G.P. van Galen

Fine motor deficiencies in children diagnosed as DCD based on poor grapho-motor ability

A sample of 125 children from grades 4 and 5 of two normal Dutch primary schools were investigated regarding the incidence of handwriting problems and other fine motor disabilities. Handwriting quality was assessed with the concise assessment method for childrens handwriting (BHK) and the school questionnaire for teachers (SQT). Two groups of 12 children each were formed, one group of good writers and a group of poor writers selected from the lower performance range. The latter group was investigated in depth by assessing general and fine motor ability using the Movement Assessment Battery for Children (M-ABC test) and the Motor Performance School Readiness Test (MSRT). We hypothesised that poor handwriting is part of a wider neuromotor condition characterised by faster and cruder movements, lack of inhibition of co-movements and poor co-ordination of fine motor skills. To test the theory kinematic measures of drawing movements were collected on the flower-trail-drawing item of the M-ABC test. Moreover, the experimental group of poor writers received physiotherapy during a three-month period and was tested for handwriting proficiency after therapy and again nine months later. The results revealed that 34% of the group of 125 children displayed handwriting problems. The analysis confirmed that serious handwriting problems are accompanied by fine motor deficits. We suggest that in these children an enhanced level of neuromotor noise is compensated for by enhanced phasic stiffness of the limb system. This results in higher movement velocity and fewer velocity peaks. In the children who received physiotherapy the quality of handwriting improved.

Stress, neuromotor noise, and human performance: A theoretical perspective

A new theory on stress and human performance is proposed in which physical and cognitive stressors enhance the level of neuromotor noise in the information-processing system. The neuromotor noise propagates in time and space. A 2nd assumption states that such noise facilitates easy tasks but disrupts complex tasks. In 4 experiments, 2 graphic tasks (number writing and graphic aiming) were crossed with 2 stressors (cognitive stress from a dual-task situation and physical stress in the form of loud auditory noise). Reaction time (RT), movement time (MT), and axial pen pressure were measured. In the RT phase, stress was predicted to lead to decreased RT with easy tasks and to increased RT with difficult tasks. In the execution phase, biomechanical adaptation to enhanced levels of noise was expected to manifest in higher levels of limb stiffness. In all 4 experiments, an increase of axial pen pressure with higher levels of stress evidenced the generality of biomechanical adaptation as a response to stress. RT and MT showed differential effects among the 4 experiments.

Effects of motor programming on the power spectral density function of finger and wrist movements

Power spectral density analysis was applied to the frequency content of the acceleration signal of pen movements in line drawing. The relative power in frequency bands between 1 and 32 Hz was measured as a function of motoric and anatomic task demands. Results showed a decrease of power at the lower frequencies (1-4 Hz) of the spectrum and an increase in the middle (9-12 Hz), with increasing motor demands. These findings evidence the inhibition of visual control and the disinhibition of physiological tremor under conditions of increased programming demands. Adductive movements displayed less power than abductive movements in the lower end of the spectrum, with a simultaneous increase at the higher frequencies. The relevance of the method for the measurement of neuromotor noise as a possible origin of delays in motor behavior is discussed.

Decreased movement speed in girls with Turner syndrome: A problem in motor planning or muscle initiation?

In three experiments with graphical tasks we examined whether the decreased movement speed in girls with Turner Syndrome (TS) is caused either by a diminished planning capacity or by more peripheral motor execution problems. Fourteen girls with TS and 14 matched controls (mean age 11.6 years) participated. Task difficulty addressed the muscle-initiation, size-control, and shape-programming level (Van Galen, 1991). The influence of task difficulty on accuracy, velocity, velocity profile and dwell time was analyzed and confirmed that girls with TS do not plan and program their movements differently from normals. We conclude that the decreased movement speed in TS is caused by problems at the muscle initiation level.

COORDINATION OF MULTI-JOINT MOVEMENTS: AN INTRODUCTION TO EMERGING VIEWS

In this introductory paper, an overview is provided of the topics addressed in this special issue. These topics center around what is often referred to as Bernsteins problem. The first two topics both offer partial solutions to the indeterminacy problem. The first by identification of constraints acting on the neuro-musculo-skeletal system, in its interaction with the environment; the second by expanding the number of variables that are to be controlled. Regarding the first, it is argued that a distinction should be made between holonomic and nonholonomic constraints. Regarding the second, the necessity of independent control of in particular stiffness is a recurrent theme. The third and fourth topics concern choices to be made when modelling motor behavior. In particular, the level of detail at which the neuro-musculo-skeletal system is to be modelled in studies of coordination, and the merits of descriptive models offered by nonlinear dynamics are discussed. Apart from refining our models of the nervous system, the models of which are currently identified as a weak link, a major challenge for the coming years is concluded to lie in linking neuro-musculo-skeletal models to the behavioral models generated by nonlinear dynamics.

Emotionally charged earcons reveal affective congruency effects.

In the present study, the affective impact of earcons on stimulus classification is investigated. We show, using a picture–categorization task, that the affective connotation of earcons in major and minor mode (representing positive and negative valence, respectively) can be congruent or incongruent with response valence. Twenty participants classified pictures of animals and instruments in 256 trials, using positive and negative Yes or No responses. Together with the pictures, either a chord in major mode or minor mode was played. The affective valence of the chords either did or did not match the valence of responses. Response–time latencies show congruency effects of the matching and non–matching sound and response valences, indicating that it is important to carefully investigate human–computer interfaces for potential affective–congruency effects, as these can either facilitate or inhibit user performance.

Stimulus-response compatibility and affective computing: A review

Affective computing, a human-factors effort to investigate the merits of emotions while people are working with human–computer interfaces, is gaining momentum. Measures to quantify affect (or its influences) range from EEG, to measurements of autonomic nervous system responses (e.g., heart rate, blood pressure), to less objective self-reports. Here we claim that simple response-time measurements may be a viable alternative to measure (indirectly) the effects of affect on performance by providing a review of experimental paradigms and associated models of human information processing. In particular, we focus on stimulus–response compatibility paradigms that have provided important insights for human-factors research, for instance regarding the important role of the spatial layout of interface design on the efficiency of human task performance, to show that these paradigms can also be applied to investigate the role of affect in human–computer interaction.