ABSTRACT
This chapter is concerned with a particular kind of complex stimulus, namely another individual of the same species as the subject. It focuses on the individual recognition that occurs between hens and chicks, it begins with a report of an experiment that replicated this result using hens as both subjects and objects. The chapter looks at the yet more complex problem of discrimination in the face of the systematic changes of appearance that occur during development. Most of the experiments used the slide discrimination techniques made popular by Herrnstein and Loveland's pioneering experiments with pigeons. The species under investigation, however, was not the pigeon, but the domestic chicken. An individual chicken is a complex visual stimulus; its appearance can change dramatically depending on the angle from which it is seen, lighting conditions, distance from the observer, and other factors affecting visual perception.
