title: Time-Varying Distortions of Binaural Information by Bilateral Hearing Aids: Effects of Nonlinear Frequency Compression.
abstract: In patients with bilateral hearing loss, the use of two hearing aids (HAs) offers the potential to restore the benefits of binaural hearing, including sound source localization and segregation. However, existing evidence suggests that bilateral HA users' access to binaural information, namely interaural time and level differences (ITDs and ILDs), can be compromised by device processing. Our objective was to characterize the nature and magnitude of binaural distortions caused by modern digital behind-the-ear HAs using a variety of stimuli and HA program settings. Of particular interest was a common frequency-lowering algorithm known as nonlinear frequency compression, which has not previously been assessed for its effects on binaural information. A binaural beamforming algorithm was also assessed. Wide dynamic range compression was enabled in all programs. HAs were placed on a binaural manikin, and stimuli were presented from an arc of loudspeakers inside an anechoic chamber. Stimuli were broadband noise bursts, 10-Hz sinusoidally amplitude-modulated noise bursts, or consonant-vowel-consonant speech tokens. Binaural information was analyzed in terms of ITDs, ILDs, and interaural coherence, both for whole stimuli and in a time-varying sense (i.e., within a running temporal window) across four different frequency bands (1, 2, 4, and 6 kHz). Key findings were: (a) Nonlinear frequency compression caused distortions of high-frequency envelope ITDs and significantly reduced interaural coherence. (b) For modulated stimuli, all programs caused time-varying distortion of ILDs. (c) HAs altered the relationship between ITDs and ILDs, introducing large ITD-ILD conflicts in some cases. Potential perceptual consequences of measured distortions are discussed.
authors.affiliation: Department of Physiology & Biophysics, University of Colorado School of Medicine, Aurora, CO, USA Andrew.D.Brown@ucdenver.edu.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Brown
authors.affiliation: Department of Otorhinolaryngology-Head and Neck Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Francisco A
authors.initials: FA
authors.lastname: Rodriguez
authors.affiliation: Department of Otolaryngology, Hearing and Balance Center, University of Colorado School of Medicine, Aurora, CO, USA.
authors.forename: Cory D F
authors.initials: CD
authors.lastname: Portnuff
authors.affiliation: Department of Hearing & Speech Sciences, University of Maryland, College Park, MD, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Goupell
authors.affiliation: Department of Physiology & Biophysics, University of Colorado School of Medicine, Aurora, CO, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Tollin
mesh_terms: D000161:Acoustic Stimulation; D003054:Cochlear Implants; D006310:Hearing Aids; D006801:Humans; D009622:Noise; D013017:Sound Localization
keywords: binaural hearing; frequency lowering; hearing aids; sound localization