Vestibular modulation of visuomotor feedback gains in reaching

Humans quickly and sophisticatedly correct their movements in response to changes in the world, such as when reaching to a target that abruptly changes its location. The vigor of these movement corrections is time-dependent, increasing if the time left to make the correction decreases, which can be explained by Optimal feedback control (OFC) theory as an increase of optimal feedback gains. It is unknown if corrections for changes in the world are as sophisticated under full-body motion. For successful visually-probed motor corrections during full-body motion not only the motion of the hand relative to the body needs to be taken into account, also the motion of the hand in the world should be considered, because their relative positions are changing. Here, in two experiments, we show that visuomotor feedback corrections in response to target jumps are more vigorous for faster passive full-body translational acceleration than for slower acceleration, suggesting that vestibular information modulates visuomotor feedback gains. Interestingly, these corrections do not demonstrate the time-dependent characteristics that body-stationary visuomotor feedback gains typically show, such that an Optimal feedback control model fell short to explain them. We further show that the vigor of corrections generally decreased over the course of trials within the experiment, as if the sensorimotor system adjusted its gains when learning to integrate the vestibular input into hand motor control.