Mario A. Svirsky
Speech Commun. Group, Res. Lab. of Electron., MIT, 50 Vassar St., Rm. 36-525, Cambridge, MA 02139
Santiago H. Svirsky
IAVA High School, Montevideo, Uruguay
A mathematical model is proposed to account for vowel perception by users of pulsatile cochlear implants that encode one to three formant frequencies. Like the Durlach--Braida model of intensity resolution [N. I. Durlach and L. D. Braida, J. Acoust. Soc. Am. 46, 372--383 (1969)], this model incorporates an internal noise model and a decision model to account separately for errors due to poor sensitivity and response bias. The model was evaluated using published electrode identification data [Y. C. Tong and G. M. Clark, J. Acoust. Soc. Am. 77, 1881--1808 (1985)] and vowel confusion matrices obtained with stimulation schemes that employed one, two, and three formants, respectively [P. J. Blamey and G. M. Clarke, J. Acoust. Soc. Am. 88, 667--673 (1988)]. Vowel identification performance seems to be strongly influenced by the extent to which a given subject can adjust to electrical stimulation delivered to places in the cochlea that are more basal than the places that are stimulated by the same formant in a normal ear, and also by the subject's basic electrode identification capability. Results suggest that cochlear implant users are able to partially adjust to this too-basal stimulation. [Work supported by NIH Grant Nos. DC01721 and DC00075.]