Medina Sonia, Tamè Luigi, Longo Matthew R
Department of Psychological Sciences, Birkbeck, University of London, London, WC1E 7HX, UK.
Exp Brain Res. 2018 Jan;236(1):31-42. doi: 10.1007/s00221-017-5105-2. Epub 2017 Oct 10.
Identifying the spatial location of touch on the skin surface is a fundamental function of our somatosensory system. Despite the fact that stimulation of even single mechanoreceptive afferent fibres is sufficient to produce clearly localised percepts, tactile localisation can be modulated also by higher level processes such as body posture. This suggests that tactile events are coded using multiple representations using different coordinate systems. Recent reports provide evidence for systematic biases on tactile localisation task, which are thought to result from a supramodal representation of the skin surface. While the influence of non-informative vision of the body and gaze direction on tactile discrimination tasks has been extensively studied, their effects on tactile localisation tasks remain largely unexplored. To address this question, participants performed a tactile localization task on their left hand under different visual conditions by means of a mirror box; in the mirror condition, a single stimulus was delivered on participants' hand, while the reflexion of the right hand was seen through the mirror; in the object condition, participants looked at a box through the mirror, and in the right hand condition, participants looked directly at their right hand. Participants reported the location of the tactile stimuli using a silhouette of a hand. Results showed a shift in the localization of the touches towards the tip of the fingers (distal bias) and the thumb (radial biases) across conditions. Critically, distal biases were reduced when participants looked towards the mirror compared to when they looked at their right hand suggesting that gaze direction reduces the typical proximo-distal biases in tactile localization. Moreover, vision of the hand modulates the internal configuration of points' locations, by elongating it, in the radio-ulnar axis.
识别皮肤表面触觉的空间位置是我们躯体感觉系统的一项基本功能。尽管即使刺激单个机械感受传入纤维就足以产生明确的局部感知，但触觉定位也可受到诸如身体姿势等高级过程的调节。这表明触觉事件是使用不同坐标系的多种表征进行编码的。最近的报告为触觉定位任务中的系统偏差提供了证据，这种偏差被认为是由皮肤表面的超模态表征导致的。虽然身体的非信息性视觉和注视方向对触觉辨别任务的影响已得到广泛研究，但它们对触觉定位任务的影响在很大程度上仍未被探索。为了解决这个问题，参与者通过一个镜像盒在不同视觉条件下对其左手进行触觉定位任务；在镜像条件下，在参与者手上施加单个刺激，同时通过镜子看到右手的反射；在物体条件下，参与者通过镜子看一个盒子，而在右手条件下，参与者直接看他们的右手。参与者使用手的轮廓报告触觉刺激的位置。结果显示，在不同条件下，触摸的定位向手指尖（远侧偏差）和拇指（桡侧偏差）发生了偏移。至关重要的是，与看右手时相比，参与者看向镜子时远侧偏差减小，这表明注视方向减少了触觉定位中典型的近远侧偏差。此外，手的视觉通过在桡尺轴上拉长它来调节点位置的内部配置。
