It has been shown that crossing the midline affects the performance of fine motor skills but the underlying mechanisms are not well understood. This issue is particularly important with respect to the development of motor activities such as writing or pointing in children. Forty-eight right-handed children performed goal-directed movements toward targets positioned either at the midline, or in the left (contralateral side), or right (ipsilateral) hemispace. Findings revealed that movements were more accurate in ipsilateral than in contralateral space and their overall accuracy increased by 42% between 6 and 10 years of age. Differences in movement time among hemispaces depended on the joints predominantly involved in producing the movements (wrist versus fingers). Lower accuracy of movements in contralateral workspace is also present when participants do not have to cross the midline but only move within this workspace. In motor proficient children, no developmental trends were found for these hemispace effects.
Smits-Engelsman is with Avans+ University, Breda, The Netherlands, the Motor Control Lab, Dept of Kinesiology, K.U. Leuven, Belgium, and Sint Maartens Kliniek-Research, Nijmegen, The Netherlands. Swinnen is also with the Motor Control Lab, Dept of Kinesiology, K.U. Leuven. Duysens is also with Sint Maartens Kliniek-Research and Dept of Biophysics, University of Nijmegen.