Speech processing for artificial tactile speech displays

Two methods of encoding speech for tactile displays were compared in experiments which measured the discriminability of tactile representations of short speech segments. One display represented the short-term speech spectrum in time-swept mode and used vibration amplitude to encode spectral amplitude. The other represented the vocal-tract shape and length estimates as derived from LPC analysis of the speech waveform and used the number of active vibrators to encode the logarithm of cross sectional area. Both displays were applied to the thigh via a 12 × 12 matrix of vibrators. The vibrators were driven at 250 Hz during voiced segments and by random noise during unvoiced segments. Overall results show a slight superiority for the spectral display in vowel discrimination. The results of detailed analyses suggest that many of the detailed characteristics of the tactile patterns were poorly discriminated. Better models of tactile perception must be formulated before speech data compression techniques can be used effectively.