Abstract
Stepping responses slow markedly with age, posing a significant risk for falls, yet the cognitive and motor mechanisms driving this slowing remain poorly understood. The diffusion decision model (DDM), which jointly accounts for response times and accuracy, has been used to disentangle the cognitive, sensorimotor and strategic contributors to age-related slowing in upper-limb tasks. We extended this approach to a choice reaction time task with three response conditions: finger (button press), foot (seated foot tap), and step (forward step initiation from quiet standing) to determine if the reasons for age-related slowing differ across upper- and lower-limb responses and stepping responses involving the additional complexity of postural control. Healthy older adults (n = 54) responded more slowly than younger adults (n = 28) across all response conditions. DDM analysis indicated that older adults showed slower evidence accumulation rates and longer non-decision times than younger adults, reflecting less efficient information processing and slower motor execution, respectively. Younger adults also required more evidence than older adults to trigger a decision during stepping, but not in the finger or foot responses. Together, these findings indicate that age-related slowing of choice stepping is driven primarily by reduced information-processing efficiency and prolonged non-decision processes, rather than by increased response caution during action selection. More broadly, these findings demonstrate that cognitive modelling can be extended beyond traditional upper-limb tasks and applied to postural decision making in older adults to characterise the mechanisms contributing to slowed stepping, offering a foundation for targeted therapeutic interventions.