Age-Related Changes in Processing Simultaneous Amplitude Modulated Sounds Assessed Using Envelope Following Responses
- 414 Downloads
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 (sAM1FL) while the second varied in sound level (sAM2VL) and carrier frequency. EFR amplitudes to sAM1FL in the young decreased with signal-to-noise ratio (SNR), and this reduction was more pronounced when the sAM2VL carrier frequency was spectrally separated from sAM1FL. 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 sAM1FL 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.
Keywordscolliculus ASSR auditory nerve FFR EFR cochlear neuropathy synaptopathy
This study was supported by a grant from the National Institutes of Health (NIDCD R01DC011580) to ELB.
Compliance with ethical standards
Conflict of Interest
The authors declare that they have no competing interests.
- Bregman AS (1990) Auditory scene analysis: the perceptual organization of sound. MIT Press, Cambridge, MAGoogle Scholar
- Dolphin WF (1995) The envelope following response to multiple tone pair stimuli. In: 16th International-Evoked-Audiometry-Study-Group Meeting. Lyon, France, pp 1–14Google Scholar
- Greenwood DD (1990) A cochlear frequency-position function for several species--29 years later. J Acoust Soc Am 87(6):2592–2605Google Scholar
- Kiren T, Aoyagi M, Furuse H, Koike Y (1994) An experimental-study on the generator of amplitude-modulation following response. Acta Oto-Laryngologica 28–33Google Scholar
- Kujawa SG, Liberman MC (2015) Synaptopathy in the noise-exposed and aging cochlea: primary neural degeneration in acquired sensorineural hearing loss. Hear Res 330:191–199. doi: 10.1016/j.heares.2015.02.009
- Schmiedt RA, Mills JH, Boettcher FA (1996) Age-related loss of activity of auditory-nerve fibers. J Neurophys 76:2799–2803Google Scholar