Effects of Presentation Level on Spatial Hearing With and Without Bone-Conduction Amplification in Congenital Unilateral Aural Atresia.

OBJECTIVE: This study assessed the effect of ipsilateral bone-conduction amplification on spatial hearing abilities in subjects with congenital unilateral aural atresia (CUAA). PATIENTS: Twelve patients with unilateral conductive hearing loss secondary to CUAA and normal hearing in the contralateral ear were tested. Most (75%) had limited experience with a bone-conduction hearing aid (BCHA). INTERVENTION: Performance was evaluated with and without a BCHA fitted acutely on a softband. MAIN OUTCOME MEASURES: Spatial hearing abilities were evaluated in two paradigms. Spatial release from masking was evaluated by comparing masked sentence recognition with a target and two speech maskers either colocated at 0 degree or with the maskers separated at +90 degrees and -90 degrees. Sound source localization was evaluated in a 180 degrees arc of loudspeakers on the horizontal plane. Performance was evaluated at 50 and 75 dB SPL, and results were compared for patients tested with and without a BCHA.
RESULTS: Group level results indicate similar spatial release from masking in the aided and unaided conditions at both presentation levels. Localization at 50 dB SPL was similar aided and unaided, but at 75 dB SPL the root mean square error was lower unaided than aided (17.2 degrees vs 41.3 degrees; p = 0.010).
CONCLUSIONS: Use of a BCHA in patients with CUAA may interfere with auditory cues required for sound source localization when the signal level is intense enough to overcome the patient's conductive hearing loss. These findings have potential clinical implications in fitting of BCHAs to support optimal spatial hearing in patients with CUAA.