Effects of aging on cortical representations of continuous speech

Abstract

Understanding speech in a noisy environment is crucial in day-to-day interactions, and yet becomes more challenging with age, even for healthy aging. Age-related changes in the neural mechanisms that enable speech-in-noise listening have been investigated previously; however, the extent to which age affects the timing and fidelity of encoding of target and interfering speech streams are not well understood. Using magnetoencephalography (MEG), we investigated how continuous speech is represented in auditory cortex in the presence of interfering speech, in younger and older adults. Cortical representations were obtained from neural responses that time-locked to the speech envelopes using speech envelope reconstruction and temporal response functions (TRFs). TRFs showed three prominent peaks corresponding to auditory cortical processing stages: early (~50 ms), middle (~100 ms) and late (~200 ms). Older adults showed exaggerated speech envelope representations compared to younger adults. Temporal analysis revealed both that the age-related exaggeration starts as early as ~50 ms, and that older adults needed a substantially longer integration time window to achieve their better reconstruction of the speech envelope. As expected, with increased speech masking, envelope reconstruction for the attended talker decreased and all three TRF peaks were delayed, with aging contributing additionally to the reduction. Interestingly, for older adults the late peak was delayed, suggesting that this late peak may receive contributions from multiple sources. Together these results suggest that there are several mechanisms at play compensating for age-related temporal processing deficits at several stages, but which are not able to fully reestablish unimpaired speech perception.

Monitoring Disease Severity of Mild Cognitive Impairment from Single-Channel EEG Data Using Regression Analysis

“…Stimuli were constructed with a perceptual phonetic continuum from /to a/by, varying the first formant (F1) frequency parametrically between 430 and 730 Hz over five equal steps (for further stimulus details, see [ 21 ]). The synthetic five-step vowel continuum (denoted hereafter as “vw1-5”) was built in a way such that each token of 100 ms sound would differ minimally acoustically during hearing, and would still be perceived categorically [ 22 , 23 ]. As we are aware that hearing loss due to aging may alter auditory-evoked potentials from the cortical region [ 23 ], and it may affect the response of the participant, audiometric testing was performed.…”

Attention Mobilization as a Modulator of Listening Effort: Evidence from Pupillometry

“…The audiobook listening task was part of a larger study where magnetoencephalography (MEG) data were also collected during the audiobook listening task on the same participants. The method and discussion of the MEG data are reported in Karunathilake et al (2023). The audiobook task consisted of 60-s long audiobook segments from a 19 th century short story available in the public domain (male recording: Irving, 2006;female recording: Irving, 1977).…”

“…This resulted in two audiobook segments for each SNR condition. As mentioned above, in order to allow for signal averaging in an MEG study of auditory encoding (Karunathilake et al, 2023), each stimulus was repeated three times in a row. While repetition allows for stability in MEG measures of auditory processing, shifts in attention may occur as listeners anticipate and habituate to the upcoming difficulty and content of the passage.…”

“…Participants also completed a separate speech-perception-in-noise (SPIN) task at these same SNRs using sentences extracted from the audiobook that did not overlap with those used in the audiobook task. The SPIN task along with the behavioral findings from the audiobook task served as a manipulation check; for more detailed information about the SPIN task, see Karunathilake et al (2023). The minimum time between the offset of one auditory passage and the onset of the baseline epoch for the next passage was 69 seconds.…”

“…In a subsequent session, participants completed the audiobook listening task. During this task, pupillometry and magnetoencephalography (MEG) data were collected; however, only the pupillometry data are presented here (refer to Karunathilake et al, 2023 for a detailed analysis of the MEG and behavioral data). Participants were situated in a magnetically shielded chamber, lying down with their eyes 790 mm from the top of a projector screen (772 mm wide x 457 mm tall) and 914 mm from its bottom.…”