Using vocoders to the implanted ear to investigate the binaural benefit for music sound quality in single-sided deaf cochlear implant users.

Despite the poor sound quality provided by cochlear implants (CIs), single-sided deaf (SSD) CI users prefer to listen to music with the acoustic hearing (AH) and CI ears together rather than with the AH ear alone. The source of this binaural benefit remains unclear. In the present study, sound quality ratings were collected in SSD CI users for music excerpts from different genres (pop, rock, and classical). A novel vocoder-to-the-CI (VCI) approach was used to control the spectral and temporal information delivered to the CI ear. Custom sine-wave vocoders were designed for each participant according to the frequency allocation in their clinical map. Sound quality ratings were collected with CI-only, AH-only, and CI+AH listening. CI+AH ratings were significantly higher than AH-only ratings when unprocessed stimuli or vocoded stimuli with spectro-temporal information were delivered to the CI ear. There were no significant differences among CI+AH ratings for the unprocessed stimuli, vocoded stimuli with spectro-temporal information, and vocoded stimuli with greatly reduced temporal cues, suggesting that the binaural benefit was largely driven by similar spectral information across ears. Effects of genre were minimal. CI+AH ratings for unprocessed music were significantly correlated with CI-only ratings (r = 0.57, p < 0.001), with the slope (0.97) suggesting that the binaural benefit was largely additive between the AH and CI ears. VCI appears to be a fruitful approach to control the spectral and temporal information delivered to the CI ear without directly manipulating CI users' clinical processors.