Binaural fusion in single-sided deaf cochlear implant users

Single-sided deaf (SSD) cochlear implant (CI) patients often have difficulty with spatial perception, which may be partly due to limited fusion of acoustic and electric hearing. In the present study, we investigated binaural fusion in SSD CI patients.

Eight adult SSD CI patients participated in the study. Binaural fusion was measured using speech and non-speech stimuli. Listeners indicated whether they heard 1 or 2 auditory images, the diffuseness of the sound, and lateralization of sounds in a virtual space.

Binaural fusion and similarity ratings were highly variable across participants. Across all participants and stimuli, a single auditory image was perceived only 40.23 ± 38.46% of the time. Sensitivity to stimulus types varied greatly across participants, but in no consistent manner. Diffuseness was significantly larger for words and environmental sounds than for sentences and tones. When one image was perceived, stimuli were generally lateralized towards the center. When two images were perceived, the mean lateralization was 57.11 ± 56.67 degrees.

Binaural fusion in the present SSD CI users was much less than observed in previous studies with bilateral CI users, possibly due to differences in stimulation patterns between acoustic and electric hearing and interaural frequency mismatch.