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.

Sensitivity to binaural cues was studied in 11 bilateral cochlear implant users, all of whom received both of their cochlear implants as adults, but who varied in the age at onset of deafness, from pre-lingual to childhood-onset to adult-onset. Sensitivity to interaural timing difference ͑ITD͒ and interaural level difference ͑ILD͒ cues was measured at basal, middle, and apical pitch-matched places of stimulation along the cochlear arrays, using a stimulation rate of 100 Hz. Results show that there is a trend for people whose onset of deafness occurred during adult life or late childhood to retain at least some sensitivity to ITDs, whereas people with onset of deafness earlier in life were insensitive to ITDs. In contrast, ILD cue sensitivity was present in all subjects. There were no effects of place of stimulation on binaural sensitivity, suggesting that there is no indication of a dependence of ITD sensitivity on apical vs basal electrode location.

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.