Ruth Litovsky, Ph.D.
Director, Binaural Hearing and Speech Lab, Waisman Center
Professor, Oros Family Chair
Department of Communication Sciences & Disorders
Successful Pathways to Outcomes in Bilateral Cochlear Implantation
Binaural hearing is a critically important auditory process which enhances our ability to navigate in noisy, complex listening environments. Bilateral cochlear implants are provided to a growing number of children, and adults, depending on the standard of care and insurance coverage. Bilateral hearing typically improves localization of sounds and segregation of speech from background noise compared with unilateral hearing. However, patients typically perform worse than normal hearing listeners. We use several approaches to understand factors that contribute to reduced performance in individuals with BiCIs. One factor is the asymmetry in hearing across the ears, which reduces how well information across the two ears is integrated, fused, and leads to good spatial hearing. A second factor is difference across the ears in neural health; poor neural health can include many aspects of reduced ability of the neural element to encode and transmit information with fidelity. In the binaural system, poor neural health in one of the two ears can promote a ‘bottleneck’ for information processing, meaning that even if one ear transmits good information, lack of fidelity in the other ear promotes poor binaural hearing. Because CI processors do not preserve binaural cues with fidelity, we use research processors to generate multi-channel binaural stimulation strategies that introduce different rates of stimulation across the electrode arrays, thereby preserving rates that are important for both binaural sensitivity and speech understanding. In addition, eye gaze studies reveal developmental factors that in decision-making that are not observed with measures of threshold. Finally, pupillometry studies provide insight into the impact of integrating inputs from two ears, whereby in some instances improved performance with two ears can be “costly” in the listening effort domain.