Shibata Daisuke, Santello Marco
Kinesiology Program, School of Nutrition and Health Promotion, Arizona State University, Tempe, Arizona; and.
School of Biological and Health Systems Engineering, Arizona State University, Tempe, Arizona
J Neurophysiol. 2017 Nov 1;118(5):2935-2943. doi: 10.1152/jn.00211.2017. Epub 2017 Aug 23.
Dexterous manipulation relies on the ability to modulate grasp forces to variable digit position. However, the sensorimotor mechanisms underlying such critical ability are not well understood. The present study addressed whether digit force-to-position modulation relies entirely on feedback of digit placement and force, or on the integration of such feedback with motor commands responsible for digit positioning. In two experiments, we asked 25 subjects to estimate the index fingertip position relative to the thumb (perception test) or to grasp and lift an object with an asymmetrical mass distribution while preventing object roll (action test). Both tests were performed after subjects' digits were placed actively or passively at different distances (active and passive condition, respectively) and without visual feedback. Because motor commands for digit positioning would be integrated with position and force feedback in the active condition, we hypothesized this condition to be characterized by greater accuracy of digit position estimation and digit force-to-position modulation. Surprisingly, discrimination of digit position and force-to-position modulation was statistically indistinguishable in the active and passive conditions. We conclude that voluntary commands for digit positioning are not essential for accurate estimation of finger position or modulation of digit forces to variable digit position. Thus digit force-to-position modulation can be implemented by integrating sensory feedback of digit position and voluntary commands of digit force production following contact. This study was designed to understand the sensorimotor mechanisms underlying digit force-to-position modulation required for manipulation. Surprisingly, estimation of relative digit position and force-to-position modulation was accurate regardless of whether the digits were passively or actively positioned. Therefore, accurate estimation of digit position does not require an efference copy of active digit positioning, and the hypothesized advantage of active over passive movement on estimation of end-point position appears to be task and effector dependent.
灵巧操作依赖于根据手指位置变化来调节抓握力的能力。然而，这种关键能力背后的感觉运动机制尚未得到充分理解。本研究探讨了手指力到位置的调节是完全依赖于手指放置和力的反馈，还是依赖于这种反馈与负责手指定位的运动指令的整合。在两个实验中，我们要求25名受试者估计食指指尖相对于拇指的位置（感知测试），或者在防止物体滚动的同时抓握并提起一个质量分布不对称的物体（动作测试）。这两个测试都是在受试者的手指分别主动或被动放置在不同距离后（分别为主动和被动条件）且没有视觉反馈的情况下进行的。由于在主动条件下，用于手指定位的运动指令会与位置和力的反馈整合在一起，我们假设这种条件下手指位置估计和手指力到位置的调节会具有更高的准确性。令人惊讶的是，在主动和被动条件下，手指位置的辨别和力到位置的调节在统计学上没有差异。我们得出结论，手指定位的自主指令对于准确估计手指位置或根据手指位置变化调节手指力并非必不可少。因此，手指力到位置的调节可以通过整合手指位置的感觉反馈和接触后手指力产生的自主指令来实现。本研究旨在了解操作所需的手指力到位置调节背后的感觉运动机制。令人惊讶的是，无论手指是被动还是主动定位，相对手指位置的估计和力到位置的调节都是准确的。因此，准确估计手指位置并不需要主动手指定位的传出副本，并且主动运动相对于被动运动在估计终点位置方面的假设优势似乎取决于任务和效应器。
