Aging Neural Systems and Communication Difficulties - PROJECT SUMMARY/ABSTRACT Age-related speech recognition difficulty and its association with poorer memory, increased fatigue, social isolation, and cognitive decline are major public health concerns with the current aging population. Older adults consistently show increased listening difficulties compared to younger adults, including poorer understanding and memory for speech in noise. The long-term objective of this research is to investigate age-related brain differences that affect (1) how quickly and (2) how much information is used during the perceptual recognition of speech in noise. We will use a perceptual decision-making framework to characterize differences in the speed of evidence accumulation and height of decision criteria, which can affect the accuracy and latency of speech recognition. Older adults appear to accumulate evidence more slowly and use more cautious decision criteria than younger adults. Brain imaging studies have linked evidence accumulation and decision criteria- setting to distinct brain systems, which also decline with older age. However, the contribution of perceptual decision-making to age-related listening difficulties is not yet known. The interrelated Aims 1-2 for the current research will test the overarching hypothesis that age-related declines in perceptual decision-making processes limit understanding and memory for speech in noise, commonly observed for older adults. The Aim 1 neuroimaging experiments manipulate how quickly evidence accumulates, to characterize the degree to which older adults accumulate evidence more slowly than younger adults based on uncertain and noisy sensory information. We predict that slower evidence accumulation measures are associated with poorer understanding and delayed recognition memory for older adults compared to younger adults. Structural diffusion imaging data will be collected for white matter tracts to determine whether declines in the connections between brain regions are associated with slower evidence accumulation. The Aim 2 neuroimaging experiments manipulate decision criteria, to characterize age-related differences in how much evidence is collected in challenging listening conditions. Older adults often respond more slowly and cautiously in noisy conditions compared to younger adults, regardless of task difficulty. Older adults also demonstrate poorer memory for targets and better recognition of distractors than younger adults. We predict that decision criteria variation will be associated with poorer understanding and memory for speech in noise. Structural gray matter measures will be collected to examine neural declines accounting for age-related differences in decision criteria, given that frontal brain regions linked to criteria show lower volume for many older adults. Perceptual decision-making can explain differences in speech recognition performance outside of the neuroimaging environment, so this research is a critical first step to developing measures to characterize an individual's listening difficulties and guiding effective rehabilitation strategies.
