PITCH COMPARISONS OF ACOUSTICALLY AND ELECTRICALLY-EVOKED AUDITORY SENSATIONS

Cochlear implant users with some residual hearing in the non implanted ear compared the pitch sensations produced by acoustic pure tones and pulsatile electric stimuli. Pitch comparisons were obtained for pure tones and electrical stimuli presented at different positions (electro des) in the scala tympani, keeping the electric pulse rate fixed at 10 0, 250, or 800 pps. Similarly, pitch comparisons were obtained for ele ctrical stimuli with variable pulse rates presented to two fixed elect rode positions (apical and basal) in the cochlea. Both electrode posit ion and pulse rate influenced the perceived pitch of the electrical si gnal and 'matched' electric and acoustic signals were found over a wid e range of frequencies. There was a large variation between listeners. For some stimuli, listeners had difficulty in deciding whether the ac oustic or electric stimulus was higher in pitch. Despite the variabili ty, consistent trends were obtained from the data: higher frequencies tended to be matched by more basal electrodes for all pulse rates. Hig her frequencies tended to be marched by higher pulse rates for both el ectrode positions. The electrode positions that 'matched' pure tones w ere more basal than predicted from the characteristic frequency coordi nates of the basilar membrane in a normal human cochlea.