| With the help of external stimuli,tactile display enables human beings to perceive information similar to visual images through skin sensation,and can perceive the color and texture of objects,which are the frontiers and research hotspots in the field.Electrical stimulation is one of the most important methods in tactile display,with the advantages of small volume,quick response,high information density and simple convenience compared with mechanical stimulation,vibration stimulation,pneumatic stimulation,ultrasonic stimulation and jet stimulation.It is one of the most promising technical means in functional applications such as,sensory substitution,rehabilitation therapy,intelligent prosthesis and remote exercise,virtual reality and game entertainment and so on.The electrotactile biological model and the suitable stimulation experiment are the basic problems of the electrostimulation method in the study of tactile display.With model research and experimental analysis,we can master the physiological characteristics and basic data of the tactile display,thus providing the design basis and guidelines for the design of the display devices,which is of great value for future research and development of tactile display.1)The study of the mechanism of the electrotactile perception and the analysis of the influencing factors.The tactile perception mostly includes three independent stages,namely,"sensation","transimission" and "perception".The formation of electrotactile perception is very complex.Electrostimulation not only induces the nerve impulses at the stage of "sensation",but also directly acts on the nerve fibers at the "transmission" stage.They are superimposed on each other and eventually produce perception in the cortical projection area.The paper discusses the possible factors influencing the touch sensation.It is found that the tactile perception is not only influenced by the stimulation current,the characteristics of electrode and the mode of contact,but also affected by the individual factors such as skin characteristics and psychological tendency.In addition,environmental factors can also influence the perception.In this paper,the effect of skin resistance was studied,and the key factors of steady/non-steady contact conditions were analyzed,which are good for further model construction and experimental research.2)The biological model study of electrotactile under non-steady condition.The biological models of tactile sensation include skin model,skin electrode contact model and neuron model.The effect of external currents on tactile receptors and nerve fibers is closely related to the characteristics of the former two models.Under the non-steady contact condition,the time of external input is very short,the mechanism of the model is very complex,and the sensation output is uncertain.In this paper,we studied the electroporation and electroleakage effects of skin and found that the capacitive induced by the electroporation effect has great influence on the ultra short process.And then,the impedance model of skin under the non-steady contact is constructed.It is found that the voltage and current characteristics of the ultra instaneous process are mainly relevant to the resistance of subcutaneous and the capacitance of epidermis.In addition,it is reported that anodic stimulation may cause sensory drift.The paper studies the phenomenon by using the neuron conduction model.It is found that the sensation displacement is positively correlated with the square of the stimulation depth,and negatively correlated with the space between electrodes(separation electrode)/ insulation layer thickness(concentric electrode).3)The research and development of the electrotactile devices.In order to carry out experimental research,an electrotactile stimulation device with 3*3 electrode array has been developed.A kind of dynamic scanning display method of electrode array is proposed to realize multipoints almost real-time stimulation through high speed switch on/off.In addition,the paper also proposes an electrotactile data structure and file format.We further established the full pixel mapping between visual image RGB and the three elements of tactile image to realize cross-modal transformation and reversible mapping.4)The experimental study of the electrotactile threshold.In this paper,the 1-up and 1-down psychophysics method is used to study the perceptual threshold of the electrotactile.In the experimental scheme,36 experimental scenarios were designed,including contact mode,stimulation position and current frequency,and regional environment,gender,age and body fat density factors.The recruitment of subjects in the central,southern and northern regions of China was generally consistent with the normal conditions.In data analysis,statistics and ANOVA were used to study the influence factors on the thresholds.The experimental results showed that the steady / non-steady contact mode has a significant effect on the perception threshold(F(1,11)=9.76,P=0.01).In the non-steady condition,the threshold is positively correlated with frequency,and palm has a higher threshold compared to cheek and finger.In addition,in the middle and young age,the female threshold is lower than that of the male,while the average values of men and women is almost consistent at the age of 18-25 and 46-55.This paper further discusses the effects of skin impedance characteristics and selection characteristics of tactile receptors on perception threshold.It is suggested that skin may have skin effect,which may be one of the most factors in lifting the perception threshold and electric burn under high frequency condition.5)EEG experimental study of electrotactile.Psychophysical methods have certain subjectivity in evaluating the tactile stimulation from the aspect of psychological sensitivity,and the confidence is depended on large samples.In order to objectively evaluate the perception threshold under non-steady conditions,the paper introduces the method of EEG(Electroencephalography)and ERP(Event Related Potential).In the experiment,the paper mainly studied the power spectrum of the electrotactile EEG experiment and the Oddball paradigm.Results show that the 50% sensory threshold of the non-steady contact induced the inhibition of the alpha rhythm in the central C region of the lateral brain(50%),the enhancement of Beta,Gamma rhythm(>90%).We can deduce that electrostimulation can lead to tension or anxiety,which leads to the power spectrum migration from low frequency to high frequency;in addition,the small probability events of the Oddball can induce obvious positive jump of EEG,but do not get the ideal P300 component.The reason may be due to the problem of synchronous imbalance between stimulation and EEG.This problem needs to be studied in the future. |
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