Abstract
Purpose. Although the underlying principles of spatiomotor dynamics of human movement execution are broadly understood, it is unknown whether memory-guided hand-movements operate by the same principles as vision-guided ones. Methods. Complex raised-line images were learned by groups of blind and blindfolded-sighted participants using Cognitive-Kinesthetic Drawing Training (Likova, 2012), and then drawn from memory. The dynamics of the drawn image trajectories were captured on a touch-sensitive tablet to analyze their velocity/line-curvature relations; wavelet auto- and cross-correlation analyses determined the corresponding temporal offsets. Results. The velocity/curvature analysis showed that, although velocity varied inversely with line curvature, the established model of arm-motion kinematics as a simple 1/3 power relation between velocity and curvature is an insufficient characterization of their coupling. Instead, the drawing dynamics conforms to a hyperbolic power relation, asymptoting to a maximum speed for regions of shallow curvature for both groups of participants. For the blind participants, the hyperbolic power for drawing velocity was 0.94, i.e., significantly steeper in the high curvature regions where it had effect than the 1/3 of the simple power law; for the blindfolded-sighted, the hyperbolic power was even steeper at 2.18. The cross-correlation analysis between the velocity of the memory-guided motion and curvature of the drawn trajectory revealed an asymmetric anticipatory relationship, with the velocity reaching its minimum before the point of maximum curvature. Conclusions. This study investigated for the first time the spatiomotor dynamics of motion guided solely by memory along complex drawing trajectories. Overall, the high-power hyperbolic fit we have found showed that the dynamics of non-visual memory-guided hand motion significantly deviated from the simple 1/3 power law established for vision-guided motion. This deviation is expressed at the curvature extremes (very shallow or very tight curvature); the 1/3 power is approximated only in the medium-curvature regions of the transition between those extremes.