Effect of waveform shape and polarity on loudness and on place pitch for cochlear implant users.

Abstract

It has been shown that, for pseudomonophasic pulses presented in monopolar mode, less current is needed to achieve the same loudness when the short-high phase is anodic than when it is cathodic. Experiment 1 extended that finding, obtained with the Advanced Bionics (AB) device, to waveforms that can be implemented in other devices, using 99-pps, 32-μs/phase pulse trains. For AB and MedEl devices, stimuli were triphasic pulses whose central phase had twice the amplitude of the first and third phases. For the Nucleus device, stimuli were pairs of biphasic pulses with opposite leading polarity, each with a 58-μs interphase-gap, separated by 8 μs—resulting in two adjacent same-polarity phases in the center of the waveform. The current level needed was always 1–2 dB lower when the central portion was anodic than when it was cathodic—including for electrode 1 of the MedEl device, which is inserted deep into the cochlea. Experiment 2 showed that, for pseudomonophasic pulses in bipolar mode, (a) pitch is lower when the “short-high” pulse is anodic relative to the more-apical than to the more-basal electrode and (b) intermediate pitches can be produced by variations in waveform shape and polarity applied to the same bipolar pair.