Department of Organismal Biology and Anatomy, University of Chicago, Chicago, Illinois, United States of America.
Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium.
PLoS Biol. 2019 Aug 27;17(8):e3000431. doi: 10.1371/journal.pbio.3000431. eCollection 2019 Aug.
Motion is an essential component of everyday tactile experience: most manual interactions involve relative movement between the skin and objects. Much of the research on the neural basis of tactile motion perception has focused on how direction is encoded, but less is known about how speed is. Perceived speed has been shown to be dependent on surface texture, but previous studies used only coarse textures, which span a restricted range of tangible spatial scales and provide a limited window into tactile coding. To fill this gap, we measured the ability of human observers to report the speed of natural textures-which span the range of tactile experience and engage all the known mechanisms of texture coding-scanned across the skin. In parallel experiments, we recorded the responses of single units in the nerve and in the somatosensory cortex of primates to the same textures scanned at different speeds. We found that the perception of speed is heavily influenced by texture: some textures are systematically perceived as moving faster than are others, and some textures provide a more informative signal about speed than do others. Similarly, the responses of neurons in the nerve and in cortex are strongly dependent on texture. In the nerve, although all fibers exhibit speed-dependent responses, the responses of Pacinian corpuscle-associated (PC) fibers are most strongly modulated by speed and can best account for human judgments. In cortex, approximately half of the neurons exhibit speed-dependent responses, and this subpopulation receives strong input from PC fibers. However, speed judgments seem to reflect an integration of speed-dependent and speed-independent responses such that the latter help to partially compensate for the strong texture dependence of the former.
大多数手动交互都涉及皮肤和物体之间的相对运动。触觉运动感知的神经基础研究大多集中在方向如何编码上，但对速度如何编码知之甚少。已表明感知速度取决于表面纹理，但以前的研究仅使用了粗糙的纹理，这些纹理仅涵盖了有限的有形空间尺度范围，并且为触觉编码提供了有限的窗口。为了填补这一空白，我们测量了人类观察者报告自然纹理速度的能力-这些纹理跨越了触觉体验的范围，并涉及到所有已知的纹理编码机制-在皮肤上进行扫描。在并行实验中，我们记录了灵长类动物神经和躯体感觉皮层中单个单位对以不同速度扫描的相同纹理的反应。我们发现，速度感知受到纹理的强烈影响：有些纹理被系统地感知为比其他纹理移动得更快，有些纹理比其他纹理提供了更多有关速度的信息。同样，神经和皮层中的神经元反应强烈依赖于纹理。在神经中，尽管所有纤维都表现出与速度相关的反应，但 Pacinian 小体相关（PC）纤维的反应受速度的影响最大，并且可以最好地解释人类的判断。在皮层中，大约有一半的神经元表现出与速度相关的反应，而这群神经元从 PC 纤维中接收强烈的输入。然而，速度判断似乎反映了速度相关和速度不相关反应的整合，使得后者有助于部分补偿前者对纹理的强烈依赖性。
