Comparison of current waveforms for the electrical stimulation of residual low frequency hearing

Many cochlear prostheses employ charge-balanced biphasic current pulses. These pulses have little energy at low frequencies resulting in limited stimulation of low frequency hearing by mechanical responses to the electrical stimulus. However, if electro-mechanical transduction within the cochlea is nonlinear, electrical stimulation with asymmetric, charge-balanced current pulses may result in a mechanical response with significantly more low frequency energy. We estimated the mechanical response at low frequencies to pulsatile electrical stimulation of the cochlea. The auditory nerve compound action potential evoked by low frequency tones was forward-masked by a train of symmetric or asymmetric current pulses. Masking by asymmetric current pulses was not significantly different from masking by symmetric pulses matched for pulse duration and charge. In conclusion, there appears to be no advantage to using asymmetric current pulses for the mechanical stimulation of residual low frequency hearing by electrical stimulation of the cochlea.