The study of animal behavior and intelligence has a fairly long tradition, starting with Romanes naive mentalism. With a few noble exceptions, like Tolman and Kohler, psychological research on animals has been dominated by the behaviorist paradigm, and only in the last fifteen years has there been a substantial growth of interest in the analysis of cognitive processes in animals. This renewed impetus towards a cognitive approach, as opposed to a strict behaviorist perspective, resulted from both internal problems and external influences: on the one hand, there were difficulties in explaining all instances of behavior within the traditional S-R approach; on the other, mental concepts were gaining a new scientific respectability, thanks to the development of human cognitive psychology and artificial intelligence