Emphasizing the ‘positive’ in positive reinforcement: Using non-binary rewarding for training monkeys on cognitive tasks

Abstract

Non-human primates constitute an indispensable model system for studying higher brain functions at the neurophysiological level. They can be trained on highly demanding cognitive tasks, and studies involving these animals elucidated the neuronal mechanisms of various cognitive and executive functions, such as visual attention, working memory, and decision-making. The training of behavioral tasks used to study these processes builds on reinforcement learning and involves many discrete stages. It may takes several months, but frequently lasts a year or longer. The training is usually based on applying a liquid reward as the reinforcer to strengthen the desired behavior, and absence of the reward if the animals response was wrong. We here propose an alternative, non-binary rewarding scheme that aims to minimize unrewarded behavior. We show the potential of this alternative scheme to significantly speed up the training of an animal at various stages, without trade-off in accessible task difficulty or task performance.