1,721,397 research outputs found
Kijk eens diep met je ogen
Full text linkDe bal misslaan tijdens de tennisles, de puck niet kunnen raken tijdens het uurtje hockey, een schitterende vangbal verkwanselen, de auto niet geparkeerd krijgen. Onhandig, gebrek aan coördinatie, luidt dikwijls het verdict. Maar soms is er ook iets anders aan de hand, of beter, aan de ogen. Bij elke beweging die we uitvoeren, gebruiken we immers informatie die via de ogen binnenkomt om de actie mee te controleren en bij te sturen. Zo blijkt dieptezicht een belangrijke rol te spelen in vele balsporten, maar helpt het evenzeer om blik- en andere schade in het verkeer te vermijden.status: Publishe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Learning and instruction in physical education and sport:focus on tactical versus skill-based approaches for teachinginvasion games
No full textAdvance knowledge effects on hand movements and postural adjustments in catching
No full textThe skill of catching has drawn attention to motor control researchers because reaching out and grasping a ball has very fine spatiotemporal requirements. These actions precisely illustrate the human visuomotor system’s capacities of closely coupling visual information of the environment (an approaching ball) to one’s own movement (reaching the hand towards the ball and closing the fingers at time). However, the role of advance knowledge as a non-instantaneously available information source that might influence arm and hand kinematics, has been often overlooked when studying the control of such visually guided interceptive actions. Therefore, the present thesis covers some original research experiments investigating the effect of advance knowledge. Additionally, it was questioned how advance knowledge could have an effect on the postural adjustments that accompany a catching action.
Research: Four studies were conducted with good ball catchers. From a standing position, they were required to catch tennis balls while task conditions were either varied from trial-to-trial or repeated several times. Movement execution was registered to enable a three-dimensional analysis of arm and hand kinematics.
In the first study, it was shown that implicit advance knowledge of ball speed, gathered through the repetition of trials in blocks of the same ball speed, had an effect on hand movements. With advance knowledge, the initial hand movement was more scaled to ball speed than when catching in a random situation with unknown ball speed. Although expectancy of the upcoming ball speed is proposed to yield these functional differences, an alternative explanation suggests that the observed differences can be explained as a consequence of trial-by-trial history in which the movement is prepared based on the preceding trials without much cognitive involvement.
In a second study, this trial-by-trial history effect was minimized during a catching task during which a visual occlusion could emerge. In one condition, explicit advance knowledge of occlusion (no, early or late) was provided before each trial, in the other condition no such information was given. Again, differences in arm and hand kinematics were observed that can be attributed to expectations of occlusion. Such explicit advance knowledge resulted in an adapted wrist transport and increased grasping time, while a higher maximal wrist velocity allowed to overcome the uncertainty of unexpected occlusions.
A next step was to test whether advance knowledge would also influence the postural adjustments for catching and how this was integrated with the movement kinematics. Because detailed information on the particular mechanism of postural control during catching was lacking, postural adjustments when raising the arm for catching were first compared to a well-documented arm raising task in reaction to the appearance of the ball. It was shown that different postural adjustments are imminent between the two tasks: an ankle strategy in accordance with an inverted pendulum mechanism for catching and an additional counter-rotating mechanism at hip level for reaction-time arm raising.
In a final study, the findings of more scaled arm kinematics when advance knowledge of ball speed is available were confirmed. Also, it was shown that this advance knowledge additionally permits a smaller postural response when catching at high ball speed.
Conclusions: The reported research findings confirm the influence of advance knowledge on movement behaviour during interceptive actions. Although advance knowledge did not increase catching performance in skilled participants, the associated adaptations, depending on the advance knowledge context, underscore its importance. Theoretically, these advance knowledge effects imply some cognitive representation which is hard to reconcile with a strict ecological perspective that minimizes any cognitive mediation. Conversely, a computational approach conceptualizes advance knowledge as an optimizing prior in the constitution of a complete representation of task and environment. The observed effects of advance knowledge might not permit a judgement call on both perspectives, nevertheless they emphasize a certain cognitive involvement, whether it be full-blown or not, guiding visuomotor behaviour. From a practical point of view, the current findings warn researchers to acknowledge the influence of advance knowledge in the design of experiments and advice practitioners to account for these effects in sports and daily-life environments
- …
