A differential effect of concurrent verbal activity on right arm movements rightwards and leftwards

Twenty right-handed male subjects had to follow a target which moved horizontally with a velocity of 40 degrees/s either rightwards or leftwards by moving their right arm. During the pursuit movement, subjects had to speak a sentence or to accomplish this procedure without speaking. It could be shown that while subjects spoke, the pursuit movement was performed more inaccurately than during the control session. Furthermore, it was shown that during concurrent speaking, pursuit movements rightwards were more inaccurate than movements to the left. This result is in line with theoretical implications according to which visually guided right-arm movements rightwards are controlled by a neural network located in the left hemisphere, whereas right-arm movements leftwards are controlled by a neural network distributed over both hemispheres.