Enhanced Neural Speech Tracking in Aging and Hearing Loss: The Role of Stochastic Resonance

Tracking the envelope of speech in the brain is important for speech comprehension. Recent research suggests that acoustic background noise can enhance neural speech tracking, enabling the auditory system to robustly encode speech even under unfavorable conditions. Aging and hearing loss are associated with internal, neural noise in the auditory system, which raises the question whether additional acoustic background noise can enhance neural speech tracking in older adults. In the current electroencephalography study, younger (~25.5 years) and older adults (~68.5 years) listened to spoken stories either in quiet (clear) or in the presence of background noise at a wide range of different signal-to-noise ratios. In younger adults, neural speech tracking was enhanced by minimal background noise, indicating the presence of stochastic resonance, that is, the response facilitation through noise. In contrast, older adults, compared to younger adults, showed enhanced neural speech tracking for clear speech and speech masked by minimal background noise, but the acoustic noise led to little enhancement in neural tracking in older people. The data demonstrate different sensitivity of the auditory cortex to speech masked by noise between younger and older adults. The results are consistent with the idea that the auditory cortex of older people exhibits more internal, neural noise that enhances neural speech tracking - through stochastic resonance - but that additional acoustic noise does not further support speech encoding. The work points to a highly non-linear auditory system that differs between younger and older adults.