The Effect of Age on Visuomotor Learning Processes
Vachon, Chad Michael
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People can rapidly adapt their movements to a wide array of changes in our environment or the motor apparatus, although this ability can decline with age. Adaptation of movements, such as reaching with altered visual feedback, is thought to rely on the quality of sensory feedback and how well we can predict our movements. Cognitive strategies can also contribute to how quickly adaptation can occur. Age-related declines in sensory acuity and cognitive function, such as strategy use, may explain poorer adaptation in older adults compared to younger adults. The current study tested the effects of instruction and strategy use on how well older (n=38) and younger (n=42) adults were able to compensate for a 30o visuomotor rotation during reach-training, and use this strategy afterwards when reaching without a cursor. Next, training-induced changes in proprioceptive and predicted estimates of the adapted hand in these two age groups were compared. This was done by having older and younger adults estimate the location of their unseen hand when it was either moved out by a robot (passive localization: proprioception only, no prediction) or was moved by the participant themselves (active localization: prediction and proprioception) before and after visuomotor adaptation. The difference between these localization tasks represents changes in predicted or efferent-based estimates. Instruction benefitted older adults less than younger adults during initial reach training, but a similar pattern in reach aftereffects in the two age groups suggests that older adults strategy use could be evoked during no-cursor reaches after sufficient training. Following visuomotor adaptation, older adults, whether instructed or not, showed larger visually driven changes in their passive or proprioceptive hand estimates but not their efferent-based or predicted estimates of hand position. These results suggest that older adults do not differ much from younger adults in their ability to adapt their reaching movements implicitly or use cognitive strategies; however their estimates of updated hand proprioception are more affected by visual training.