the Pavlovian learning process can be extended to account for generalization and generalization decrement (cf. Rescorla, 1976). The argument presented in this article is based on the premise that an adequate account for the effects of generalization must lie at the core of

Abstract: Contents: Preface. R.R. Mowrer, S.B. Klein, The Transitive Nature of Contemporary Learning Theory. A.R. Wagner, S.E. Brandon, A Componential Theory of Pavlovian Conditioning. J.C. Denniston, H.I. Savastano, R.R. Miller, The Extended Comparator Hypothesis: Learning by Contiguity, Responding by Relative Strength. R.A. Rescorla, Experimental Extinction. W. Timberlake, Motivational Modes in Behavior Systems. R.M. Church, K. Kirkpatrick, Theories of Conditioning and Timing. A.G. Baker, R.A. Murphy, F. Vallee-Tourangeau, R. Mehta, Contingency Learning and Causal Reasoning. B.W. Balleine, Incentive Processes in Instrumental Conditioning. G. Hall, Perceptual Learning: Association and Differentiation. A. Tomie, Autoshaping and Drug-Taking. N. DeSousa, F. Vaccarino, Neurobiology of Reinforcement: Interaction Between Dopamine and Cholecystokinin Systems. V.M. LoLordo, T.L. Taylor, Effects of Uncontrollable Aversive Events: Some Unsolved Puzzles. A.L. Riley, G.R. Simpson, The Attenuating Effects of Drug Preexposure on Taste Aversion Conditioning: Generality, Experimental Parameters, Underlying Mechanisms, and Implications for Drug Use and Abuse. D.J. Levis, K.E. Brewer, The Neurotic Paradox: Attempts by Two-Factor Fear Theory and Alternative Avoidance Models to Resolve the Issues Associated With Sustained Avoidance Responding in Extinction.

Abstract: Publisher Summary This chapter describes the potential explanatory power of a specific response rule and its implications for models of acquisition. This response rule is called the “comparator hypothesis.” It was originally inspired by Rescorla's contingency theory. Rescorla noted that if the number and frequency of conditioned stimulus–unconditioned stimulus (CS–US) pairings are held constant, unsignaled presentations of the US during training attenuate conditioned responding. This observation complemented the long recognized fact that the delivery of nonreinforced presentations of the CS during training also attenuates conditioned responding. The symmetry of the two findings prompted Rescorla to propose that during training, subjects inferred both the probability of the US in the presence of the CS and the probability of the US in the absence of the CS and they then established a CS–US association based upon a comparison of these quantities. The comparator hypothesis is a qualitative response rule, which, in principle, can complement any model of acquisition.