Are the elderly able to appropriately reprogram their actions?

Movement reprogramming in a task requiring timing accuracy was investigated in young and elderly individuals. The task consisted of manually hitting a hemiball in synchrony with the arrival of a moving light stimulus running through an electronic trackway. Movement reprogramming was required by unexpectedly changing the regular stimulus velocity at different moments before the due time of arrival at the interception position. Such changes produced times after velocity decrease (TAVD) between 150 ms and 750 ms, representing the periods of time available for generation of new movement timing specifications. Effect of probability of stimulus velocity change was investigated by comparing the conditions of 25% and 50% of chance of velocity decrease. Analysis of performance in conditions of velocity decrease showed an enlargement of temporal error as a function of longer TAVDs up to 300-375 ms. In conditions in which TAVDs were longer than 375 ms young participants showed a progressive improvement of accuracy over time, while the elderly were unable to improve their performance even for a TAVD of 750 ms. A trend toward a more efficient reprogramming with reduced uncertainty was observed only in the young. These results indicate that movement reprogramming is a continuous process in young individuals, but it is impaired in the elderly, preventing an appropriate reorganization of the action.