Sex differences in lateralisation of fine manual skills in children.

One hundred and twelve children (55 boys and 57 girls) were tested using two tasks taken from the Movement Assessment Battery for Children. The girls had a larger between-hands asymmetry than boys on the threading nuts on bolt task, thus indicating they were more lateralised. On the other task, placing pegs, no such sex differences were found. We present our findings as a warning to others that even though two tasks are assumed to measure the same, in this case unimanual performance, differences in task constraints will exist. Such differences may constitute a confounding factor when trying to infer about lateralisation based on behavioural tasks.

Spatial and temporal constraints on performance in children with movement co-ordination problems.

Eight 10-year-old children manifesting movement co-ordination problems (MCP), as assessed by the Movement Assessment Battery for Children (MABC), and a matched control group of eight children of a similar age without such problems, were required to carry out a laboratory ball-catching task. The task was constrained in such a way as to allow separate kinematic analyses of reaching (Experiment 1) and grasping (Experiment 2) subactions. Significant differences between the groups, in favour of the control group, were found with respect to both spatial and temporal performance in intercepting the moving ball. The MCP children were shown to initiate reaching movements later and to initiate grasping movement of the fingers earlier in time than the controls. MCP children also made more spatial errors. These findings are discussed in the context of the distinction made in the neuropsychological literature between proximal and distal motor control systems and the visual perceptual system.

Hand preference in children with developmental coordination disorders: cause and effect?

Inter- and intra-modal matching by eight-year-old children diagnosed as having hand-eye coordination problems (HECP) and categorized as left-handed, together with a left-handed control group of children without such problems, were tested using a manual sensory matching task. The task required the children to locate target pins, visually (seen target), proprioceptively (felt target) or in combination (felt and seen target), while matching to the located target was always carried out without vision. Performance was superior when the target was located visually or visually/proprioceptively for both groups of children. These results question the conclusion that intra-modal will always be more accurate than inter-modal matching. When the combined scores for both hands were analyzed, the HECP children showed inferior performance to the control children in both inter- and intra-modal matching. Separate right and left hand analyses, demonstrated that the differences between the HECP group and control children could be accounted for by lowered performances when the right hand (nonpreferred) was used to match the located target position. Putative neurological disorders related to the development of the hemisphere controlling the nonpreferred hand (left hemisphere) are invoked to account for the poor performance with the nonpreferred hand of the HECP children.

Dynamics of hand preference in 4 year-old children.

Hand preference in groups of 4 year-old children towards either end of the skill continuum (as determined by the Movement ABC test) was explored by means of a catching task in which the 'direction of approach of the ball' was used as a control parameter within a dynamical systems framework. In Condition 1, the ball direction was systematically scaled in degrees from the right side of the subject to the left and vice versa. In Condition 2, the spatial location of the ball direction was varied randomly, rather than systematically, over the same range as for Condition 1. In both conditions, the two groups of children were shown to switch between hands (from left to right and vice versa) at well-defined positions on the scale. The different scale values obtained when ball direction was scaled from left to right compared with right to left were used to define hysteresis areas. These areas were more extensive and located more to the left of the midline for the group towards the less skilled end of the continuum than for those towards the more skilled end. Additionally, the less-skilled children were shown to use the right hand more to catch the balls delivered to the left side than did the more skilled children. In Condition 3, objects were placed on the table of the ball-delivery apparatus in order to make the catching action more complicated. The less skilled group were shown to use the right hand more than the left hand in all catching positions whereas the more skilled group showed an equal usage of both catching regimes.

The application of co-ordination dynamics to the analysis of discrete movements using table-tennis as a paradigm skill.

The purpose of this experiment was to explore the application of co-ordination dynamics to the analysis of discrete rather than cyclical movements. Subjects, standing in a fixed position, were required to return table-tennis balls delivered to different spatial locations in the direction of a fixed target. This was achieved in condition 1 by systematically scaling, from left to right and vice versa, the 'spatial location' of the ball-identified as a control parameter. In condition 2, the control condition, the spatial location was varied randomly over the same range. The changes between regimes of the stroke co-ordination pattern, defined at two different levels, (1) organisational--forehand or backhand drive. and (2) kinematic-the distance of the bat at ball-bat contact relative to the leading edge of the table, were identified as collective variables, the values of which changed spontaneously at the transition points exposed by the control parameter. The switch between regimes was shown to be dependent upon the direction of scaling, i.e. a hysteresis effect was identified in both conditions. These findings confirm that the conceptual and methodological frameworks of co-ordination dynamics can be applied, appropriately, to the analysis of discrete movements. Moreover, it would seem that control parameter values (spatial location of the ball) do not necessarily have to be scaled in a systematic way in order to produce the required effects.

