Analysis of learning in retarded monkeys.

Sixteen rhesus monkeys were either subjected to diets high in phenylalanine or parachlorophenyalanine either pre- or postpartum; there were 16 controls. Subjects were tested after removal from the PKU diet on a series of learning tasks. No support was found for suggestions that PKU monkeys a do worse if task difficulty is increased or b have an attentional or short-term memory storage deficit. Equivocal support was found suggesting that c PKU monkeys may have stronger initial biases and d do not attend to the relevant dimension. The most support was found for the hypothesis that e PKU subjects are more emotional which would account for a disruption in performance following negative reinforcement, and difficulty in changing an initial or a learned response pattern. The literature on learning in human PKU and induced PKU in animals is reviewed.