Mitchell G Longstaff

A nonlinear analysis of the temporal characteristics of handwriting

Motor skills provide us with an almost infinite variety of ways in which we can interact with the world. This paper considers the problem of how the psychomotor system translates a stable motor memory into an invariant spatial output within an infinitely variable biomechanical and environmental context. Initially the validity of a novel methodology, based on the concatenation of handwriting velocity data over several trials to form long time series, combined with singular value decomposition to reduce noise, was confirmed. The data analyzed were the horizontal and vertical velocity of the stylus as eight participants wrote the pseudo-word madronal on a computer graphics tablet. Nonlinear dynamic analysis techniques such as examination of delay portraits, as well as calculation of the correlation dimension and Lyapunov spectra were applied to test the hypothesis that handwriting velocity profiles are chaotic. The findings that the largest Lyapunov exponents were positive, the sums of Lyapunov spectra components were negative and the correlation dimensions were low and fractional supported this hypothesis. We conclude by proposing that the psychomotor actions found in handwriting are a product of a chaotic dynamic process whose initial conditions depend on the environmental and biomechanical context.

Discrete and dynamic scaling of the size of continuous graphic movements of parkinsonian patients and elderly controls

Objectives: To systematically investigate the ability of Parkinson’s disease patients to discretely and dynamically scale the size of continuous movements and to assess the impact of movement size on outcome variability. Methods: Ten patients with Parkinson’s disease (mean age 72 years) were compared with 12 healthy elderly controls (mean age 70 years). The subjects wrote with a stylus on a graphics tablet. In experiment 1 they drew circles, matching the size of five target circles ranging in magnitude from a radius of 0.5 cm up to 2.5 cm. In experiment 2 they drew spirals with a radius of at least 2 cm. In both experiments the drawings were initially performed as accurately as possible then as fast and accurately as possible. Results: In both experiments the patients and controls drew at a similar speed. The within trial variability of the pen trajectory was greater for patients than controls, and increased disproportionately with the size of the movement. When the emphasis was on size rather than variability (circles), the patients’ drawing movements were the same size as controls. When the emphasis was on accuracy of pen trajectory (that is, minimum variability) rather than size (spirals), the patients’ drawing movements were smaller than controls. Conclusions: The movements made by Parkinson’s disease patients are hypometric partly as an adaptive strategy used to reduce movement variability. This strategy is used primarily when the requirement to make accurate movements outweighs the need to make large movements.

Movement precues in planning and execution of aiming movements in Parkinson's disease

Two experiments tested how changing a planned movement affects movement initiation and execution in idiopathic Parkinsons disease (PD) patients. In Experiment 1, PD patients, elderly controls, and young adults performed discrete aiming movements to one of two targets on a digitizer. A precue (80% valid cue and 20% invalid cue of all trials) reflecting the subsequent movement direction was presented prior to the imperative stimulus. All groups produced slower reaction times (RTs) to the invalid precue condition. Only the subgroup of patients with slowest movement time showed a significant prolongation of movement for the invalid condition. This suggests that, in the most impaired patients, modifying a planned action also affects movement execution. In Experiment 2, two-segment aiming movements were used to increase the demand on movement planning. PD patients and elderly controls underwent the two precue conditions (80% valid, 20% invalid). Patients exhibited longer RTs than the controls. RT was similarly increased for the invalid condition in both groups. The patients, however, exhibited longer movement times, lower peak velocities, and higher normalized jerk scores of the first segment in the invalid condition compared to the valid condition. Conversely, the controls showed no difference between the valid and invalid cue conditions. Thus, PD patients demonstrated substantially pronounced movement slowness and variability when required to change a planned action. The results from both experiments suggest that modifying a planned action may continue beyond the initiation phase into the execution phase in PD patients.

Detecting nonlinearity in psychological data: Techniques and applications

Modern graphical and computational techniques for detecting nonlinearity in psychological data sets are presented. These procedures allow researchers to determine the information complexity of temporal data, using physiological and psychological measurements, and to provide evidence for chaos in time series contaminated by measurement noise. Problems with noise reduction and appropriate experimental control, using surrogate time series, are discussed, and applications of the technology are illustrated, using response time, handwriting, and typing data sets. In an experimental application of appropriate nonlinear analysis procedures, the results of a time series prediction experiment confirm that some subjects are sensitive to chaos. In contrast to previous attempts demonstrating sensitivity to chaos, the experiment reported here employs surrogate series to control for linear stochastic aspects of the stimulus sequences, such as autocorrelation. Recommendations for the selection of appropriate software for performing nonlinear analyses are presented, including a comprehensive list of World-Wide Web sites offering such software.

Writing, Reading, and Listening Differentially Overload Working Memory Performance Across the Serial Position Curve.

Previous research has assumed that writing is a cognitively complex task, but has not determined if writing overloads Working Memory more than reading and listening. To investigate this, participants completed three recall tasks. These were reading lists of words before recalling them, hearing lists of words before recalling them, and hearing lists of words and writing them as they heard them, then recalling them. The experiment involved serial recall of lists of 6 words. The hypothesis that fewer words would be recalled overall when writing was supported. Post-hoc analysis revealed the same pattern of results at individual serial positions (1 to 3). However, there was no difference between the three conditions at serial position 4, or between listening and writing at positions 5 and 6 which were both greater than recall in the reading condition. This suggests writing overloads working memory more than reading and listening, particularly in the early serial positions. The results show that writing interferes with working memory processes and so is not recommended when the goal is to immediately recall information.

Investigating the lower level demands of writing: handwriting movements interfere with immediate verbal serial recall

ABSTRACT The research identifies if handwriting captures attention for significant periods, resulting in a decline in working memory performance. Additionally, the experiments isolate whether the movements produced during handwriting contribute to that interference. To do this, verbal serial recall was compared between three different tasks − a listening task; a listening + handwriting task (i.e., motor and verbal demands); and a listening + handwriting-like drawing task (i.e., motor demands), in two experiments. Results showed that verbal serial recall was worse in the handwriting and drawing conditions compared to the listening condition. The handwriting and drawing conditions did not differ. In a third experiment, handwriting fluency was compared between a recall and no-recall task. This showed that handwriting fluency remains stable despite the addition of a verbal working memory task. In conclusion, the handwriting movements capture attention for significant periods, with little deterioration in recall due to the verbal component of handwriting.

Fine motor movements while drawing during the encoding phase of a serial verbal recall task reduce working memory performance

The time-based resource-sharing (TBRS) model of working memory indicates that secondary tasks that capture attention for relatively long periods can result in the interference of working memory processing and maintenance. The current study investigates if discrete and continuous movements have differing effects on a concurrent, verbal serial recall task. In the listening condition, participants were asked to recall spoken words presented in lists of six. In the drawing conditions, participants performed the same task while producing discrete (star) or continuous (circle) movements. As hypothesised, participants recalled more words overall in the listening condition compared to the combined drawing conditions. The prediction that the continuous movement condition would reduce recall compared to listening was also supported. Fine-grained analysis at each serial position revealed significantly more words were recalled at mid serial positions in the listening condition, with worst recall for the continuous condition at position 5 compared to the listening and discrete conditions. Kinematic analysis showed that participants increased the size and speed of the continuous movements resulting in a similar duration and number of strokes for each condition. The duration of brief pauses in the discrete condition was associated with the number of words recalled. The results indicate that fine motor movements reduced working memory performance; however, it was not merely performing a movement but the type of the movement that determined how resources were diverted. In the context of the TBRS, continuous movements could be capturing attention for longer periods relative to discrete movements, reducing verbal serial recall.