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

Abstract

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.

Looking to the future of visual assessment using driving simulation

“…In contrast, road conditions with greater perceptual, motor and/or cognitive demands could have exposed the limits of the compensatory strategies being used (e.g. Raw, Kountouriotis, Mon-Williams, & Wilkie, 2012) and highlighted conditions under which driving safety would not meet the required level to retain a driving licence.…”

“…Without a great deal of care such uncontrolled tasks will merely lead to similar limitations as possessed by realworld driving tests (namely lack of control over conditions making interpretation of driving errors/ behaviours difficult) whilst failing to exploit the various benefits of using simulation to assess specific aspects of driving skill. Raw et al, 2012, andSmith et al, 2015).…”

“…These range from a simple desktop computer and monitor with a joystick attachment, to fixed-based simulators with large field-of-view displays (Figure 2A), through to an actual car mounted on a large bespoke motion-base platform (like the University of Leeds Driving Simulator; G. K. ; Figure 2B). The precise form of the required driving simulation will vary depending on the need of the tester and the likely deficits of the testee: from testing steering control on an empty road (Raw et al, 2012; Figure 3A), through to full city simulations with vulnerable road users walking through the city (Smith et al, 2015; Figure 4A). Raw et al, 2012 andSmith et al, 2015, and …”

“…The precise form of the required driving simulation will vary depending on the need of the tester and the likely deficits of the testee: from testing steering control on an empty road (Raw et al, 2012; Figure 3A), through to full city simulations with vulnerable road users walking through the city (Smith et al, 2015; Figure 4A). Raw et al, 2012 andSmith et al, 2015, and …”

Intraindividual variability and falls in older adults.

“…Furthermore, the control of gait and posture shifts from sub-cortical pathways to cortical networks in conditions such as Parkinson's disease (Morris, Iansek, Matyas, & Summers, 1996). A decline in motor function because of old age can lead to a variety of compensatory behaviors (Holt et al, 2013;Raw, Kountouriotis, Mon-Williams, & Wilkie, 2012) that may be strategic, explicit and under conscious cognitive control. Indeed, in dual-task conditions (e.g., speaking while walking) older adults may not reallocate resources appropriately and therefore fail to compensate adequately (Harley, Wilkie, & Wann, 2009).…”