Several generations of theorists concerned with associative learning have wrestled with issues of "stimulus selection." In this chapter we describe the essential problem that has required such persistent attention and discuss certain of the theoretical attempts to deal with it. We do not intend to provide a comprehensive historical treatment of the problem area nor an exhaustive survey of the relevant data. For this purpose recent discussions by Mackintosh (1965a), SutherJand and Mackintosh (1971), and Trabasso and Bower (1968) are especially commendable. Nor do we intend to offer abrief for some particular theoretical position. In writing about the issues today we are less impressed with any single definitive solution to the problem of stimulus selection (or even with any continuous progress toward consensual resolution) than we are with the more general theoretical insights that have been spawned by the persistent obligation to so mehow deal with the facts of stimulus selection. As different theorists have approached the different faces of thc problem, they have developed theoretical machinery that has remained to form much of the workings of our theories of learning. Thus, we have chosen to illustrate some of the past
and present attempts to deal with the problem of stimulus selection so as to emphasize the theoretical legacy that is involved and the current implications for our understanding of the associative process.