Optimizing Binaural Cue Perception with Combined Cochlear Implant and Acoustic Stimulation

Currently, bimodal listeners are normally fitted with a standard cochlear implant (CI) sound processor and hearing aid. This configuration has been shown to be advantageous compared to only the CI. We recently found that bimodal listeners with sufficient residual hearing can be sensitive to binaural cues: interaural level differences and interaural time differences in the envelope and transients of the signal. However, with current clinical devices bimodal listeners do not appear to make advantage of binaural cues, due to poor cue transmission by the devices. We have developed two sound processing strategies to improve this: SCORE bimodal and MEnS. The SCORE bimodal strategy aims to equalise loudness growth for both modalities using real-time application of models of loudness perception for acoustic and electric stimulation. As SCORE was found to improve loudness perception and not to interfere with speech perception and, it seems beneficial to implement it in clinical devices. The MEnS strategy introduces temporal modulations on all stimulated electrodes, synchronously with modulations present in the acoustic signal, based on measurement of the peaks occurring at the rate of the fundamental frequency in voiced phonemes. Compared to the ACE strategy, interaural time difference detection and interaural-time-difference based lateralisation was significantly improved with just noticeable differences with MEnS well within the physically relevant range. The application of these two strategies could lead to improved sound source localisation and binaural unmasking with bimodal stimulation.status: publishe