SPEECH-INTELLIGIBILITY AS A FUNCTION OF THE NUMBER OF CHANNELS OF STIMULATION FOR SIGNAL PROCESSORS USING SINE-WAVE AND NOISE-BAND OUTPUTS

Vowels, consonants, and sentences were processed through software emul ations of cochlear-implant signal processors with 2-9 output channels. The signals were then presented, as either the sum of sine waves at t he center of the channels or as the sum of noise bands the width of th e channels, to normal-hearing listeners for identification. The result s indicate, as previous investigations have suggested, that high level s of speech understanding can be obtained using signal processors with a small number of channels. The number of channels needed for high le vels of performance varied with the nature of the test material. For t he most difficult material-vowels produced by men, women, and girls-no statistically significant differences in performance were observed wh en the number of channels was increased beyond 8. For the least diffic ult material-sentences-no statistically significant differences in per formance were observed when the number of channels was increased beyon d 5. The nature of the output signal, noise bands or sine waves, made only a small difference in performance. The mechanism mediating the hi gh levels of speech recognition achieved with only few channels of sti mulation may be the same one that mediates the recognition of signals produced by speakers with a high fundamental frequency, i.e., the leve ls of adjacent channels are used to determine the frequency of the inp ut signal. The results of an experiment in which frequency information was altered but temporal information was not altered indicates that v owel recognition is based on information in the frequency domain even when the number of channels of stimulation is small. (C) 1997 Acoustic al Society of America. [S0001-4966(97)04010-1] PACS numbers: 43.71.Es, 43.71.Ky, 43.66.Ts [WS].