VIBROTACTILE AND ELECTROTACTILE PERCEPTION OF TIME-VARYING PULSE TRAINS

To establish the best strategy for transmitting speech-derived informa tion via a single tactile channel, measurements were made on the perce ption of frequency-and/or amplitude-modulated pulse-train stimuli, wit h a comparison of the electrotactile and vibrotactile modalities. In o ne experiment, vibrotactile perception of 2-oct step changes in stimul us frequency was found to be significantly better than electrotactile on a timescale appropriate for the transmission of speech features (e. g., with practiced subjects, information transfer of 69% with 200-ms v ibrotactile stimuli, 32% with 200-ms electrotactile stimuli). Percepti on of step changes in stimulus amplitude was similar in the two modali ties when changes in amplitude were tailored to match the different dy namic ranges available. In a second experiment, vibrotactile perceptio n of voice fundamental frequency with various codings was investigated . Both experiments showed information transfer for vibrotactile stimul i to be greater when frequency and amplitude modulation were used toge ther rather than with one or the other in isolation (sentence-stress i dentification scores: 66% for FM stimuli, 69% for AM stimuli, 80% for FM/AM stimuli). It is concluded that frequency- and amplitude-modulate d vibratory stimulation is a good choice in a practical device for the profoundly hearing impaired.