Perception of Interaural Phase Differences With Envelope and Fine Structure Coding Strategies in Bilateral Cochlear Implant Users.

Only 12 bilateral cochlear implant users were tested in the main speech-in-noise experiment, and only 7 did the phase-discrimination experiment, so the results may not represent all implant users. All implant users had at least 10 active electrode contacts and speech reception thresholds below 0 dB SNR, so people with fewer active channels or poorer baseline speech scores were not included. Interindividual variability was large, especially for phase discrimination; four of seven users reached thresholds below the test limit with FS4, and two were close to normal-hearing listeners. FS4 used fine structure on only four apical channels, while the speech test used multichannel stimulation, and channel interactions may distort interaural timing cues. The study did not find a significant correlation between phase-discrimination thresholds and binaural speech benefit with FS4, so good phase detection did not predict better speech-in-noise benefit. Normal-hearing listeners were tested with headphones or vocoder processing, not the same clinical listening situation as implant users.

Do not conclude that FS4 produces a larger binaural speech-in-noise benefit than HDCIS. The benefit was 0.6 dB with FS4 and 0.5 dB with HDCIS, and the analysis found no interaction between strategy and condition.