H. T. A. Whiting

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

SummaryThis 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 onehanded 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 taumargins 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.

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.

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

Abstract 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.

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.

Sex differences in lateralisation of fine manual skills in children

Abstract.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.

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 (λ 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 skeleto-muscular 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 springload 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 λ 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.

Chapter 8 Catching:A motor learning and developmental perspective

Publisher Summary Catching has attracted considerable attention in the psychological literature from two perspectives: motor development and human performance/motor learning. Historically, motor development research has been largely descriptive in nature and directed toward developmental changes in the patterns of movement coordination with age, primarily as observed in phylogenetic skills, such as walking, running, crawling, and sucking. In contrast, motor learning research has been largely addressed either to theoretical questions using narrowly constrained laboratory tasks or, on limited occasions, ontogenetic skills—such as driving a motor vehicle, typewriting, or piloting an aircraft. This chapter sketches out a coherent research line over the past few decades—that can be categorized under the rubric human performance/motor learning. The chapter focuses on the development of catching behavior in which there is much less coherency, but a number of interesting experimental lines that provide prospects for future work.