"Electrotactile Feedback System Using Psychophysical Mapping Functions"
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Abstract: Advancements in movement restoration have accelerated in recent years while the restoration of somatosensation has progressed relatively slowly.  This dissertation attempts to correct this oversight by developing an electrotactile feedback system which might be used to restore the sense of touch.

 Initially, the perceptual parameters of the skin regions likely to be used as a source of tactile information (the fingertip) and a destination for electrotactile feedback (the back of the neck) were evaluated.  The perceptual parameters of tactile threshold sensitivity, spatial acuity, and gain scaling ability were collected from subjects for both regions of skin.  These same parameters were also gathered for electrotactile stimulation of the neck.  The threshold sensitivity and spatial acuity of the fingertip was found to be much greater than on the back of the neck, yet the perceptual gain scaling parameters of the neck were similar to that of the finger tip.  Furthermore, the psychometric functions for electrical stimulation on the neck differed markedly in gain sensitivity from that of mechanical stimulus.  A mathematical mapping between the two modalities was then calculated based upon the tactile and electrotacile characterization data which was collected.

An electrotactile feedback system was developed based upon the calculated mapping function, allowing conversion of force applied to an artificial sensor on the fingertip to a perceptually equivalent electrical stimulus on the neck.

The system proved to be quite effective: Subjects were able to effectively evaluate electrical stimulus that was derived from application of force to the sensor on the fingertip.  The perceptual gain scaling for the feedback system matched that of natural mechanical stimulation.

A grip force matching task was evaluated in test subjects with normal tactile sensation, anesthesia of the fingers, and anesthesia of the fingers with restored tactile information via the electrotactile feedback system.  The relative loss in grip force matching ability under anesthesia was mild, indicating a strong ability for individuals to generate arbitrary force levels without any form of feedback.  The electrotactile feedback system offered some grip force matching improvement beyond the generally good ability to match grip force while anesthetized.