Contralateral Routing of Signal Disrupts Monaural Sound Localization

Abstract

Objectives: In the absence of binaural hearing, individuals with single-sided deafness can adapt to use monaural level and spectral cues to improve their spatial hearing abilities. Contralateral routing of signal is the most common form of rehabilitation for individuals with single-sided deafness. However, little is known about how these devices affect monaural localization cues, which single-sided deafness listeners may become reliant on. This study aimed to investigate the effects of contralateral routing of signal hearing aids on localization performance in azimuth and elevation under monaural listening conditions. Design: Localization was assessed in 10 normal hearing adults under three listening conditions: (1) normal hearing (NH), (2) unilateral plug (NH-plug), and (3) unilateral plug and CROS aided (NH-plug + CROS). Monaural hearing simulation was achieved by plugging the ear with E-A-Rsoft™ FX™ foam earplugs. Stimuli consisted of 150 ms high-pass noise bursts (3–20 kHz), presented in a random order from fifty locations spanning ±70° in the horizontal and ±30° in the vertical plane at 45, 55, and 65 dBA. Results: In the unilateral plugged listening condition, participants demonstrated good localization in elevation and a response bias in azimuth for signals directed at the open ear. A significant decrease in performance in elevation occurs with the contralateral routing of signal hearing device on, evidenced by significant reductions in response gain and low r2 value. Additionally, performance in azimuth is further reduced for contralateral routing of signal aided localization compared to the simulated unilateral hearing loss condition. Use of the contralateral routing of signal device also results in a reduction in promptness of the listener response and an increase in response variability. Conclusions: Results suggest contralateral routing of signal hearing aids disrupt monaural spectral and level cues, which leads to detriments in localization performance in both the horizontal and vertical dimensions. Increased reaction time and increasing variability in responses suggests localization is more effortful when wearing the contralateral rerouting of signal device.