On the coordination of two-handed movements.

Abstract

In a set of three experiments, we show that after an auditory "go" signal, subjects simultaneously initiate and terminate two-handed movements to targets of widely disparate difficulty. This is the case when the movements required are (a) lateral and away from the midline of the body (Experiment 1), (b) toward the midline of the body (Experiment 2), and (c) in the forward direction away from the body midline (Experiment 3). Kinematic data obtained from high-speed cinematography (200 frames/sec) point to a tight coordinative coupling between the two hands. Although the hands move at entirely different speeds to different points in space, times to peak velocity and acceleration are almost perfectly synchronous. We believe that the brain produces simultaneity of action as the optimal solution for the two-handed task by organizing functional groupings of muscles (coordinative structures) that are constrained to act as a single unit.

A cross-modal interference effect in grasping objects

“…Similar patterns were observed for both the left and the right hands. Such response attraction between the two hands has been previously reported by Kelso, Southard, and Goodman (1979) in their study of coordination in bimanual reaching and, more recently, by Jackson, Jackson, and Kritikos (1999) in a bimanual reach-to-grasp task. In line with our predictions, the present findings demonstrate selective interference effects of the distractor on the grasping component of the reaching hand, suggesting that the interference elicited by proprioceptive and haptic information from the distractor selectively affects the grasping component of the reaching hand.…”

“…Besides, it is worth noting that in the protocol in which the distractor was actively grasped, both hands performed the same type of grasping action. This implies that an identical motor program was engaged for both hands, and hence, we can rule out any interference effect due to competition between the concurrent execution of two different motor programs, which was the case in other studies (Gentilucci et al, 1998;Kelso et al, 1979). Therefore, the interference effect we observed was most likely to have been relevant to the input from the distractor itself.…”

Combined effects of planning and execution constraints on bimanual task performance

“…Apart from these new Wndings we replicated some well known phenomena from the literature. That is, reaction times and movement times were longer in bimanual trials compared to unimanual trials (e.g., Kelso et al 1979;Jackson et al 2002;Mason and Bryden 2007), and interlimb coupling was higher when moving in symmetry than in asymmetry (e.g., Swinnen et al 1991;Carson 1995;Semjen et al 1995).…”

Doing two things at once: The role of temporal compatibility

“…According to Fitts' law (Fitts & Peterson, 1964), movement duration should decrease as this task is made easier by the use of larger targets. Kelso et al (1979) examined the case in which the right and left hands were to move to targets of different sizes. If Fitts' law were to hold for each hand separately, the two hands would move at different speeds, and the two movements would have different durations.…”