Latash M L, Gelfand I M, Li Z M, Zatsiorsky V M
Department of Kinesiology, Pennsylvania State University, University Park 16802, USA.
Exp Brain Res. 1998 Dec;123(3):255-62. doi: 10.1007/s002210050567.
We investigated force-sharing among three fingers which acted in parallel and produced ramp profiles of total force from zero to the maximal voluntary force. The feedback to the subject was provided by a visual signal on the monitor and could correspond to the sum of forces of all the fingers or to the sum of forces of two fingers, while the force of the third finger was added with a coefficient 2 or 0.5. If the subjects did not know about the distorted feedback, they showed a template-sharing pattern within the whole range of total force values. This pattern did not depend on which finger force was multiplied and by which coefficient. If the subjects knew in advance how the feedback signal would be calculated, they tried to perform the task using either only the finger whose force was multiplied by 2 or two fingers when the force of the third one was multiplied by 0.5. Further into the trial, however, they were unable to track the ramp pattern using only one or two fingers and demonstrated a search activity that could continue until the end of the trial or lead eventually to a three-finger sharing pattern similar to the template pattern used in cases of undistorted feedback. We conclude that the limited number of preferred sharing pattern within the studied task reflects an organization of the fingers into a structural unit (involving one, two, or all three fingers) by the central nervous system. The availability of structural units defines the presence of stable solutions available for the system.
我们研究了三根并行作用的手指之间的力分配情况，这些手指产生从零到最大随意力的总力斜坡曲线。通过监视器上的视觉信号向受试者提供反馈，该反馈可以对应于所有手指的力之和，或者对应于两个手指的力之和，而第三根手指的力则乘以系数2或0.5后相加。如果受试者不知道反馈被扭曲，他们在总力值的整个范围内都呈现出一种模板共享模式。这种模式不取决于哪根手指的力被乘以系数以及乘以哪个系数。如果受试者事先知道反馈信号将如何计算，当第三根手指的力乘以0.5时，他们会尝试仅使用力被乘以2的那根手指或两根手指来执行任务。然而，在试验后期，他们无法仅用一根或两根手指追踪斜坡模式，而是表现出一种搜索活动，这种活动可能会持续到试验结束，或者最终导致一种类似于在未扭曲反馈情况下使用的三指共享模式。我们得出结论，在所研究的任务中，有限数量的偏好共享模式反映了中枢神经系统将手指组织成一个结构单元（涉及一根、两根或三根手指）。结构单元的可用性定义了系统可用的稳定解决方案的存在。
