Evaluation of a cochlear-implant processing strategy incorporating phantom stimulation and asymmetric pulses

OBJECTIVE To evaluate a speech-processing strategy in which the lowest frequency channel is conveyed using an asymmetric pulse shape and "phantom stimulation", where current is injected into one intra-cochlear electrode and where the return current is shared between an intra-cochlear and an extra-cochlear electrode. This strategy is expected to provide more selective excitation of the cochlear apex, compared to a standard strategy where the lowest-frequency channel is conveyed by symmetric pulses in monopolar mode. In both strategies all other channels were conveyed by monopolar stimulation. DESIGN Within-subjects comparison between the two strategies. Four experiments: (1) discrimination between the strategies, controlling for loudness differences, (2) consonant identification, (3) recognition of lowpass-filtered sentences in quiet, (4) sentence recognition in the presence of a competing speaker. STUDY SAMPLE Eight users of the Advanced Bionics CII/Hi-Res 90k cochlear implant. RESULTS Listeners could easily discriminate between the two strategies but no consistent differences in performance were observed. CONCLUSIONS The proposed method does not improve speech perception, at least in the short term.