Björn Herrmann1,2, Vanessa C. Irsik3, Ingrid S. Johnsrude3,4
1Rotman Research Institute, Baycrest, Toronto, Canada
2Department of Psychology, University of Toronto, Toronto, Canada
3Department of Psychology, University of Western Ontario, London, Canada
4School of Communication Sciences & Disorders, University of Western Ontario, London, Canada
It is increasingly clear that age-related hearing impairment is a dysfunction of the entire auditory system, from periphery to cortex. Poorer auditory peripheral function is associated with a loss of neural inhibition along the auditory pathway, including auditory cortex, that renders neurons hyperactive and hyperresponsive to sounds. This auditory-system hyperactivity may impair speech intelligibility when background sound is present. Neural hyperactivity has been extensively studied using electrophysiological recordings in non-human mammals but is less explored in humans. In this presentation, we will describe work on hyperactivity associated with aging and hearing loss in humans. Specifically, we will describe how neural synchronization to low-frequency amplitude modulations in sounds differs between younger and older adults, likely as a result of hyperexcitability, and provide behavioral data that test predictions for speech-in-noise intelligibility derived from this electrophysiological work. Neural synchronization in auditory cortex is enhanced in older compared to younger adults. Further, the propensity of neural activity to synchronize with different amplitude-modulation shapes in sounds changes with age: auditory cortex of older adults is more sensitive to damped (sharp attack) compared to ramped (gradual attack) envelope shapes, whereas younger adults show the opposite pattern. Our behavioral data, in contrast, reveal better speech intelligibility when background noise is modulated with damped compared to ramped envelope shapes in both age groups. We also present recent work demonstrating that the way amplitude-modulated background maskers affect speech intelligibility in older compared to younger adults critically depends on the naturalness of speech (disconnected sentences vs. engaging stories). We will wrap up this presentation by briefly talking about open questions and challenges related to the study of auditory-system hyperactivity in humans.
Acknowledgements: This research was supported by the Canadian Institutes of Health Research (MOP133450 to I.S. Johnsrude). BH was supported by a BrainsCAN Tier I postdoctoral fellowship (Canada First Research Excellence Fund; CFREF) and the Canada Research Chair program.