Spatiomotor dynamics of hand movements during the drawing of memory-guided trajectories without visual feedback.

Although the underlying principles of the spatiomotor dynamics during human movement execution are now broadly understood to conform to a minimum jerk principle, the question addressed in the present analysis is whether different principles operate during human drawing movements without visual input, deriving from studies of the Likova Cognitive-Kinesthetic Memory-Drawing Training. For two groups of participants, completely blind, and sighted but temporarily blindfolded, this analysis shows that the consensus model of arm-motion kinematics as a simple one-third power relationship of drawing speed to the local curvature of the line being drawn is not a sufficient characterization of their coupling. Instead, the drawing dynamics without visual feedback conform to a hyperbolic power relationship, with a coupling power of approximately 1.0 for regions of the highest curvature, asymptoting to curvature-independence for regions of shallow curvature, for both blind and blindfolded groups. Thus, the asymptotic power was much higher than the one-third power predicted by the minimum jerk principle. In detail, the maximum-velocity asymptote for both groups averaged about 6 cm/s for drawing from memory, increasing to more than twice as fast for mindless scribbling. We conclude that the more elaborate operating principle of a hyperbolic saturation function, with a power asymptote of about 1.0, may be interpreted as an adaptive implementation approximating the Minimum Jerk Principle of the simple one-third power law relating velocity and curvature.