The efficient learner.

The research to be reported examines the concept of efficiency, defined as the relation of metabolic energy expended to mechanical work done. The development of movement coordination was investigated in the context of the hypothesis that an increase in coordination would be accompanied by a parallel reduction in overall energy expenditure, relative to the increase in energy expenditure demanded by improvements in work output. The task involved learning to make cyclical, slalom-like, ski movements on a ski apparatus. Development of coordination was indexed by changes in the timing of forcing while on-line measurements of oxygen consumption were used as indices of energy expenditure. Six female volunteers served as subjects in nine training sessions. The change in the coordination pattern, between the subject and the apparatus, as indexed by the development of the phase lag, was paralleled by an improvement in efficiency. It was concluded that learning the skill used in this study involves a search by the system for perception-action couplings (phase relations in the present study) that require minimal energy expenditure.

Differential contributions of the two hemispheres in intra-modal proprioceptive sensory matching in 7-10-year-old boys.

This study explores putative differential contributions of the two hemispheres when 7-10-year-old right-hand and left-hand preferent boys are required to carry out a 'foot-hand' target location and matching task. The task required subjects to locate a target pin with the big-toe (felt target), and match the located target position with the hand, without vision. Right-handed (n=25) and left-handed (n=22) boys were tested in a four-condition design. Two intra-hemispheric conditions (right foot locating-right hand matching, left foot locating-left hand matching), and two inter-hemispheric conditions (right foot locating-left hand matching, left foot locating-right hand matching) were used. When the criterion for handedness was writing hand only the results were found to be confounded by the large number of subjects with indeterminate handedness (isolated by use of the Edinburgh Handedness Inventory) originally assigned to the left-handed group. Reclassification of the handedness groups, on the basis of this inventory, showed the pure-left handers to be as good on those conditions mediated by the right hemisphere as pure right handers were with those conditions mediated by the left. These findings are discussed with respect to the contention that left handers are not just 'reversed' right handers.

Development of proprioceptive sensitivity.

The development of proprioceptive sensitivity was studied in 140 children between the ages of 5.8 and 11.8 years using a so-called foot-hand task. Ten boys and ten girls were included in each age group. The task required the children to locate a target pin with the "big toe" (felt target) and match the located target position with the hand, without vision. There were four conditions: location of targets by the right big toe: matching located target position with the right hand (RfRh) and left hand (RfLh); and location of targets by the left big toe: matching located target position with the left hand (LfLh) and right hand (LfRh). The results showed a significant developmental trend in proprioceptive sensitivity, when the absolute error scores for boys and girls were combined, with most of the improvement occurring between the ages of 5.8 and 7.8 years. The most interesting and novel finding seems to be the significant two-way interaction between age and sex--the clearest differences manifesting themselves in the age group 9.9 years. Separate within-sex group analyses showed the trend to be determined by the results for the girls, the trend being absent in the results for the boys. Furthermore only the boys showed a significant difference between the intra- and inter-hemispheric conditions. We propose that these differences may only manifest themselves in particular tasks, i.e. there may be a sex-task interaction. The implications of this proposal for theoretical interpretations of the phenomenon of inter-hemispheric processing as well as possible sources of the task differences are briefly discussed.

Proximal versus distal control in proprioceptively guided movements of motor-impaired children.

Two groups of 7-year-old children diagnosed as motor-impaired (N = 6) or as controls (N = 6) were required to perform a task that involved locating targets under a table-top with one hand while attempting to match the position of the target with the other, on the table-top (intra-modal matching), always without visual control. The experimental design involved three different conditions: proximal control (P), distal control (D) or both (PD). Target distance errors were analysed in terms of absolute (AE) and variable error. When the scores for each hand were combined, the motor-impaired group showed inferior mean performance (AE scores) on all three conditions as compared with the control children and were also more variable in their behaviour. Analyses of scores achieved with the right and the left hand separately, however, demonstrated that the difference could largely be attributed to the scores obtained when matching with the right hand in conditions P and PD, and matching with the left hand in condition D. Possible explanations of these findings are discussed in the context of 'delay' (developmental lag) and/or 'deviancy' (neurological lesion/disconnection).

