Age effects on voluntary and automatic adjustments in anti-pointing tasks

Abstract

We examined the effects of age on automatic and voluntary motor adjustments in pointing tasks. To this end, young (20-25 years) and middle-aged adults (48-62 years) were instructed to point at a target that could unexpectedly change its location (to the left or right) or its color (to green or red) during the movement. In the location change conditions, participants were asked to either adjust their pointing movement toward the new location (i.e., normal pointing) or in the opposite direction (i.e., anti-pointing). In the color change conditions, participants were instructed to adjust their movement to the left or right depending on the change in color. The results showed that in a large proportion of the anti-pointing trials, participants made two adjustments: an early initial automatic adjustment in the direction of the target shift followed by a late voluntary adjustment toward the opposite direction. It was found that the late voluntary adjustments were delayed for the middle-aged participants relative to the young participants. There were no age differences for the fast automatic adjustment in normal pointing, but the early adjustment in anti-pointing tended to be later in the middle-aged adults. Finally, the difference in the onset of early and late adjustments in anti-pointing adjustments was greater among the middle-aged adults. Hence, this study is the first to show that aging slows down voluntary goal-directed movement control processes to greater extent than the automatic stimulus-driven processes.

Fig. 1

From left to right, the change-trials are illustrated for the normal pointing, anti-pointing and color change conditions. For each condition, the trial proceeds from bottom to top

Fig. 2

Three-dimensional representation of non-change (blue lines heading toward the center of the screen) and change-trials to the left (green lines finishing on the right side of the screen) in the anti-pointing condition for a young participant. The black rectangle represents the screen, and the green circle represents the starting button

Fig. 3

Averaged change-trial (black) and non-change-trial (grey) lateral speed profiles in the anti-pointing condition for a young participant. Indicated are the first or early adjustment (--) and the second or late (-.-) adjustment to a target shift to the right (at 102 and 298 ms, respectively)

Fig. 4

Moments of adjustment during change-trials for young and middle-aged adults in normal pointing, anti-pointing (i.e., first or early and second or late adjustment) and color change conditions