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Sensitivity to interaural time differences and localization accuracy in cochlear implant users with combined
Monika Körtje1, Uwe Baumann1, Timo Stöver2
1Audiological Acoustics, ENT Department, University Hospital Frankfurt, Goethe University Frankfurt, Frankfurt am Main, Germany.
Plos One
|October 19, 2020
Summary
Cochlear implant users with electric-acoustic stimulation (EAS) showed normal interaural time difference (ITD) sensitivity but poor sound localization. Device time delays likely impair binaural timing cues for better hearing.
Area of Science:
- Audiology
- Neuroscience
- Biomedical Engineering
Background:
- Cochlear implants (CIs) with electric-acoustic stimulation (EAS) aim to improve hearing by combining electrical stimulation of the cochlea with acoustic amplification.
- Assessing the impact of EAS on auditory perception, specifically sound localization and interaural time difference (ITD) sensitivity, is crucial for understanding binaural hearing capabilities in CI users.
Purpose of the Study:
- To evaluate the localization accuracy and ITD sensitivity in individuals using CIs with EAS.
- To compare the performance of EAS users with that of a normal-hearing control group.
Main Methods:
- Eight CI users with EAS and 24 normal-hearing individuals participated.
- Experiment 1 involved measuring mean localization error (MLE) for various sound incidence angles using different noise stimuli.
- Experiment 2 measured just noticeable differences (JND) for ITDs with pure tones at different frequencies.
Main Results:
- EAS users exhibited significantly higher MLE (8.5°–14.7°) compared to normal-hearing subjects (1.8°).
- EAS users performed at chance level in differentiating front vs. back sound incidence.
- JND-ITDs for EAS users were comparable to controls for 125 Hz, but not significantly correlated with MLE.
Conclusions:
- EAS users demonstrate near-normal ITD sensitivity in low-frequency acoustic hearing.
- Acoustic localization accuracy in EAS users was substantially lower than in normal-hearing individuals.
- Potential signal processing time delays between bilateral devices may degrade binaural timing cue transfer, impacting localization.
