Spatial Speech-in-Noise Performance in Bimodal and Single-Sided Deaf Cochlear Implant Users

Abstract

This study compared spatial speech-in-noise performance in two cochlear implant (CI) patient groups: bimodal listeners, who use a hearing aid contralaterally to support their impaired acoustic hearing, and listeners with contralateral normal hearing, i.e., who were single-sided deaf before implantation. Using a laboratory setting that controls for head movements and that simulates spatial acoustic scenes, speech reception thresholds were measured for frontal speech-in-stationary noise from the front, the left, or the right side. Spatial release from masking (SRM) was then extracted from speech reception thresholds for monaural and binaural listening. SRM was found to be significantly lower in bimodal CI than in CI single-sided deaf listeners. Within each listener group, the SRM extracted from monaural listening did not differ from the SRM extracted from binaural listening. In contrast, a normal-hearing control group showed a significant improvement in SRM when using two ears in comparison to one. Neither CI group showed a binaural summation effect; that is, their performance was not improved by using two devices instead of the best monaural device in each spatial scenario. The results confirm a “listening with the better ear” strategy in the two CI patient groups, where patients benefited from using two ears/devices instead of one by selectively attending to the better one. Which one is the better ear, however, depends on the spatial scenario and on the individual configuration of hearing loss.

Unilateral acoustic degradation delays attentional separation of competing speech

“…While such a scenario mimics hearing in people with single-sided deafness (SSD) after CI implantation, a significant amount of unilateral CI users suffers from hearing loss also on the contralateral side, which is treated with a hearing aid in case of bimodal listeners (for comparison of spatial speech-in-noise performance of SSD and bimodal listeners, see e.g. Williges et al, 2019).…”

Cochlear Implantation in Cases of Asymmetric Hearing Loss: Subjective Benefit, Word Recognition, and Spatial Hearing

“…In contrast, CI users do not appear to use low-frequency interaural time differences, relying instead on interaural level differences for localization ( Dirks et al., 2019 ; Dorman et al., 2015 ). Similarly, for most conditions, the spatial release from masking (SRM) observed when comparing masked speech recognition for colocated and spatially separated sources can be explained by reduced masker energy in the high frequencies contralateral to the noise source ( Dirks et al., 2019 ; Williges et al., 2019 ). This has led some researchers to argue that the binaural benefit associated with SRM experienced by CI users is really just a monaural effect, indicating reliance on cues from the side with the better signal-to-noise ratio (SNR).…”

Improved binaural speech reception thresholds through small symmetrical separation of speech and noise

“…Beside the monaural assessment of the head shadow effect, binaural signal processing may result in binaural summation, which is the difference in SRT between listening with two ears and listening with the better monaural ear, or the binaural squelch [14]. The binaural squelch effect describes the benefit in speech intelligibility that is obtained when adding an ear with a poorer SNR, assuming that both ears have the same monaural performance [8]. The two aspects of the better-ear effect can be considered as rather passive effects per se, while the binaural summation and even more the squelch effect might be viewed as higher order influence in the auditory processing pathway [7].…”

“…Understanding the basal processes a bit better might help to improve device fitting. Binaural hearing has a huge positive effect on speech perception in spatially distributed noise and is the focus of many trials for users of hearing technologies [ 6 – 8 ]. The binaural neural processing of the interaural level difference (ILD) and interaural time difference (ITD) as, e.g.…”