Motor constancy and the upsizing of handwriting

Although handwriting can vary in size, it remains remarkably similar in form, demonstrating motor constancy (equivalence). A consideration of changes in writing size may indicate: (1) how rescaling is accomplished, and (2) those invariant features that remain constrained under size variation. In the experiment reported here nine participants wrote the word “minimum” (without dotting “i’s”) in cursive text, under three size conditions on a SmartBoard. The standard deviation of stroke slope did not change its relationship to mean stroke slope, but stroke durations and lengths did vary. Kinematic analysis indicated that the number of submovements, their efficiency, and their kinematic structure varied across the three writing size conditions. The results suggested that motor constancy does not merely reflect a simple change in a single parameter of scale.