Title: Does Bilateral Experience Lead to Improved Spatial Unmasking of Speech in Children Who Use Bilateral Cochlear Implants?
Legend: We vary the spatial locations of target speech and masking speech, so they are co-located (A) or separated (B). The difference in speech reception thresholds between (A) and (B) indicates advantage from spatial cues (spatial release from masking; SRM). In (C) we show SRM (dB), for children with bilateral cochlear implants (BiCIs), as a function of the number of months of bilateral experience, and for normal hearing children and adults.Children with normal hearing benefit from spatial separation of target, and masking speech performance is not significantly different from adults. In children with BiCIs, early on after activation of the implants (3-6 months), SRM was negative, suggesting that having maskers on the side causes poor speech understanding, likely because the microphones over-amplify maskers relative to target speech. With additional experience, children with bilateral cochlear implants can segregate speech from maskers. Some implanted children performed on par with NH children. Future work using engineering approaches is aimed at restoring binaural functioning to children with BiCIs.
Citation: Litovsky, R.Y. and Misurelli, S.M. (2016). Does Bilateral Experience Lead to Improved Spatial Unmasking of Speech in Children Who Use Bilateral Cochlear Implants? Otology & Neurotology, 37:e35–e42. PMCID: PMC4712724, DOI: 10.1097/ MAO.0000000000000905
Abstract: Children who are born with bilateral sensorineural deafness are candidates for surgical placement of cochlear implants, which convey auditory information through electrical stimulation of the 8th nerve. Many children today receive cochlear implants in both ears, i.e., bilateral CIs (BiCIs). The most compelling argument for bilateral vs. unilateral cochlear implants is to provide access to auditory cues that facilitate sound localization, and segregation of speech from background sounds. The latter is measured by comparing speech reception thresholds when: target and maskers are co-located (A) vs. separated (B). Positive values indicate benefit of spatial separation (spatial release from masking; SRM). Children ages 4-9 were assessed at annual intervals following activation of BiCIs, and compared with performance of children with normal hearing (NH) with the same chronological age. Results showed that in NH children, SRM is well developed, with no statistically significant difference from adults. In children with BiCIs, within 3-6 months of bilateral experience, SRM was negative, suggesting that performance was worse with maskers on the side, likely because the microphones over-amplify maskers relative to target speech. With additional BiCI experience, SRM improved; some implanted children performed on par with NH children. However, most implanted children did not reach the same level of performance as NH children, suggesting that spatial cues are not preserved with fidelity when presented through clinical cochlear implant processors. Future work using engineering approaches are aimed at restoring binaural functioning to children with BiCIs. This work was funded by NIH-NIDCD.
About the Lab: Research in the Litovsky lab focuses on the ability of children and adults to hear in complex auditory environments (e.g., classrooms, restaurants, playgrounds and “cocktail parties”). We are typically faced with the challenge of interpreting sounds as they reach the ears, learning to ignore echoes and other irrelevant, distracting signals. The brain has specialized circuits that compute sound location, and separate important sounds from background noise. We study the contribution of binaural hearing, and the limitations that are experienced by people with hearing loss. In particular, we focus on a unique population of people who are deaf and use cochlear implants. In addition to studying spatial hearing, such as sound localization skills and speech understanding in noise, we are interested in cognitive development and its implications for auditory processing. Another aspect of our research focuses on the effect that challenging listening situations has on listening effort, and the amount of cognitive load exerted during psychophysical testing. Finally, our reverse engineering approaches focus on possible ways in which bilateral cochlear implants can be improved by synchronizing the devices across the ears, and utilizing novel strategies to stimulate electrodes in the cochlea that restore near-normal binaural hearing.