Hans-Leo Teulings

Digital recording and processing of handwriting movements

Abstract Methods of recording and processing handwriting movements by means of a computer-controlled digitizer are discussed. It is concluded that the presence of measurement ‘noise’ in the sampled movements makes it necessary to choose high sampling frequencies in combination with low-pass digital filters, especially if time derivatives have to be estimated. However, increasing the sampling frequency beyond some critical value does not improve the signal-to-quantization-noise ratio unless the raw samples are preprocessed by summing groups of samples. In order to correct for occasional nonsimultaneous sampling of the x - and y -coordinates a second type of preprocessing is required (linear interpolation). Subsequently, it is shown that low-pass filtering and differentiation can be carried out in the frequency domain, using FFT, if suitable extrapolation time functions and filter characteristics are chosen. Finally, various automatic procedures for the division of movement patterns into meaningful segments and a procedure for estimating the accuracy of the digitizer are proposed.

The independent monitoring of form and scale factors in handwriting

Abstract In an experimental study on movement latencies and durations of letter-writing tasks we tested a three-stage model of the retrieval and initiation of handwriting movements. In this model it is assumed that the process of preparation of handwriting movements consists of the retrieval of a non-muscle-specific motor program in stage one, the substitution of actual parameters into that program in stage two, and finally, the recruitment of an appropriate number of motor units for the execution of the program in the anatomical and physical context in stage three. The pattern of additivities and interactions in the latency data, due to variations of letter size, slope of the base line, and sequencing of letter strokes, was consistent with our three-stage model of complex motor behavior. Furthermore, the analysis of movement times for separate letter strokes revealed a process that involves the unpacking of later strokes during the execution of earlier ones.

Control of stroke size, peak acceleration, and stroke duration in Parkinsonian handwriting

Abstract This research is supported by a grant from the USA National Institute of Neurological Diseases and Stroke (NS 17421) awarded to George E. Stelmach, and the Nijmegen University Research Pool (SW4/88). We thank Jim Phillips for editorial assistance, Frans Gremmen for statistical support, Hein Tibosch, for designing and implementing some of the algorithms, and Halya Czerepacha for textual help. The researchers wish to thank the subjects from the Madison Area Parkinson Support Group for their motivated cooperation.

Time, Size and Shape in Handwriting: Exploring Spatio-temporal Relationships at Different Levels

Time, the organizational principle of every motor skill, manifests itself in several ways in the case of handwriting. First, time is systematically involved in the preparation of movements before their onset and during their performance. The study of reaction times and movement times in handwriting (see Thomassen et al., 1984) has revealed temporal features of the processing stages of writing performance; there are relevant analogies with speech and typewriting (see the review by Sternberg et al., Note 1; and Shaffer, 1985, chapter 15 of the present volume).

Invariants in Handwriting: The Information Contained in a Motor Program

Publisher Summary This chapter presents an experiment that demonstrates a method for determining whether the spatial characteristic or the temporal characteristic of a handwriting pattern is more invariant over replications under normal conditions and under voluntary transformations or extraordinary execution conditions. This method employs three criterions. The first criterion employs the signal-to-noise amplitude ratio of a characteristic. The signal is the average characteristic, while its noise comprises the fluctuations between the average and a specific replication. The second criterion employs intercharacteristic correlation coefficients. The third criterion is concerned with the robustness of a characteristic (expressed by the intercondition correlation) across various instructed global transformations of the movement pattern, such as writing at a different size or speed, or with respect to some arbitrary manipulation of the writing conditions, such as writing without visual feedback or writing on a low-friction surface while reducing proprioceptive feedback. The experimental results consistently showed that the spatial structure was more invariant than the temporal structure. The apparent findings of invariant temporal characteristics in handwriting movements may be because of the motor system that produces the smoothest trace to satisfy the desired spatial outcome. Temporal invariance may also be derived from spatial invariance.

Preparation of partly precued handwriting movements: The size of movement units in handwriting

Abstract In the present study we investigated whether individual strokes or complete letters form “movement units” in cursive handwriting. In various reaction time (RT) paradigms (choice-RT, precue-RT, and simple-RT) we tested which definition of a unit provides the best explanation for the reaction-time and movement-duration data that we observed. In the choice-RT condition we found that congruence of complete letters facilitated reaction time, but congruece of strokes within letters did not. This was also found to hold in the precue conditions where, some time prior to the imperative stimulus, a precue was presented, specifying either the first or the second letter of the writing pattern. Furthermore, analysis of movement durations revealed that the strokes immediately preceding and following the connection stroke between two identical letters were delayed. These results consistently point towards the notion that the movement pattern of a well-practised letter is handled as a single unit.

