Bilateral Cochlear Implants

The comparison of measured binaural performance with the better of two monaural measures (one from each ear) may lead to underestimated binaural benefit due to statistical sampling bias that favors the monaural condition. The mathematical basis of such bias is reviewed and applied to speech reception thresholds measured in 32 bilateral cochlear implant (CI) users for coincident and spatially separated speech and noise. It is shown that the bias increases with test-retest variation and is maximal for uncorrelated samples of identical underlying performance in each ear. When measured differences between ears were assumed to reflect actual underlying performance differences, the bias averaged across the CI users was about 0.2 dB for coincident target and noise, and 0.1 dB for spatially separated conditions. An upper-bound estimate of the bias, based on the assumption that both ears have the same underlying performance and observed differences were due to test-retest variation, was about 0.7 dB regardless of noise location. To the extent that the test-retest variation in these data is comparable to other studies, the results indicate that binaural benefits in bilateral cochlear implant users are not substantially underestimated (on for average) when binaural performance is compared with the better ear in each listening configuration.

Section: Conclusion and Discussionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Statistical bias in the assessment of binaural benefit relative to the better ear

Hoesel

Litovsky

2011

“…SRM obtained with our CI participants at the typical H 0 M 90 configuration (3-4 dB) falls within the range covered by previous reports and reviewed , although BCI users' SRM is on the low end. The headshadow effect measured from our UCI users (6 dB) also falls in the range covered by previous reports and reviewed by Van Hoesel (2011) and is a very good match to that measured by Culling et al (2012). Summation and squelch results are compared with the results from Litovsky et al (2006) in the bilateral-CI-users section below.…”

Section: A Speech-facing Srm and Hobsupporting

confidence: 74%

“…Additional measures of summation (2.9 dB at H 0 M 0 ) and squelch (2.0 dB at H 0 M 90 and 2.6 dB at H 30 M 180 ) from BCI users were found to be significantly larger than previously reported in the literature. These correspond to the "diotic" and "binaural" benefits reviewed by Van Hoesel (2011). Compared to summation outcomes reported in the Litovsky et al (2006) multi-center study (the effect they call binaural redundancy), our mean summation seems larger than their 1.5 dB, but their range, À6 to þ9 dB, was comparable to ours, À3.5 to þ6.5 dB.…”

Section: Bilateral CI Userssupporting

confidence: 66%

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

Grange

Culling

2016

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.

“…This last factor points to a well-known characteristic of BiCIs: The lack of binaural coordination between the CI speech processors in the two ears, which likely causes binaural cues to be weak, absent or inconsistent (van Hoesel, 2011;Litovsky, 2011a,b). BiCI users are essentially fit with two monaural systems, which are not coordinated regarding their sampling time or onset time, thus the chances that binaural cues are preserved with fidelity is minimal (van Hoesel, 2011).…”

Section: B Srmmentioning

confidence: 97%

Spatial release from masking in children with normal hearing and with bilateral cochlear implants: Effect of interferer asymmetry

Misurelli

Litovsky

2012

Spatial release from masking (SRM) was measured in groups of children with bilateral cochlear implants (BiCIs, average ages 6.0 and 7.9 yr) and with normal hearing (NH, average ages 5.0 and 7.8 yr). Speech reception thresholds (SRTs) were measured for target speech in front (0°), and interferers in front, distributed asymmetrically toward the right (+90°/+90°) or distributed symmetrically toward the right and left (+90°/-90°). In the asymmetrical condition both monaural "better ear" and binaural cues are available. In the symmetrical condition, listeners rely heavily on binaural cues to segregate sources. SRM was computed as the difference between SRTs in the front condition and SRTs in either the asymmetrical or symmetrical conditions. Results showed that asymmetrical SRM was smaller in BiCI users than NH children. Furthermore, NH children showed symmetrical SRM, suggesting they are able to use binaural cues for source segregation, whereas children with BiCIs had minimal or absent symmetrical SRM. These findings suggest that children who receive BiCIs can segregate speech from noise under conditions that maximize monaural better ear cues. Limitations in the CI devices likely play an important role in limiting SRM. Thus, improvement in spatial hearing abilities in children with BiCIs may require binaural processing strategies.