Michael T. Turvey Claudia Carello University of Connecticut Haskins Laboratories
It has been suggested frequently that the human movement system is hierarchical, with each level solving a particular class of motor problems in the assembling of an act. In Bernstein's hierarchy, the tasks of forming, synergies of large muscle groups and different patterns of locomotion are solved by Level B--the level of muscular-articular links or the level of synergies. Bernstein suggested that this level developed in evolution to subserve all the locomotion forms made possible by articulated bodies and their articulated appendages. The achievements of the level of synergies are both remarkable and insular. They are remarkable because they have to do with the formation of patterns among limbs and limb segments that are stable against fluctuations and perturbations and reproducible in their basic details, even though they involve very many components of different sizes (e.g., muscles, cells) interacting in many different ways and at many different rates. They are insular because the patterns produced by the level of synergies are independent of environmental requirements. To be sure, they are exploited by higher levels in meeting such requirements, but they are purely patterns.
How patterns are formed and selected has been a topic high on the agenda of science in the nearly five decades that have passed since Bernstein wrote On Dexterity and Its Development. Physicists, mathematicians, physiologists, biologists, and psychologists have been engaged in shaping theory and conducting experiments toward an understanding of how the many different parts of a thing (a liquid, an organism) can cooperate to produce spatial, temporal, and functional order. They have been busily trying to understand synergies in the broadest sense. We suspect that Bernstein would have liked this interdisciplinary enterprise,