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Two-dimensional Movement in Time: Handwriting, Drawing, and Pen Gestures


Handwriting and Drawing are two different means of human information storage and communication, produced by the same single two-dimensional output system: a pointed writing implement, usually driven by the arm, which leaves a visible trace on a flat surface. Handwriting conveys symbolical data, whereas Drawing conveys iconic data. The third data type, Pen Gestures, consists of unique symbols, as used by book editors and in pen computers, requiring a function to be executed. Contrary to speech, handwriting is not an innate neural function, and must be trained over several years. During the training process, handwriting evolves from a slow feedback process involving active attention and eye-hand coordination to a fast automatic and ballistic process. The atomic movement unit in handwriting is a stroke, which is a movement trajectory bounded by two points of high curvature and a corresponding dip in the tangential movement velocity. The typical modal stroke duration is of the order of 100 ms, and varies less for increased movement amplitudes than one would expect: For a large range, writers exert an increased force in order to maintain a preferred rhythm of movement (10 strokes/s, 5 Hz). Once ``fired'' cortically, such a stroke cannot be corrected by visual feedback. The handwriting process evolves in a continuous process of concurrent planning and execution, the planning process being 2--3 characters in advance of the execution process. Writing errors convey the fact that during writing several processes take place, including phonemic-to-graphemic conversion (spelling), and graphemic-to-allographic conversion (``font choice'').

Table E.1 gives an overview of parameters that may be controlled with a pen.

Table E.1 : Parameters controlled by a pen

Esprit Project 8579/MIAMI (Schomaker et al., '95)
Thu May 18 16:00:17 MET DST 1995