Stimulus features affecting psychophysical detection thresholds for electrical stimulation of the cochlea .3. Pulse polarity

Effects of initial-phase polarity on psychophysical detection thresholds for electrical stimulation of the cochlea were examined in four nonhuman primates using trains of biphasic and triphasic charge-balanced pulses. Initial-phase polarity had small but consistent effects on the levels and slopes of threshold versus phase duration functions. These effects were consistent with the hypothesis that the initial-phase polarity affects the site of action potential initiation. Thresholds for biphasic pulses were lower than those for triphasic pulses, suggesting that the system is responsive to both positive and negative phases of the stimulus. Interactions between initial-phase polarity, pulse waveform, and phase duration were observed. (C) 1996 Acoustical Society of America.