PubMed Health⌕ Search

Biomedical subjects

A Mark Williams

Publications and source records attributed to A Mark Williams.

24 records · Page 2Linked to original sources
PubMed2002

Learning from demonstrations: the role of visual search during observational learning from video and point-light models.

In this study, we examined the visual search strategies used during observation of video and point-light display models. We also assessed the relative effectiveness of video and point-light models in facilitating the learning of task outcomes and movement patterns. Twenty-one female novice soccer players were divided equally into video, point-light display and no-model (control) groups. Participants chipped a soccer ball onto a target area from which radial and variable error scores were taken. Kinematic data were also recorded using an opto-electrical system. Both a pre- and post-test were performed, interspersed with three periods of acquisition and observation of the model. A retention test was completed 2 days after the post-test. There was a significant main effect for test period for outcome accuracy and variability, but observation of a model did not facilitate outcome-based learning. Participants observing the models acquired a global movement pattern that was closer to that of the model than the controls, although they did not acquire the local relations in the movement pattern, evidenced by joint range of motion and angle-angle plots. There were no significant differences in learning between the point-light display and video groups. The point-light display model group used a more selective visual search pattern than the video model group, while both groups became more selective with successive trials and observation periods. The results are discussed in the context of Newell's hierarchy of coordination and control and Scully and Newell's visual perception perspective.

Adult↗
PubMed2002

Visual search, anticipation and expertise in soccer goalkeepers.

We used a novel methodological approach to examine skill-based differences in anticipation and visual search behaviour during the penalty kick in soccer. Expert and novice goalkeepers were required to move a joystick in response to penalty kicks presented on film. The proportion of penalties saved was assessed, as well as the frequency and time of initiation of joystick corrections. Visual search behaviour was examined using an eye movement registration system. Expert goalkeepers were generally more accurate in predicting the direction of the penalty kick, waited longer before initiating a response and made fewer corrective movements with the joystick. The expert goalkeepers used a more efficient search strategy involving fewer fixations of longer duration to less disparate areas of the display. The novices spent longer fixating on the trunk, arms and hips, whereas the experts found the kicking leg, non-kicking leg and ball areas to be more informative, particularly as the moment of foot-ball contact approached. No differences in visual search behaviour were observed between successful and unsuccessful penalties. The results have implications for improving anticipation skill at penalty kicks.

Adult↗
PubMed2002

Age-related differences in vision and proprioception in a lower limb interceptive task: the effects of skill level and practice.

This study examined age-related differences in the role of visual proprioception during a lower limb interceptive action and how this varies as a function of skill and practice. In Experiment 1, skilled and less-skilled 8-, 10-, and 12-year-old boys controlled a soccer ball using their preferred foot under full vision and when sight of the effector was occluded. With the exception of the high-skilled 12-year-olds and low-skilled 8-year-olds, participants showed a decrement in peformance when denied access to visual proprioception. In Experiment 2, the effect of practicing under different informational constraints was examined for 12 year-old boys. Children performed varying amounts of practice under full vision, or in a condition where sight of the foot was occluded, before being transferred to the alternative viewing condition. Participants who practiced under occluded viewing conditions showed greater relative improvement in performance over practice and transfer sessions compared with a full vision control group. Some support is provided for the manipulation of visual informational constraints as an effective pedagogical approach to motor learning.

Age Factors↗
PubMedDate not supplied

Changes in coordination, control and outcome as a result of extended practice on a novel motor skill.

It has been proposed that, when learning a motor skill, individuals initially freeze degrees of freedom to simplify control. There is limited empirical evidence to support this proposition. We examined this issue by monitoring the performance of a non-skilled individual learning a soccer chip shot with his non-dominant leg over 9 days of practice (425 trials). Principal component analysis was used to examine dimensional change. The most dramatic change occurred at the hip, with the range of motion decreasing during the first 5 days of practice and then increasing thereafter. A reverse pattern was observed at the knee and ankle. While showing a progression in control from proximal to distal, a further phase was observed where primary control was passed back to the hip. The degree of linear coupling between the joints also increased with practice until day 5, after which independent control was observed. The number of controlled dimensions did not change across practice. Radial error decreased over practice and kinematics relating to the hip were most predictive of error, especially early in practice. Freezing degrees of freedom was a strategy implemented across the first half of practice, after which point-independent control was gradually restored enabling successful consistent performance.

Adult↗
PubMedDate not supplied

Anticipation and visual search behaviour in expert soccer goalkeepers.

A novel methodological approach is presented to examine the visual search behaviours employed by expert goalkeepers during simulated penalty kick situations in soccer. Expert soccer goalkeepers were classified as successful or unsuccessful based on their performance on a film-based test of anticipation skill, thereby allowing an intra-group comparison of visual search behaviour on the task. The anticipation test required participants to move a joystick in response to penalty kick situations presented on a large screen. The proportion of penalties saved was assessed as well as the frequency and time of initiation of joystick corrections. Visual search behaviour was examined using a portable eye movement registration system. The successful experts were more accurate in predicting the height and direction of the penalty kick, waited longer before initiating a response and appeared to spend longer periods of time fixating on the non-kicking leg compared with the non-successful experts.

Adult↗