Bilateral Cochlear Implants in Children: Localization Acuity Measured with Minimum Audible Angle

Abstract

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.

Lateralization of Interimplant Timing and Level Differences in Children Who Use Bilateral Cochlear Implants

“…None of the 8 participants who used only one cochlear implant could correctly localize sound sources even at the maximum angle tested (70º). Litovsky (2006a) similarly showed that 9 out of 13 pediatric bilateral implant users had minimum audible angles less than 40º and of these, 8 could distinguish angles smaller than 20º. Two of six children using one implant and one hearing aid had MAAs similar to the bilateral implant users, but the remaining children in this group performed much worse than the average child with bilateral implants.…”

“…Further, Galvin and colleagues (Galvin et al 2007) reported that children who received their second CI after 4 years of age did not show any improvement using both implants over unilateral conditions on tests of sound localization after 6-13 months of bilateral experience. Litovsky (Litovsky et al 2006a;Litovsky et al 2006b;Litovsky et al 2004) also report high degrees of variability within groups of implanted children, which could not always be attributed to duration of deafness or length of bilateral implant use. In order to better predict and promote improved outcomes with bilateral cochlear implants, further research is needed to gain understanding into what factors determine localization abilities in these children.…”

“…The above research groups have shown that children with bilateral implants have the ability to identify differences in sound sources (Galvin et al 2008;Grieco-Calub et al 2008;Litovsky et al 2006a;Litovsky et al 2006b;Litovsky et al 2004). However, despite observed improvements over unilateral performance, many bilaterally implanted children were not able to localize sounds in space as accurately as their peers with normal hearing.…”

“…However, a number of studies have investigated behavioural measures of bilateral cochlear implant use including free-field sound localization (the identification of sound sources from one of several speakers) (Galvin et al 2007;Galvin et al 2008;Litovsky et al 2006a;Litovsky et al 2006b;Litovsky et al 2004;Van Deun et al 2009b) and measurements of minimum audible angle (MAA) (the smallest discernable change in the location of a sound that can be consistently measured) (Grieco-Calub et al 2008;Litovsky et al 2006a;Litovsky et al 2006b). These studies have shown that many children with bilateral cochlear implants are better at identifying sound sources using two CIs rather than a single CI (Galvin et al 2008;Grieco-Calub et al 2008).…”

Design and fabrication of multichannel cochlear implants for animal research

“…Other novel applications of cochlear implants currently being studied include the use of bilateral implants or bimodal stimulation to improve localization ability (van Hoesel and Tyler, 2003;Seeber et al, 2004;Verschuur et al, 2005;Litovsky et al, 2006), speech perception in the presence of noise (Au et al, 2003;van Hoesel and Tyler, 2003;Vermeir et al, 2003;Ching et al, 2004;Ramsden et al, 2005) and the creation of "virtual channels" by proportionally dividing stimulus current between two or more electrode sites to generate a potentially large number of perceptually distinct pitches using a minimum number of electrode sites (McDermott and McKay, 1994;Donaldson et al, 2005;Kwon and van den Honert, 2006). In each of these areas animal experiments could play an important role in understanding the complex interactions between multiple inputs and how specific electrode design features might be optimized for each purpose.…”