Neurocognitive mechanisms of age-related decline in global motion perception

Age-related declines in global motion perception (GMP) may result from alterations in visual noise in combination with morphological changes in the visual cortices. However, the neurocognitive mechanisms that link cortical structural alterations to deficits in noise modulation remain unclear. In this study, we integrated psychophysical method, the perceptual template model (PTM), and structural magnetic resonance imaging to investigate the relationships among brain structure, cognitive processes, and perceptual performance underlying GMP aging. We compared motion coherence thresholds (MCT) of 106 younger and 94 older healthy adults using random-dot kinematograms. The PTM characterized age-related changes in internal additive noise and external noise, while voxel- and surface-based morphometry assessed gray matter volume, cortical thickness, and surface area in visual regions. Mediation models examined how changes in noise mediate the relationship between cortical structure and perceptual performance. PTM analysis revealed that reduced GMP in older adults was significantly associated with increased internal additive noise and external noise. Morphometric analyses indicated that GMP decline was associated with reductions in gray matter volume in right V4v, as well as cortical thinning in left V5 and right V8. Mediation analysis further demonstrated that internal additive noise fully mediated the relationship between cortical thickness in left V5 and MCT, whereas external noise partially mediated the relationships between right V4v gray matter volume and MCT, and between right V8 cortical thickness and MCT. These findings suggest that age-related cortical thickness reduction in left V5 amplifies internal noise, while cortical atrophy in right V4v and V8 impairs the extraction of motion signals from external noise. Overall, this study proposes a novel framework for understanding age-related GMP decline by linking cortical morphology, noise alterations, and perceptual performance.