This study investigated the effects of uni- and bimanual hand movements on the efficiency of within- and between-hands response preparation in a spatial cuing task. Predictions were derived from the Grouping Model of finger preparation, inspired by insights from neurophysiology (i.e., the concepts of transcollosal facilitation and cognitive overruling of basic neural coordination patterns). Sixteen participants performed the finger cuing task with one, two, or no hand(s) moving. Reaction time results revealed that unimanual and bimanual hand movements had similar effects on within-hand preparation but differential effects on between-hands preparation. This finding demonstrates a strong dissociation between within- and across-hands finger preparation, suggesting distinct underlying mechanisms as hypothesized by the Grouping Model.