Contribution of monaural and binaural cues to sound localization in listeners with acquired unilateral conductive hearing loss: Improved directional hearing with a bone-conduction device

Department of Biophysics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
Hearing research (Impact Factor: 2.85). 04/2012; 286(1-2):9-18. DOI: 10.1016/j.heares.2012.02.012
Source: PubMed

ABSTRACT Sound localization in the horizontal (azimuth) plane relies mainly on interaural time differences (ITDs) and interaural level differences (ILDs). Both are distorted in listeners with acquired unilateral conductive hearing loss (UCHL), reducing their ability to localize sound. Several studies demonstrated that UCHL listeners had some ability to localize sound in azimuth. To test whether listeners with acquired UCHL use strongly perturbed binaural difference cues, we measured localization while they listened with a sound-attenuating earmuff over their impaired ear. We also tested the potential use of monaural pinna-induced spectral-shape cues for localization in azimuth and elevation, by filling the cavities of the pinna of their better-hearing ear with a mould. These conditions were tested while a bone-conduction device (BCD), fitted to all UCHL listeners in order to provide hearing from the impaired side, was turned off. We varied stimulus presentation levels to investigate whether UCHL listeners were using sound level as an azimuth cue. Furthermore, we examined whether horizontal sound-localization abilities improved when listeners used their BCD. Ten control listeners without hearing loss demonstrated a significant decrease in their localization abilities when they listened with a monaural plug and muff. In 4/13 UCHL listeners we observed good horizontal localization of 65 dB SPL broadband noises with their BCD turned off. Localization was strongly impaired when the impaired ear was covered with the muff. The mould in the good ear of listeners with UCHL deteriorated the localization of broadband sounds presented at 45 dB SPL. This demonstrates that they used pinna cues to localize sounds presented at low levels. Our data demonstrate that UCHL listeners have learned to adapt their localization strategies under a wide variety of hearing conditions and that sound-localization abilities improved with their BCD turned on.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Monaural spectral features are important for human sound-source localization in sagittal planes, including front-back discrimination and elevation perception. These directional features result from the acoustic filtering of incoming sounds by the listener's morphology and are described by listener-specific head-related transfer functions (HRTFs). This article proposes a probabilistic, functional model of sagittal-plane localization that is based on human listeners' HRTFs. The model approximates spectral auditory processing, accounts for acoustic and non-acoustic listener specificity, allows for predictions beyond the median plane, and directly predicts psychoacoustic measures of localization performance. The predictive power of the listener-specific modeling approach was verified under various experimental conditions: The model predicted effects on localization performance of band limitation, spectral warping, non-individualized HRTFs, spectral resolution, spectral ripples, and high-frequency attenuation in speech. The functionalities of vital model components were evaluated and discussed in detail. Positive spectral gradient extraction, sensorimotor mapping, and binaural weighting of monaural spatial information were addressed in particular. Potential applications of the model include predictions of psychophysical effects, for instance, in the context of virtual acoustics or hearing assistive devices.
    The Journal of the Acoustical Society of America 08/2014; 136(2-2):791-802. DOI:10.1121/1.4887447 · 1.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Adults with unilateral hearing loss often demonstrate decreased sound localization ability and report that situations requiring spatial hearing are especially challenging. Few studies have evaluated localization abilities combined with training in this population. The present pilot study examined whether localization of two sound types would improve after training, and explored the relation between localization ability or training benefit and demographic factors. Eleven participants with unilateral severe to profound hearing loss attended five training sessions; localization cues gradually decreased across sessions. Localization ability was assessed pre- and post-training. Assessment stimuli were monosyllabic words and spectral and temporal random spectrogram sounds. Root mean square errors for each participant and stimulus type were used in group and correlation analyses; individual data were examined with ordinary least squares regression. Mean pre-to post-training test results were significantly different for all stimulus types. Among the participants, eight significantly improved following training on at least one localization measure, whereas three did not. Participants with the poorest localization ability improved the most and likewise, those with the best pre-training ability showed the least training benefit. Correlation results suggested that test age, age at onset of severe to profound hearing loss and better ear high frequency audibility may contribute to localization ability. Results support the need for continued investigation of localization training efficacy and consideration of localization training within rehabilitation protocols for individuals with unilateral severe to profound hearing loss. Copyright © 2014 Elsevier B.V. All rights reserved.
    Hearing Research 11/2014; 319. DOI:10.1016/j.heares.2014.11.005 · 2.85 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The precedence effect is a prerequisite for faithful sound localization in a complex auditory environment, and is a physiological phenomenon in which the auditory system selectively suppresses the directional information from echoes. Here we investigated how neurons in the inferior colliculus respond to the paired sounds that produce precedence-effect illusions, and whether their firing behavior can be modulated through inhibition with gamma-aminobutyric acid (GABA). We recorded extracellularly from 36 neurons in rat inferior colliculus under three conditions: no injection, injection with saline, and injection with gamma-aminobutyric acid. The paired sounds that produced precedence effects were two identical 4-ms noise bursts, which were delivered contralaterally or ipsilaterally to the recording site. The normalized neural responses were measured as a function of different inter-stimulus delays and half-maximal interstimulus delays were acquired. Neuronal responses to the lagging sounds were weak when the inter-stimulus delay was short, but increased gradually as the delay was lengthened. Saline injection produced no changes in neural responses, but after local gamma-aminobutyric acid application, responses to the lagging stimulus were suppressed. Application of gamma-aminobutyric acid affected the normalized response to lagging sounds, independently of whether they or the paired sounds were contralateral or ipsilateral to the recording site. These observations suggest that local inhibition by gamma-aminobutyric acid in the rat inferior colliculus shapes the neural responses to lagging sounds, and modulates the precedence effect.
    Neural Regeneration Research 02/2014; 9(4):420-9. DOI:10.4103/1673-5374.128250 · 0.23 Impact Factor