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Brain stem and cortical mechanisms underlying the binaural masking level difference in humans: an auditory steady-state response study.
Ear Hear. 2004 Feb; 25(1):57-67.EH

Abstract

OBJECTIVE

The behavioral binaural masking level difference (BMLD) is believed to reflect brain stem processing. However, this conflicts with transient auditory evoked potential research that indicates the auditory brain stem and middle latency responses do not demonstrate the BMLD. The objective of the present study is to investigate the brain stem and cortical mechanisms underlying the BMLD in humans using the brain stem and cortical auditory steady-state responses (ASSRs).

DESIGN

A 500-Hz pure tone, amplitude-modulated (AM) at 80 Hz and 7 (or 13) Hz, was used to elicit brain stem and cortical ASSRs, respectively. The masker was a 200-Hz-wide noise centered on 500 Hz. Eleven adult subjects with normal hearing were tested. Both ASSR (brain stem and cortical) and behavioral thresholds for diotic AM stimuli (when the signal and noise are in phase binaurally: SoNo) and dichotic AM stimuli (when either the signal or noise is 180 degrees out-of-phase between the two ears: SpiNo, SoNpi) were investigated. ASSR and behavioral BMLDs were obtained by subtracting the threshold for the dichotic stimuli from that for the diotic stimuli, respectively. Effects for modulation rate, signal versus noise phase changes, and behavioral versus ASSR measure on the BMLD were investigated.

RESULTS

Behavioral BMLDs (mean = 8.5 to 10.5 dB) obtained are consistent with results from past research. The ASSR results are similar to the pattern of results previously found for the transient auditory brain stem responses and the N1-P2 cortical auditory evoked potential, in that only the cortical ASSRs (7 or 13 Hz) demonstrate BMLDs (mean = 5.8 dB); the brain stem ASSRs (80 Hz) (mean = 1.5 dB) do not. The ASSR results differ from the previous transient N1-P2 studies, however, in that the cortical ASSRs show a BMLD only when there is a change in the signal interaural phase, but not for changes of noise interaural phase.

CONCLUSIONS

Results suggest that brain processes underlying the BMLD occur either in a different pathway or beyond the brain stem auditory processing underlying the 80-Hz ASSR. Results also suggest that the cortical ASSRs have somewhat different neural sources than the transient N1-P2 responses, and that they may reflect the output of neural populations that previous research has shown to be insensitive to binaural differences in noise.

Authors+Show Affiliations

School of Audiology & Speech Sciences, University of British Columbia, Vancouver, B.C., Canada.No affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

14770018

Citation

Wong, Winnie Y S., and David R. Stapells. "Brain Stem and Cortical Mechanisms Underlying the Binaural Masking Level Difference in Humans: an Auditory Steady-state Response Study." Ear and Hearing, vol. 25, no. 1, 2004, pp. 57-67.
Wong WY, Stapells DR. Brain stem and cortical mechanisms underlying the binaural masking level difference in humans: an auditory steady-state response study. Ear Hear. 2004;25(1):57-67.
Wong, W. Y., & Stapells, D. R. (2004). Brain stem and cortical mechanisms underlying the binaural masking level difference in humans: an auditory steady-state response study. Ear and Hearing, 25(1), 57-67.
Wong WY, Stapells DR. Brain Stem and Cortical Mechanisms Underlying the Binaural Masking Level Difference in Humans: an Auditory Steady-state Response Study. Ear Hear. 2004;25(1):57-67. PubMed PMID: 14770018.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Brain stem and cortical mechanisms underlying the binaural masking level difference in humans: an auditory steady-state response study. AU - Wong,Winnie Y S, AU - Stapells,David R, PY - 2004/2/11/pubmed PY - 2004/6/23/medline PY - 2004/2/11/entrez SP - 57 EP - 67 JF - Ear and hearing JO - Ear Hear VL - 25 IS - 1 N2 - OBJECTIVE: The behavioral binaural masking level difference (BMLD) is believed to reflect brain stem processing. However, this conflicts with transient auditory evoked potential research that indicates the auditory brain stem and middle latency responses do not demonstrate the BMLD. The objective of the present study is to investigate the brain stem and cortical mechanisms underlying the BMLD in humans using the brain stem and cortical auditory steady-state responses (ASSRs). DESIGN: A 500-Hz pure tone, amplitude-modulated (AM) at 80 Hz and 7 (or 13) Hz, was used to elicit brain stem and cortical ASSRs, respectively. The masker was a 200-Hz-wide noise centered on 500 Hz. Eleven adult subjects with normal hearing were tested. Both ASSR (brain stem and cortical) and behavioral thresholds for diotic AM stimuli (when the signal and noise are in phase binaurally: SoNo) and dichotic AM stimuli (when either the signal or noise is 180 degrees out-of-phase between the two ears: SpiNo, SoNpi) were investigated. ASSR and behavioral BMLDs were obtained by subtracting the threshold for the dichotic stimuli from that for the diotic stimuli, respectively. Effects for modulation rate, signal versus noise phase changes, and behavioral versus ASSR measure on the BMLD were investigated. RESULTS: Behavioral BMLDs (mean = 8.5 to 10.5 dB) obtained are consistent with results from past research. The ASSR results are similar to the pattern of results previously found for the transient auditory brain stem responses and the N1-P2 cortical auditory evoked potential, in that only the cortical ASSRs (7 or 13 Hz) demonstrate BMLDs (mean = 5.8 dB); the brain stem ASSRs (80 Hz) (mean = 1.5 dB) do not. The ASSR results differ from the previous transient N1-P2 studies, however, in that the cortical ASSRs show a BMLD only when there is a change in the signal interaural phase, but not for changes of noise interaural phase. CONCLUSIONS: Results suggest that brain processes underlying the BMLD occur either in a different pathway or beyond the brain stem auditory processing underlying the 80-Hz ASSR. Results also suggest that the cortical ASSRs have somewhat different neural sources than the transient N1-P2 responses, and that they may reflect the output of neural populations that previous research has shown to be insensitive to binaural differences in noise. SN - 0196-0202 UR - https://www.unboundmedicine.com/medline/citation/14770018/Brain_stem_and_cortical_mechanisms_underlying_the_binaural_masking_level_difference_in_humans:_an_auditory_steady_state_response_study_ L2 - https://doi.org/10.1097/01.AUD.0000111257.11898.64 DB - PRIME DP - Unbound Medicine ER -