'Putting your foot in it'! A window into clumsy behaviour.

Intra-modal matching by 7-year-old children diagnosed as having hand-eye co-ordination problems (HECP) and a control group of children without such problems was tested using a target location and matching task. The 'foot-hand' task required the children to locate a target pin with the 'big-toe' (felt target) and match the located target position with the hand, without vision. There were four conditions: location via right foot-matching the located target with the right hand (RfRh) and left hand (RfLh) and location via left foot-matching the located target with the left hand (LfLh) and right hand (LfRh). Both groups demonstrated better performance in the intra- as compared to the inter-hemispheric conditions, suggesting that the corpus callosum is not yet fully mature at this age. The HECP children showed inferior performance to the control children in three of the four conditions, the conditions where the right hemisphere was involved and/or information had to be transported across the corpus callosum (RfLh; LfLh; LfRh). Two possible explanations of these findings are put forward and discussed: right hemisphere insufficiency with or without dysfunctional corpus callosum.

We can cure your child's clumsiness! A review of intervention methods.

Intervention procedures for treatment of clumsiness have come in many guises. We have looked at some of the most powerful methods put forward in the past 30 years--Perceptual-motor training (PMT), Sensory Integration Therapy (SIT), and some promising new approaches. Both the PMT and the SIT have been heavily criticised. It is hard to find support for the idea that the programmes improve academic skills or that they have more than a limited effect on perceptual-motor development as claimed. The more recently introduced Kinaesthetic training is shown to have an effect on general motor competence but that this may be better explained in terms of the general principles on which this training procedure lies rather than the influence on Kinaesthesis per se. Since other recent studies have also shown a dependence on similar general principles, it might be asked whether it is the teacher rather than the programmes that accounts for the differences shown between different intervention programmes.

Inter- and intra-sensory modality matching in children with hand-eye co-ordination problems.

Inter- and intra-sensory modality matching by 8-year-old children diagnosed as having hand-eye co-ordination problems (HECP) and by a control group of children without such problems were tested using a target-location and pointing task. The task required the children to locate target pins visually (seen target), with the hand (felt target) or in combination (felt and seen target), while pointing to the located target was always carried out without vision. The most striking finding, for both the control and the HECP children, was the superiority of performance when the target had to be located visually. When combined scores for both hands were analysed, the HECP children showed inferior performance to the control children in both inter- and intra-modal matching. Analyses of the scores achieved with the preferred and non-preferred hand separately, however, demonstrated that the differences between the HECP and the control children could, in the main, be attributed to lowered performances when the non-preferred hand was used for pointing to the target. When pointing with the preferred hand, the only significant difference between the groups was when the target was visually located, the control children showing superior performance. Pointing with the non-preferred hand gave rise to significant differences, in favour of the control children, when the target was located visually, with the hand or in combination. These findings suggest that earlier studies, using only the preferred hand or a combination of the scores of both hands, might need to be qualified. Putative neurological disorders in the HECP children are invoked to account for the poor performance with the non-preferred hand.

Inter- and intrasensory modality matching in children with hand-eye coordination problems: exploring the developmental lag hypothesis.

This study set out to explore the suggestion that the problems experienced by 8-year-old children diagnosed as clumsy in the area of hand-eye coordination (HECP) might be attributed to a developmental lag. The performances of this group of HECP children were compared with those of groups of 5-year-old and 8-year-old controls without such deficits, when required to carry out a task involving pointing, without vision, to targets located, visually, visually/proprioceptively, or proprioceptively, the dependent variable being the distance error score from the centre of the target. The performances of the HECP children, when vision or vision/proprioception was used to locate the targets, were shown to be inferior to those of the two control groups of children thereby supporting a visual deficit hypothesis. When the targets had to be located proprioceptively, the performance of the HECP children was shown to be similar to that of the 5-year-olds, while both groups were inferior to the 8-year-olds, thereby supporting a developmental lag hypothesis in proprioceptive terms. However, when the scores for the preferred and non-preferred hands were analysed separately a marked deterioration in the performances of both the 5-year-old controls and the HECP children was observed while the 8-year-old controls were unaffected. While this finding supports a developmental lag explanation of the inferior performances of the HECP children, it was necessary to qualify such an explanation when the within-group performances using the preferred and non-preferred hands were compared. Only the HECP children, under the visual/proprioceptive or proprioceptive conditions, showed significant performance differences, in favour of the preferred hand. This finding was taken as a suggestion that the developmental lag exhibited by the HECP children might have pathological overtones possibly related to the development of the corpus callosum.

