The Merits of Bilateral Application of Bone-Conduction Devices in Children With Bilateral Conductive Hearing Loss

OBJECTIVES: This study aims to characterize lateralization of sounds and localization of sounds in children with bilateral conductive hearing loss (BCHL) when listening with either one or two percutaneous bone conduction devices (BCDs). DESIGN: Sound lateralization was measured with the minimum audible angle test in which children were asked to indicate from which of the two visible speakers the sound originated. Sound localization was measured with a test in which stimuli were presented from speakers that were not visible to the children. In the sound localization test, 150 ms broadband noise bursts were presented, and sound level was roved over a 20-dB range. Because speakers were not visible the localization response was not affected by any visual cue. The sound localization test provides a clear distinction between lateralization and localization of sounds. Ten children with congenital BCHL and one child with acquired BCHL participated. RESULTS: Both lateralization and sound localization were better with bilateral BCDs compared with the unilaterally aided conditions. In the bilateral BCD condition, lateralization was close to normal in nearly all the children. The localization test demonstrated lateralization rather than sound localization behavior when listening with bilateral BCDs. Furthermore, in the unilateral aided condition, stimuli presented at different sound levels were mainly perceived at the same location. CONCLUSIONS: This study demonstrates that, in contrast to listening with two BCDs, children demonstrated difficulties in lateralization of sounds and in sound localization when listening with just one BCD (i.e., one BCD turned off). Because both lateralization and sound localization behavior were tested, it could be demonstrated that these children are more able to lateralize than localize sounds when listening with bilateral BCDs. The present study provides insight in (sub-optimal) sound localization capabilities of children with congenital BCHL in the unilateral-aided and bilateral-aided condition. Despite the sub-optimal results on sound localization, this study underlines the merits of bilateral application of BCDs in such children. In patients with congenital bilateral conductive hearing loss (BCHL), bilateral application of bone conduction devices (BCDs) is not the standard treatment (Liu et al. 2013). Based on systematic reviews of the existing literature, several authors have concluded that more studies are needed to provide convincing evidence on the advantage of bilateral BCD application over listening with a unilateral BCD (Colquitt et al. 2011; Janssen et al. 2012; Johnson et al. 2017). Patients with BCHL cannot access binaural cues when listening with only one BCD. With two BCDs, these patients may gain increased access to binaural cues, allowing for improved localization abilities (Zeitooni et al. 2016). Binaural processing of our auditory world provides important benefits like, improved directional hearing, increased safety (Stelling-Konczak et al. 2016), feelings of comfort and understanding of speech in noisy listening conditions (Avan et al. 2015). Hence, it is important to provide patients with BCHL and their caretakers with evidence on the merits of hearing rehabilitation with two BCDs.