Relationship between neural phase-locked responses to speech and speech-in-noise perception in young and older adults

Auditory phase-locked responses are affected by aging and it has been proposed that this increases the challenges experienced during speech perception in noise (SPiN). However, the proposal lacks direct support. This issue was addressed by measuring speech-evoked phase-locked responses at subcortical (frequency-following responses, FFRs) and cortical (theta-band phase-locking, θ-PLV) levels, and studying the relationship between the phase-locked responses and SPiN (word report accuracies in spoken sentences in noise) in adults across a wide age-range (19-75 years old). It was found that: (1) FFR magnitudes declined with age after hearing loss was controlled for; (2) θ-PLV increased with age, suggesting cortical hyperexcitability in audition; (3) SPiN correlated positively with FFR magnitudes obtained in quiet and with θ-PLV obtained in noise, suggesting that impacts of age effects (smaller FFR magnitudes and greater θ-PLV) on SPiN perception differ at subcortical and cortical levels. The current study thus provides evidence for different mechanisms at subcortical and cortical levels by which age affects speech-evoked phase-locked activities and SPiN.