| As one of the five senses of human body,touch plays an important role in the communication between human and the world.During the tactile perception,frictional vibrations give mechanical stimulation to the tactile sensor in the skin,which is converted into potential signal through the mechanical energy signal.Potential signals then pass through the afferent nerve,spinal cord,and brain stem,and finally pass to the cerebral cortex.The brain processes it to create a sense of touch.Therefore,frictional vibration is the "stimulator" of tactile perception.Tactile perception involves skin perception,brain perception and subjective perception.At present,most of the research is carried out on specific materials such as sandpaper,fabric and glass,but there is no research on the specific surface parameters affecting the tactile sensation of materials.In addition,most of the research focuses on the tribology and biomechanics of skin.This article aims to study the impact of different texture shapes on human tactile perception.Comprehensive cognitive behavioral,biotribology,biomechanics,and cognitive neuroscience help to understand the formation process and cognitive mechanism.It can provide important technical support and theoretical support for the development of the tactile reproduction of persons with disabilities,human-computer interactionand and the quantitative evaluation of the texture of touch-skin products.The main research work and conclusions are as follows.Subjective evaluation methods and tribological experiment methods are used to study human tactile perception under different texture shapes.By conducting cognitive behavioral experiments,the subjective scores of the sharpness,stickiness and comfort of different texture shapes were obtained.Tribological experiments were conducted to study the friction mechanism of finger skin when touching different texture shapes.The sliding contact models of fingers on different textured surfaces were established by finite element software,and the stress of the mechanical receptors in the skin was analyzed.The results show that touching the rounded sample has the highest comfort;touching the sharp sample has the greatest sharpness;touching the smooth sample has the largest stickiness.The results of friction test show that different texture shapes will affect the proportion of the adhesive friction and the deformation friction.And the adhesive friction is the main contributing factor when the smooth sample is touched.As the sharpness of the sample surface texture increases,the contribution proportion of the deformation friction will increase.Through finite element analysis,it can be concluded that the stress distribution inside the model is mainly affected by the actual contact area between the finger and the samples.The stress value when touching sharp sample is the largest,and the stress value when touching smooth sample is the smallest.The study also found that the sense of adhesion is mainly affected by the adhesive friction.The deformation friction caused by the texture shape will increase the sense of sharpness,while comfort is affected by the friction mechanism and the stress on the tactile receptors.fMRI with high spatial resolution was used to study the formation position and activation intensity of texture-induced tactile sensation in the brain.The results show that when the subject touches different textured shapes,the tactile sense of the brain's activation functional areas mainly involves the primary somatosensory cortex,the secondary somatosensory cortex,the primary motor cortex,the somatosensory cortex,and the auxiliary motor cortex.And the somatosensory cortex is dominant.In addition,the activation area of the contralateral brain area(left brain)is greater than that of the ipsilateral brain area(right brain).The largest activated voxel group occurs near the central sulcus of the left brain,including the central anterior gyrus and the central posterior gyrus.The brain area excited by the rounded texture surface is only the left brain,the brain area is small in scope,and the activation intensity is low;the sharp texture stimulates the left and right brain areas and all were positively activated;the sense of adhesion induced by the flat-angled sample involves a higher range and intensity of the brain area,and there is a negative activation phenomenon on the same side.The difference in brain function between sharp and rounded is the combined somatosensory cortex,which is the smallest;the difference between rounded and the flat is the secondary somatosensory cortex and the combined somatosensory cortex.The difference between sharp and flat is the secondary somatosensory cortex and somatosensory association cortex,which is the largest.The electrophysiological method with high time resolution was used to study the brain cognition under different texture shapes.The event-related potential test was performed to obtain the EEG signals when the subjects touched different shapes of samples.According to the strict requirements of the event-related potential method on trigger synchronization,a passive touch test bench was designed.According to the characteristics of the original signal,such as low signal-to-noise ratio and many artifacts,the signal is pre-processed such as denoising and filtering.In view of the characteristics of non-stationary and non-linear of EEG signals,the signals induced by three texture shapes was comprehensively analyzed from the perspectives of time domain,time-frequency domain and non-linearity.The results show that,among the characteristics of tactile-induced P300,the peak of P300 is mainly affected by tactile comfort.The peak of P300 decreases with increasing comfort,and there is no significant difference in latency of P300.At the same time,the delta rhythm is the dominant rhythm in the texture-induced tactile EEG signal.In addition,through recursive analysis,it can be seen that the trajectory period of the EEG signal induced by tactile stimulation is very large.The perception of more difficult samples will make the state of the EEG system change faster,and the more comfortable touch will make the state of the EEG system more stable.Based on the subjective evaluation results,friction test results,finite element simulation results,fMRI results,and tactile EEG results,it can be found that among the three texture samples,when the finger touches the flat sample,the actual contact area is the largest,making the adhesive friction force large,and the stress on the receptors is small.It gives a greater sense of adhesion and less sharpness.At the same time,excessive adhesion friction will reduce comfort.The sense of adhesion brought by the flat texture will activate the large brain area and strong activation intensity.In addition,because the texture characteristics of the flat texture is the least obvious,the state of the EEG system changes faster.When the finger touches the sharp sample,the actual contact area is the smallest,the deformation friction and the stress on the receptors are greater,so it gives a greater sharpness and less stickiness,and excessive deformation friction will also reduce comfort.A sharpness sense will positively activate the left and right brain regions.When touching the rounded sample,the friction and the stress on the receptors are moderate,so compared to the other textured surfaces,the texture of rounded corners brings better comfort,and the range of activated brain area is small.In addition,the high comfort will also reduce the peak of tactile-induced P300.This paper has 44 figures,11 tables and 106 references. |
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