COUPLING AND LATERALIZATION IN BIMANUAL COORDINATION AT 7, 8, AND 9 YEARS OF AGE

We studied the role of the preferred hand in bimanual coordination using an apparatus like the X-Y plotter first described by Preilowski (1975). Subjects were children of 7 to 9 years, an age period when laterality, hemispheric interaction, and bimanual coordination have been demonstrated to change. The task required the children to draw a pattern by rotating two cranks either at the same velocity or with a 2:1 velocity ratio, with parallel or mirror movements. Although subjects moved their two hands at the same velocity with relative ease, the right-hand output of right-handers significantly exceeded their left-hand output. At age 7, the error was less systematically deviated toward the right-hand-controlled axis using parallel as opposed to mirror movements. This difference did not persist at 8 and 9 years of age. When subjects were required to move one hand twice as fast as the other, performance did not vary as a function of which hand moved faster. However, the lines drawn were more wavy in the left-hand-faster than in the right-hand-faster condition as long as visual feedback was provided. These results suggest that a unilateral control of the two hands as a coordinative structure occurs earlier when interhemispheric interaction is not a critical factor.