Bone-anchored hearing systems (BAHSs) provide sound location–dependent input to the normal ear for reducing the head shadow effect in the case of single-sided deafness (SSD).Background
Patients with SSD can be fit with a BAHS positioned on the impaired side. Despite successful outcomes and some reports of spatial hearing capabilities, little data are available regarding the physiologic performance of BAHSs in response to free-field sounds.Methods
Cochlear microphonics (CMs) were recorded from five chinchillas before and after destruction of one cochlea. A BAHS (Cochlear Baha) was fitted on the deafened side. CM measurements were made in response to tones, with and without the BAHS, to free-field sounds presented ipsilateral to the SSD, on the side of the normal ear, and along the midline. Stimuli were also presented directly through the BAHS and an earphone to generate sounds with interaural time and level differences approximating free-field sounds.Results
With the BAHS, CM thresholds were decreased (re: no BAHS) by approximately 10 dB for sources ipsilateral to the SSD, approximately 14 dB for midline sources, and approximately 5 dB for sources contralateral to the SSD. Changes in CM amplitudes and thresholds were sound location dependent. CM amplitudes were modulated by interaural time and level differences generated by the linear interaction of BAHS and acoustic signals.Conclusion
This study suggests that BAHS can provide input to the normal ear that is modulated by sound location, which serves to reduce the head shadow effect and may also offer cues to sound location.