Time-to-contact measures capture modulations in posture based on the precision demands of a manual task

The integration between posture and manual control while performing fitting tasks of varying difficulty was investigated. Participants fit a block into either a small (high precision) or large (low precision) opening while standing on a force plate. Postural time-to-contact was used to quantify changes in posture that occurred during the fitting movement. Results suggest that posture became more stabilized when fitting through the small opening (postural time-to-contact values were higher) compared to when fitting through the large opening. Additionally, when fitting through the small opening, individuals modulated sway based on the instantaneous demands of the task. Specifically, time-to-contact was lower towards the end of a fitting movement (as the individual prepared to fit the block through the opening) compared to the beginning of the movement. These results suggest that the dynamics of postural sway are constantly changing based on the constraints of a concurrent task.