Learning about associatively activated stimulus representations: Implications for acquired equivalence and perceptual learning

Abstract

Pavlovian conditioning is taken to reflect the formation of links between the central representations of stimuli. A link will be formed when presentation of the relevant stimuli is scheduled in a way that ensures that two representations are activated concurrently. Once this has occurred, a representation can be activated not only by the occurrence of the appropriate stimulus but also by way ofthe link. Evidence is reviewed to suggest that activation produced by this second route is, in some ways, functionally equivalent to direct activation; in particular, an associatively activated representation (an image) appears capable of forming further associative links with other event representations. Learning about associatively activated stimulus representations may playa role in a range of phenomena. Its contribution to the following is discussed: sensory preconditioning, second-order conditioning, acquired equivalence and distinctiveness, equivalence class formation, and the perceptual learning effect. Finally,consideration is given to the way in which existing theories of associative learning might be modified in order to accommodate this process.What may be termed the standard model ofclassical conditioning (Hall, 1994;Roitblat, 1987) holds that excitatory associations will be formed when the central representations of events are activated concurrently. These representations (or nodes; e.g., Wagner, 1981) are assumed, for the sake of theoretical convenience, to bear a direct relationship to the events described by the experimenter as stimuli. Thus, the node that corresponds to the conditioned stimulus (CS) will be activated when that event is presented to the animal; presentation of an unconditioned stimulus (US) will generate activity in a separate node corresponding to that stimulus. There is, however, a second route by which activity may be generated in a stimulus node. The existence ofan associative link between nodes functions, according to our standard assumptions, to allow activation of one node produced, for example,

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“…Although a detailed consideration of the relative merits of associative versus functional accounts of the findings is beyond the scope of the present article (but see G. Hall, 1996;Smeets & BarnesHolmes, 2003), there are other reasons to caution against a sensory preconditioning account. First, such an account would obviously need to explain the observed between-group generalization test differences at test, which could not have been due to other factors known to influence sensory preconditioning outcomes, such as US inflation (White & Davey, 1989), because both groups received an identical number of Pavlovian training trials.…”

“…Second, we used a "one-to-many" conditional discrimination training design that tends to reliably lead to the emergence of stimulus equivalence in humans but not necessarily nonhumans (Urcuioli, Zentall, & DeMarse, 1995). Any associative explanation based on sensory preconditioning of the emergence of combined symmetry and transitivity (B-C and C-B) test relations would at least need to account for the relative absence of such abilities in nonhumans that are otherwise capable of associative learning (G. Hall, 1996). Finally, it should remain an important requirement that any account of the present findings be as parsimonious as possible and generate a high number of testable predictions.…”

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