Saling M, Mescheriakov S, Molokanova E, Stelmach G E, Berger M
Institute of Normal and Pathological Physiology, Slovak Academy of Science, Bratislava, Slovakia.
Exp Brain Res. 1996 Mar;108(3):493-500. doi: 10.1007/BF00227272.
Past studies have examined the coupling of reach and grasp components during prehensile movements. Many of these studies have supported the view that these components reflect the output of two parallel, though temporally coupled, motor programs. When the grip aperture is Altered prior to the onset of prehension from its usual, normally flexed position to one of maximal finger extension, our previous work has shown that the grasp component appears to reorganize itself during the reach. This reorganization, consisting of a brief closing and reopening of the grip aperture, only slightly influenced the temporal components of the wrist transport. The present experiment continues this research theme by examining the characteristics of grip aperture reorganization through the comparison of the kinematics of prehension components during movements to two different size objects under normal and Altered grip aperture conditions. It was hypothesized that if the grip reorganization is task dependent it should be related to object size. The experiment found that in the Altered grip condition reorganization did occur, as indicated by a slight closing and reopening of the aperture without influencing the transport of the wrist. The amplitude of and the time to the observed inflection point in the aperture time course were related to object size. The velocity of grip closing for the large object showed double peaks, with the first substantially smaller than the second. Moreover, for the small object, the velocity of grip aperture closing also was double peaked, but the difference between peaks was less pronounced. These changes in grip velocity suggest that the grip reorganization is related to object size. No effect of Altered aperture was observed on the transport component. For both object sizes in the Altered condition, the final peak velocity of grip aperture was statistically significantly correlated with transport time and time to peak deceleration. In contrast, such correlations were not observed for the initial peak velocity of the grip aperture. Furthermore, time to maximum grip aperture was correlated with both time to peak wrist velocity and time peak to wrist deceleration. Thus, as the reach progressed toward the object, the grip and transport components became more interdependent. The results are consistent with the notion that, when a well-practiced, coordinated act such as prehension is confronted with an Altered grip posture at the onset of the reach, the grip can be reorganized during the transport to preserve the relative timing between them. Thus these data add to the growing awareness that not only is there temporal coupling between the reach and grasp components but that these components may be integrated by higher-order control mechanism.
过去的研究考察了抓握动作中伸手和抓握成分的耦合。这些研究中有许多支持这样一种观点，即这些成分反映了两个并行的、尽管在时间上耦合的运动程序的输出。当抓握孔径在抓握开始前从其通常的、正常弯曲的位置改变为最大手指伸展位置之一时，我们之前的研究表明，抓握成分在伸手过程中似乎会重新组织自身。这种重新组织包括抓握孔径的短暂闭合和重新打开，对腕部移动的时间成分影响很小。本实验通过比较在正常和改变抓握孔径条件下向两个不同大小物体移动时抓握成分的运动学特征，继续这一研究主题。假设如果抓握重新组织依赖于任务，那么它应该与物体大小有关。实验发现，在改变抓握条件下确实发生了重新组织，表现为孔径的轻微闭合和重新打开，而不影响腕部的移动。孔径时间进程中观察到的拐点的幅度和时间与物体大小有关。大物体抓握闭合的速度显示出双峰，第一个峰明显小于第二个峰。此外，对于小物体，抓握孔径闭合的速度也呈双峰，但峰之间的差异不太明显。抓握速度的这些变化表明抓握重新组织与物体大小有关。未观察到改变孔径对移动成分有影响。在改变条件下的两种物体大小中，抓握孔径的最终峰值速度与移动时间和峰值减速时间在统计学上均显著相关。相比之下，抓握孔径的初始峰值速度未观察到这种相关性。此外，最大抓握孔径时间与腕部峰值速度时间和腕部减速峰值时间均相关。因此，随着伸手动作向物体推进，抓握和移动成分变得更加相互依赖。这些结果与这样一种观点一致，即当一个熟练的、协调的动作（如抓握）在伸手开始时面临抓握姿势改变时，抓握可以在移动过程中重新组织，以保持它们之间的相对时间关系。因此，这些数据进一步增强了人们的认识，即不仅伸手和抓握成分之间存在时间耦合，而且这些成分可能由高阶控制机制整合。
