Johansson R S, Riso R, Häger C, Bäckström L
Department of Physiology, Umeå University, Sweden.
Exp Brain Res. 1992;89(1):181-91. doi: 10.1007/BF00229015.
In manipulating 'passive' objects, for which the physical properties are stable and therefore predictable, information essential for the adaptation of the motor output to the properties of the current object is principally based on 'anticipatory parameter control' using sensorimotor memories, i.e., an internal representation of the object's properties based on previous manipulative experiences. Somatosensory afferent signals only intervene intermittently according to an 'event driven' control policy. The present study is the first in a series concerning the control of precision grip when manipulating 'active' objects that exert unpredictable forces which cannot be adequately represented in a sensorimotor memory. Consequently, the manipulation may be more reliant on a moment-to-moment sensory control. Subjects who were prevented from seeing the hand used the precision grip to restrain a manipulandum with two parallel grip surfaces attached to a force motor which produced distally directed (pulling) loads tangential to the finger tips. The trapezoidal load profiles consisted of a loading phase (4 N/s), plateau phase and an unloading phase (4 N/s) returning the load force to zero. Three force amplitudes were delivered in an unpredictable sequence; 1 N, 2 N and 4 N. In addition, trials with higher load rate (32 N/s) at a low amplitude (0.7 N), were superimposed on various background loads. The movement of the manipulandum, the load forces and grip forces (normal to the grip surfaces) were recorded at each finger. The grip force automatically changed with the load force during the loading and unloading phases. However, the grip responses were initiated after a brief delay. The response to the loading phase was characterized by an initial fast force increase termed the 'catch-up' response, which apparently compensated for the response delay--the grip force adequately matched the current load demands by the end of the catch-up response. In ramps with longer lasting loading phases (amplitude greater than or equal to 2 N) the catch-up response was followed by a 'tracking' response, during which the grip force increased in parallel with load force and maintained an approximately constant force ratio that prevented frictional slips. The grip force during the hold phase was linearly related to the load force, with an intercept close to the grip force used prior to the loading. Likewise, the grip force responses evoked by the fast loadings superimposed on existing loads followed the same linear relationship.(ABSTRACT TRUNCATED AT 400 WORDS)
在操作“被动”物体时，其物理属性稳定因而可预测，使运动输出适应当前物体属性所需的信息主要基于利用感觉运动记忆进行的“预期参数控制”，即基于先前操作经验对物体属性的内部表征。体感传入信号仅根据“事件驱动”控制策略间歇性地介入。本研究是关于操作“主动”物体时精确抓握控制系列研究中的首个，这些“主动”物体施加不可预测的力，无法在感觉运动记忆中得到充分表征。因此，操作可能更依赖即时的感觉控制。被阻止看手的受试者用精确抓握来约束一个带有两个平行抓握面的操作手柄，该手柄连接到一个力电机上，力电机产生指向手指尖远端的（拉力）负载。梯形负载曲线包括加载阶段（4N/s）、平稳阶段和卸载阶段（4N/s），卸载阶段将负载力恢复到零。三个力幅值以不可预测的顺序施加；1N、2N和4N。此外，在低幅值（0.7N）下具有更高加载速率（32N/s）的试验叠加在各种背景负载上。记录每个手指处操作手柄的运动、负载力和抓握力（垂直于抓握面）。在加载和卸载阶段，抓握力随负载力自动变化。然而，抓握反应在短暂延迟后启动。对加载阶段的反应以初始快速力增加为特征，称为“追赶”反应，这显然补偿了反应延迟——在追赶反应结束时，抓握力充分匹配了当前的负载需求。在加载阶段持续时间更长（幅值大于或等于2N）的斜坡中，追赶反应之后是“跟踪”反应，在此期间，抓握力与负载力平行增加，并保持近似恒定的力比，以防止摩擦滑动。保持阶段的抓握力与负载力呈线性关系，截距接近加载前使用的抓握力。同样，叠加在现有负载上的快速加载所引发的抓握力反应遵循相同的线性关系。（摘要截选至400字）
