Sound Localization in Toddlers with Normal Hearing and with Bilateral Cochlear Implants Revealed Through a Novel "Reaching for Sound" Task.

Abstract

Spatial hearing abilities in children with bilateral cochlear implants (BiCIs) are typically improved when two implants are used compared with a single implant. However, even with BiCIs, spatial hearing is still worse compared to normal-hearing (NH) age-matched children. Here, we focused on children who were younger than three years, hence in their toddler years. Prior research with this age focused on measuring discrimination of sounds from the right versus left. This study measured both discrimination and sound location identification in a nine-alternative forced-choice paradigm using the "reaching for sound" method, whereby children reached for sounding objects as a means of capturing their spatial hearing abilities. Discrimination was measured with sounds randomly presented to the left versus right, and loudspeakers at fixed angles ranging from ±60° to ±15°. On a separate task, sound location identification was measured for locations ranging from ±60° in 15° increments. Thirteen children with BiCIs (27-42 months old) and fifteen age-matched (NH). Discrimination and sound localization were completed for all subjects. For the left-right discrimination task, participants were required to reach a criterion of 4/5 correct trials (80%) at each angular separation prior to beginning the localization task. For sound localization, data was analyzed in two ways. First, percent correct scores were tallied for each participant. Second, for each participant, the root-mean-square-error was calculated to determine the average distance between the response and stimulus, indicative of localization accuracy. All BiCI users were able to discriminate left versus right at angles as small as ±15° when listening with two implants; however, performance was significantly worse when listening with a single implant. All NH toddlers also had >80% correct at ±15°. Sound localization results revealed root-mean-square errors averaging 11.15° in NH toddlers. Children in the BiCI group were generally unable to identify source location on this complex task (average error 37.03°). Although some toddlers with BiCIs are able to localize sound in a manner consistent with NH toddlers, for the majority of toddlers with BiCIs, sound localization abilities are still emerging.