Effects of hand and age upon abductive and adductive movements: a kinematic analysis.

Older and younger dextral subjects performed targeting movements to left and right with their preferred and nonpreferred hands upon a computer graphics tablet. Kinematic analysis revealed that older subjects produced larger constant errors than younger, paused more, and differed from younger individuals in a number of ways with respect to adductive/abductive asymmetries. The right hand was associated with shorter stroke durations and higher peak velocities, and both shorter times to peak velocity and from peak velocity to zero, suggesting superior ballistic preprogramming by the preferred right hand which was also more accurate. While both hands showed small abductive superiorities in terms of peak velocity and time from peak to zero, the largest directional asymmetries, stroke duration, showed leftward superiorities by both hands. We cannot therefore conclude either that experience with the rightward patterns of writing or that a reported tendency towards mirror-symmetrical movements by the two hands can account for the present results. Rather a right-hemisphere mediation of visually directed movements into left hemispace, along with a left-hemisphere mediation of fast, precise, temporal sequencing may jointly determine observable asymmetries. These may appear as a vector representing the opposing contributions of the two specialized hemispheres.