The spatiotemporal structure of control variables during catching.

The discrepancy between traditional (force scaling models) and the more recently conceived dynamic explanations of load compensation (lambda model) was the departure point for the present study. By using the complex "open" motor skill of catching a ball--rather than the traditional "closed" skills--under "normal" (baseline) conditions and under conditions where a spring load was applied to the catching hand (thereby changing the dynamics of the skeletomuscular system) it was hoped to provide further clarification of this issue. Traditional force scaling models, in this respect, would predict that maximal closing velocity of the grasp action, and movement time would not be significantly different between a control and a spring-load condition. In contrast, a dynamic system perspective would maintain that spring loading would be compensated for by a change in the rate of shift of the reciprocal command (R-command). The obtained results showed a significant difference for conditions with regard to the maximal closing velocity of the grasp action, the baseline condition being higher than the two spring-load conditions. Furthermore, a significant difference was found for the aperture at moment of catch, the aperture at moment of catch being smaller in the baseline condition than that under the two spring-load conditions. With regard to the temporal variables, no significant differences were obtained. A comprehensive overall explanation of the obtained data in terms of the force scaling models was not realisable. It may be that findings supporting such theories are task specific and that for constrained tasks--such as catching a ball--different underlying organisational principles apply. The lambda model, however, could explain adequately the obtained results. It was concluded that, except for the preparatory phase associated with load compensation before the onset of the movement of the ball, the spatiotemporal structure of the control pattern underlying catching remains the same (invariant) in both baseline and load conditions. Thereby, the spatiotemporal structure of the resulting movement changes under the influence of the load and thus is not the same for load and baseline condition.

Interference between saccadic eye and goal-directed hand movements.

The aim of the present study was to investigate the nature of the interference effect when the eye is accompanied by a goal-directed hand movement rather than when the eye moves alone. Latencies of eye and hand movements in response to small and large visual target stimuli were measured while employing dual-task methodology. Experiments 1 and 2 were designed to investigate whether the interference effect is related to a specific temporal bottleneck, i.e. the eye and hand motor systems share limited available processes at a specific point in time. The findings of robust interference effects independent of the temporal organization of eye and hand contradicted this notion. The interference effect was not present in experiment 3, where response preparation and target-localization mechanisms were limited by providing subjects with advance information about target position. Experiment 4 employed randomized target positions again and highly salient stimuli, the latter only limiting target-localization processes. The absence of an interference effect adds weight to the argument that visual spatial attentional mechanisms involved in target localization constitute the locus of the interference. Neurophysiological implications of these findings are discussed.

Reaction time latencies of eye and hand movements in single- and dual-task conditions.

The goal of this study was to investigate whether ocular and hand motor systems operate independently or whether they share processes. Using dual-task methodology, reaction time (RT) latencies of saccadic eye and hand motor responses were measured. In experiment 1, the hand and eye motor systems produced rapid, aimed pointing movements to a visual target, which could occur either to the left or right of a central fixation point. Results showed that RT latencies of the eye response were slower in the dual-task condition than in the single-task condition, whereas the RT latencies of the hand response were virtually the same in both conditions. This interference effect indicated that the ocular and manual motor systems are not operating independently when initiating saccadic eye and goal-directed hand movements. Experiment 2 employed the same experimental paradigm as experiment 1, except for one important modification. Instead of a goal-directed hand movement to the target stimulus, subjects had to make a button-press response with either the index or middle finger of the right hand dependent upon whether the stimulus occurred to the right or left of the control fixation point. The aim of experiment 2 was to investigate the issue whether the observed interference effect in experiment 1 was specific or non-specific (e.g. overhead costs due to coordinating any two responses). The finding that saccadic eye movements and button-press responses in the dual-task condition could be initiated without delay relative to the single-task conditions, supports the specific interference interpretation.

The visual guidance of catching.

