Lipreading sentences with vibrotactile vocoders: Performance of normal‐hearing and profoundly deaf subjects

Three vibrotactile vocoders were compared in a training study involving aided and unaided lipreading: (1) the Queen's University/Central Institute for the Deaf vocoder, with one‐third octave filter spacing and logarithmic output compression (CIDLog) [Engebretson and O'Connell, IEEE Trans. Biomed. Eng. BME‐33, 712–716 (1986)]; (2) the same vocoder with linear output equalization (CIDLin); and (3) the Gallaudet University vocoder designed with greater resolution in the second formant region, relative to the CID vocoders, and linear equalization (GULin). Nine normal‐hearing and four profoundly hearing‐impaired adults participated in the training study. Four of the normal‐hearing subjects were assigned to either of two control groups, a group that received no vocoder, and a group that received the previously studied CIDLog vocoder [Brooks and Frost, J. Acoust. Soc. Am. 74, 34–39 (1983); Weisenberger et al., J. Acoust. Soc. Am. 86, 1764–1775 (1989)]. The remaining subjects were assigned to the linear vocoders....