Evaluation of a tactile vocoder for work recognition.

Normal subjects learned to identify words through a tactile vocoder. The vocoder employed 16 filter channels, each with a bandwidth of 1/3 octave, with center frequencies ranging from 200-8000 Hz. The output of each filter was detected and after logarithmic amplification the resulting outputs were transmitted to a 16-channel solenoid array placed on the subject's ventromedial forearm. Words, spoken "live voice," were used as stimuli; the subject was able to feel both the vocalization of the reader and herself and, most importantly, extensive training was provided. In 40.5 h one subject learned 70 words and a second subject reached criterion on 150 words in the comparatively short time of 55 h. Words that were poorly identified initially were identified more readily with increased experience. Phonetic identification tests showed that the features of voicing, nasality, and frication were reliably recognized, indicating the tactile vocoder will be useful in providing information to complement lipreading. Finally, subjects learned rapidly to generalize word-learning to unfamiliar readers.