Effects of phase duration and electrode separation on loudness growth in cochlear implant listeners

Loudness estimates were obtained in a group of four adult subjects implante d with the Nucleus-22 multielectrode cochlear implant device, for a range o f pulse amplitudes and different fixed phase durations and electrode separa tions. The stimulus was a 200-ms long train of biphasic pulses presented at 500 pulses/s. Subjects estimated loudness as a number from 0 ("don't hear it") to 100 (''uncomfortably loud''). Loudness was found to grow exponentia lly with pulse amplitude, at a rate that was dependent upon the phase durat ion as well as the electrode separation. An equation of the form L = e((lam bda+gamma M)(D theta)I), where L is the estimated loudness, M is the separa tion between electrodes of a stimulating pair, D is the phase duration, I i s current amplitude, and lambda, gamma, and theta are constants, appears to describe the observed data adequately. The findings are remarkably consist ent across subjects. (C) 2000 Acoustical Society of America. [S0001-4966(00 )01103-6].