title: Horizontal sound localization in cochlear implant users with a contralateral hearing aid.
abstract: Interaural differences in sound arrival time (ITD) and in level (ILD) enable us to localize sounds in the horizontal plane, and can support source segregation and speech understanding in noisy environments. It is uncertain whether these cues are also available to hearing-impaired listeners who are bimodally fitted, i.e. with a cochlear implant (CI) and a contralateral hearing aid (HA). Here, we assessed sound localization behavior of fourteen bimodal listeners, all using the same Phonak HA and an Advanced Bionics CI processor, matched with respect to loudness growth. We aimed to determine the availability and contribution of binaural (ILDs, temporal fine structure and envelope ITDs) and monaural (loudness, spectral) cues to horizontal sound localization in bimodal listeners, by systematically varying the frequency band, level and envelope of the stimuli. The sound bandwidth had a strong effect on the localization bias of bimodal listeners, although localization performance was typically poor for all conditions. Responses could be systematically changed by adjusting the frequency range of the stimulus, or by simply switching the HA and CI on and off. Localization responses were largely biased to one side, typically the CI side for broadband and high-pass filtered sounds, and occasionally to the HA side for low-pass filtered sounds. HA-aided thresholds better than 45 dB HL in the frequency range of the stimulus appeared to be a prerequisite, but not a guarantee, for the ability to indicate sound source direction. We argue that bimodal sound localization is likely based on ILD cues, even at frequencies below 1500 Hz for which the natural ILDs are small. These cues are typically perturbed in bimodal listeners, leading to a biased localization percept of sounds. The high accuracy of some listeners could result from a combination of sufficient spectral overlap and loudness balance in bimodal hearing.
authors.affiliation: Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, P.O. Box 9101, 6500 GL, Nijmegen, The Netherlands.
authors.forename: Lidwien C E
authors.initials: LCE
authors.lastname: Veugen
authors.affiliation: Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, P.O. Box 9101, 6500 GL, Nijmegen, The Netherlands.
authors.forename: Maartje M E
authors.initials: MME
authors.lastname: Hendrikse
authors.affiliation: Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, P.O. Box 9101, 6500 GL, Nijmegen, The Netherlands; Department of Otorhinolaryngology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, The Netherlands.
authors.forename: Marc M
authors.initials: MM
authors.lastname: van Wanrooij
authors.affiliation: Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, P.O. Box 9101, 6500 GL, Nijmegen, The Netherlands; Department of Otorhinolaryngology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, The Netherlands.
authors.forename: Martijn J H
authors.initials: MJH
authors.lastname: Agterberg
authors.affiliation: Advanced Bionics European Research Centre (AB ERC), Hannover, Germany.
authors.forename: Josef
authors.initials: J
authors.lastname: Chalupper
authors.affiliation: Department of Otorhinolaryngology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, The Netherlands.
authors.forename: Lucas H M
authors.initials: LHM
authors.lastname: Mens
authors.affiliation: Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, P.O. Box 9101, 6500 GL, Nijmegen, The Netherlands; Department of Otorhinolaryngology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, The Netherlands.
authors.forename: Ad F M
authors.initials: AFM
authors.lastname: Snik
authors.affiliation: Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, P.O. Box 9101, 6500 GL, Nijmegen, The Netherlands. Electronic address: J.vanOpstal@donders.ru.nl.
authors.forename: A
authors.initials: A
authors.lastname: John van Opstal
mesh_terms: D000161:Acoustic Stimulation; D000368:Aged; D000369:Aged, 80 and over; D001307:Auditory Perception; D002138:Calibration; D019929:Cochlear Implantation; D003054:Cochlear Implants; D003463:Cues; D003638:Deafness / Q000628:therapy*; D005260:Female; D006309:Hearing; D006320:Hearing Tests; D006801:Humans; D008297:Male; D008875:Middle Aged; D013016:Sound; D013017:Sound Localization; D013067:Speech Perception
keywords: Bimodal stimulation; Binaural cues; Cochlear implants; Directional hearing; Sound localization