Binaural Sensitivity in Children with Normal Hearing and Children with Bilateral Cochlear Implants

Binaural hearing provides a listener with access to interaural time and interaural level differences (ITDs and ILDs). Binaural hearing aids in spatial hearing skills, such as sound localization or the ability to segregate speech in noisy environments. These spatial hearing abilities are vital for young children, as they spend a remarkable amount of time in noisy environments, such as a classrooms or playgrounds. Children with normal hearing (NH) perform well on spatial hearing tasks by the age of 4-5. Although children with bilateral cochlear implants (BiCIs) perform better than children with unilateral implants, they still perform worse than their NH peers when tested on the same tasks. Some factors that may be responsible for this gap in performance include (1) the lack of temporal fine structure present in current clinical processing, (2) neural degradation due to lack of early acoustic hearing, (3) surgical issues leading to differing depths of electrode array insertion between the two ears, and (4) the lack of temporal synchronization between the two implants.;The specific aims of this dissertation are to (1) investigate the extent to which the high-rate amplitude modulated stimuli are the limiting factor in performance by studying the ability of NH children to utilize envelope ITDs as transmitted by stimuli that renders fine structure information for ITDs imperceptible, (2) examine binaural sensitivity to binaural cues in children with BiCIs using low-rate pulsatile stimuli on pitch matched pairs to understand whether children with BiCIs have the ability to utilize these cues, (3) examine the effects of perceived interaural pitch mismatch on a pitch comparison task and a task measuring ITD sensitivity to evaluate the efficacy of pitch matching in children, (4) examine the effects of stimulus rate on ITD sensitivity in order to determine if high-rate amplitude modulated stimuli can elicit ITD sensitivity, and (5) investigate cognitive factors that may predict performance on tasks of binaural sensitivity, to better understand if specific cognitive factors may be predictors of binaural performance. Together, the five aims of this dissertation are designed to provide a better insight into why children with BiCIs demonstrate poor spatial hearing abilities.