Currently, relatively little is known about what drives the choice of limb for goal-oriented reaching. Traditionally, the explanation has been tied predominately to motor dominance as manifested in handedness. This article offers data and an argument suggesting that handedness can be modified by attentional (spatial) information. Although motor dominance may be the controlling factor in the programming and execution of reaching movements at the midline and hemispace ipsilateral (same side) to the dominant limb, attentional information alters the programming of movements in what would be contralateral space. The general trend of behavior is characterized by reaching on the same side as the stimulus, in ipsilateral fashion, a phenomenon explained by kinesthetic efficiency and hemispheric bias.

This study was motivated by the emerging hypothesis that right-handers are more strongly lateralized and perform better on various aspects of functional asymmetry than do left-handers. Right-and left-handers •were observed for hand selection responses to a unimanual task of reaching for a small cube in positions of right-and left hemispace, prompting hemispheric decision-making related to hand dominance and attentional (visuospatial) stimuli. As predicted, left-handers did not respond with their preferred limb as consistently across positions as did right-handers. Additional inspection of the task suggests that being less lateralized may not be a disadvantage in this context, and that environmental influence may play a significant role in hand selection for a particular motor event.Resume Cette etude avait pour but de verifier une nouvelle hypothese voulant que les droitiers soient plus fortement lateralises et reussissent mieux que les gauchers dans differents aspects de l'asymetrie fonctionnelle. Nous avons observe la preference manuelle de droitiers et de gauchers au cours d'un test unimanuel ou ils devaient atteindre un petit cube, qui, place soit a droite, soit a gauche, sollicitait la prise de decision reliee a. la dominance manuelle et aux stimuli attentionnels (visuospatiaux). Comme prevu, les gauchers n'ont pas repondu aussi regulierement que les droitiers en fonction de leur region frontale dominante. Un examen supplementaire du test suggere que, dans ce contexte, etre moins lateralise ne constitue pas necessairement un desavantage, et que l'incidence de l'environnement peut jouer un role important dans la preference manuelle pour un element moteur precis.

This experiment examined the use of attentional stimuli for reaching in hemispace by strong right-dominant adults and children. Driving the hypothesis was the notion that developmental factors associated with use of attentional information may affect the programming of reaching movements in hemispace. Although the general pattern of responses was similar for both samples, children did not use attentional cues to program reaching movements in contralateral hemispace as effectively as adults. This result suggests that motor dominance and perhaps other factors were pivotal in motor programming for children. One possible explanation for the general behavior observed underlies an attentional hemispheric bias for a tendency to use the hand that is on the same side as the stimulus.