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Auditory Brainstem Models: Adapting Cochlear Nuclei Improve Spatial Encoding by the Medial Superior Olive in
Andrew Brughera1,2, Jason Mikiel-Hunter3, Mathias Dietz4
1Department of Linguistics, and the Australian Hearing Hub, Macquarie University, Macquarie Park, New South Wales, Australia. andrew.brughera@mq.edu.au.
Summary
The brain emphasizes early sounds for sound localization, especially during rising sound energy. Computational models show this auditory processing is frequency-dependent and crucial for understanding speech in noisy environments.
Area of Science:
- Auditory Neuroscience
- Computational Auditory Neuroscience
- Acoustics
Background:
- Listeners localize sound sources based on early-arriving direct sound, despite later reflections.
- The auditory pathway, including the medial superior olive (MSO), encodes interaural-time-difference (ITD) for spatial hearing.
- Perceptual weighting of ITD is stronger for rising sound energy, particularly at 600 Hz compared to 200 Hz.
Purpose of the Study:
- To computationally investigate how neural adaptation and binaural coincidence detection in the MSO emphasize ITDs in early-arriving sounds.
- To explore the frequency-dependent weighting of ITDs during rising sound energy.
- To link these auditory processing mechanisms to unambiguous sound source lateralization in reverberant conditions.
Main Methods:
- Developed computational models of spherical bushy cells (SBCs) and MSO neurons.
- Incorporated neural adaptation and binaural coincidence detection mechanisms.
- Simulated auditory processing at different frequencies (200 Hz and 600 Hz) and sound energy profiles (rising vs. peak).
Main Results:
- Model MSO neurons reproduced the emphasis on rising sound energy for ITD encoding, with adaptation playing a key role.
- A hemispheric population model showed stronger weighting of ITDs during rising sound energy at 600 Hz than at 200 Hz.
- The model linked enhanced spatial information processing during rising sound energy to accurate speech source lateralization in reverberation.
Conclusions:
- Neural adaptation prior to binaural encoding, combined with MSO neuron properties, effectively emphasizes ITDs in early-arriving sound.
- The frequency-dependent weighting of ITDs during rising sound energy is computationally supported.
- This mechanism contributes to robust sound source localization and speech intelligibility in complex acoustic environments.
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