Localization of Low- and High-Frequency Sounds in Cochlear Implant Recipients Using a Contralateral Hearing Aid

Background and ObjectivesThe ability to localize sounds is partly recovered in patients using a cochlear implant (CI) in one ear and a hearing aid (HA) on the contralateral side. Binaural processing seems effective at least to some extent, despite the difference between electric and acoustic stimulation in each ear. To obtain further insights into the mechanisms of binaural hearing in these listeners, localization of low- and high-frequency sounds was tested.Study DesignThe study used a within-subject design, where participants were tasked with localizing sound sources in the horizontal plane. The experiment was conducted in an anechoic chamber, where an array of seven loudspeakers was mounted along the 24 azimuthal angle span from -90 degrees to +90 degrees. Stimuli were applied with different frequencies: broadband noise and high- and low-frequency noise.SubjectsTen CI recipients participated in the study. All had an asymmetric hearing loss with a CI in the poorer ear and an HA on the contralateral side.Main Outcome MeasuresAccuracy of sound localization in terms of angular error and percentage of correct localization scores.ResultsThe median angular error was 40 degrees in bimodal conditions for both broadband noise and high-frequency noise stimuli. The angular error increased to 47 degrees for low-frequency noise stimuli. In the unilaterally aided condition with an HA, only a median angular error of 78 degrees was observed.ConclusionsIrrespective of the frequency composition of the stimuli, this group of bimodal listeners showed some ability to localize sounds. Angular errors were larger than those reported in the literature for bilateral CI users or single-sided deaf listeners with a CI. In the unilateral listening condition with HA, only localization of sounds was not possible for most subjects.