Neural frequency-tagging of syllables in naturalistic speech is sensitive to background noise and age-related hearing...

Healthy aging is often accompanied by a loss of hearing sensitivity and a reduced ability to understand speech in both quiet and noisy environments. From a physiological perspective, neural oscillations are thought to fundamentally contribute to parse the speech signal into meaningful units and to extract linguistically relevant information at multiple hierarchical levels. Given that syllables are essential structural elements of the speech signal that recur with quasi-rhythmic periodicity and are firmly anchored in slow amplitude modulations of the acoustic envelope, we exploited the potential of frequency-tagging to examine effects of pure-tone hearing loss and background noise on syllable representation at the neural level.

We used electroencephalography and compared peak amplitudes in a narrow-band frequency range corresponding to the syllabic speech rate in two samples of older adults with normal hearing (N=44) and mild-to-moderate age-related hearing loss (N=38) while participants listened to naturalistic sentences presented in quiet or embedded in multi-talker babble noise.

The behavioral indices confirmed that the multi-talker babble noise condition was more demanding, and that hearing loss was generally associated with reduced intelligibility, but not with lower comprehension. Notably, the effects of background noise and hearing loss were also clearly represented at the cortical level, with similar neural response properties. In fact, both acoustically and physiologically impoverished speech signals were expressed in a weaker neural representation of syllables.

These results provide neurophysiological evidence for an analogous but qualitatively different neural attenuation of syllable representation under adverse listening conditions and in individuals with pure-tone hearing loss.