The Brain and Mind Institute, University of Western Ontario, London, Ontario, Canada.
Movement Control and Neuroplasticity Research Group, Department of Movement Sciences, Biomedical Sciences Group, KU Leuven, Leuven, Belgium.
J Neurophysiol. 2021 Apr 1;125(4):1348-1366. doi: 10.1152/jn.00374.2020. Epub 2021 Jan 20.
Observation of object lifting allows updating of internal object representations for object weight, in turn enabling accurate scaling of fingertip forces when lifting the same object. Here, we investigated whether lift observation also enables updating of internal representations for an object's weight distribution. We asked participants to lift an inverted T-shaped manipulandum, of which the weight distribution could be changed, in turns with an actor. Participants were required to minimize object roll (i.e., "lift performance") during lifting and were allowed to place their fingertips at self-chosen locations. The center of mass changed unpredictably every third to sixth trial performed by the actor, and participants were informed that they would always lift the same weight distribution as the actor. Participants observed either erroneous (i.e., object rolling toward its heavy side) or skilled (i.e., minimized object roll) lifts. Lifting performance after observation was compared with lifts without prior observation and with lifts after active lifting, which provided haptic feedback about the weight distribution. Our results show that observing both skilled and erroneous lifts convey an object's weight distribution similar to active lifting, resulting in altered digit positioning strategies. However, minimizing object roll on novel weight distributions was only improved after observing error lifts and not after observing skilled lifts. In sum, these findings suggest that although observing motor errors and skilled motor performance enables updating of digit positioning strategy, only observing error lifts enables changes in predictive motor control when lifting objects with unexpected weight distributions. Individuals are able to extract an object's size and weight by observing interactions with objects and subsequently integrate this information in their own motor repertoire. Here, we show that this ability extrapolates to weight distributions. Specifically, we highlighted that individuals can perceive an object's weight distribution during lift observation but can only partially embody this information when planning their own actions.
观察物体的提升过程可以更新物体重量的内部表示，从而在提升相同物体时准确调整指尖力的大小。在这里，我们研究了观察提升过程是否也可以更新物体重量分布的内部表示。我们要求参与者轮流与演员一起提升一个倒置的 T 形操纵杆，其重量分布可以改变。参与者在提升过程中被要求将物体的滚动最小化（即“提升表现”），并可以将指尖放置在自选择的位置。演员每进行第三到第六次试验时，质心都会不可预测地改变，参与者被告知他们将始终提升与演员相同的重量分布。参与者观察到错误的（即物体向其较重的一侧滚动）或熟练的（即最小化物体滚动）提升过程。观察后的提升表现与没有预先观察的提升表现以及提供关于重量分布的触觉反馈的主动提升表现进行了比较。我们的结果表明，观察熟练和错误的提升过程都可以传达物体的重量分布，类似于主动提升过程，从而改变了指尖的定位策略。然而，只有在观察错误的提升过程后，而不是在观察熟练的提升过程后，新的重量分布上最小化物体滚动的表现才会得到改善。总之，这些发现表明，尽管观察运动错误和熟练的运动表现可以更新指尖定位策略，但只有观察错误的提升过程才能在提升具有意外重量分布的物体时改变预测性运动控制。个体通过观察与物体的相互作用来提取物体的大小和重量，然后将这些信息整合到自己的运动技能中。在这里，我们表明这种能力可以推断到重量分布上。具体来说，我们强调个体可以在提升观察过程中感知物体的重量分布，但在规划自己的动作时只能部分体现这些信息。
