Retaining one’s balance in movement is one of the more complicated sensory and motor tasks that humans routinely accomplish. Elite athletic activities make the task of maintaining bipedal locomotion all the more difficult; no other species, I would argue, not even the kangaroo or gibbon, engages in a repertoire of bipedal activities even remotely close to as varied as that of humans. We walk, run, skip, hop, and combinations of all three; we kick while running, jump over a range of obstacles, cross balance beams and tight ropes, ride unicycles; some of our species even juggle soccer balls, play badminton and volleyball with our feet (no kidding, in Brazil I used to see futevolei — ‘foot-volleyball’ — on the beach… amazing), balance objects on our feet and a host of other activities. And, in the example I want to start discussing, some of us even invert our bodies and become bipedal on our hands, sometimes to extraordinary effect.
In order to accomplish these sorts of tasks, we use our ‘sense of balance.’ I hesitate to call it a sense, though, because the systems of perception, forms of analysis that we do, and reactions that we use to preserve our equilibrium are actually a complicated system, a set of shifting constellations of interio- and exterioceptions, differently weighted and compared depending upon our environment and task, and a host of active patterns of physical compensation, most of them only vaguely conscious, at best, that keep us upright. Equilibrium is a perceptual-motor system in the sense discussed by James J. Gibson (1979), perhaps even more baroque the visual perception system (his favourite example).
Minimally, a brief ecological psychology of balance would need to include at least the following: the vestibular system; information from the visual system including the horizon line, parallax, relation of centre of field of vision to visual references, and movement in peripheral vision; sensations on the soles of the feet as well as at joints and other forms of proprioception; sense receptors at the back of the neck as well as a sense of the head’s alignment in space and in relation to the body; the gravity-resisting muscles, usually those of the lower body, and the reflexes that move them to compensate for perturbations in balance.
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