Depth recognition thresholds of tactile perception for fine stripe texture of bar shapes

[Objective] Although tactile perception plays a crucial role in human perception of the external world, human understanding of tactile perception remains limited due to the complexity of its mechanism and the multitude of perceptual units involved. The friction between surface textures and finger skin provides vibratory stimuli on the skin surface during tactile perception, thereby activating the somatosensory areas. It is necessary to evaluate the tactile perception of fine textures based on the friction behavior of skin and the related cortical activity in response to the texture stimuli. [Methods] Different fine stripe texture depths (5, 10, 15, 20, 25, and 30 µm) were designed and processed using laser engraving. The depth recognition threshold of tactile perception for fine texture was systematically investigated using subjective evaluation, surface friction and vibration, and the neurophysiological response of the brain. The effects of the texture stimulus intensity and neuronal excitability on tactile perception were verified by a single-channel neural mass model. [Results] An increase in the fine texture depth was associated with an increase in the subjective human texture sense, the degree of correct texture recognition, and the proportion of deformation friction. The average depth recognition threshold of tactile perception was found to be 11.60µm. The load index, the maximum spectral amplitude of the vibration signal, the recurrence parameter entropy, the length of the longest vertical line segment, and the peak of P300 exhibited a substantial positive correlation with the fine texture depth. The latency of P300 showed a substantial negative correlation with the fine texture depth. When the texture depth exceeded the depth recognition threshold of tactile perception, the maximum spectral amplitude and nonlinear characteristic parameters of the touch vibration signal increased remarkably. The main frequency of the vibration signal also increased to be within the perceptual frequency range of the Pacinian corpuscle. As a result, the vibration signal system transformed from a homogenous state to a disrupted state. Furthermore, the intensity and the area of activation of the brain regions, the neuronal activity of the brain, the processing intensity, and the tactile recognition speed of the brain increased remarkably. Amplitude of the main frequency of the simulated electroencephalogram (EEG) signal increased with an increase in the mean value of the input signal. This trend was consistent with that of the real EEG signal, which indicated that the increase in the tactile intensity due to the increase in the texture depth was one of the reasons for the increase in amplitude of the main frequency of the tactile EEG signal. The main frequency of the simulated EEG signal decreased with an increase in the ratio of excitatory synaptic gain to inhibitory synaptic gain. This trend was consistent with that of the real EEG signal, which indicated that the increased excitability of the neuronal populations excited by the increase in texture depth was one of the reasons for the decrease in the main frequency of the tactile EEG signal. [Conclusions] The depth recognition thresholds of tactile perception for fine stripe textures, the finger touch tribological behavior, the frequency domain and nonlinear features of the touch vibration signals, and the time and frequency domain features of EEG signals undergo remarkable variations during touching and sensing. The single-channel neural mass model can effectively simulate real EEG signals. © 2024 Press of Tsinghua University. All rights reserved.