Effect of pulse rate on loudness growth functions in cochlear implant users

Aim of this evaluation was the comparison of loudness growth functions measured at two different pulse widths. The loudness growth functions were measured via a loudness scaling procedure with direct electrical stimulation. The stimulus was a pulse train presented on a single electrode with a defined amplitude and pulse width. 13 cochlear implant (CI) users with Advanced Bionics implants participated and for each of them the loudness scaling procedure was conducted with a constant pulse width of 33.2 mu s and an individually determined minimal pulse width at which the upper dynamic range could be stimulated without reaching the compliance limit of the implant; the actual range was 18 mu s to 40.4 mu s. Our results indicate that for low loudness levels (threshold to about soft) the pulse width is significantly affecting the perceived loudness. When doubling the pulse width from 18 to 36 mu s, the charge had to be on average 1.98 dB higher for "very soft" loudness levels. For higher loudness levels no influence of the pulse width was observed.