What drives children's limb selection for reaching in hemispace?

Arguably, the act of reaching constitutes one of the most devoted lines of contemporary developmental research. In addition to the underlying dynamical characteristics of motor coordination, a key element in programming is limb selection, a phenomenon (handedness) that has so far resisted any reasonable unified explanation. From a more contemporary view, two factors appear to have the most influence on hand selection for a given task: motor dominance and attentional information related to task demands. This study was designed to determine what factor(s) influence choice of limb for reaching in hemispace in reference to motor dominance, object proximity, and a hemispheric bias favoring use of the hand on the same side as the stimulus. Strong right-handed children were asked to reach and retrieve a small object across right and left hemispace locations beginning with the arms uncrossed and arms-crossed. With the arms-crossed condition, an imagined and actual movement execution was administered. Results from the uncrossed condition supported previous reported findings for adults and children. That is, participants responded ipsilaterally using the hand on the same side as the stimulus, thus supporting the case for object proximity and hemispheric bias. However, in the arms-crossed condition the vast majority of participants preferred keeping the limbs crossed in response to right and left hemispace stimuli, which leads to the suggestion that object proximity rather than hemispheric bias was the driving factor in this context. The behavioral pattern for imagined and actual movement was not significantly different. Overall, the findings add to the growing acceptance that limb selection is task and context dependent, rather than a biologically based invariant feature of motor behavior.