Smooth pursuit eye movements contribute to anticipatory force control during mechanical stopping of moving objects

Abstract

When stopping a closing door or catching an object, humans process the motion of inertial objects and apply reactive limb force over short period to interact with them. One way in which the visual system processes motion is through extraretinal signals associated with smooth pursuit eye movements (SPEM). We conducted three experiments to investigate how SPEM contribute to anticipatory and reactive hand force modulation when interacting with a virtual object moving in the horizontal plane. We hypothesized that SPEM signals are critical for timing motor responses, anticipatory control of hand force, and task performance. Participants held a robotic manipulandum and attempted to stop an approaching simulated object by applying a force impulse (area under force-time curve) that matched the objects virtual momentum upon contact. We manipulated the objects momentum by varying either its virtual mass or its speed under free gaze or constrained gaze conditions. We examined gaze variables, timing of hand motor responses, anticipatory force control, and overall task performance. Our results show that when SPEM were constrained, anticipatory modulation of hand force prior to contact decreased. However, constraining SPEM did not seem to affect the timing of the motor response or the task performance. Together, these results suggest that SPEM may be important for anticipatory control of hand force prior to contact and may also play a critical role in anticipatory stabilization of limb posture when humans interact with moving objects. New and NoteworthyWe show for the first time that smooth pursuit eye movements (SPEM) play a role in modulation of anticipatory control of hand force to stabilize posture against contact forces. SPEM are critical for tracking moving objects, facilitate processing motion of moving objects, and are impacted during aging and in many neurological disorders, such as Alzheimers disease and Multiple Sclerosis. These results provide a novel basis to probe how changes in SPEM could contribute to deficient limb motor control in older adults and patients with neurological disorders.