Ayala Maria N, 't Hart Bernard Marius, Henriques Denise Y P
Centre for Vision Research, York University, Toronto, ON, Canada.
Department of Psychology, York University, Toronto, ON, Canada.
Exp Brain Res. 2015 Dec;233(12):3433-45. doi: 10.1007/s00221-015-4411-9. Epub 2015 Aug 20.
When reaching towards objects, the human central nervous system (CNS) can actively compensate for two different perturbations simultaneously (dual adaptation), though this does not simply occur upon presentation. Dual adaptation is made more difficult when the desired trajectories and targets are identical and hence do not cue the impending perturbation. In cases like these, the CNS requires contextual cues in order to predict the dynamics of the environment. Not all cues are effective at facilitating dual adaptation. In two experiments, we investigated the efficacy of two contextual cues that are intrinsic to the CNS, namely hand as well as body posture in concurrently adapting to two opposing visuomotor rotations. For the hand posture experiment, we also look at the role of extended training. Participants reached manually to visual targets with their unseen hand represented by a cursor that was rotated either 30° clockwise or counterclockwise, determined randomly on each reach. Each rotation was associated with a distinct hand posture (a precision or power grip, respectively) in one experiment and a distinct body rotation (10° leftward or rightward turn of the seat, respectively, while fixating straight) in the second experiment. Critically, the targets (and thus, the required cursor trajectories) were identical in both rotations. We found that how people held the tool or oriented their body while reaching is sufficient for concurrently adapting separate visuomotor mappings such that over time, reach errors significantly decrease. Extended practice did not lead to further benefits though. These findings suggest that when the required cursor movements are identical for different visuomotor mappings, dual adaptation is still possible given sufficient intrinsic contextual cues.
在伸手够取物体时，人类中枢神经系统（CNS）能够同时主动补偿两种不同的扰动（双重适应），不过这种情况并非在扰动出现时就简单地发生。当期望的轨迹和目标相同时，双重适应会变得更加困难，因为此时无法提示即将到来的扰动。在这类情况下，中枢神经系统需要情境线索来预测环境的动态变化。并非所有线索都能有效地促进双重适应。在两项实验中，我们研究了中枢神经系统固有的两种情境线索的有效性，即手部以及身体姿势在同时适应两种相反的视觉运动旋转时的作用。对于手部姿势实验，我们还考察了强化训练的作用。参与者用未被看到的手手动伸向视觉目标，手由一个光标表示，光标随机每次伸向目标时顺时针或逆时针旋转30°。在一项实验中，每次旋转都与一种独特的手部姿势（分别为精确抓握或强力抓握）相关联，在第二项实验中，每次旋转都与一种独特的身体旋转（座椅分别向左或向右转10°，同时直视前方）相关联。关键的是，两次旋转中的目标（以及因此所需的光标轨迹）是相同的。我们发现，人们在伸手时持握工具的方式或身体的朝向足以同时适应不同的视觉运动映射，以至于随着时间的推移，伸手误差会显著减小。不过，强化练习并没有带来进一步的益处。这些发现表明，当不同视觉运动映射所需的光标运动相同时，给定足够的内在情境线索，双重适应仍然是可能的。
