The representation of stimulus conjunction in theories of associative learning : a context-dependent added-elements model

This paper briefly reviews three theories concerning elemental and configural approaches to stimulus representation in associative learning and presents a new Context-dependent Added Elements Model (C-AEM). This model takes an elemental approach to stimulus representation where individual stimuli are represented by single units and stimulus compounds activate both those units and configurational units corresponding to each conjunction of two or more stimuli. Activity across these units is scaled such that each stimulus always contributes the same amount of activity to the system whether they are presented in isolation or in compound; the configurational units ‘borrow’ activity from representation units for individual stimuli (and from each other). This scaling is affected by the extent to which stimuli interact with each other perceptually. Hence, the model is conceptually similar to Wagner’s (2003) Replaced Elements Model but lacks features that explicitly code for the absence of stimuli (i.e., inhibited elements). Simulations of the model are reported for a range of generalization and discrimination learning tasks, conflicting results from which have previously been taken to provide support for either configural or elemental theories of learning