Age-related differences in force variability and visual display.

It is well established that older adults are more variable in their force output and that this age-related decrement is mediated by visuomotor processing. The purpose of this investigation was to examine whether the type of visual display impacts age-related differences in the control of force output. In order to address this question, young and old participants produced constant isometric force via index finger abduction to 3 force levels [5, 10, and 20% of their maximal voluntary contraction (MVC)]. Visual feedback was presented with either a compensatory or a pursuit display. A compensatory display provides visual feedback about force amplitude in relation to the criterion target whereas a pursuit display provides visual feedback about the force trajectory in relation to the criterion target and preview of the target path of the force trajectory. The magnitude of force variability was indexed with standard deviation and coefficient of variation. The structure of force output was indexed with spectral slope and approximate entropy. As expected, older adults were more variable and had more structured force output compared to younger adults. Moreover, this age-related difference in force control was paramount in pursuit displays. Overall, the findings suggest that age-related differences in force control are centrally mediated. It is proposed that older adults have deficits in visuomotor processing and this may be partly related to age-related decrements in the control of eye movements.