Department of Neuroscience, Canadian Centre for Behavioural Neuroscience, University of Lethbridge, Lethbridge, AB, T1K 3M4, Canada.
Exp Brain Res. 2013 Apr;225(4):465-77. doi: 10.1007/s00221-012-3386-z. Epub 2013 Jan 4.
The Dual Visuomotor Channel theory proposes that skilled reaching is composed of a Reach that directs the hand in relation to the extrinsic properties of an object (e.g., location) and a Grasp that opens and closes the hand in relation to the intrinsic properties of an object (e.g., size). While Reach and Grasp movements are often guided by vision, they can also be performed without vision when reaching for a body part or an object on one's own body. Memory of a recently touched but unseen object can also be used to guide Reach and Grasp movements although the touch-response memory durations described are extremely brief (Karl et al. in Exp Brain Res 219:59-74, 2012a). The purpose of the present study was to determine whether repeated nonvisual reaching for a consistent object could calibrate Reach and Grasp movements in a way similar to those guided by vision. The nonvision group wore vision-occluding goggles and reached for fifty consecutive trials for a round donut ball placed on a pedestal. The control group performed the same task with vision. Frame-by-frame video analysis and linear kinematics revealed that nonvision participants consistently used an elevated Reach trajectory, in which the hand, rather than being directed toward the target in the horizontal plane, was first elevated above the target before being lowered to touch and locate it. First contact was established with the dorsal surface of the target, and thus, adjustments in contact locations were often required for purchase. Although nonvision participants initially used an open and extended hand during transport, with practice they began to scale digit aperture to object size with an accuracy and temporal relation similar to vision participants. The different ways in which the Reach and Grasp movements respond to nonvisual learning are discussed in relation to support for the dual channel theory of reaching and to the idea that the Reach and Grasp channels may be differentially dependent on online visual guidance.
双视动通道理论提出，熟练的伸手动作由两部分组成：一是伸手，用于将手相对于物体的外在属性（例如位置）进行定位；二是抓握，用于将手相对于物体的内在属性（例如大小）进行开合。虽然伸手和抓握动作通常由视觉引导，但当伸手去够身体的某个部位或自己身上的某个物体时，也可以在没有视觉的情况下完成。当伸手去够一个之前摸到但现在看不见的物体时，也可以使用记忆来引导伸手和抓握动作，尽管所描述的触摸-反应记忆持续时间极短（Karl 等人，2012a，实验脑研究 219:59-74）。本研究的目的是确定重复进行无视觉的伸手去够一个固定物体的动作，是否可以像视觉引导那样校准伸手和抓握动作。无视觉组佩戴视觉遮挡护目镜，连续伸手够 50 次放在基座上的圆形面包圈。对照组则在有视觉的情况下完成相同的任务。逐帧视频分析和线性运动学揭示，无视觉参与者始终使用一种抬高的伸手轨迹，手不是在水平平面上直接指向目标，而是先被抬高到目标上方，然后再降低去触摸和定位目标。首先与目标的背面接触，因此，通常需要调整接触位置以进行抓握。虽然无视觉参与者在运输过程中最初使用张开的手，但随着练习，他们开始根据目标大小调整手指张开程度，其准确性和时间关系与有视觉参与者相似。文中讨论了伸手和抓握动作以不同方式对无视觉学习的反应，这与对伸手双通道理论的支持以及伸手和抓握通道可能对在线视觉引导具有不同依赖性的观点有关。
