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Advance knowledge effects on hand movements and postural adjustments in catching

Pieter Tijtgat UGent (2012)
abstract
The 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.
Please use this url to cite or link to this publication:
author
promoter
UGent
organization
year
type
dissertation (monograph)
subject
keyword
Advance knowledge, Postural adjustments, Ball catching
pages
207 pages
publisher
Ghent University. Faculty of Medicine and Health Sciences
place of publication
Ghent, Belgium
defense location
Gent : Aula Universiteit (Academieraadzaal)
defense date
2012-06-19 17:30
ISBN
9789461970527
language
English
UGent publication?
yes
classification
D1
additional info
dissertation consists of copyrighted material
copyright statement
I have transferred the copyright for this publication to the publisher
id
2957296
handle
http://hdl.handle.net/1854/LU-2957296
date created
2012-07-06 13:56:44
date last changed
2012-07-09 08:51:18
@phdthesis{2957296,
  abstract     = {The 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{\textquoteright}s capacities of closely coupling visual information of the environment (an approaching ball) to one{\textquoteright}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.},
  author       = {Tijtgat, Pieter},
  isbn         = {9789461970527},
  keyword      = {Advance knowledge,Postural adjustments,Ball catching},
  language     = {eng},
  pages        = {207},
  publisher    = {Ghent University. Faculty of Medicine and Health Sciences},
  school       = {Ghent University},
  title        = {Advance knowledge effects on hand movements and postural adjustments in catching},
  year         = {2012},
}

Chicago
Tijtgat, Pieter. 2012. “Advance Knowledge Effects on Hand Movements and Postural Adjustments in Catching”. Ghent, Belgium: Ghent University. Faculty of Medicine and Health Sciences.
APA
Tijtgat, P. (2012). Advance knowledge effects on hand movements and postural adjustments in catching. Ghent University. Faculty of Medicine and Health Sciences, Ghent, Belgium.
Vancouver
1.
Tijtgat P. Advance knowledge effects on hand movements and postural adjustments in catching. [Ghent, Belgium]: Ghent University. Faculty of Medicine and Health Sciences; 2012.
MLA
Tijtgat, Pieter. “Advance Knowledge Effects on Hand Movements and Postural Adjustments in Catching.” 2012 : n. pag. Print.