ABSTRACT
This chapter aims to sketch the kind of theory that most researchers in the area seem to hold, if only implicitly. It shows that this theory is not wholly satisfactory. To test theories of natural object discrimination, the chapter looks at the discrimination of less natural objects, or unnatural groupings of natural objects. It analyses some of the discriminations that pigeons either fail to learn, or learn very slowly. The most general way of characterizing the kinds of experiments that interest us is as multiple stimulus discrimination. Subjects are presented with many different stimuli and have relatively few possible kinds of response; in the limiting, and typical, case the only possibilities are to peck or not to peck. The chapter reviews some discriminations that either seem to be, or in fact were, tailor made for easy learning if the linear feature model is correct—but which prove difficult or impossible for pigeons to master.
