Smits-Engelsman B C M, Van Galen G P, Duysens J
NICI, University of Nijmegen, The Netherlands.
Exp Brain Res. 2002 Jul;145(2):222-30. doi: 10.1007/s00221-002-1115-8. Epub 2002 May 7.
According to Fitts' law, there is speed-accuracy trade-off in a wide variety of discrete aiming movements. However, it is unknown whether the same law applies to cyclic aiming movements. In the present study, a comparison is made between discrete versus cyclic aiming movements. A group of 24 healthy participants made graphical pen movements in 12 different aiming tasks in which successive finger and wrist movements were emphasized, consecutively executed as discrete and cyclic movements and varying in three target widths. In the cyclic condition, aiming movements consisted of back-and-forth movements that were performed in immediate succession for 20 s. In the discrete condition, back-and-forth aiming movements were drawn as 20 single strokes, starting after a go signal and stopping after reaching the target area. The targets had various levels of spatial accuracy and the movements had different directions (from lower left to upper right; from lower right to upper left) elicit either predominantly wrist or finger movements. The amount of information processed per unit of time (bits per second; index of performance, IP), tangential velocity, the pen pressure, and the ratio of peak-over-mean velocity were studied to gain understanding about the differences in control between discrete and cyclic movements. It was found that the IP and movement velocity were almost twice as large in cyclic versus discrete movements. In contrast, the axial pen pressure and the ratios of peak-over-mean velocity were much lower in cyclic movements (1.24 N versus 0.94 N; 2.26 N versus 1.81 N). The results of our study indicate that the predicted constant IP does not hold for rapid cyclic aiming movements and that speed-accuracy trade-off is different. It is concluded that cyclic movements exploit the energetic and physiological properties of the neuromotor system. Expected differences in brain activity related to discrete and cyclic aiming movements are discussed as well as several neurophysiological mechanisms, which predict more economic force recruitment and information processing in cyclic than in discrete movements.
根据菲茨定律，在各种各样的离散瞄准动作中存在速度-准确性权衡。然而，同样的定律是否适用于循环瞄准动作尚不清楚。在本研究中，对离散瞄准动作和循环瞄准动作进行了比较。一组24名健康参与者在12种不同的瞄准任务中进行图形笔移动，这些任务强调连续的手指和手腕动作，分别作为离散动作和循环动作连续执行，且目标宽度有三种变化。在循环条件下，瞄准动作由连续进行20秒的来回动作组成。在离散条件下，来回瞄准动作被绘制成20个单笔画，在开始信号后开始，到达目标区域后停止。目标具有不同程度的空间准确性，动作有不同方向（从左下角到右上角；从右下角到左上角），会引发主要是手腕或手指的动作。研究了单位时间内处理的信息量（每秒比特数；性能指标，IP）、切向速度、笔压力以及峰值与平均速度之比，以了解离散动作和循环动作在控制方面的差异。结果发现，循环动作中的IP和动作速度几乎是离散动作中的两倍。相比之下，循环动作中的轴向笔压力和峰值与平均速度之比要低得多（1.24牛对0.94牛；2.26牛对1.81牛）。我们的研究结果表明，预测的恒定IP不适用于快速循环瞄准动作，速度-准确性权衡也有所不同。得出的结论是，循环动作利用了神经运动系统的能量和生理特性。还讨论了与离散和循环瞄准动作相关的大脑活动的预期差异以及几种神经生理机制，这些机制预测循环动作比离散动作在力量募集和信息处理方面更经济。
