School of Psychology, Faculty of Medicine and Health, University of Leeds, Leeds, United Kingdom.
School of Mechanical Engineering, Faculty of Engineering, University of Leeds, Leeds, United Kingdom.
PLoS One. 2018 Feb 22;13(2):e0193185. doi: 10.1371/journal.pone.0193185. eCollection 2018.
The duration of reach-to-grasp movements is influenced by the size of the contact surfaces, such that grasping objects with smaller contact surface areas takes longer. But what is the influence of asymmetric contact surfaces? In Experiment 1a, participants reached-to-lift wooden blocks off a table top, with the contact locations for the thumb and index finger varying in surface size. The time taken to lift the block was driven primarily by the thumb contact surface, which showed a larger effect size for the dependent variable of movement duration than the index finger's contact surface. In Experiment 1b participants reached-to-grasp (but not lift) the blocks. The same effect was found with duration being largely driven by contact surface size for the thumb. Experiment 2 tested whether this finding generalised to movements towards conical frusta grasped in a different plane mounted off the table top. Experiment 2 showed that movement duration again was dictated primarily by the size of the thumb's contact surface. The thumb contact surface was the visible surface in experiments 1 and 2 so Experiment 3 explored grasping when the index finger's contact surface was visible (participants grasped the frusta with the index finger at the top). An interaction between thumb and finger surface size was now found to determine movement duration. These findings provide the first empirical report of the impact of asymmetric contact surfaces on prehension, and may have implications for scientists who wish to model reach-to-grasp behaviours.
伸手抓取动作的持续时间受接触表面大小的影响，因此，抓取接触面积较小的物体需要更长的时间。但是，不对称的接触表面有什么影响呢？在实验 1a 中，参与者伸手从桌面提起木块，拇指和食指的接触位置的接触面积大小不同。提起木块的时间主要取决于拇指的接触面积，拇指的接触面积对运动持续时间这一因变量的影响比食指的接触面积大。在实验 1b 中，参与者伸手但不提起木块。同样的发现表明，持续时间主要受拇指接触面积大小的影响。实验 2 检验了这一发现是否适用于在远离桌面的另一个平面上抓取的锥形截锥体的运动。实验 2 表明，运动持续时间再次主要由拇指的接触面积决定。在实验 1 和 2 中，拇指的接触面积是可见的表面，因此实验 3 探索了当食指的接触面积可见时的抓取情况（参与者用食指的顶部抓住截锥体）。现在发现，拇指和食指接触面积的相互作用决定了运动持续时间。这些发现首次提供了关于不对称接触表面对抓握影响的经验证据，可能对希望对伸手抓取行为进行建模的科学家具有一定的启示意义。
