Movement strategies in vertical aiming of older adults
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The current study examined the movement kinematics of older adults when aiming to vertically oriented targets. Late middle-age and early old-age participants completed 20 trials to a small target located downward or upward by 0.16 m from a home position at shoulder height. Aiming direction had a significant effect, resulting in more submovements, which were mostly reflective of undershooting when aiming to the downward compared to upward target. In trials containing a submovement, both groups exhibited shorter total movement time, concomitant with a decrease in duration of the primary movement and an increase in submovement amplitude, when aiming to the downward target. Measures of dispersion also differed in accord with the amplitude of submovements, such that there was greater spatial and temporal variability in the primary movement when aiming in the downward direction. While there was limited evidence of a difference between the groups, there were significant correlations between age and several dependent measures when aiming to the downward target. Of note, in trials containing submovements, older participants exhibited larger amplitude and longer duration submovements, as well as shorter amplitude primary movement. Spatial variability at peak velocity also increased as a function of age when aiming downward, but not in trials without submovements. An explanation related to physical limits on movement production is discounted given the lack of consistent findings between trial types. Instead, we suggest older participants' exhibit strategic differences in movement kinematics when aiming to vertically located targets, and that these change progressively with age in order to maintain speed-accuracy relations.
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