Differential effects of reward and punishment on reinforcement-based motor learning and generalization

Reward and punishment have long been recognized as potent modulators of human behavior. Although reinforcement learning is a significant motor learning process, the exact mechanisms underlying how the brain learns movements through reward and punishment are not yet fully understood. Beyond the memory of specific examples, investigating the ability to generalize to new situations offers a better understanding of motor learning. This study hypothesizes that reward and punishment engage qualitatively different motivational systems with different neurochemical and neuroanatomical substrates, which would have differential effects on reinforcement-based motor learning and generalization. To test this hypothesis, two groups of participants learn a motor task in one direction and then relearn the same task in a new direction, receiving only performance-based reward or punishment score feedback. Our findings support our hypothesis, showing that reward led to slower learning but promoted generalization. On the other hand, punishment led to faster learning but impaired generalization. These behavioral differences may be due to different tendencies of movement variability in each group. The punishment group tended to explore more actively than the reward group during the initial learning phase, possibly due to loss aversion. In contrast, the reward group tended to explore more actively than the initial learning phase during the generalization test phase, seemingly recalling the strategy that led to the reward. These results suggest that reward and punishment may engage different neural mechanisms during reinforcement-based motor learning and generalization, with important implications for practical applications such as sports training and motor rehabilitation.