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Directional dependence of interaural envelope delays
1Department of Neuroscience, University of Florida, Gainesville 32610.
The Journal of the Acoustical Society of America
|May 1, 1990
Summary
This study measured interaural envelope delays in humans using a novel method to estimate ear canal transfer functions. Results show these delays increase with sound source angle, potentially aiding sound localization.
Area of Science:
- Auditory Neuroscience
- Acoustics
- Human Perception
Background:
- Sound localization relies on binaural cues, including interaural time differences (ITDs) and interaural level differences (ILDs).
- Interaural envelope delays (IEDs) offer another potential cue, particularly at higher frequencies where ITDs become ambiguous.
- Understanding IEDs requires accurate measurement of sound arriving at each ear, considering the head and outer ear's influence.
Purpose of the Study:
- To measure interaural envelope delays (IEDs) in human subjects across various sound source locations.
- To develop and validate a method for estimating the complex directional transfer function (CDTF) of the external ear, independent of microphone placement.
- To investigate the relationship between IEDs and sound source position to understand their role in auditory localization.
Main Methods:
- Six human subjects participated in the study.
- A movable sound source emitted signals bandpassed between 3 and 16 kHz.
- Complex directional transfer functions (CDTFs) were estimated for both ears. Interaural envelope delays were computed by convolving CDTFs with critical-band filters, computing envelopes, and cross-correlating them.
Main Results:
- Interaural envelope delays (IEDs) and interaural group delays varied with critical-band center frequency and sound source elevation.
- A first-order approximation showed IEDs increased monotonically with the angle of incidence relative to the median plane.
- These findings align with predictions for microphones on a rigid sphere, suggesting a consistent physical basis for IEDs.
Conclusions:
- The developed method accurately estimates ear canal transfer functions, enabling precise IED measurements.
- Measured interaural envelope delays exhibit a predictable relationship with sound source location.
- Interaural envelope delays likely contribute significantly to the human ability to localize sounds, especially at higher frequencies.