ASA 125th Meeting Ottawa 1993 May

3aPP11. Temporal pitch coding for cochlear implantees: The effects of carrier rate and amplitude modulation of pulsatile electrical stimuli.

Colette M. McKay

Hugh J. McDermott

Graeme M. Clark

Univ. of Melbourne and Australian Bionic Ear and Hear. Res. Inst., 384--388 Albert St., East Melbourne 3002, Australia

The pitch evoked by sinusoidally amplitude-modulated current pulse trains on single electrodes was studied. Modulation frequencies of 100, 150, and 200 Hz, together with carrier pulse rates from 200 to 1200 Hz were studied. The results showed that, in general, the pitch of the stimulation was close to but higher than that of a nonmodulated pulse train of rate equal to the modulation frequency. This general rule did not hold, however, whenever the carrier rate was both less than four times and not a multiple of the modulation frequency. Modulation depth was also found to significantly affect the pitch when less than approximately 7% of the current. In this region, the pitch rose uniformly with reduction in modulation depth and became equivalent to that of the carrier rate near the modulation detection threshold. The results of this investigation have relevance to speech processing schemes utilizing pulsatile stimulation, in which modulations in the processor output at the fundamental frequency of speech may provide a voice pitch percept to implantees. [Work supported by NIH.]