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Age-Related Changes in Processing Simultaneous Amplitude Modulated Sounds Assessed Using Envelope Following Responses
Aravindakshan Parthasarathy1,2, Jesyin Lai1, Edward L Bartlett3
1Department of Biological Sciences, Purdue University Interdisciplinary Life Sciences Program, and the Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, USA.
Journal of the Association for Research in Otolaryngology : JARO
|February 25, 2016
Summary
Age-related hearing loss impacts sound segregation, with peripheral auditory nerve processing playing a key role. Even with age, the auditory system can separate sounds, but central mechanisms are needed at lower signal-to-noise ratios.
Area of Science:
- Neuroscience
- Auditory Neuroscience
- Gerontology
Background:
- Real-world listening requires separating target sounds from background noise.
- Age-related hearing loss significantly impairs sound segregation, especially in complex auditory environments.
- Envelope following responses (EFRs) offer objective neurophysiological measures of auditory processing.
Purpose of the Study:
- To investigate age-related changes in auditory processing and sound segregation.
- To examine the neural mechanisms underlying sound segregation in young and aged rats.
- To compare EFRs in response to simultaneous amplitude-modulated tones under varying signal-to-noise ratios.
Main Methods:
- Obtained EFRs from young and aged Fischer-344 rats exposed to two simultaneous sinusoidally amplitude-modulated (sAM) tones.
- Varied the sound level and carrier frequency of one sAM tone while keeping the other fixed.
- Utilized a computational model of the auditory nerve to replicate and interpret EFR findings.
Main Results:
- EFR amplitudes decreased with decreasing signal-to-noise ratio (SNR) in young rats, more so with spectral separation.
- Aged rats showed similar trends but with overall lower EFR amplitudes.
- Computational modeling indicated that peripheral processing, specifically low-frequency neuron tails, underlies sound segregation, not neurons tuned to the target frequency.
Conclusions:
- Sound segregation in these conditions relies primarily on peripheral auditory processing, irrespective of age.
- Age-related changes in EFRs can be partly explained by neural threshold changes and neural loss, with synaptic loss being a significant factor.
- Central neural contributions to sound segregation appear limited to very low SNRs.
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