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Pitch perception by cochlear implant subjects
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1987
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Electrical stimulation of the auditory nerve can partially restore hearing, producing percepts that resemble acoustic loudness, pitch, and timbre. The study aims to determine how stimulus parameters affect percepts to inform speech encoding with electrical stimulation. The authors examined how level, repetition rate, and stimulation location influence percepts in cochlear implant subjects. Pitch discrimination worsens with higher stimulation rates up to a saturation point of 200–1000 pps, place‑pitch varies with subject but follows cochlear tonotopy, and its discriminability depends on current spread, while level effects are significant yet highly individual; these findings inform speech‑processing strategies and relate to acoustic pitch perception.
Direct electrical stimulation of the auditory nerve can be used to restore some degree of hearing to the profoundly deaf. Percepts due to electrical stimulation have characteristics corresponding approximately to the acoustic percepts of loudness, pitch, and timbre. To encode speech as a pattern of electrical stimulation, it is necessary to determine the effects of the stimulus parameters on these percepts. The effects of the three basic stimulus parameters of level, repetition rate, and stimulation location on subjects’ percepts were examined. Pitch difference limens arising from changes in rate of stimulation increase as the stimulating rate increases, up to a saturation point of between 200 and 1000 pulses per second. Changes in pitch due to electrode selection depend upon the subject, but generally agree with a tonotopic organization of the human cochlea. Further, the discriminability of such place-pitch percepts seems to be dependent on the degree of current spread in the cochlea. The effect of stimulus level on perceived pitch is significant but is highly dependent on the individual tested. The results of these experiments are discussed in terms of their impact on speech-processing strategies and their relevance to acoustic pitch perception.