The Benefit of Bilateral Versus Unilateral Cochlear Implantation to Speech Intelligibility in Noise

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Bilateral cochlear implants (CIs) have provided some success in improving spatial hearing abilities to patients, but with large variability in performance. One reason for the variability is that there may be a mismatch in the place-of-stimulation arising from electrode arrays being inserted at different depths in each cochlea. Goupell et al. [(2013b). J. Acoust. Soc. Am. 133(4), [2272][2273][2274][2275][2276][2277][2278][2279][2280][2281][2282][2283][2284][2285][2286][2287] showed that increasing interaural mismatch led to non-fused auditory images and poor lateralization of interaural time differences in normal hearing subjects listening to a vocoder. However, a greater bandwidth of activation helped mitigate these effects. In the present study, the same experiments were conducted in post-lingually deafened bilateral CI users with deliberate and controlled interaural mismatch of single electrode pairs. Results show that lateralization was still possible with up to 3 mm of interaural mismatch, even when off-center, or multiple, auditory images were perceived. However, mismatched inputs are not ideal since it leads to a distorted auditory spatial map. Comparison of CI and normal hearing listeners showed that the CI data were best modeled by a vocoder using Gaussian-pulsed tones with 1.5 mm bandwidth. These results suggest that interaural matching of electrodes is important for binaural cues to be maximally effective.

Section: A Implication Of Mismatch and Binaural Processesmentioning

confidence: 99%

Effect of mismatched place-of-stimulation on binaural fusion and lateralization in bilateral cochlear-implant users

Kan¹,

Stoelb²,

Litovsky³

et al. 2013

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“…[see reviews in Van Hoesel (2011) and Culling et al (2012)]. In this configuration and in a sound-treated room, SRM reaches only 3 to 5 dB (e.g., Litovsky et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Head orientation benefit to speech intelligibility in noise for cochlear implant users and in realistic listening conditions

Grange

Culling

2016

Self Cite

Cochlear implant (CI) users suffer from elevated speech-reception thresholds and may rely on lip reading. Traditional measures of spatial release from masking quantify speech-reception-threshold improvement with azimuthal separation of target speaker and interferers and with the listener facing the target speaker. Substantial benefits of orienting the head away from the target speaker were predicted by a model of spatial release from masking. Audio-only and audio-visual speech-reception thresholds in normal-hearing (NH) listeners and bilateral and unilateral CI users confirmed model predictions of this head-orientation benefit. The benefit ranged 2–5 dB for a modest 30° orientation that did not affect the lip-reading benefit. NH listeners' and CI users' lip-reading benefit measured 3 and 5 dB, respectively. A head-orientation benefit of ∼2 dB was also both predicted and observed in NH listeners in realistic simulations of a restaurant listening environment. Exploiting the benefit of head orientation is thus a robust hearing tactic that would benefit both NH listeners and CI users in noisy listening conditions.

“…The sensitivity of listeners to changes in interaural correlation appears to be closely related to the binaural masking level difference (BMLD) (Koehnke et al, 1986;Goupell and Litovsky, 2014), which can be considered a simplification of the situation where listeners demonstrate improved speech understanding in noise for spatially separated talkers vs co-located talkers (e.g., Bronkhorst and Plomp, 1988;Culling et al, 2004;Hawley et al, 2004). In fact, binaural models that incorporate BMLD sensitivity can make extremely accurate speech-in-noise intelligibility predictions for a variety of spatial configurations, types of listening environments, and types of listeners (Lavandier and Culling, 2010;Culling et al, 2012). a) Author to whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity to interaural envelope correlation changes in bilateral cochlear-implant users

Goupell

Litovsky

2015

Provision of bilateral cochlear implants (CIs) to people who are deaf is partially justified by improved abilities to understand speech in noise when comparing bilateral vs unilateral listening conditions. However, bilateral CI listeners generally show only monaural head shadow with little improvement in speech understanding due to binaural unmasking. Sensitivity to change in interaural envelope correlation, which is related to binaural speech unmasking, was investigated. Bilateral CI users were tested with bilaterally synchronized processors at single, pitch-matched electrode pairs. First, binaural masking level differences (BMLDs) were measured using 1000 pulse-per-second (pps) carriers, yielding BMLDs of 11.1 6 6.5 and 8.5 6 4.2 dB for 10-and 50-Hz bandwidth masking noises, respectively. Second, envelope correlation change just-noticeable differences (JNDs) were measured. Stimuli presented at 1000 pps yielded lower JNDs than those presented at 100 pps. Furthermore, perfectly correlated reference stimuli produced lower JNDs than uncorrelated references, and uncorrelated references generally produced immeasurable JNDs. About 25% of JNDs measured in the CI listeners were in the range of JNDs observed in normal-hearing listeners presented CI simulations. In conclusion, CI listeners can perceive changes in interaural envelope correlation, but the poor performance may be a major limiting factor in binaural unmasking tested to date in realistic listening environments.