Graduate School of Human and Environmental Studies, Kyoto University, Japan.
Faculty of Integrated Human Studies, Kyoto University, Japan.
Hum Mov Sci. 2024 Aug;96:103256. doi: 10.1016/j.humov.2024.103256. Epub 2024 Aug 1.
In this study, we investigated how the temporal properties of the preparation phase for upper limb movements are affected by the reaching direction and distance. Twelve right-handed participants performed three motor tasks: two types of reaching movements and one finger-lifting movement. The reaching movements were performed from the home position to 15 target locations (five directions and three distances) as quickly and precisely as possible under two conditions: pre-cueing the target to allocate the sufficient time for the motor-planning process before movement initiation, and no-cuing. The finger lifting movement was performed by lifting the index finger (from the home position) upward in the air as quickly as possible. The reaction time (RT), movement time (MT), and kinematics of the index finger were obtained for each condition. In addition, differential RTs (DRT) were calculated by subtracting the RT for no-cue lifting from that for no-cue reaching, thereby implicitly representing the time required for the motor-planning process for reaching movements. The results indicated the anisotropy of the DRTs being larger in the forward and left-forward directions than that in the right-forward direction, and larger in the forward direction than that in the right direction for the middle distance. It is suggested that the temporal costs of the motor-planning process depend on the movement direction and distance. In the kinematic analysis, the MTs showed the anisotropy being the largest in the left-forward among all directions. Meanwhile, the time from peak velocity to terminate the movement (TFPV) was significantly longer in the left-forward direction when no-cueing the target than when pre-cueing. These results suggest that reaching movement is refined during the online-control process to accomplish the intended performance if a reaching movement under the no-cue condition is initiated before building sufficient motor planning, especially in the direction requiring large temporal costs. It is likely that humans achieve their intended movements by allocating the temporal costs required before and after movement initiation according to the difficulty of motor control which varies with the direction and distance.
在这项研究中，我们调查了上肢运动准备阶段的时间特性如何受到运动方向和距离的影响。十二名右利手参与者进行了三项运动任务：两种类型的伸手动作和一种手指抬起动作。伸手动作是从起始位置快速而精确地移动到 15 个目标位置（五个方向和三个距离），有两种条件：目标预提示，在运动启动前为运动规划过程分配足够的时间，以及无提示。手指抬起动作是通过将食指（从起始位置）向上快速抬起至空中。记录了每种条件下的反应时间（RT）、运动时间（MT）和食指运动学。此外，通过从无提示抬手的 RT 中减去无提示伸手的 RT，计算出差异 RT（DRT），从而隐含地表示伸手运动的运动规划过程所需的时间。结果表明，DRT 的各向异性在前进和左前方向比右前方向更大，在中距离时在前进方向比在右方向更大。这表明运动规划过程的时间成本取决于运动方向和距离。在运动学分析中，MT 显示在所有方向中，左前方向的各向异性最大。同时，当无目标提示时，从峰值速度到停止运动的时间（TFPV）在左前方向显著长于目标预提示时。这些结果表明，如果在建立足够的运动规划之前发起无提示条件下的伸手运动，则伸手运动在在线控制过程中会得到细化，以完成预期的表现，尤其是在需要较大时间成本的方向上。人类可能会根据运动控制的难度，根据运动启动前后所需的时间成本来分配时间成本，从而实现预期的运动。运动控制的难度因方向和距离而异。
