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Published on: December 20, 2024
Horizontal sound localization in cochlear implant users with a contralateral hearing aid.
Lidwien C E Veugen1, Maartje M E Hendrikse1, Marc M van Wanrooij2
1Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, P.O. Box 9101, 6500 GL, Nijmegen, The Netherlands.
Bimodal hearing with a cochlear implant (CI) and hearing aid (HA) often results in poor sound localization. Binaural cues, like interaural level differences (ILDs), are likely used but are perturbed, causing biased sound perception.
Area of Science:
- Auditory Neuroscience
- Audiology
- Bioacoustics
Background:
- Interaural differences in time (ITD) and level (ILD) are crucial for horizontal sound localization and speech understanding.
- The availability of these binaural cues for hearing-impaired individuals using bimodal cochlear implant (CI) and contralateral hearing aid (HA) fitting is not well understood.
Purpose of the Study:
- To assess the sound localization behavior of bimodal listeners.
- To determine the contribution of binaural (ILDs, temporal fine structure and envelope ITDs) and monaural cues to horizontal sound localization in bimodal listeners.
- To investigate the impact of frequency band, level, and envelope on bimodal sound localization.
Main Methods:
- Evaluated sound localization in fourteen bimodal listeners with matched Phonak HA and Advanced Bionics CI processors.
- Systematically varied stimulus frequency band, level, and envelope to isolate cue contributions.
- Analyzed localization bias and performance across different listening conditions.
Main Results:
- Bimodal sound localization performance was generally poor, with significant bias.
- Sound bandwidth strongly influenced localization bias, typically favoring the CI side for broadband/high-pass and occasionally the HA side for low-pass stimuli.
- HA-aided thresholds below 45 dB HL were a prerequisite, but not sufficient, for directional hearing.
Conclusions:
- Bimodal sound localization likely relies on ILD cues, even at low frequencies where natural ILDs are minimal.
- Perturbed binaural cues in bimodal fitting lead to biased sound localization perception.
- High localization accuracy may depend on sufficient spectral overlap and loudness balance between the CI and HA.
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