Biomimetic Fitting of Cochlear Implants Using New Insight on Stapedius Reflex
Stapedius reflex measurements are one of the few objective methods that can be used for fitting cochlear implants. Research published by ERCD scientists now shows how reflex thresholds differ between electric stimulation (ESRT) and free sound field acoustic stimulation. The paper also describes a new biomimetic method of cochlear implant fitting using the ESRT measurement.
Aim of the study was to determine the relation between stapedius reflex thresholds in cochlear implant users evoked once through direct electric stimulation on single channels (ESRT) and once through acoustic stimulation in free sound field. For comparison, stapedius reflex thresholds were obtained in free sound field in a normal-hearing control group. N=29 experienced CI users (34 ears) and N=10 normal hearing listeners participated in this study. For each participant a new ESRT-based fitting was created. Stapedius reflex thresholds were obtained for this new fitting in free sound field for different loudness adjustments. Acoustic stimuli for eliciting the stapedius reflex were narrow band noise signals covering the audiometric frequency range. ESRT-based fitting resulted in different stapedius reflex behaviour compared to normal-hearing listeners.
Reflex thresholds also exhibited a frequency dependence, with lower thresholds for higher frequency acoustic stimuli. A linear relation between upper stimulation levels on the implant channels and corresponding stapedius reflex thresholds evoked in free sound field was found. This correlation may be a guideline for electrical dynamic range fitting of the cochlear implant. This allows the implant system to mimic the natural reflex behaviour in the best possible way and potentially avoid under-and overstimulation.
Publication
- Franke-Trieger, A., Mattheus, W., Seebacher, J., Zahnert, T., & Neudert, M. (2021). Stapedius reflex evoked in free sound field in cochlear implant users compared to normal-hearing listeners. International Journal of Audiology, 1–9. https://doi.org/10.1080/14992027.2020.1866780