Department of Biobehavioral Sciences, Teachers College, Columbia University, 525 West 120th street, box 93, New York, NY 10027, USA.
Exp Brain Res. 2011 Jul;212(1):119-24. doi: 10.1007/s00221-011-2704-1. Epub 2011 May 6.
In addition to hand shaping, previous studies have shown that subjects adapt placement of individual digits to object properties such as its weight and center of mass. However, the extent to which digit placement varies based on task context is unknown. In the present study, we investigated where subjects place their digits on a bottle when the upcoming task (lift versus pour) and object content (i.e., amount of liquid: empty, half, and full) were manipulated. Our results showed that subjects anticipated both the upcoming task and content by varying digit placement when grasping the bottle prior to the onset of manipulation. Specifically, subjects increased the vertical distance between the thumb and index finger for pouring but not for lifting. This larger moment arm might have been established to decrease the amount of force required to tilt the bottle. Content also affected digit placement: the digits were placed higher and were wrapped more around the bottle with increasing content. This strategy may maximize grip surface contact, and hence grasp stability. These findings extend previous research showing that grasp planning not only takes place at a macroscopic level (whole-hand position relative to an object), but also at the level of individual digit placement. This finer level of control appears to be sensitive to the expected mechanical properties of the object and how these may affect grasp stability throughout the upcoming manipulation.
除了手工塑造，先前的研究表明，个体的手指放置位置会适应物体的特性，如重量和质心。然而，基于任务情境的手指放置变化程度尚不清楚。在本研究中，我们调查了在即将到来的任务（提起或倾倒）和物体内容（即液体量：空瓶、半瓶和满瓶）发生变化时，被试将手指放在瓶子的什么位置。我们的结果表明，在进行操作之前，被试通过在抓取瓶子时改变手指位置来预测即将到来的任务和内容。具体来说，被试在倾倒时增加了拇指和食指之间的垂直距离，但在提起时没有增加。这个更大的力臂可能是为了减少倾斜瓶子所需的力。内容也影响了手指的放置位置：随着内容的增加，手指放置的位置更高，并且更缠绕在瓶子周围。这种策略可能最大限度地增加了握把表面的接触，从而提高了抓握的稳定性。这些发现扩展了先前的研究，表明抓握规划不仅发生在宏观层面（手相对于物体的整体位置），还发生在个体手指放置的层面。这种更精细的控制水平似乎对物体的预期机械性能敏感，以及这些性能如何影响整个即将到来的操作过程中的抓握稳定性。
