Differential Effects of Age and Simulated Sensory-Motor Constraints on Digit Symbol Substitution Test Performance

BACKGROUND: Cognitive performance in later life is shaped by both central processing declines and sensorimotor limitations. This study examined the impact of simulated sensory and motor constraints on Digit Symbol Substitution Test (DSST) performance and compared younger adults under such constraints with older adults. METHODS: 84 young adults (19-37 years) were assigned to one of four conditions: no constraints, visual impairment glasses, motor constraints (gloves), or both. 20 older adults (60-75 years) completed the task without restrictions. Participants practiced the DSST over six weeks and completed recognition and reconstruction tasks assessing symbol-digit memory. RESULTS: Older adults consistently performed worse than all younger groups across pre- and posttest, practice and memory tasks, confirming age-related declines in processing speed and memory. Younger adults largely compensated for simulated constraints, with no significant overall performance difference between constrained and unconstrained groups. However, the constraints affected practice-related improvement: constrained younger adults showed a flatter linear increase and a stronger leveling off of performance gains across sessions than unconstrained younger adults. Recognition and reconstruction were unaffected by restrictions among younger adults. CONCLUSIONS: Overall, in DSST-like tasks, age influenced overall performance and memory more than temporary peripheral limitations. Younger adults' cognitive-motor resources could offset moderate constraints, although these altered learning trajectories.