Perception of distance between two touches varies with orientation on the hand, with distances aligned with hand width perceived as larger than those aligned with hand length. Similar anisotropies are found on other body parts (e.g., the face), suggesting they may reflect a general feature of tactile organization, but appear absent on other body parts (e.g., the belly). Here, we investigated tactile-distance anisotropy on the foot, a body part structurally and embryologically similar to the hand, but with very different patterns of functional usage in humans. In three experiments, we compared the perceived distance between pairs of touches aligned with the medio-lateral and proximal-distal foot axes. On the hairy skin of the foot dorsum, anisotropy was consistently found, with distances aligned with the medio-lateral foot axis perceived as larger than those in the proximo-distal axis. In contrast, on the glabrous skin of the sole, inconsistent results were found across experiments, with no overall evidence for anisotropy. This shows a pattern of anisotropy on the foot broadly similar to that on the hand, adding to the list of body parts showing tactile-distance anisotropy, and providing further evidence that such biases are a general aspect of tactile spatial organization across the body. Significance: The perception of tactile distance has been widely used to understand the spatial structure of touch. On the hand, anisotropy of tactile distance perception is well established, with distances oriented across hand width perceived larger than those oriented along hand length. We investigated tactile-distance anisotropy on the feet, a body part structurally, genetically, and developmentally homologous to the hands, but with strikingly different patterns of functional usage. We report highly similar patterns of anisotropy on the hairy skin of the hand dorsum and foot dorsum. This suggests that anisotropy arises from the general organization of touch across the body.

两次触摸之间的距离感知随手的方向而变化，与手宽对齐的距离比与手长对齐的距离更大。在其他身体部位（例如，面部）上发现了类似的各向异性，表明它们可能反映了触觉组织的一般特征，但在其他身体部位（例如，腹部）上似乎不存在。在这里，我们研究了足部的触觉距离各向异性，这是一个在结构和胚胎学上与手相似的身体部位，但在人类中具有非常不同的功能使用模式。在三个实验中，我们比较了与中外侧和近端远侧足轴对齐的触摸对之间的感知距离。在足背的多毛皮肤上，始终发现各向异性，与中外侧足轴对齐的距离被感知为大于近远轴的距离。相比之下，在鞋底的无毛皮肤上，在整个实验中发现了不一致的结果，没有各向异性的总体证据。这显示了脚上的各向异性模式与手上的模式大致相似，增加了显示触觉距离各向异性的身体部位列表，并提供了进一步的证据，表明这种偏差是整个身体触觉空间组织的一般方面。意义：触觉距离的感知已被广泛用于理解触觉的空间结构。另一方面，触觉距离感知的各向异性已经确立，跨手宽度方向的距离比沿着手长方向的距离更大。我们研究了脚上的触觉距离各向异性，这是一个在结构、遗传和发育上与手同源的身体部位，但功能使用模式截然不同。我们报告了手背和足背的多毛皮肤上高度相似的各向异性模式。这表明各向异性源于全身触摸的一般组织。