Faculty of Environment and Information Studies, Keio University, Tokyo, Japan.
Research Institute for Electronic Science, Hokkaido University, Sapporo, Japan.
Sci Rep. 2021 Jun 3;11(1):11737. doi: 10.1038/s41598-021-90661-1.
The human hand can detect both form and texture information of a contact surface. The detection of skin displacement (sustained stimulus) and changes in skin displacement (transient stimulus) are thought to be mediated in different tactile channels; however, tactile form perception may use both types of information. Here, we studied whether both the temporal frequency and the temporal coherency information of tactile stimuli encoded in sensory neurons could be used to recognize the form of contact surfaces. We used the fishbone tactile illusion (FTI), a known tactile phenomenon, as a probe for tactile form perception in humans. This illusion typically occurs with a surface geometry that has a smooth bar and coarse textures in its adjacent areas. When stroking the central bar back and forth with a fingertip, a human observer perceives a hollow surface geometry even though the bar is physically flat. We used a passive high-density pin matrix to extract only the vertical information of the contact surface, suppressing tangential displacement from surface rubbing. Participants in the psychological experiment reported indented surface geometry by tracing over the FTI textures with pin matrices of the different spatial densities (1.0 and 2.0 mm pin intervals). Human participants reported that the relative magnitude of perceived surface indentation steeply decreased when pins in the adjacent areas vibrated in synchrony. To address possible mechanisms for tactile form perception in the FTI, we developed a computational model of sensory neurons to estimate temporal patterns of action potentials from tactile receptive fields. Our computational data suggest that (1) the temporal asynchrony of sensory neuron responses is correlated with the relative magnitude of perceived surface indentation and (2) the spatiotemporal change of displacements in tactile stimuli are correlated with the asynchrony of simulated sensory neuron responses for the fishbone surface patterns. Based on these results, we propose that both the frequency and the asynchrony of temporal activity in sensory neurons could produce tactile form perception.
人手可以同时感知到接触表面的形状和质地信息。人们认为，皮肤位移的检测（持续刺激）和皮肤位移的变化（瞬态刺激）是通过不同的触觉通道介导的；然而，触觉形状感知可能同时使用这两种类型的信息。在这里，我们研究了触觉感受器中编码的触觉刺激的时间频率和时间相干性信息是否可以用于识别接触表面的形状。我们使用鱼骨触觉错觉（FTI）作为人类触觉形状感知的探针，这是一种已知的触觉现象。这种错觉通常发生在具有光滑条和相邻区域粗糙纹理的表面几何形状上。当用指尖来回刷动中央条时，人类观察者会感知到一个中空的表面几何形状，尽管条实际上是平的。我们使用被动式高密度针矩阵来提取接触表面的垂直信息，抑制表面摩擦引起的切向位移。在心理学实验中，参与者通过用不同空间密度（1.0 和 2.0 毫米针距）的针矩阵在 FTI 纹理上描摹来报告凹陷的表面几何形状。人类参与者报告说，当相邻区域中的针同步振动时，感知到的表面凹陷的相对幅度急剧下降。为了解释 FTI 中触觉形状感知的可能机制，我们开发了一个感觉神经元的计算模型，以从触觉感受野中估计动作电位的时间模式。我们的计算数据表明：（1）感觉神经元反应的时间异步与感知到的表面凹陷的相对幅度相关；（2）触觉刺激中位移的时空变化与模拟的鱼骨表面图案中感觉神经元反应的异步相关。基于这些结果，我们提出感觉神经元的时间活动的频率和异步都可以产生触觉形状感知。
