Stereo hearing with unilateral bone conduction amplification

Abstract Conductive hearing loss results when the neural integrity of the auditory system is healthy, but sound is prevented from reaching the cochlea in its entirety. Unilateral Congenital Aural Atresia (UCAA) is a birth defect in which there is no external ear canal, resulting in the reduction of sound able to reach the middle ear. Two primary options for correcting this conductive hearing loss are canalplasty or a bone anchored hearing device (BAHD). We want to compare the benefit level from these options, specifically in two conditions: sound localization and the ability to detect speech from one ear while there is competing background noise presented to the other ear. While canalplasty has been well studied, there is little research available on whether a unilateral bone conduction implant will provide any benefit in these binaural tasks. The purpose of this study is to determine the effect BAHD use has on localization and speech in noise understanding, so that audiologists and ENTs can advise patients of their treatment options. A stereo computer and semi-circular speaker setup was used to determine sound-localization accuracy of the participants by having them select which speaker they thought the signal noise was being presented from. Performance was quantified through percent correct and root mean squared of error in degrees azimuth. Speech in noise understanding was assessed through four different test conditions in which the participant chose the color and number spoken by a randomized recording, while competing noise played from the opposite hemifield. Data were analyzed in terms of signal-to-noise ratio. Two separate studies were designed for this dissertation. In the single-subject design, one participant had asymmetrical conductive hearing loss and took both tests twice a day, alternating BAHD use daily, for a total of six days. In the multi-subject design, six patients with UCAA each took both tests while unaided, and then again with their BAHD activated. Results showed that while BAHD use does not produce significant benefits in localization or speech in noise comprehension for all users, the unaided thresholds for asymmetry of hearing and air-bone gaps (ABGs) are predictive of whether an individual will benefit from implantation or not in these tasks. More specifically, if pre-implantation thresholds are poor (~\u3e44dB), then activation of the BAHD improves these two aspects of binaural processing; conversely, with relatively minor asymmetry BAHD activation makes binaural processing worse