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Biomedical subjects

G P van Galen

Publications and source records attributed to G P van Galen.

12 recordsLinked to original sources
PubMed2003

Distraction affects the performance of obstacle avoidance during walking.

In this study, dual-task interference in obstacle-avoidance tasks during human walking was examined. Ten healthy young adults participated in the experiment. While they were walking on a treadmill, an obstacle suddenly fell on the treadmill in front of their left leg during either midswing, early stance, or late stance of the ipsilateral leg. Participants were instructed to avoid the obstacle, both as a single task and while they were concurrently performing a cognitive secondary task (dual task). Rates of failure, avoidance strategy, and a number of kinematic parameters were studied under both task conditions. When only a short response time was available, rates of failure on the avoidance task were larger during the dual task than during the single task. Smaller crossing swing velocities were found during the dual task as compared with those observed in the single task. The difference in crossing swing velocities was attributable to increased stiffness of the crossing swing limb. The results of the present study indicated that divided attention affects young and healthy individuals' obstacle-avoidance performance during walking.

Adult↗
PubMed2001

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 children's 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.

Achievement↗
PubMed2000

Error, stress and the role of neuromotor noise in space oriented behaviour.

In this article both movement errors and successful movements are considered to be the product of varying ratios of muscle force signals and the composite of neuromotor noise in which the force signal is embedded. Based on earlier work we derived four propositions, which together form a theoretical framework for understanding the incidence of error in conditions of time pressure and mental load. These propositions are: (1) motor behaviour is an inherently stochastic and therefore noisy process; (2) biophysical, biomechanical and psychological factors all contribute to the level of neuromotor noise in a movement signal; (3) endpoint variability of movement is related to the signal-to-noise ratio of the forces which drive the moving limb to the target; and (4) optimal signal-to-noise ratios in motor output can be arrived at by adjusting limb stiffness. In an experiment with a graphical aiming task in which subjects made pen movements to targets varying in width and distance, we tested the prediction that time pressure and dual task load would influence error rates and movement noisiness, together resulting in biomechanical adaptations of pen pressure. The latter is seen as a manifestation of a biomechanical filtering strategy to cope with increased neuromotor noise levels. The results confirmed that especially under time pressure error rates and movement noise were enhanced, while pen pressure was higher in both conditions of stress.

Adolescent↗
PubMed1998

Axial pen force increases with processing demands in handwriting.

In two experiments, during handwriting movements, the on-line visual feedback of either slant (Experiment 1) or size (Experiment 2) was transformed to study the time course and biomechanics of the participants' compensations for these distortions. Fluency, movement time, and axial pen force were measured. According to our theory, changing the scaling factor of slant or size is equivalent to a processing demand that is reflected in deteriorated signal-to-noise ratios (SNRs) in the neuromotor system. At the behavioral level, deteriorated SNRs will result in less fluent writing, which can be compensated by applying a biomechanical noise-filtering strategy of increased limb stiffness. This strategy will lead to increased axial pen force, and, with higher degrees of difficulty, to a loss of movement speed. Results revealed decrements in writing fluency together with increments in axial pen force and increments in movement time when compensations to the feedback transformations coincided with the more difficult task conditions. These findings contrast with the traditional resource theory (Kahneman, 1973) in which chronometric measures alone indicate increased processing demands.

Biomechanical Phenomena↗
PubMed1998

Neuromotor control in handwriting and drawing: introduction and overview.

In this introduction to the Special Issue on Neuromotor Control in Handwriting and Drawing, an overview is given of the themes and sub-themes covered by these proceedings of the eighth Biennial Conference of the International Graphonomics Society (IGS) on handwriting and other graphic tasks, held in Genoa, Italy, 24-28 August, 1997. Section overviews are given for Neuromuscular and Biophysical Models; Learning and Cognitive Models; and Neuropsychological Issues. Moreover, to guide researchers in the field, this introduction also provides a summary list of major publications following the preceding IGS conferences.

Art↗
PubMed1997

Exploration of surface-textures in congenitally blind infants.

The haptic exploratory procedures that eight congenitally blind infants aged 8-24 months used to explore a gradient surface texture were investigated. Exploration of the gradient texture was examined over five sessions with 2 weeks between sessions, followed after 1 week by a sixth session, in which exploration of the gradient texture was compared to exploration of two other textures. Results showed that the infants have a wide range of exploratory strategies available and that the older infants can use these strategies in a specific manner. Results are discussed with reference to current ideas about the exploratory possibilities of congenitally blind infants. Use of texture in the stimulation of exploration of blind infants is discussed.

Blindness↗
PubMed1993

Neuromotor noise and poor handwriting in children.