Constancy in stationary and progressive handwriting

Abstract The present study investigates the effect of combining left-to-right progression with the repeated, continuous production of simple writing patterns, or graphemes. It is argued that in cursive handwriting the presence of a steady left-to-right progression force, superimposed on the grapheme-producing movements, and thus affecting e.g. their spatial features, is unlikely. More specially, it is hypothesized (1) that typical segments of familiar graphemes remain constant, i.e. they are not affected by progression; (2) that the production of the vertical component of progressive patterns such as sinusoids is different from that of similar vertical oscillations in a stationary mode; and (3) that increasing practice with certain graphemes, as reflected by age, leads to greater constancy under progression. Subjects were asked first to produce a specific grapheme repeatedly in an overlapping (stationary) mode, and then, following a signal, to continue the repeated pattern in a rightward moving (progressive) mode as in cursive handwriting. Three different graphemes were used and the subjects were from four age groups (age 7, 9, 11 and adults). The dependent variables were changes in the spatial, temporal, and force characteristics of the writing movement as a function of changing over from the stationary to the progressive mode. In general, the data confirm the hypotheses to the extent that the operation of superimposed progression force must be rejected. The discussion pays specific attention to the remaining possibility of the execution of motor programs whose execution under the progression mode could involve local compensation for a steady rightward force.

The Elementary Units of Programming in Handwriting

Publisher Summary posited by Sternberg, Knoll, Monsell, and Wright to be a stress group in speech production and a key stroke in typing. This chapter presents a series of experiments that attempts to create conditions so that the effects upon RT and duration per unit may be observed in simple handwriting tasks. To encourage motor programming, well-trained subjects were required to perform simple handwriting sequences in a very short time. The writing sequences chosen for the experiments were patterns of repetitive up-and-down strokes so that these short units may form production units of a motor program. Results suggested that the main distinction of writing production was that the more or less orthogonal movement components involved in the writing process limited the speed of writing movements. The experimental results also suggested that either the down stroke or the unidirectional stroke was the more likely production unit, thereby indicating the possibility that the actual units varied according to the form of the writing output.

Response characteristics of prepared and restructured handwriting

Abstract Handwriting responses were investigated under advance planning and movement restructuring conditions to examine if individual stroke characteristics were affected when a handwriting response had to be restructured prior to initiation. A movement priming paradigm was employed that created a strong bias for the execution of one handwriting pattern compared to that of another through expectancy manipulations. Two experiments are reported which contrasted the production of a well-prepared handwriting pattern to that of an unprepared version of the same pattern. In Experiment 1, subjects prepared and executed writing patterns that were spatially and temporally different, while in Experiment 2, the preparation was spatially identical, but required a change in the force-time relationship. Reaction time and the movement execution characteristics (i.e., duration, maximum velocity, and length per stroke) were determined and compared. The data revealed that most of the advance planning benefits were localized in initiation processes with some evidence for “on line” programming. As the ratios between writing strokes were well preserved, comparisons of writing size as a function of preparation generally supported space-time invariance.

Motor Programming and Temporal Patterns in Handwriting

Over the past decade there has been considerable interest in the process by which motor commands pass from some abstract representation in the brain to a functional code at the muscular leveI.l4 The term most frequently used in conjunction with this aspect of movement specification is that of a motor program. Henry and Rogers’ and Keele4 purported the motor program to be a specification of parameters of action such as force, velocity, duration, and sequencing of the involved muscles. Over the years this idea has changed so that today a motor program is thought of as an abstract non-muscle-specific representation of motor acts. Recently, an increasing number of studies have investigated motor programs in complex motor tasks, such as the production of words,’.’ type~riting,’.’~ and piano playing: in an attempt to describe the characteristics of these programs. Handwriting, involving the coordination of orthogonal muscle systems of the forearm, hand, and fingers, with intricate timing relationships, is another skill that is proving to be useful for studying the nature of motor programming. As described from a motor control perspective, handwriting can be viewed as the production of flexion and extension movements of the thumb, index, middle, and ring fingers, and abduction and adduction of the hand around the wrist joint. For the most part, vertical strokes of letters are produced by thumb-finger flexions and extensions, and horizontal strokes are produced by hand abduction and adductions. A steady rotation about the shoulder produces left-to-right progression. Despite the rich theoretical motor control aspects of handwiting, most research until recently has concentrated on handwriting characteristics and pathologic abnormalities.”~’* However, the widely quoted description of the handwriting simulated by Hollerbach,’’ the expanding research effort from the Psychological Laboratory at the University of Nijmegen,l4-I6 and the time-space constancy data by Viviani and Terzuolo” have all increased interest in handwriting as a skill for gaining insight into the representation of complex actions and the structure and organization of motor commands.