Abstract
The purpose of this study was to examine the effects of reverberation on the ability of listeners with bilateral cochlear implants (BCIs) to localize speech in anechoic and reverberant environments. Two specific research questions were addressed: (1) how do listeners with BCIs localize sounds in different environments compared to listeners with normal hearing (NH)? and (2) at what reverberation time (RT60) does localization performance begin to decline for both groups of subjects? Six adults with BCIs and ten with NH participated. All subjects completed a virtual localization test in simulated anechoic and reverberant environments (0.0, 0.2, 0.6, and 0.9 s RT60) in quiet. A three-word phrase was presented at 70 dBSPL from nine simulated source locations in the frontal-horizontal plane (± 900). Root-mean-square localization error (RMSLE) in degrees was calculated. Results revealed localization accuracy significantly decreased as reverberation time increased for both groups of subjects. Listeners with BCIs had significantly poorer localization accuracy than listeners with NH in all conditions. Their RMSLE changed from 320 in anechoic condition to 600 in RT60 0.9s condition, while corresponding change for listeners with NH was only from 170 to 220. In addition, localization performance of listeners with BCIs started to decrease at a shorter reverberation time (RT60 0.6s) compared to those with NH (RT60 0.9s). In conclusion, reverberation significantly degraded localization performance, with a greater influence on listeners with BCIs than listeners with NH. In addition, bilateral experience is likely to help listeners with BCIs achieve a better localization outcome over time. It is important to apply the information obtained in this study to optimize binaural benefit for listeners with BCIs in everyday listening situations.
Highlights
Cochlear implants have been shown to provide remarkable hearing benefits to people with severe-to-profound sensorineural hearing loss who receive little or no benefit from hearing aids [1]
The results showed a bilateral cochlear implants (BCIs) benefit to sound localization compared to unilateral cochlear implant (UCI), but the study did not vary the RT60 or test in an anechoic room, so the effect of reverberation in their study cannot be quantified
Their Root-mean-square localization error (RMSLE) changed from 32° in anechoic condition to 60° in RT60 0.9 s condition, while corresponding change for listeners with normal hearing (NH) was only from 17° to 22°
Summary
Cochlear implants have been shown to provide remarkable hearing benefits to people with severe-to-profound sensorineural hearing loss who receive little or no benefit from hearing aids [1]. Due to the limitations of current signal processing strategies and implant compression circuits, binaural cues (interaural time and level cues) that are important for accurate sound localization, are not fully preserved by the CI devices [2]. Listeners with bilateral cochlear implants (BCIs) have difficulty localizing sounds in typical listening environments, and have poorer than normal localization performance [2,3]. Studies have revealed adverse effects of reverberation on listeners with normal hearing (NH). Their localization performance was consistently poorer in a reverberant room than in an absorbent room [4] and localization accuracy of continuous broadband noise decreased significantly with increasing RT60/ RT30 [5,6]. Sound localization is crucial for both communication and safety; it is important to understand the effect of reverberation on the ability of listeners with BCIs to locate sound sources
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