Behavioral/Cognitive The Temporal Evolution of Feedback Gains Rapidly Update to Task Demands

Recent theoretical frameworks such as optimal feedback control suggest that feedback gains should modulate throughout a movement and be tuned to task demands. Here wemeasured the visuomotor feedback gain throughout the course ofmovementsmade to “near ” or “far ” targets in human subjects. The visuomotor gain showed a systematic modulation over the time course of the reach, with the gain peaking at the middle of the movement and dropping rapidly as the target is approached. This modulation depends primarily on the proportion of themovement remaining, rather than hand position, suggesting that themodulation is sensitive to task demands. Model-predictive control suggests that the gains should be continuously recomputed throughout a movement. To test this, we investigated whether feedbackgainsupdatewhen the taskgoal is alteredduringamovement, that iswhen the target of the reach jumped.Wemeasured the visuomotor gain either simultaneously with the jump or 100 ms after the jump. The visuomotor gain nonspecifically reduced for all target jumps whenmeasured synchronously with the jump. However, the visuomotor gain 100ms later showed an appropriate modula-tion for the revised task goal by increasing for jumps that increased the distance to the target and reducing for jumps that decreased the distance.We conclude that visuomotor feedback gain shows a temporal evolution related to task demands and that this evolution can be flexibly recomputed within 100 ms to accommodate online modifications to task goals