Non-linear development of postural control and strategy use in young children: a longitudinal study.

This longitudinal analysis confirmed a non-monotonic pattern of postural control development in children from age 5 to 8 years suggested by previous cross-sectional studies. Postural control was considered in terms of control strategy and its variability operationalized by mean and standard deviation of center of pressure (COP) velocity; and of effectiveness and its variability operationalized by mean and standard deviation of COP anteroposterior (a-p) excursion. Periods of significant variability were used to indicate behavioral transitions. Seventeen healthy children (nine males, eight females) aged 5-6 years (61.5-75 months) were tested at 3- to 4-month intervals up to age 8 years (83-97 months) in eyes-open quiet stance on a force platform for 30 s in each of ten trials. Data were reorganized into six developmental categories based on adjacent test dates prior to (-1) and after (+1, +2, +3, +4) a subject's trial with the lowest COP velocity (0). Developmental category is proposed to represent level of sensorimotor integrative skill. Within-subject ANCOVAs revealed a significant effect (P<0.0001) for developmental category with covariance due to height, weight and actual age removed. Post hoc tests showed a significant effect (P<0.0001) on measures of strategy. However, differences in COP velocity (type of strategy used) and differences in its variability (denoting a transition between strategies) were not always coincident. Performance outcome (COP a-p excursion) changed near linearly across categories. It was concluded that a non-monotonic change in control strategy as indicated by COP velocity describes the development of quiet stance equilibrium. A transition occurs from a primarily open-loop to incorporation of open- and closed-loop components of control. Honing of strategy used precedes and follows transitions. Constriction of velocity and excursion may typify the early stages of bimodal strategy. Developmental categories describe affiliation with the strategy employed and may represent differentiable levels of sensorimotor integrative skill. They may be more useful in assessing progression of equilibrium control than consecutive age in years.

The utilization of visual information in the control of reciprocal aiming movements.

Two experiments examined on-line processing during the execution of reciprocal aiming movements. In Experiment 1, participants used a stylus to make movements between two targets of equal size. Three vision conditions were used: full vision, vision during flight and vision only on contact with the target. Participants had significantly longer movement times and spent more time in contact with the targets when vision was available only on contact with the target. Additionally, the proportion of time to peak velocity revealed that movement trajectories became more symmetric when vision was not available during flight. The data indicate that participants used vision not only to 'home-in' on the current target, but also to prepare subsequent movements. In Experiment 2, liquid crystal goggles provided a single visual sample every 40 ms of a 500 ms duty cycle. Of interest was how participants timed their reciprocal aiming to take advantage of these brief visual samples. Although across participants no particular portion of the movement trajectory was favored, individual performers did time their movements consistently with the onset and offset of vision. Once again, performance and kinematic data indicated that movement segments were not independent of each other.

The roles of talent, physical precocity and practice in the development of soccer expertise.

Here we consider the potential contributions of talent, physical precocity and deliberate practice in the development of soccer expertise. After presenting a working definition of 'talent', we examine how coaches perceive and select potential talent. Our findings suggest that much of what coaches see as early talent may be explained by physical precocity associated with a relative age advantage. Finally, as a test of the model of Deliberate Practice, we review the results of studies that assessed the progress of international, national and provincial players based on accumulated practice, amount of practice per week and relative importance and demands of various practice and everyday activities. A positive linear relationship was found between accumulated individual plus team practice and skill. Various practical suggestions can be made to improve talent detection and selection and to optimize career practice patterns in soccer.

Coupling of eye, finger, elbow, and shoulder movements during manual aiming.

Temporal and spatial coupling of point of gaze (PG) and movements of the finger, elbow, and shoulder during a speeded aiming task were examined. Ten participants completed 40-cm aiming movements with the right arm, in a situation that allowed free movement of the eyes, head, arm, and trunk. On the majority of trials, a large initial saccade undershot the target slightly, and 1 or more smaller corrective saccades brought the eyes to the target position. The finger, elbow, and shoulder exhibited a similar pattern of undershooting their final positions, followed by small corrective movements. Eye movements usually preceded limb movements, and the eyes always arrived at the target well in advance of the finger. There was a clear temporal coupling between primary saccade completion and peak acceleration of the finger, elbow, and shoulder. The initiation of limb-segment movement usually occurred in a proximal-to-distal pattern. Increased variability in elbow and shoulder position as the movement progressed may have served to reduce variability in finger position. The spatial-temporal coupling of PG with the 3 limb segments was optimal for the pick up of visual information about the position of the finger and the target late in the movement.

Manual asymmetries and saccadic eye movements in right-handers during single and reciprocal aiming movements.

