Reward-dependent selection of feedback gains impact rapid motor decisions

Target reward influences motor planning strategies through modulation of
movement vigor. Considering current theories of sensorimotor control
suggesting that movement planning consists in selecting a goal-directed
control strategy, we sought to investigate the influence of reward on
feedback control. Here we explored this question in three human reaching
experiments. First, we altered the explicit reward associated with the
goal target and found an overall increase in feedback gains for higher
target rewards, highlighted by larger velocities, feedback responses to
external loads, and background muscle activity. Then, we investigated
whether the differences in target rewards across multiple goals impacted
rapid motor decisions during movement. We observed idiosyncratic switching
strategies dependent on both target rewards and, surprisingly, the
feedback gains at perturbation onset: the more vigorous movements were
less likely to switch to a new goal following perturbations. To gain
further insight into a causal influence of the feedback gains on rapid
motor decisions, we demonstrated that biasing the baseline activity and
reflex gains by means of a background load evoked a larger proportion of
target switches in the direction opposite to the background load
associated with lower muscle activity. Together, our results demonstrate
an impact of target reward on feedback control and highlight the
competition between movement vigor and flexibility.