Novak K E, Miller L E, Houk J C
Northwestern University, Department of Physiology, Chicago, IL 60611, USA.
Exp Brain Res. 2002 Jun;144(3):351-64. doi: 10.1007/s00221-002-1060-6. Epub 2002 Apr 13.
Rapid targeted movements are subject to special control considerations, since there may be inadequate time available for either visual or somatosensory feedback to be effective. In our experiments, subjects rapidly rotated a knob to align a pointer to one of several targets. We recognized three different types of movement segments: the primary movement, and two types of submovement, which frequently followed. The submovements were initiated either before or after the end of the primary movement. The former, or "overlapping" type of submovement altered the kinematics of the overall movement and was consequently difficult to detect. We used a direct, objective test of movement regularity to detect overlapping submovements, namely, examining the number of jerk and snap zero crossings during the second half of a movement. Any overlapping submovements were parsed from the overall movement by subtracting the velocity profile of the primary movement. The velocity profiles of the extracted submovements had near-symmetric bell shapes, similar to the shapes of both pure primary movements and nonoverlapping submovements. This suggests that the same neural control mechanisms may be responsible for producing all three types of movement segments. Overlapping submovements corrected for errors in the amplitude of the primary movement. Furthermore, they may account for the previously observed, speed-dependent asymmetry of the velocity profile. We used a nonlinear model of the musculoskeletal system to explain most of the kinematic features of these rapid hand movements, including how discrete submovements are superimposed on a primary movement. Finally, we present a plausible scheme for how the central nervous system may generate the commands to control these rapid hand movements.
快速的目标导向运动需要特殊的控制考量，因为视觉或体感反馈可能没有足够的时间来有效发挥作用。在我们的实验中，受试者快速旋转旋钮，将指针与几个目标之一对齐。我们识别出三种不同类型的运动片段：主运动，以及经常随之出现的两种子运动类型。子运动在主运动结束之前或之后启动。前一种，即“重叠”类型的子运动改变了整体运动的运动学特征，因此很难被检测到。我们使用了一种直接、客观的运动规律性测试来检测重叠子运动，即检查运动后半段的急动度和加速度突变过零点的数量。通过减去主运动的速度曲线，从整体运动中解析出任何重叠子运动。提取的子运动的速度曲线具有近似对称的钟形，类似于纯主运动和非重叠子运动的形状。这表明相同的神经控制机制可能负责产生所有三种类型的运动片段。重叠子运动纠正了主运动幅度的误差。此外，它们可能解释了先前观察到的、与速度相关的速度曲线不对称性。我们使用肌肉骨骼系统的非线性模型来解释这些快速手部运动的大多数运动学特征，包括离散子运动如何叠加在主运动上。最后，我们提出了一个关于中枢神经系统如何生成控制这些快速手部运动的指令的合理方案。
