title: Sound localization under perturbed binaural hearing.
abstract: This paper reports on the acute effects of a monaural plug on directional hearing in the horizontal (azimuth) and vertical (elevation) planes of human listeners. Sound localization behavior was tested with rapid head-orienting responses toward brief high-pass filtered (>3 kHz; HP) and broadband (0.5-20 kHz; BB) noises, with sound levels between 30 and 60 dB, A-weighted (dBA). To deny listeners any consistent azimuth-related head-shadow cues, stimuli were randomly interleaved. A plug immediately degraded azimuth performance, as evidenced by a sound level-dependent shift ("bias") of responses contralateral to the plug, and a level-dependent change in the slope of the stimulus-response relation ("gain"). Although the azimuth bias and gain were highly correlated, they could not be predicted from the plug's acoustic attenuation. Interestingly, listeners performed best for low-intensity stimuli at their normal-hearing side. These data demonstrate that listeners rely on monaural spectral cues for sound-source azimuth localization as soon as the binaural difference cues break down. Also the elevation response components were affected by the plug: elevation gain depended on both stimulus azimuth and on sound level and, as for azimuth, localization was best for low-intensity stimuli at the hearing side. Our results show that the neural computation of elevation incorporates a binaural weighting process that relies on the perceived, rather than the actual, sound-source azimuth. It is our conjecture that sound localization ensues from a weighting of all acoustic cues for both azimuth and elevation, in which the weights may be partially determined, and rapidly updated, by the reliability of the particular cue.
authors.affiliation: Department of Biophysics, Radboud University Nijmegen, Geert Grooteplein 21, 6525 EZ Nijmegen, The Netherlands.
authors.forename: Marc M
authors.initials: MM
authors.lastname: Van Wanrooij
authors.forename: A John
authors.initials: AJ
authors.lastname: Van Opstal
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D001306:Auditory Pathways / Q000033:anatomy & histology / Q000502:physiology*; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology*; D003463:Cues; D003638:Deafness / Q000503:physiopathology; D007839:Functional Laterality / Q000502:physiology; D006309:Hearing / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D009415:Nerve Net / Q000033:anatomy & histology / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology; D012683:Sensory Deprivation / Q000502:physiology; D013017:Sound Localization / Q000502:physiology*; D013028:Space Perception / Q000502:physiology