In this article Power Spectral Density Analysis of the velocity profile of handwriting tasks is applied to estimate movement noise in poor and proficient writers. It is hypothesized that poor writers are less effective in the inhibition of neuromotor noise. Evidence for this theory is found in an analysis of electronically sampled handwriting movements of 48 children from grade 2, 3 and 4 (mean ages 8, 9 and 10, resp.). Twenty-four were poor and 24 were good writers, as judged by their teachers. Subjects were matched on age, sex, handedness and educational level. They performed handwriting tasks consisting of simple garlands and arcades, or meaningless words built from the letters 'e', 'n' and 'm'. In the tasks stroke accuracy, size and rotational direction were systematically varied. The results reveal that movement times were not different between the two groups, but poor writers and good writers used different movement strategies. Movements of the less proficient children were larger and were produced with higher movement velocities. Power Spectral Density Analysis disclosed that handwriting movements of poor writers were substantially more noisy than those of proficient writers, with a consistent peaking of the noise energy in that region of the spectrum which is representative for neuromotor tremor. Also, poor writers were less successful in adapting the level of noise to increased accuracy demands of the tasks. The results support the view that deviant biomechanical strategies might be responsible for deficient motor performance.

Child↗
PubMed1993

Phonological and orthographic demands in the production of handwriting.

In an experimental handwriting task, with two parts, we varied the phonological and orthographic complexity of visually presented nonwords. Twelve adult subjects had to write these nonwords in shorthand as well as in Latin script. Phonological complexity was varied by presenting a nonword which included two identical vowel characters. These were either phonologically similar (simple condition) or phonologically different (complex condition). Orthographic complexity was varied by using nonwords which either have a graphemic format for shorthand that corresponds with the graphemic format that is applied for Latin script (simple condition) or a graphemic format for shorthand which is discrepant from the Latin script format (complex condition). It appeared that a higher degree of phonological and orthographic complexity led to a slower and less fluent performance in graphemes that preceded the actual locus of complexity of the nonword. Furthermore, complexity effects were by far the strongest under the production of shorthand. The results are interpreted from the point of view of a psychomotor theory of handwriting, which assumes that the spelling process of visually presented nonwords may follow a phonological or an orthographic (sublexical) route. The finding that orthographic complexity interferes with the production of a phonologically oriented task such as shorthand is interpreted as evidence in favour of an interactive transmission of information between these two processing routes.

Adult↗
PubMed1990

Phonological and motoric demands in handwriting: evidence for discrete transmission of information.

In an experiment with handwriting tasks effects of phonological and motoric task factors upon reaction time and movement time were measured to test implications of a discrete information processing account of the task. The model is built up of serially organized stages, each of which monitors one specific type of operation, necessary to generate a message. The serial structure of the model is defined as the limitation that higher levels of the model provide their output to the next lower processor in the hierarchy, and receive their input from the next higher stage. The parallel character of the model is exemplified through the assumption that all processors are active at the same time and concurrently with the real time production of writing movements. The study adds evidence that a serial architecture of processors can be compatible with the parallel processing of a message as long as more abstract operations are prepared more in advance to real-time movements than operations lower in the hierarchy. In the experiment the prediction was tested that the time course of the manifestation of phonological and motoric task demands reflects the discrete and serial structure of the model.

Adult↗
PubMed1990

Effects of spatial and motor demands in handwriting.

Four experiments were conducted to study response programming in handwriting tasks. Twelve right-handed subjects wrote acoustically presented words and phrases, and their handwriting was digitally recorded. Changes in latency, movement time, trajectory length, and pen pressure were studied as a function of response complexity (i.e., word length, complexity of initial letter, and spacing distance). The lengthening of the spatiotemporal parameters preceding the more complex structures is interpreted to be a reflection of the effects of mental load. The results further indicate that the choice of a programming strategy is dependent on the structural complexity of the task. Writing pressure decreased as a function of increased sequence length. The findings support a hierarchical model of handwriting.

Journal Article↗
PubMed1990

Practice and the dynamics of handwriting performance: evidence for a shift of motor programming load.

Sixteen adult subjects were served in an experiment in which the writing of six unfamiliar graphemes was practiced. To investigate the learning process, we analyzed the absolute and relative changes of movement time of the first three consecutive segments as a function of practice. The results showed that movement time of all three segments decreased. This decrease was significantly less in the first segment that it was in the second and third segment, however. We interpret these effects of practice, from an information-processing viewpoint, as follows: (a) Initially separate response segments become integrated in more comprehensive response chunks, and (b) the preparation of later segments of the grapheme is realized more and more during the real-time execution of the initial segment. The results further revealed that these learning effects were more pronounced in graphemes composed of familiar segments than in graphemes that contained unfamiliar segments. Finally, it turned out that similarity between initial and final segments hindered the writing speed of the first segment; the effect of similarity was independent of the above-mentioned effects of practice. The latter effect is interpreted as confirming evidence for the view that the preparation of later segments of a grapheme is reflected by changes of movement time of the first segments of a grapheme.

Journal Article↗