Sensory substitution system of two-channel electrotactile stimulation for transmitting verbal information

We have aimed at developing a sensory substitution system for transmitting verbal information. In this work, we propose a basic two-channel electrotactile stimulation system and examine the usefulness of the system. The verbal information to be provided consists of two items: one is the object and another is the location (direction) of the object in the surrounding of the subject Three objects and three directions are utilized in this work. Each of the nine possibilities was transmitted to the subject as a skin stimulus consisting of two consecutive stimulation patterns; the first pattern represents the direction and the second the object. Stimulation pattern for each item was generated by two-channel voltage-pulse trains, which elicited a movement impression on the subject's skin. The electrical stimulus was delivered on the dorsal carpal area of the left hand. High percentage of recognition (average: 92%, standard deviation: 4.2) was obtained. Recognition percentages were improved by giving the subject a prior explanation about each stimulation pattern and increasing the stimulus intensity up to 95 % of the pain threshold.