Proprioceptive integration in motor control
Muscle vibration alters both perceived limb position and velocity by increasing type Ia afferent firing rates, although these afferents mainly encode velocity. Predictive frameworks of sensori-motor control, such as Active Inference and Optimal Feedback Control, suggest that velocity signals should inform position estimates. Such a function would predict that errors in perceived limb position and velocity should be correlated, but this prediction remains empirically underexplored. We hypothesized that an online evaluation of the integral of sensed velocity influences the perceived arm position during active movements. Such a mechanism would explain how vibratory stimulation of velocity-sensitive Ia afferents leads to the classic pattern of biased movement endpoint accuracy. Using a virtual reality-based reaching task, we investigated how vibration-biased proprioceptive feedback influences voluntary movement control. Our results suggest that muscle vibration biases perceived movement velocity, with downstream effects on perceived limb position and reflexive corrections of movement speed. We found that (i) antagonist vibration during active movement caused participants to both overestimate their movement speed while also slowing down, (ii) movement speed and endpoint errors were correlated, with muscle vibration affecting both, and (iii) adjustments in movement speed to muscle vibration are sufficiently fast to be reflexive. Together, these findings support the hypothesis that proprioceptive velocity signals are integrated to augment inference of position, consistent with predictive frameworks of sensorimotor control.