I..M Dushyanthi Karunathilake1, Jason L. Dunlap2, Janani Perera2, Alessandro Presacco3, Lien Decruy4, Samira Anderson2, Stefanie E. Kuchinsky5, Jonathan Z. Simon1,4,6
Department of Electrical and Computer Engineering, University of Maryland, College Park, USA
2Department of Hearing and Speech Sciences, University of Maryland, College Park, USA
3Department of Electrical Engineering, Universidad Nacional Autonóma de México, Mexico City, Mexico
4Institute for systems Research, University of Maryland, College Park, USA,
5Audiology and Speech Pathology Center, Walter Reed National Military Medical Center, Bethesda, USA
6Department of Biology, University of Maryland, College Park, USA 

The ability to selectively attend to speech in a noisy environment is crucial for everyday interactions, but this skill becomes more challenging with aging. Yet, the effects of aging on the neural mechanisms underlying selective attention and speech-in-noise perception are not well understood. In this magnetoencephalography (MEG) study, we investigate how continuous speech is represented in the cortex, in 18 younger and 17 older adults, while attending to one speaker and ignoring the other, at different signal-to-noise ratios. The low frequency (1-10 Hz) neural responses that track the low frequency speech stimulus envelope, both attended and unattended, were investigated using temporal response function (TRF) and envelope reconstruction. The TRFs showed three prominent peaks (M50TRF, M100TRF and M200TRF), representing distinct auditory processing stages. Compared to younger adults, older adults exhibited enhanced speech envelope tracking and TRF peak amplitudes, possibly due to several mechanisms. Envelope tracking decreased with the task difficulty and aging further affected this reduction. Integration window analysis revealed that the overrepresentation starts as early as ~50-100 ms and longer integration time windows were needed for older adults to achieve maximal reconstruction accuracy. With regard to the TRFs, M50TRF was relatively early and M200TRF was delayed in older adults, suggesting speech perception is altered from the early processing stages. Further, only in older adults, increasing task difficulty enlarged and reduced the peak amplitude of M100TRF and M200TRF respectively, but latencies were delayed for both groups. This later effect was even larger with aging, suggesting additional cortical processing is engaged in difficult listening situations. Interestingly, M200TRF amplitudes negatively correlated to the latencies in older adults, suggesting that there are other neural mechanisms contributing to M200TRF modulation. In sum, these results reveal age-related temporal processing deficits and late cortical processing (200 ms) that potentially compensate for age-related impairments in speech perception.

Acknowledgements: This work was supported by the National Institutes of Health grants P01-AG055365 and R01-DC014085. The views expressed in this abstract are those of the author and do not reflect the official policy of the Department of Army/ Navy/ Air Force, Department of Defense, or U.S. Government.