Effects of Noise and Reverberation on Sound Localization for Listeners with Bilateral Cochlear Implants

Sound localization ability, which is crucial for both communication and safety, is often degraded by noise and reverberation for listeners with hearing loss and those with normal hearing. Cochlear implants have provided great hearing benefits to individuals with severe-to-profound sensorineural hearing loss. However, even with two devices, cochlear implant users still have difficulty localizing sounds in typical listening environments. In addition, there have been no systematic investigations of the combined effects of noise and reverberation on localization performance for listeners with bilateral cochlear implants (BCIs). The purpose of this study was to investigate the effects of noise and reverberation on the ability of listeners with BCIs to localize speech. Six adults with BCIs and ten with normal hearing (NH) listened to a three-word phrase (mark the spot) presented via circumaural earphones (Sennheiser HD 265) from nine simulated locations in the frontal-horizontal plane (± 90°). The intensity of the speech was 70 dBSPL for a source at 0°. The intensity at each ear for sources at other locations varied due to the head-shadow effect. All subjects completed a virtual localization test in quiet, and at 0, -4, and -8 dB signal-to-noise-ratio (SNR) in anechoic and reverberant (0.2, 0.6, and 0.9s RT60) environments. BCI users were also tested at +8 and +4 dB SNR. Speech-spectrum noise was presented from 0° azimuth; its level was changed to achieve the different SNRs. Root-mean-square localization error in degrees was calculated. Results reveal that BCI users have significantly poorer localization accuracy than NH listeners in all conditions. BCI users\u27 localization performance started to decrease at a higher SNR (+4 dB) and shorter RT60 (0.2s) than NH listeners (-4 dBSNR, 0.6s RT60). The combination of noise and reverberation began to degrade localization of BCI users at a higher SNR and shorter RT60 (SNR+4/RT0.9 or SNR0/RT0.2) than NH listeners (SNR0/RT0.9 or SNR-4/RT0.6). It is important to apply the information obtained in this study to optimize binaural benefit for BCI users in everyday listening situations