Tactile substitution system for transmitting a few words to a prosthetic hand user.

This paper describes an efficient system for transmitting a few words (verbal information) to a prosthetic hand user by using a two-channel electrotactile stimulation capable of generating apparent movements, which is applied to the upper arm area of the left hand via surface concentric electrodes. If the prosthetic hand user gets verbal information about interaction between the prosthesis and the environment, e.g., the prosthetic hand just touched a doorknob, he/she will be able to open or close the door even in the darkness, and also to handle an object on the top of a shelf out of his/her view. In this study, verbal information was provided regarding which finger touches the object (three states), and the fingers angle (two states). Consequently, six states of verbal information could be sent. We therefore designed five stimulation patterns (duration 600 - 800 ms) comprising several burst profiles in which each burst was composed of several pulses (interval of biphasic pulses, 2.85 ms) modulated in amplitude. The recognition experiments using 10 healthy subjects showed that the mean percentage of recognition was about 94% (standard deviation: 3.9). These results suggested the possible applicability of the proposed system to assist prosthetic hand users.