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 generalised spatial and temporal compensations and deficits associated with old age. In Experiment 1 participants used a handheld 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 whilst 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/road-edge). Corner-cutting is thus less risky on wider paths and we found that cornercutting 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 to the old, suggesting the old group compensated for decreased motor skill with "middle-of-the-road" behaviour. Enforcing increased speed caused all participants to increase corner-cutting. Thus, older participants showed spatial compensation for decreased skill by biasing their position towards 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.

Handedness, a preference towards using the right or left hand, is established in early childhood. Such specialisation allows a higher level of skill to be maintained in the preferred hand on specific tasks through continuous practice and performance. Hand asymmetries might be expected to increase with age because of the time spent practising with the preferred hand. However, neurophysiological work has suggested reduced hemispheric function lateralisation in the aging brain, and behavioural studies have found reduced motor asymmetries in older adults (Przybla, Haaland, Bagesterio and Sainburg 2011). We therefore tested the predictions of behavioural change from reduced hemispheric function by measuring tracing performance (arguably one of the most lateralised of human behaviours) along paths of different thickness in a group of healthy young and older adults. Participants completed the task once with their preferred (right) hand and once with their non-preferred (left) hand. Movement Time (MT) and Shape Accuracy (SA) were dependant variables. A composite measure of MT and SA, the Speed Accuracy Cost Function (SACF) provided an overall measure of motor performance. Older participants were slower and less accurate when task demands were high. Combined analyses of both hands revealed reduced asymmetries in MT and SACF in the older group. The young were significantly faster when tracing with their preferred hand but older participants were equally slow with either hand. Our results are consistent with the growing literature reporting decreased hemispheric function lateralisation in the aging brain.

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