Sensory and intrinsic coordination of movement.

A recently generalized theory of perceptual guidance (general tau theory) was used to analyse coordination in skilled movement. The theory posits that (i) guiding movement entails controlling closure of spatial and/or force gaps between effectors and goals, by sensing and regulating the tau s of the gaps (the time-to-closure at current closure rate), (ii) a principal way of coordinating movements is keeping the tau s of different gaps in constant ratio (known as tau-coupling), and (iii) intrinsically paced movements are guided and coordinated by tau-coupling onto a tau-guide, tau g, generated in the nervous system and described by the equation tau g = 0.5 (t-T 2/t) where T is the duration of the body movement and t is the time from the start of the movement. Kinematic analysis of hand to mouth movements by human adults, with eyes open or closed, indicated that hand guidance was achieved by maintaining, during 80 85% of the movement, the tau-couplings tau alpha-tau r and tau r-tau g, where tau r is tau of the hand-mouth gap, tau alpha is tau of the angular gap to be closed by steering the hand and tau g is an intrinsic tau-guide.