The quantal nature of controlling stimulus-response relations as measured in tests of stimulus generalization.

This paper is a selective review of research that addresses the validity of two interpretations of stimulus generalization. One interpretation, referred to as the descriptive stimulus-control interpretation, proposes that during stimulus generalization a continuous relation exists between stimulus and response dimensions. The other interpretation, referred to as the quantal interpretation, proposes that a stimulus-response relation functions as a unit that may or may not occur. From the latter viewpoint, the continuity typically obtained during generalization tests is deemed to be artifactual and to result from averaging across multiple controlling stimulus-response relations. Studies examining the contribution of these multiple relations to generalization gradients are reviewed. With few exceptions, the quantal interpretation appears to better characterize the results of these studies. Implications for peak shift, selection of analytical level, and identification of the behavioral unit are discussed, as well as factors that may determine the acceptability of the quantal interpretation.