This chapter illustrates how the SD/SLH model (presented in Chapter 11) describes situations in which a CS behaves as a simple CS or as an occasion setter. We will analyze its performance in (a) a simultaneous FP discrimination with a strong feature and a weak target, (b) a simultaneous FP discrimination with a weak feature and a strong target, (c) a simultaneous FN discrimination, (d) a serial FP discrimination, (e) a serial FN discrimination, and (f) a contextual discrimination. As in previous chapters, in each case, we first present sample empirical data from test sessions administered after training, then show simulations of those data from the model, and finally detail the mechanisms by which the model acquires those discriminations.

It will be shown that a CS acts as a simple CS (through its direct associations with the US) or an occasion setter (through its indirect associations with the US via the hidden units), depending on the strength of its direct association with the US (a function of its intensity, duration and the CS–US interval) and the requirements of the task at hand.

Distinctions between occasion setting and simple conditioning

Investigations of the nature of learning in feature-positive (FP) and feature-negative (FN) conditional discriminations (Jenkins & Sainsbury, 1969) were the starting point for much of the research in occasion setting.