This study evaluated functional benefits from bilateral stimulation in 20 children ages 4 -14, 10 use two CIs and 10 use one CI and one HA. Localization acuity was measured with the minimum audible angle (MAA). Speech intelligibility was measured in quiet, and in the presence of 2-talker competing speech using the CRISP forced-choice test. Results show that both groups perform similarly when speech reception thresholds are evaluated. However, there appears to be benefit (improved MAA and speech thresholds) from wearing two devices compared with a single device that is significantly greater in the group with two CI than in the bimodal group. Individual variability also suggests that some children perform similarly to normal-hearing children, while others clearly do not. Future advances in binaural fitting strategies and improved speech processing schemes that maximize binaural sensitivity will no doubt contribute to increasing the binaurally-driven advantages in persons with bilateral CIs. KeywordsBilateral; Binaural; Cochlear implant; Hearing aid; Children; Speech; Localization Cochlear implants (CIs) have become a powerful means of providing hearing to deaf persons. Although the vast majority of CI users can understand speech in a quiet situation (Zeng, 2004;Stickney et al, 2004;Holt & Kirk, 2005), and report improvement in quality of life postimplantation (Summerfield et al, 2002), they have continued difficulties under many circumstances. For instance, most CI users have difficulty locating sounds in their environments; all sounds appear to be coming either directly from their ear, or inside their head. In addition, their ability to understand speech in everyday, noisy and reverberant environments is quite poor (e.g., Fu et al, 1998;Nelson & Jin, 2004;Stickney et al, 2004Stickney et al, , 2005. Continuous efforts are being made to improve performance with single CIs by developing better speech processing strategies (e.g., Rubinstein & Hong, 2003;Green et al, 2005;Nie et al, 2005;Yang & Fu, 2005).Bilateral CIs (BI-CIs) are also being provided to a growing number of patients in an attempt to increase quality of life and to improve listening in everyday noisy situations. This clinical approach is primarily rooted in the assumption that, since normal-hearing people rely on two ears (binaural hearing) for sound localization and speech understanding in noise, deaf individuals should also have two good ears in order to maximize their performance. Bilaterally implanted adults show some clear and significant benefits when using two CIs compared with a single CI. As in normal hearing persons, speech understanding in noise is better in bilateral NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript users when both ears are activated compared with a monaural condition (Gantz et al, 2002;Tyler et al, 2002;Muller et al, 2002;Litovsky et al, 2004;Schleich et al, 2004). The benefits are thought to arise from a combination of effects, including the head shadow effect, binaural squelch and binaural...
Children with sequential BI cochlear implants represent a unique population of individuals who have undergone variable amounts of auditory deprivation in each ear. Our findings suggest that many but not all of these children perform better on measures of localization acuity with two cochlear implants compared with one and are better at the task than children using the cochlear implant + hearing aid. These results must be interpreted with caution, because benefits on other tasks as well as the long-term benefits of BI cochlear implants are yet to be fully understood. The factors that might contribute to such benefits must be carefully evaluated in large populations of children using a variety of measures.
This report highlights research projects relevant to binaural and spatial hearing in adults and children. In the past decade we have made progress in understanding the impact of bilateral cochlear implants (BiCIs) on performance in adults and children. However, BiCI users typically do not perform as well as normal hearing (NH) listeners. In this paper we describe the benefits from BiCIs compared with a single CI, focusing on measures of spatial hearing and speech understanding in noise. We highlight the fact that in BiCI listening the devices in the two ears are not coordinated, thus binaural spatial cues that are available to NH listeners are not available to BiCI users. Through the use of research processors that carefully control the stimulus delivered to each electrode in each ear, we are able to preserve binaural cues and deliver them with fidelity to BiCI users. Results from those studies are discussed as well, with a focus on the effect of age at onset of deafness and plasticity of binaural sensitivity. Our work with children has expanded both in number of subjects tested and age range included. We have now tested dozens of children ranging in age from 2-14 years. Our findings suggest that spatial hearing abilities emerge with bilateral experience. While we originally focused on studying performance in free-field, where real world listening experiments are conducted, more recently we have begun to conduct studies under carefully controlled binaural stimulation conditions with children as well. We have also studied language acquisition and speech perception and production in young CI users. Finally, a running theme of this research program is the systematic investigation of the numerous factors that contribute to spatial and binaural hearing in BiCI users. By using CI simulations (with vocoders) and studying NH listeners under degraded listening conditions, we are able to tease apart limitations due to the hardware/software of the CI systems from limitations due to neural pathology.
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