Early working memory changes under auditory load: A predictor of speech-in-noise perception in younger adults

Understanding speech in noisy environments is challenging, even for normal-hearing individuals, due to the complex interactions between auditory sensory processing and cognitive functions. The auditory system transforms acoustic signals into perceptual representations that are actively maintained and manipulated by working memory (WM). WM enables the retention and integration of incoming auditory information, supporting speech perception. While age-related speech perception decline is well documented in older adults, early signs of cognitive decline remain less explored in younger adults. This may be explained by the fact that conventional assessments conducted in quiet settings may not be sufficiently sensitive to detect such early signs of decline. The current study aims to explore early changes in WM abilities among adults aged 20-40 years by introducing background noise in the assessment task. Eighty normal-hearing participants were divided into four age-based groups (5-year intervals) and tested using forward digit span, backward digit span, and operation span tasks. Additionally, SNR-50 (signal-to-noise ratio at which 50% of the stimuli are correctly identified) was measured to assess speech perception in noise. Results showed a gradual age-related decline in WM performance, with significant reductions in backward and operation span performance appearing in the 35-40 age group, especially under noisy conditions. Moreover, significant negative correlations were observed between SNR-50 and WM across both quiet and noisy conditions. The findings suggest that WM decline may begin earlier than traditionally assumed in challenging auditory environments. This highlights the importance of assessing auditory cognition under ecologically valid conditions and supports cognitive load theory by demonstrating how noise increases cognitive demand, impairing performance.