Objectives:
Older adults often face challenges in comprehending speech in noisy environments, a difficulty attributable to declines in both peripheral and central auditory processing. This difficulty is influenced not only by hearing capabilities but also by cognitive functions. Recent research has demonstrated the crucial roles of delta oscillations (1 to 4 Hz) in segmenting verbal input into discrete units, such as words and phrases, and theta oscillations (4 to 8 Hz) in facilitating the decoding of acoustic elements in speech. The purpose of this study is to investigate how hearing ability and cognitive function are related to neural tracking. The aim is to understand the underlying processes of speech comprehension in noise among older adults.
Design:
Electroencephalography (EEG) data were collected from 23 young adults (20 to 35 years) and 23 older adults (65 to 80 years) with normal hearing levels. Cognitive assessments were conducted on the older adults to measure their cognitive functions. The study assessed both groups' neural tracking of the speech envelope as well as their behavioral performance in understanding speech within Speech-Shaped Noise (SSN). All participants underwent an EEG experiment conducted over two sessions: the first session involved listening to a 12-minute story without background noise, while the second session tested speech understanding in noise using matrix sentences presented under SSN at noise levels matched to individual Sentence Recognition Score (SRS).
Results:
The behavioral analysis showed that age significantly impacts the hit rates and response times of speech recognition, especially under challenging noise conditions. Notably, significant differences in neural tracking within the theta band were observed between the age groups, while no significant differences were found in the delta band. Furthermore, there was a notable divergence in the relationship between theta-band neural tracking and the cognitive test results among the older adults, depending on whether they had a higher or lower Speech Reception Threshold (SRT). Pearson’s correlation analysis showed that older adults with higher SRT had a negative correlation between neural tracking and word recall, but a positive correlation with visual pattern recall. Conversely, those with lower SRT displayed a positive, but not significant, trend in word recall and a significant negative correlation with visual pattern recall.
Conclusions:
The study found that age significantly influenced both the hit rate and response time, especially in more challenging noise conditions. Significant differences in neural tracking within the theta band were observed between the age groups, while no significant differences emerged in the delta band. Additionally, older adults with higher SRT demonstrated different correlation patterns in theta band neural tracking across various cognitive tests. This study contributes to a better understanding of the relationship between auditory and cognitive processes and aids in comprehending the neural mechanisms involved in speech processing in noise.