Depth Recognition Thresholds of Tactile Perception for Fine Texture of Bionic Hexagonal

Appropriate design of surface texture can contribute to the sensitivity of tactile perception, grasp reliability and touch comfort. Hexagonal texture is a common texture found on animal body surfaces in nature. The bionic hexagonal textures exhibited good tribological and adhesion properties. At present, the formation and conduction pathways of human tactile sensation as well as the tactile perception of textured surface have been systematically studied. However, little studies elucidated the correlation between skin friction as well as vibration features and brain activity during tactile perception of fine textures. Therefore, in this paper, the effects of depth and touching direction of micron-sized bionic hexagonal textures on the depth recognition threshold of tactile perception were systematically investigated based on subjective evaluation, skin friction and vibrations, and neurophysiological response of the brain. The influence of intensity of texture stimuli and neuronal excitability on tactile perception were verified using a single-channel neural mass model. The results showed that as the texture depth increased, the subjective texture sense and recognition rate of the hexagonal texture increased. Also, the adhesive friction component decreased and deformation friction component increased with the increase of texture depth. The vibration features during tactile friction were extracted, and the results showed that the dominant frequency of the vibration signal spectrum and the maximum amplitude increased with the increase of texture depth. As the texture depth reached the recognition threshold for tactile perception, the deformation friction component and the amplitude of the dominant frequency was increased significantly. The texture depth reached the tactile recognition threshold depth before the P100 and P200 components of the ERP curves were excited. The depth of bionic hexagonal texture was observed significantly positively correlated with P300 amplitude and negatively correlated with P300 latency. The dominant frequency amplitude of vibration signals and the deformation friction component generated from touching along the flat direction was larger than that of touching along the tip direction. It suggested that the bionic hexagonal texture was more easily perceived during touching along the flat direction. The P300 amplitude of ERP curves excited by touching along the flat direction was higher, and the latency was shorter. It indicated that the process of brain was faster and more attentional resources were involved in tactile perception during touching along the flat direction. The neural mass model showed that the input and amplitude of the simulated EEG signals for touching along the flat direction were lager than those for touching along the tip direction, suggesting that the enhancement of tactile stimulation produced by touching along the flat direction is one of the reasons for the increase in the amplitude of the dominant frequency of the EEG signals.