Sentence recall and neurophysiological effects of the “2-Sentence Problem” under time compression in younger and older listeners

Understanding how auditory cognitive load impacts speech recognition is critical for improving communication strategies across the lifespan. This study investigated the effects of two auditory cognitive load factors – sentence count (one vs two sentences) and speech rate (natural vs time-compressed) – on delayed sentence recall in younger and older listeners with normal and near-normal hearing. Forty participants (20 younger, M = 21.15 ± 1.18 years; 20 older, M = 64.50 ± 6.19 years) completed a sentence-recall task under four conditions combining sentence count and speech rate. Neural and physiological responses were recorded using systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS). Participants also provided subjective workload ratings (NASA-TLX) and completed assessments of working memory and temporal processing speed. Results showed that increased sentence count and faster speech rate significantly reduced recall accuracy, with older adults being more negatively affected, particularly under time compression. Higher working memory capacity was associated with better performance on two-sentence conditions, and better temporal processing speed supported time-compressed sentence recall in older listeners. Younger adults demonstrated strong premotor cortex activation during listening, while older adults had weak premotor cortex activation isolated to the higher-load conditions, consistent with possible compensatory strategies and reduced neural efficiency. Galvanic skin response suggested blunted reactivity in older adults under increased load. Subjective workload ratings reflected greater perceived effort in older adults, particularly during time-compressed conditions. These findings highlight age-related differences in cognitive and neurophysiological responses to auditory load and emphasize the importance of multimodal approaches for understanding effortful listening.