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A Method for Tracking the Time Evolution of Steady-State Evoked Potentials
Published on: May 25, 2019
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Wave interference at the contralateral ear helps explain non-monotonic envelope interaural time differences as a
Paul G Mayo1, Andrew D Brown2, Matthew J Goupell1
1Department of Hearing and Speech Sciences, University of Maryland, College Park, Maryland 20742, USA.
JASA Express Letters
|April 1, 2023
Summary
Interaural time differences (ITDs) for high-frequency sounds can be non-monotonic with azimuth. A geometric head model explains this by including the sound path around the head, impacting spatial hearing models.
Area of Science:
- Acoustics and psychoacoustics
- Auditory perception
- Bioacoustics
Background:
- Interaural time differences (ITDs) are crucial for sound localization.
- Conventional models treat ITDs as monotonic functions of sound source azimuth.
- Recent data show non-monotonic envelope ITDs (ENV-ITDs) for high-frequency sounds (≥2 kHz).
Purpose of the Study:
- To explain the mechanism behind non-monotonic ENV-ITDs.
- To investigate the role of sound path around the head in ITD perception.
- To refine spatial hearing models for acoustic and electric hearing.
Main Methods:
- Development of a simple, time-dependent geometric model of an elliptic head.
- Analysis of sound paths (front-traveling and back-traveling) around the modeled head.
- Mathematical modeling to predict ENV-ITDs based on head geometry and sound path interactions.
Main Results:
- The model successfully demonstrates how the delayed, back-traveling sound path contributes to non-monotonic ENV-ITDs.
- Non-monotonicity arises from the constructive and destructive interference of sound waves arriving via different paths.
- The findings align with empirical observations from binaural manikin studies.
Conclusions:
- The back-traveling sound path is a significant factor in high-frequency ENV-ITDs.
- This geometric model provides a mechanistic explanation for non-monotonic spatial cues.
- Implications for understanding and improving spatial hearing in both natural and impaired hearing systems.
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