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      Age-Related Changes in Processing Simultaneous Amplitude Modulated Sounds Assessed Using Envelope Following Responses

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          Abstract

          Listening conditions in the real world involve segregating the stimuli of interest from competing auditory stimuli that differ in their sound level and spectral content. It is in these conditions of complex spectro-temporal processing that listeners with age-related hearing loss experience the most difficulties. Envelope following responses (EFRs) provide objective neurophysiological measures of auditory processing. EFRs were obtained to two simultaneous sinusoidally amplitude modulated (sAM) tones from young and aged Fischer-344 rats. One was held at a fixed suprathreshold sound level (sAM1 FL) while the second varied in sound level (sAM2 VL) and carrier frequency. EFR amplitudes to sAM1 FL in the young decreased with signal-to-noise ratio (SNR), and this reduction was more pronounced when the sAM2 VL carrier frequency was spectrally separated from sAM1 FL. Aged animals showed similar trends, while having decreased overall response amplitudes compared to the young. These results were replicated using an established computational model of the auditory nerve. The trends observed in the EFRs were shown to be due to the contributions of the low-frequency tails of high-frequency neurons, rather than neurons tuned to the sAM1 FL carrier frequency. Modeling changes in threshold and neural loss reproduced some of the changes seen with age, but accuracy improved when combined with an additional decrease representing synaptic loss of auditory nerve neurons. Sound segregation in this case derives primarily from peripheral processing, regardless of age. Contributions by more central neural mechanisms are likely to occur only at low SNRs.

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          Author and article information

          Contributors
          ebartle@purdue.edu
          Journal
          J Assoc Res Otolaryngol
          J. Assoc. Res. Otolaryngol
          JARO: Journal of the Association for Research in Otolaryngology
          Springer US (New York )
          1525-3961
          1438-7573
          23 February 2016
          April 2016
          : 17
          : 2
          : 119-132
          Affiliations
          [ ]Department of Biological Sciences, Purdue University Interdisciplinary Life Sciences Program, and the Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN USA
          [ ]Eaton-Peabody Labs, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, MA USA
          Article
          PMC4791415 PMC4791415 4791415 554
          10.1007/s10162-016-0554-z
          4791415
          26905273
          cf1ac78c-23f5-4d03-99d2-6a72ee7dc67c
          © Association for Research in Otolaryngology 2016
          History
          : 10 June 2015
          : 27 January 2016
          Funding
          Funded by: FundRef http://dx.doi.org/10.13039/100000055, National Institute on Deafness and Other Communication Disorders;
          Award ID: R01DC011580
          Award Recipient :
          Categories
          Research Article
          Custom metadata
          © Association for Research in Otolaryngology 2016

          colliculus,cochlear neuropathy,EFR,FFR,auditory nerve,ASSR,synaptopathy

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