Standing, walking, reaching and the manipulation of objects are challenging if not impossible tasks and the ability of these pa-tients to perceive by eye proves to be a poor substitute for their inability to perceive by muscle. The purpose of this keynote lecture is to summarize investigations into the rhythmic coordinations of contralateral limbs and the nonvisible perception of the properties of handheld wielded objects, two major achievements of the level of muscular-articular links. Understanding the bases for these achievements requires both classical dynamics and contemporary nonlinear, qualitative dynamics. The nested body segments can be interpreted as a nest-ing of inertia tensors. If the normal relation between an arm s spatial axes and the arm s inertial eigenvectors is broken by means of an attached splint, the positioning of the occluded arm is systematically altered relative to vi-sual targets.
People point with the arm s eigenvectors rather than the arm s longitudinal axis.
When the position of one forearm is matched nonvisually with that of the other, under conditions in which splints have rotated the eigenvectors relative to the limb segment s spatial axes, the matching is in terms of the respective forearm eigenvectors rather than elbow angles. Despite the internal complexity of two limbs sharing a temporally repeating pattern, at their own level they seem to follow a relatively uncomplicated coordination law. Theory and experiments show that the collective dynamics can be modeled by a first order motion equation in relative phase. The equation successfully predicts interlimb coordination equilibria and their bifurcations as a function of movement speed and differences between limbs in natural frequency. The body s functional asymmetry shows up as a modification of the fundamental coupling function and attentional effects in bimanual coordination are revealed as parameterizations of the modified coupling function.