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A Method to Study Adaptation to Left-Right Reversed Audition
Published on: October 29, 2018
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Neural coding of sound envelope in reverberant environments
Michaël C C Slama1, Bertrand Delgutte2
1Eaton-Peabody Laboratories, Massachusetts Eye & Ear Infirmary, Boston, Massachusetts 02114, Speech and Hearing Bioscience and Technology Program, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
Summary
Reverberation degrades speech amplitude envelope coding in the auditory system. However, the brain compensates for this, showing robust neural coding of speech signals even in noisy environments.
Area of Science:
- Neuroscience
- Auditory Neuroscience
- Signal Processing
Background:
- Speech comprehension relies on temporal modulations in the speech signal's amplitude envelope.
- Environmental reverberation significantly weakens these crucial modulations.
- Understanding how the auditory system processes amplitude envelope under reverberation is vital for speech perception research.
Purpose of the Study:
- To investigate the impact of reverberation on the neural coding of the speech amplitude envelope.
- To identify mechanisms underlying the auditory system's robustness to reverberation.
- To compare neural responses to amplitude modulation (AM) in anechoic versus reverberant conditions.
Main Methods:
- Single-unit recordings were conducted in the inferior colliculus (IC) of unanesthetized rabbits.
- Sinusoidally amplitude-modulated (AM) broadband noise stimuli were used.
- Stimuli were presented in both simulated anechoic and reverberant environments.
Main Results:
- Reverberation impaired both rate and temporal coding of AM in IC neurons.
- Temporal coding degradation was less severe than stimulus modulation attenuation, suggesting neural compensation.
- A compressive modulation input-output function (MIOF) partly explained this compensation.
- Some neurons exhibited enhanced temporal coding for reverberant stimuli, independent of envelope distortion or static decorrelation.
Conclusions:
- The auditory system employs dual mechanisms for robust amplitude envelope coding in reverberation.
- A general mechanism benefits all stimuli with low modulation depths.
- A specialized mechanism, possibly linked to interaural correlation fluctuations, enhances coding for reverberant sounds.
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