EFAS Congress edition:11 location:Budapest date:19-22 June 2013
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, and it was recently found that bimodal listeners with sufficient residual hearing are 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 use binaural cues, due to poor cue transmission by the devices. We present 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 existing models of loudness for acoustic and electric stimulation. SCORE was evaluated using loudness balancing, speech perception and sound source localisation experiments with 6 bimodal listeners. As SCORE was found not to interfere with speech perception and to improve loudness perception, 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. It was evaluated by measuring the just noticeable difference in interaural time difference of 5 bimodal listeners. Compared to the ACE strategy, performance was significantly improved with just noticeable differences well within the physically relevant range.
The application of these two strategies could lead to improved sound source localisation and binaural unmasking.