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The control of pen pressure in handwriting: A subtle point.
Wann, J. & Nimmo-Smith, I.
Human Movement Science, 10, 223-246.
Year of publication:
Despite an extensive body of research on the control of planar pen movements in handwriting, relatively little attention has been directed towards the control of pen-pressure. The introduction to this paper uses a computer simulation to demonstrate that the effects of static and sliding friction may be subtle but can significantly alter the dynamics of pen control. These simulations lead to hypotheses on human strategies which may reduce the disruptive effects of friction. Specifically, it is proposed that subtle modulations in the general level of normal force are necessary if the relative pen dynamics are to remain stable across changes in pen speed. Empirical data were collected from 11 adult subjects writing repetitions of a series of words in different script sizes, at different speeds and on different surfaces. Axial pen pressure was recorded in synchrony with x,y position information. The resulting pressure records are used to explore some hypotheses of previous researchers on pressure variability, as well as the hypotheses developed from the computer simulations. Finally a theoretical model is presented of a "perceptual instrument" that may serve to explain the sensitivity apparent amongst competent writers in the modulation of pen-pressure.