PITCH PERCEPTION IN PATIENTS WITH A MULTICHANNEL COCHLEAR IMPLANT USING VARIOUS PULSES WIDTH

Cochlear implants have been designed to partially restore hearing to t hose people who are totally deaf. Multichannel cochlear implants offer the opportunity to evoke acoustic perceptions like loudness and pitch , elicited by a controllable pattern of electric stimulation by means of electrodes placed in different places along the cochlear length. In this study, two psychophysical experiments were conducted with 4 pati ents, 1 prelingually and 3 postlingually-deafened, implanted with the multi-channel cochlear prosthesis Nucleus 22. Experiments were carried out to study the effect of varying the width of the electric biphasic pulsatile stimuli on the discriminative abilities of the pitch percep tion. The tests involved place pitch ranking and pulse rate discrimina tion. Place pitch ranking was studied by determining the just noticeab le difference in pitch pairs (jnd-pp), defined as the pair of nearest electrodes which elicit different pitch perception. Pulse rate discrim ination was studied by determining the just noticeable difference in p ulse rate (jnd-pr) defined as the minimal difference in stimulus repet ition rate over a given electrode, which elicits different pitch perce ptions. Both experiments were conducted using pulses of 400, 200, 100 and 50 mu s/phase. The results indicated that in spite of the differen ces in pathologies and personal histories, both jnd-pp and jnd-pr decr ease by diminishing the pulse width. Speech perceptual data, measured for various pulse widths, validates the usefulness of decreased pulse width which yields favorable results in the psychophysical tests.