Animals develop an internal representation of their world that guides action. We do not know all the details, but it seems reasonable to assume that there is something fixed about any representation quite independently of the valences – values, goods and bads, motives – attached to aspects of it. Things look as they look, whether or not good or bad consequences are associated with them. The valences are essential, although they are often omitted from cognitive accounts. But without a motive, “the rat is left buried in thought at the choice point,” as Edwin Guthrie famously said of cognitive behaviorist E. C. Tolman.

Search images may be an exception, since the object before the viewer flips from being invisible to being seen. And the “flip” is often accompanied by reinforcement – the bird brushing a cryptic moth that flies off and is then “seen” and eaten. Representations of very complex objects may have to be acquired through a history of explicit reinforcement. Medieval teachers believed that Latin is learned only through the birch, and this general view of the motivation required for complex learning was almost universal until recently. Still, for recognition of simple stimuli, no special training seems to be necessary. The effect of reward and punishment is to give value to certain objects or places, as represented, rather than to create or modify the representations themselves.

Is performance then determined solely by the animal's representation? In this chapter, I argue that there is at least one other factor that must be taken into account: competition among activities for available time. These two factors, competition and external stimuli, taken together account for numerous experimental results on generalization and discrimination. The rest of the chapter explains how competition and stimulus control contribute to discrimination, behavioral contrast, generalization, and peak shift.

Inhibitory and excitatory control

Animals need to know both what to do and what not to do; hence, stimuli can have both inhibitory and excitatory effects. But, as we saw in earlier chapters, when an animal is not doing one thing, it is probably doing something else. Moreover, animals are highly “aroused” under the conditions typical of operant conditioning experiments – hunger, combined with frequent access to small amounts of food. Behavioral competition is then especially intense: The animals have a lot to do and limited time in which to do it.