“…When such effects were subjected to more rigorously controlled experiments using animals as subjects, differences in learning ability were not always forthcoming. For example, Zimmerman, Geist, and Strobel (1975) failed to report differences in delayed-response, leaming-set, objectdiscrimination, and simple reversal-leaming tasks in monkeys. Likewise, Remley, Armstrong, Gilman, and Mercer (1980) reported that rats raised on a protein-deficient diet from weaning to maturity did not differ from normal littermates in terms of two-way active avoidance and blackwhite visual discrimination performance.…”