EGOCENTRIC AND ALLOCENTRIC CONSTRAINTS IN THE EXPRESSION OF PATTERNS OF INTERLIMB COORDINATION

Tasks that are easy when performed in isolation become difficult when performed simultaneously in the upper and/or lower limbs. This observa tion points to basic CNS constraints in the organization of patterns o f interlimb coordination. The present studies provide evidence for the existence of two basic coordinative constraints whose effects mal be additive under certain conditions. On one hand, the egocentric constra int denotes a general preference for moving the limbs ton ard or away from the longitudinal axis of the body in a symmetrical fashion and is of primary importance during the coordination of homologous limbs. On the other hand, the allocentric constraint refers to a general prefer ence to move the limbs in the same direction in extrinsic space and pe rtains to the coordination of nonhomologous limbs (e.g., various combi nations of the upper and lower limbs). In the present context, constra ints are considered as expressions of basic features of CNS operation that give way to preferred coordination patterns to which the system i s naturally drawn or biased. The identification and description of the e constraints is considered of critical importance to obtain a better understanding of the control of coordination patterns.