Knight Frances Le Cornu, Longo Matthew R, Bremner Andrew J
Sensorimotor Development Research Unit, Department of Psychology, Goldsmiths, University of London, United Kingdom.
Department of Psychological Sciences, Birkbeck, University of London, United Kingdom.
Cognition. 2014 May;131(2):254-62. doi: 10.1016/j.cognition.2014.01.005. Epub 2014 Feb 19.
The tactile surface forms a continuous sheet covering the body. And yet, the perceived distance between two touches varies across stimulation sites. Perceived tactile distance is larger when stimuli cross over the wrist, compared to when both fall on either the hand or the forearm. This effect could reflect a categorical distortion of tactile space across body-part boundaries (in which stimuli crossing the wrist boundary are perceptually elongated) or may simply reflect a localised increased in acuity surrounding anatomical landmarks (in which stimuli near the wrist are perceptually elongated). We tested these two interpretations across two experiments, by comparing a well-documented bias to perceive mediolateral tactile distances across the forearm/hand as larger than proximodistal ones along the forearm/hand at three different sites (hand, wrist, and forearm). According to the 'categorical' interpretation, tactile distances should be elongated selectively in the proximodistal axis thus reducing the anisotropy. According to the 'localised acuity' interpretation, distances will be perceptually elongated in the vicinity of the wrist regardless of orientation, leading to increased overall size without affecting anisotropy. Consistent with the categorical account, we found a reduction in the magnitude of anisotropy at the wrist, with no evidence of a corresponding localised increase in precision. These findings demonstrate that we reference touch to a representation of the body that is categorically segmented into discrete parts, which consequently influences the perception of tactile distance.
触觉表面形成覆盖身体的连续薄片。然而,两次触摸之间的感知距离在不同的刺激部位有所不同。与两次触摸都落在手部或前臂上相比,当刺激跨越手腕时,感知到的触觉距离更大。这种效应可能反映了触觉空间在身体部位边界处的分类扭曲(即跨越手腕边界的刺激在感知上被拉长),或者可能仅仅反映了围绕解剖标志的局部敏锐度增加(即靠近手腕的刺激在感知上被拉长)。我们通过比较一个有充分记录的偏差来测试这两种解释,即在三个不同部位(手部、手腕和前臂),感知到的前臂/手部中外侧的触觉距离比沿着前臂/手部近端到远端的距离更大。根据“分类”解释,触觉距离应该在前近端到远端轴上有选择地拉长,从而减少各向异性。根据“局部敏锐度”解释,无论方向如何,手腕附近的距离在感知上都会被拉长,导致整体尺寸增加而不影响各向异性。与分类解释一致,我们发现手腕处各向异性的大小有所降低,没有证据表明精度相应地局部增加。这些发现表明,我们将触觉参照到身体的一种分类为离散部分的表征上,这进而影响了对触觉距离的感知。