Impairment of online control of reaching movements with aging: A double-step study

This study investigated the influence of aging on the online control of goal-directed arm movements through visual feedback of target position. Two groups of human adults, aged 28 and 56 years on average, reached with their unseen hand for targets that were unexpectedly displaced sideways at movement onset. Both stationary and displaced targets were continuously illuminated, briefly lit or not visible. When no visual information of target position was available, only an auditory signal indicated the location of the target. Results showed that when the target remained stationary, visual information enhanced movement accuracy for both age groups. When the target was displaced, visual information contributed to greater and earlier corrections for both groups. However, young adults corrected for more of the 21 degrees target displacement than older adults (95% versus 72%). Moreover, first adjustments of movement trajectory were triggered faster by young adults as compared to older adults (339 ms versus 538 ms after movement onset). Therefore, the present results highlight the impairment of older adults to monitor online movement trajectory through visual feedback processes. The detrimental effect of aging is evident when large adjustments of trajectory are necessary to reach the target. (c) 2006 Elsevier Ireland Ltd. All rights reserved.