As described in Chapter 12, Schmajuk, Lamoreux and Holland (SLH) (1998) showed that an extension of a neural network model introduced by Schmajuk and DiCarlo (SD) (1992) characterizes many of the differences that distinguish simple conditioning from occasion setting.

In the framework of their model, Schmajuk and DiCarlo (1992) proposed that the hippocampus modulates (a) the competition among simple and complex stimuli to establish associations with the unconditioned stimulus, and (b) the configuration of simple stimuli into complex stimuli. Furthermore, Schmajuk and Blair (1993, 1995) suggested that (a) nonselective aspiration lesions of the hippocampal formation impair both configuration and competition, and (b) ibotenic acid selective lesions of the hippocampus proper impair only stimulus configuration.

These assumptions are somewhat similar to the ones made in Chapter 6 for the SLG model, in which we assumed that CS1–CS2, CS–CX, CX–CX and CX–CS associations, instead of the configural associations, were impaired by the selective hippocampal lesions (HPLs). In both models, we assume that competition is eliminated by nonselective lesions of the hippocampal areas.

In order to provide a theoretical account of hippocampal participation in occasion setting, the present chapter combines (a) Schmajuk, Lamoureux and Holland's (1998) account of occasion setting (see Chapter 12) with (b) Schmajuk and DiCarlo's (1992) and Schmajuk and Blair's (1993, 1995) assumptions regarding the effect of HPLs and HFLs on classical conditioning mechanisms. The results have implications for both the behavioral and neurophysiological aspects of occasion setting.