title: Neural Correlates of the Binaural Masking Level Difference in Human Frequency-Following Responses.
abstract: The binaural masking level difference (BMLD) is an auditory phenomenon where binaural tone-in-noise detection is improved when the phase of either signal or noise is inverted in one of the ears (SπNoor SoNπ, respectively), relative to detection when signal and noise are in identical phase at each ear (SoNo). Processing related to BMLDs and interaural time differences has been confirmed in the auditory brainstem of non-human mammals; in the human auditory brainstem, phase-locked neural responses elicited by BMLD stimuli have not been systematically examined across signal-to-noise ratio. Behavioral and physiological testing was performed in three binaural stimulus conditions: SoNo, SπNo, and SoNπ. BMLDs at 500 Hz were obtained from 14 young, normal-hearing adults (ages 21-26). Physiological BMLDs used the frequency-following response (FFR), a scalp-recorded auditory evoked potential dependent on sustained phase-locked neural activity; FFR tone-in-noise detection thresholds were used to calculate physiological BMLDs. FFR BMLDs were significantly smaller (poorer) than behavioral BMLDs, and FFR BMLDs did not reflect a physiological release from masking, on average. Raw FFR amplitude showed substantial reductions in the SπNocondition relative to SoNoand SoNπconditions, consistent with negative effects of phase summation from left and right ear FFRs. FFR amplitude differences between stimulus conditions (e.g., SoNoamplitude-SπNoamplitude) were significantly predictive of behavioral SπNoBMLDs; individuals with larger amplitude differences had larger (better) behavioral B MLDs and individuals with smaller amplitude differences had smaller (poorer) behavioral B MLDs. These data indicate a role for sustained phase-locked neural activity in BMLDs of humans and are the first to show predictive relationships between behavioral BMLDs and human brainstem responses.
authors.affiliation: Department of Communication Sciences and Disorders, James Madison University, 235 Martin Luther King Jr. Way, MSC 4304, Harrisonburg, VA, 22807, USA. clinarcg@jmu.edu.
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Clinard
authors.affiliation: Department of Communication Sciences and Disorders, James Madison University, 235 Martin Luther King Jr. Way, MSC 4304, Harrisonburg, VA, 22807, USA.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Hodgson
authors.affiliation: Department of Communication Sciences and Disorders, James Madison University, 235 Martin Luther King Jr. Way, MSC 4304, Harrisonburg, VA, 22807, USA.
authors.forename: Mary Ellen
authors.initials: ME
authors.lastname: Scherer
mesh_terms: D000328:Adult; D001307:Auditory Perception / Q000502:physiology*; D005260:Female; D006309:Hearing / Q000502:physiology*; D006801:Humans; D008297:Male; D009622:Noise; D011571:Psychoacoustics; D013069:Speech Reception Threshold Test; D055815:Young Adult
keywords: auditory; binaural; binaural masking level difference; frequency-following response; neurophonic; phase locking