Fig. 2.

Experimental measures. A: sketch of trajectories of the thumb and index finger for a single trial. Subjects start with their thumb and index finger pinched together and open their hand while translating to the object (gray box). The blue line indicates a perfectly linear path over which the aperture opens exactly enough to encompass the object, and the corresponding evolution of the aperture over time (right) is a straight line with infinite linearity. Contrarily, the red line indicates a path with finite linearity (left) and a curved evolution over time (right). The inverse of the maximum distance to the infinite linearity line (1 over d, as indicated) quantifies the decreased linearity. B: example of the self-similarity calculation. B1 shows 3 representatives of a family of functions, indicated by circles, triangles, and squares. B2 shows the nth moments (for n = 2, 4, 6, 8, 10) plotted vs. the 2nd moment normalized by the 0th. The markers match B1, so that each colored line is determined by contributions from each of the functions. The slope of the colored lines is then plotted in B3 and is seen to increase proportionally to the moment number, n, divided by 2. This indicates perfect self-similarity, as it is by construction. For real data bootstrapped errors are propagated through the calculation and used to determine significance. C: the object during the lift. The tilt is measured as the signed angle from the guideline (dashed line with arrows) in the coronal plane. By convention, counterclockwise tilts are positive (as shown) and clockwise tilts are negative.