Learning to suppress responses to the larger of two rewards in two species of lemurs, Eulemur fulvus and E. macaco

Six brown lemurs and four black lemurs were presented with two stimulus arrays of one and four raisins. Under a reverse-reward contingency, they received the array they did not choose. All subjects showed a strong preference for the larger array and developed a strong side preference bias. When a large-or-none reward contingency was applied (i.e. no reward followed the choice of the larger array, but this array was given for the choice of the smaller array), six of the 10 subjects overcame their side bias and learned to select the smaller array. When a correction procedure was added, all the remaining subjects mastered the task. Performance was maintained when the original reverse-reward contingency was rerun, and when novel array pairs were presented. Several months after the study, six subjects retained a significant preference for choosing the smaller of the two arrays. The results demonstrate a form of self-control in two prosimian species.