This research investigates the impact of a novel incentive structure, dyad-linked incentives, on completion of an online health behavior, a brain training exercise. Participants are randomly assigned to either an individual incentive structure, a dyad-linked incentive structure with certainty of partner success, or a dyad-linked incentive structure without certainty of partner success. Participants assigned to the individual incentive structure are offered a $0.50 bonus for achieving 500 points on a brain training exercise. Participants assigned to the dyad-linked incentive structure are offered the same bonus if they and an assigned (non-existent) partner both reach 500 points on the same exercise. Participants assigned to the dyad-linked incentive structure with certainty of partner success are told that their partner has already reached 500 points, while participants assigned to the dyad-linked incentive structure without certainty are not told of their partner's success. Participants will be given the option to complete the exercise again (“free-choice exercise”) on the following day for no additional payment.