ABSTRACT
During the evolution of a successful group of animals there also is continuous improvement in efficiency of function and, in vertebrates especially, progressively greater independence of the external environment, as, for example, in the regulation of body temperature. The comparative psychologist is that all vertebrate learning, even learning in lower vertebrates, does not appear to be of the specialized type conceived by the ethologists, the specific responses that emerge having little relevance to preconceptions about adaptive significance. Evidence of divergence is provided by attempts to demonstrate in vertebrates three phenomena found in instrumental learning experiments with laboratory rats. The first is the incentive contrast effect of Crespi. The second phenomenon is an inverse relation between amount of reward in training and resistance to extinction, rats trained with high reward extinguishing more quickly than rats trained with low reward. The third phenomenon is the partial reinforcement effect.