In order to explore the nature and amount of information in the optic array used by subjects required to carry out one-handed catching actions, the optical expansion pattern (using a deflating ball) and the duration of viewing time (using liquid crystal spectacles) of the ball were varied. Subjects were required to catch luminous balls (two of constant physical size and one of changing physical size during approach) attached to a pendulum in a totally dark room, while the liquid spectacles were closed at 0, 100, 200 or 300 ms before hand-ball contact. The results confirmed previous findings that the timing of the catching action is based on retinal expansion information and that conclusion was strengthened when an additional dependent variable (time of the maximal opening velocity of the grasp) was used. Further, for the viewing time duration manipulations, the time of the maximal closing velocity of the hand was later, while no effect was found on the time of the maximal opening velocity, when the last 300 ms of the trajectory of the ball was occluded. Adjustments to the catching action in response to the different ball sizes under the 0 ms condition differed significantly from the adjustments under the 300 ms condition. Both findings point to the importance of relative optical expansion information, available between 300 and 200 ms before ball-hand contact, in maintaining a (relatively) continuous perception-action coupling in the act of catching.

The acquisition of catching under monocular and binocular conditions.

The effects of binocular and monocular viewing on spatial and temporal errors in one-handed catching were investigated in two experiments. The first experiment-using expert catchers-recorded more spatial errors under the monocular than under the binocular condition. No significant differences in the number of temporal errors were apparent. In a second experiment, which paradigm, relatively poor catchers were trained under both vision conditions. Its objective was to investigate whether the superior results obtained under the binocular condition in the first experiment, for the number of catches and number of spatial errors, could be attributed simply to the fact that subjects had more experience with binocular than monocular viewing. The following results occurred after a period of training (a) a significant reduction in the number of spatial errors under the monocular condition, reaching a level similar to that under the binocular condition; (b) no significant reduction in the number of spatial errors when subjects transferred from monocular to binocular viewing, and significantly more spatial errors when subjects transferred from binocular to monocular viewing; and (c) a training-sequence effect. The latter effect indicates that subjects had more benefit from training in the sequence monocular-binocular than vice versa. These findings are discussed in the context of the strategies of specificity of learning and use of multisources.

A dynamical systems approach to skill acquisition.

This paper argues that the answer to the question, what has to be learned, needs to be established before the question, how is it learned, can be meaningfully addressed. Based on this conviction, some of the limitations of current and past research on skill acquisition are discussed. Motivated by the dynamical systems approach, the question of "what has to be learned" was tackled by setting up a non-linear mathematical model of the task (i.e. learning to make sideways movements on a ski apparatus). On the basis of this model, the phase lag between movements of the platform of the apparatus and the actions of the subject was isolated as an ensemble variable reflecting the timing of the subject in relation to the dynamics of the apparatus. This variable was subsequently used to study "how" the task was learned in a discovery learning experiment, in which predictions stemming from the model were tested and confirmed. Overall, these findings provided support for the hypothesis, formulated by Bernstein (1967), that one of the important effects of practice is learning to make use of reactive forces, thereby reducing the need for active muscular forces. In addition, the data from a previous learning experiment on the ski apparatus--the results of which had been equivocal--were reconsidered. The use of phase lag as a dependent variable provided a resolution of those findings. On the basis of the confirmatory testing of predictions stemming from the model and the clarification of findings from a previous experiment, it is argued that the dynamical systems approach put forward here provides a powerful method for pursuing issues in skill acquisition. Suggestions are made as to how this approach can be used to systematically pursue the questions that arise as a natural outcome of the experimental evidence presented here.

The role of predictive visual temporal information in the coordination of muscle activity in catching.

This study addresses the question as to the nature of the information on which the preactivation of the appropriate muscles in the grasping of the ball in a one-handed catching task is initiated and coordinated. High speed film and electromyograms were recorded while experiences subjects (N = 4) caught balls--projected towards them by a ball-machine at different speeds (11.9, 13.9 and 16.2 m/s--resulting in significantly different flight times of 508, 443 and 355 ms, respectively). Tau-margins (times to contact) values were calculated at the time of the initiation of the grasp movement for each subject at each speed. No significant differences were found between tau-margins at different speeds. Further, the onset of the muscle activity for the initiation of the grasp movement was shown to be independent of ball speed. These findings lend support to the contention that the initiation of the grasp movement in catching is controlled and coordinated by the optical variable tau which specifies (directly) this time-to-contact. Given that the muscle group selected includes both flexors and extensors, co-activation on the basis of tau information is evidenced.