Exploring interlimb constraints during bimanual graphic performance: effects of muscle grouping and direction.

Past studies on bimanual coordination have revealed a general preference to move the limbs in a symmetrical fashion, also denoted as the in-phase mode. Its counterpart, the asymmetrical or anti-phase mode, is performed with lower degrees of accuracy and stability. This ubiquitous tendency to activate the homologous muscle groups is referred to as the muscle grouping constraint (egocentric constraint). The present study confirmed the generalizability of this constraint across various coordination patterns, performed in the horizontal plane. In addition, evidence was generated that movement direction in extrinsic space also constrains bimanual coordination (allocentric constraint). Overall, the present observations suggest that direction is an important movement parameter that is encoded in the central nervous system and that is subject to interactions between the neural specifications of both limbs.