Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, United States.
Department of Kinesiology, University of Georgia, Athens, Georgia, United States.
J Neurophysiol. 2023 Jun 1;129(6):1293-1309. doi: 10.1152/jn.00075.2023. Epub 2023 Apr 26.
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 (SPEMs). We conducted three experiments to investigate how SPEMs 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 object's virtual momentum upon contact. We manipulated the object's momentum by varying either its virtual mass or its speed under free gaze or constrained gaze conditions. We examined gaze variables, the timing of hand motor responses, anticipatory force control, and overall task performance. Our results show that when participants were fixated at a designated location instead of following objects with SPEM, anticipatory modulation of hand force before contact decreased. However, constraining gaze by asking participants to fixate did not seem to affect the timing of the motor response or the task performance. Together, these results suggest that SPEMs may be important for anticipatory control of hand force before contact and may also play a critical role in anticipatory stabilization of limb posture when humans interact with moving objects. We show for the first time that smooth pursuit eye movements (SPEMs) play a role in the modulation of anticipatory control of hand force to stabilize posture against contact forces. SPEMs are critical for tracking moving objects, facilitate processing motion of moving objects, and are impacted during aging and in many neurological disorders, such as Alzheimer's disease and multiple sclerosis. These results provide a novel basis to probe how changes in SPEMs could contribute to deficient limb motor control in older adults and patients with neurological disorders.
当阻止关闭的门或接住物体时，人类会处理惯性物体的运动，并在短时间内施加反作用于肢体的力与之相互作用。视觉系统处理运动的一种方式是通过与平滑追踪眼球运动（SPEM）相关的视网膜外信号。我们进行了三项实验，以研究 SPEM 在与在水平面中移动的虚拟物体相互作用时如何有助于预期和反应性手部力的调节。我们假设 SPEM 信号对于运动反应的定时、手部力的预期控制和任务表现至关重要。参与者握住机器人操纵器，并通过施加与接触时物体虚拟动量匹配的力脉冲（力-时间曲线下的面积）来尝试阻止接近的模拟物体。我们通过在自由注视或约束注视条件下改变物体的虚拟质量或速度来操纵物体的动量。我们检查了注视变量、手部运动反应的定时、预期力控制和整体任务表现。我们的结果表明，当参与者在指定位置固定注视而不是用 SPEM 跟随物体时，接触前手部力的预期调节会减少。然而，通过要求参与者固定注视来约束注视似乎不会影响运动反应的定时或任务表现。这些结果表明，SPEM 可能对接触前手部力的预期控制很重要，并且在人类与移动物体相互作用时，也可能对肢体姿势的预期稳定起到关键作用。我们首次表明，平滑追踪眼球运动（SPEM）在调节接触前手部力的预期控制以稳定姿势对抗接触力方面发挥作用。SPEM 对于跟踪移动的物体很重要，有助于处理移动物体的运动，并且在衰老和许多神经障碍（如阿尔茨海默病和多发性硬化症）中受到影响。这些结果为研究 SPEM 的变化如何导致老年人和神经障碍患者肢体运动控制缺陷提供了新的基础。
