Visual-motor integration of unexpected sensory events in young and older participants: A kinematic analysis

We report a single experiment that examined the ability of young and older participants to modify their movement plan on-line during movement executio n. Participants performed a single phase aiming task under 2 different cond itions. In the experimental condition, during 76% of the trials, the index of difficulty of the task remained constant at 4.8 bits (medium target). Du ring 24% of the trials, target width changed unexpectedly at movement initi ation to either a smaller (6.1 bits) or larger (3.5 bits) target. In the co ntrol setting, participants completed trials to each target (3.5, 4.8, or 6 .1 bits); target width remained constant throughout movement in this condit ion. For both age groups, participants responded in the anticipated fashion during control trials; movement time increased as a function of target siz e, with older participants generally performing more slowly. In the experim ental condition, the young participants adapted their performance to the ne w target characteristics. In contrast, older participants adopted a conserv ative control strategy, whereby they did not adapt their performance to the new target size but instead used their programmed response for the initial target. These data suggest that older adults were operating in an open-loo p mode of control for the experimental trials and a closed-loop control mod e during the control trials. Thus, the type of control older adults adopted was dependent on the environmental context.