Effects of reward history on decision-making and movement vigor

Abstract

During foraging, animals decide how long to stay and harvest reward, and then abandon that site and travel with a certain speed to the next reward opportunity. One aspect of this behavior involves decision-making, while the other involves motor-control. A recent theory posits that control of decision-making and movements may be linked via a desire to maximize a single normative utility: the sum of all rewards acquired, minus all efforts expended, divided by time. If this is the case, then the history of rewards, and not just its immediate availability, should dictate how long one decides to stay and harvest reward, and how slowly one travels to the next opportunity. We tested this theory in a series of experiments in which humans used their hand to harvest tokens at a reward patch, and then used their arm to reach toward a subsequent opportunity. Following a history of poor rewards, people not only foraged for a longer period, but also moved slower to the next reward site. Thus, reward history had a consistent effect on both the decision-making process regarding when to abandon a reward site, and the motor control process regarding how fast to move to the next opportunity.