ABSTRACT
We have recently discovered that animals tend to approach and contact stimuli predictive of reward when such stimuli are highly localized in space. The phenomenon is called “sign-tracking” because the animals move about so as to be in close physical proximity to the signal. Not all stimuli that signal reward are amenable to approach and contact. In many procedures, signals for reward (i.e., Pavlovian CSs and instrumental discriminative stimuli) are diffuse and not highly localized in space. Examples of such signals are auditory stimuli emanating from a speaker panel or visual stimuli (e.g., chamber illumination) provided by the illumination of a diffuse array of houselights. On the other hand, there are instances where the locus of the reward signal is discrete and highly circumscribed, as in the case of illuminating a 1-inch diameter circular disk or inserting a retractable operant lever. It is this type of reward signal that concerns us here. In this chapter, we discuss the behavioral consequences of localizing signals for reward as well as the implications of the observations derived from this research for a number of phenomena in animal learning.
