Abstract
Tracking thhe 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.
Significance statement Acoustic background noise can enhance neural speech tracking in younger adults to facilitate robust speech encoding in unfavorable situations. Aging and hearing loss increase neural noise, potentially making the auditory system less sensitive to acoustic noise. Here, younger and older adults listened to spoken stories in quiet or background noise while electroencephalography was recorded. Neural speech tracking was larger for older than younger adults for speech in quiet and under minimal background noise. However, noise enhanced neural tracking only for younger, but not older adults. The results support the idea that the auditory cortex of older people exhibits more neural noise that enhances neural speech tracking through stochastic resonance, but that additional acoustic noise does not further amplify speech encoding.
Competing Interest Statement
The authors have declared no competing interest.