Movement control in older adults: does old age mean middle of the road?

Old age is associated with poorer movement skill, as indexed by reduced speed and accuracy. Nevertheless, reductions in speed and accuracy can also reflect compensation as well as deficit. We used a manual tracing and a driving task to identify generalized spatial and temporal compensations and deficits associated with old age. In Experiment 1, participants used a hand-held stylus to trace a path. In Experiment 2, participants steered along paths in a virtual reality driving simulator. In both experiments, participants were required to stay within the boundaries while we manipulated task difficulty by changing path width or movement speed. The older group showed worse performance in the highly constrained conditions. Corner cutting effectively reduces the curvature of bends but yields a greater risk of error (i.e., clipping the path or road edge). Corner cutting is thus less risky on wider paths, and we found that corner cutting increased for both age groups in both tasks when paths were wider. Crucially, we observed a greater degree of corner cutting in the young group compared with the old, suggesting the old group compensated for decreased motor skill with "middle-of-the-road" behavior. Enforcing increased speed caused all participants to increase corner cutting. Thus, older participants showed spatial compensation for decreased skill by biasing their position toward the middle of the path in both a manual and steering task. External constraints (narrow paths and fast speeds) prevented this strategy and revealed age-related declines in skills central to manual control and driving.