Cole Kelly J
Department of Integrative Physiology, The University of Iowa, S. 501 FH, Iowa City, IA 52242, USA.
Exp Brain Res. 2008 Jul;188(4):551-7. doi: 10.1007/s00221-008-1392-y. Epub 2008 Apr 29.
The brain can accurately predict the forces needed to efficiently manipulate familiar objects in relation to mechanical properties such as weight. These predictions involve memory or some type of central representation, but visual analysis of size also yields accurate predictions of the needed fingertip forces. This raises the issue of which process (weight memory or visual size analysis) is used during everyday life when handling familiar objects. Our aim was to determine if subjects use a sensorimotor memory of weight, or a visual size analysis, to predictively set their vertical lift force when lifting a recently handled object. Two groups of subjects lifted an opaque brown bottle filled with water (470 g) during the first experimental session, and then rested for 15 min in a different room. Both groups were told that they would lift the same bottle in their next session. However, the experimental group returned to lift a slightly smaller bottle filled with water (360 g) that otherwise was identical in appearance to the first bottle. The control group returned to lift the same bottle from the first session, which was only partially filled with water so that it also weighed 360 g. At the end of the second session subjects were asked if they observed any changes between sessions, but no subject indicated awareness of a specific change. An acceleration ratio was computed by dividing the peak vertical acceleration during the first lift of the second session by the average peak acceleration of the last five lifts during the first session. This ratio was >1 for the control subjects 1.30 (SEM 0.08), indicating that they scaled their lift force for the first lift of the second session based on a memory of the (heavier) bottle from the first session. In contrast, the acceleration ratio was 0.94 (0.10) for the experimental group (P < 0.011). We conclude that the experimental group processed visual cues concerning the size of the bottle. These findings raise the possibility that even with familiar objects we predict fingertip forces using an on-line visual analysis of size (along with memory of density), rather than accessing memory related to object weight.
大脑能够根据诸如重量等机械特性，准确预测有效操控熟悉物体所需的力量。这些预测涉及记忆或某种类型的中枢表征，但对尺寸的视觉分析也能准确预测所需的指尖力量。这就引出了在日常生活中处理熟悉物体时使用哪种过程（重量记忆或视觉尺寸分析）的问题。我们的目的是确定受试者在提起最近处理过的物体时，是使用重量的感觉运动记忆还是视觉尺寸分析来预测性地设定其垂直举力。两组受试者在第一次实验环节中提起一个装满水（470克）的不透明棕色瓶子，然后在另一个房间休息15分钟。两组受试者都被告知他们将在接下来的环节中提起同一个瓶子。然而，实验组回来提起一个稍小一点的装满水（360克）的瓶子，这个瓶子在外观上与第一个瓶子相同。对照组回来提起与第一次环节中相同的瓶子，该瓶子只装了部分水，所以重量也是360克。在第二次环节结束时，受试者被问及他们是否观察到两个环节之间有任何变化，但没有受试者表示意识到有具体变化。通过将第二次环节第一次提起时的峰值垂直加速度除以第一次环节最后五次提起的平均峰值加速度来计算加速度比值。对照组受试者的这个比值大于1，为1.30（标准误0.08），表明他们根据对第一次环节中（较重的）瓶子的记忆来调整第二次环节第一次提起时的举力。相比之下，实验组的加速度比值为0.94（0.10）（P<0.011）。我们得出结论，实验组处理了关于瓶子尺寸的视觉线索。这些发现增加了一种可能性，即即使对于熟悉的物体，我们也是通过对尺寸的在线视觉分析（以及密度记忆）来预测指尖力量，而不是利用与物体重量相关的记忆。
