Effects of age on motor preparation and restructuring

Abstract

Age-related decrements in motor plan restructuring were investigated. In this experiment older and younger adults performed a discrete aiming task that involved responses that were precued and responses that were modified at the time of an imperative signal. On 75% of the trials, the precue specified the response stimulus (valid trials) with respect to the movement parameters of arm (left or right) and direction (toward or away). On the remaining 25% of the trials, the response stimulus was different from the precue (invalid trials) in that the subject was required to modify a planned movement by changing the arm to be used and/or the direction of movement. The older subjects were slower than the younger in both the valid and invalid trials. Across preparatory intervals (PI) of 500, 1,000, 1,500, and 2,000 msec, older, but not younger subjects exhibited less reaction time cost for restructuring the motor plan for the direction-change condition than for the other parameter change conditions. Since there was little apparent cost of restructuring, these findings suggest that older adults did not prepare the direction of movement, and thus found it temporally more efficient to alter direction than arm or arm and direction combined.