Spatial Specificity Of Tactile Enhancement During Reaching

Tactile signals on a hand that serves as movement goal are enhanced during movement planning and execution. Here, we examined how spatially specific tactile enhancement is when humans reach to their own static hand. Participants discriminated two brief and simultaneously presented tactile stimuli: a comparison stimulus on the left thumb or little finger from a reference stimulus on the sternum. Tactile stimuli were presented either during right-hand reaching towards the left thumb or little finger, or while holding both hands still (baseline). Consistent with our previous findings, stimuli on the left hand were perceived stronger during movement than baseline. However, tactile enhancement was not stronger when the stimuli were presented on the digit that served as reach target, thus the perception across the whole hand was uniformly enhanced. In experiment 2, we also presented stimuli on the upper arm in half of the trials to reduce the expectation of the stimulus location. Tactile stimuli on the target hand, but not on the upper arm, were generally enhanced, supporting the idea of a spatial gradient of tactile enhancement. Overall, our findings argue for low spatial specificity of tactile enhancement at movement-relevant body parts, here the target hand.在运动规划与执行阶段，作为运动目标的手部触觉信号会得到增强。本研究旨在探究当人类伸手触碰自身静止手部时，触觉增强的空间特异性表现。实验中，受试者需区分两组同时呈现的短时触觉刺激：分别施加于左侧拇指或小指的比较刺激，与施加于胸骨的参照刺激。触觉刺激的施加时机分为两类：一是右手伸向左侧拇指或小指的运动过程中，二是双手保持静止的基线（baseline）阶段。与此前的研究结果一致，相较于基线阶段，运动过程中受试者对左侧手部刺激的感知强度更高。然而，当刺激施加于作为运动目标的手指时，触觉增强效应并未出现进一步提升，即整个手部的感知强度均得到了均匀增强。在实验2中，为降低受试者对刺激位置的预期，我们在半数试次中将刺激施加于上臂。通常而言，施加于目标手部的触觉刺激会得到增强，而上臂的刺激则无此现象，这一结果支持触觉增强存在空间梯度的观点。综上，本研究结果表明，与运动相关的身体部位（此处为目标手部）的触觉增强效应空间特异性较低。