Two experiments examined the coordination of eye and hand movements in right-handed subjects who completed single (Experiment 1) and reciprocal (Experiment 2) aiming movements with each hand. In both experiments eye movements preceded hand movement, and arrived well in advance of the hand to allow pickup of visual information about relative position of the hand and target to correct te ongoing movement. With reciprocal aiming differences emerged between the hands. A right hand advantage was found for movement execution, and a left hand advantage for movement initiation. Manual asymmetries were not due to practice differences between hands. Subjects made larger initial saccades and more corrective saccades when aiming with the left hand. The pattern of eye-hand coordination was consistent with Woodworth's (1899) two component model of limb control, and at odds with models of limb control which suggest that online visual pickup is of minor importance.

Developing a standardized test for the assessment of suturing skill in novice microsurgeons.

Suturing performance was assessed for 13 novice microsurgeons throughout a 4-5 day microsurgical training course. Time to complete a suture (from needle insertion to completion of tie-off) was assessed on a standardized suture task, for two sutures at the beginning and end of each training day. For days 2-4, suturing performance with actual tissue was also assessed at both the beginning and end of each day. An average learning curve for suturing performance on the standardized test was developed and demonstrated huge performance improvement. A consistent and significant relationship existed between trainees' performance on the standardized suturing test and suturing of actual tissue. Thus the standardized test appears both to reflect actual suturing performance and to be sensitive to improvements in suturing skill that result from practice.

Temporal and spatial coupling of point of gaze and hand movements in aiming.

Temporal and spatial coordination of both point of gaze (PG) and hand kinematics in a speeded aiming task toward an eccentrically positioned visual target were examined with the Optotrak 3D movement analysis system in tandem with the ASL head-mounted eye tracker. Subjects (N = 10) moved eyes, head, hand, and trunk freely. On the majority of trials, the PG pattern was a large initial saccade that undershot the target slightly, then 1 or more smaller corrective saccades to reach the target. The hand exhibited a similar pattern of first undershooting the target and then making small corrective movements. Previously (W. F. Helsen, J. L. Starkes, & M. J. Buekers, 1997), the ratio of PG and total hand response time (50%) was found to be an invariant feature of the movement. In line with those results, a striking temporal coupling was found between completion of the primary eye saccade and time to peak acceleration for the limb. Spatially, peak hand velocity coincided with completion of 50% of total movement distance. Those findings support a 2-component model of limb control.

Visual fixation and postural sway in children.

Adults are able to use a visual target to reduce quiet-standing postural sway (Lee & Lishman, 1975). The present study was designed to determine whether children, under varying postural conditions, are also able to use a visual target to reduce postural sway. A second purpose was to determine the ability of children to visually fixate under different postural conditions. An inability to visually fixate may limit the usefulness of a visual target. The results indicate that, like adults, children are able to reduce sway in the presence of a visual target. Young children are less able than older children and adults to visually fixate. In addition, children show more spontaneous visual saccades in the no-target condition than in the target condition and more saccades in the Romberg stance than in a feet-together stance. The fact that saccades decrease with increasing age, even in the seated, head-stabilized condition, precludes the possibility that increased instability of the young children is the only cause of increased number of saccades.

Performance of the vertical position in synchronized swimming as a function of skill, proprioceptive and visual feedback.

This experiment assessed the efficacy of proprioceptive and visual information for the performance of "vertical position" by synchronized swimmers. Three skill groups of 5 senior, 5 intermediate, and 5 novice synchronized swimmers performed 40 vertical positions under four conditions. The conditions were: self-initiated with and without vision, and following experimenter perturbation, with and without vision. The dependent measure was degrees of error from true vertical. Analysis indicated that either proprioception or proprioception and vision may be used in performing vertical positions. A significant main effect was found among skill groups.

Attention demands of spatially locating position of a ball in flight.

This study assessed the relative attention demands of an "open skill", that of spatially locating position of a ball in flight, using the dual task technique. 7 right-handed male university students stood behind a large Plexiglas screen and spatially matched a ball projected over a distance of 20 feet. After 1-sec. flight time the ball contacted the Plexiglas. A secondary task required response to an auditory stimulus, designed to probe ball flight at 700, 800, or 900 msec. Both vocal and manual responses to the secondary probe were recorded. No significant correlations were noted between radial error and probe RT for either manual or vocal responses. Subjects did not trade off between tasks. Radial error across all probe positions, including catch trials, showed no significant differences. Three factor analyses of variance for manual and vocal probe types showed that more attention was devoted to monitoring the ball as it neared the screen.

The attention demands of movements.

The probe technique has been employed extensively to measure the attention demands of movement control. Inherent in any RT paradigm is the potential confounding effect of anticipation. Experiment 1 studied this problem by varying probe frequency (or, conversely, catch-trial frequency) for three independent groups of subjects performing the same movement. Probe frequencies of one-third and two-thirds produced V-shaped curves of probe RT plotted against probe position within the movement, while a three-thirds condition was described by a negatively sloped linear function. Because of the different shaped curves it was recommended that a two-thirds frequency be adopted by all researchers in this area. Experiments 2 and 3 looked at the effects of movement length and movement time on the attention demands of movement. Shorter (11-cm) movements were more attention demanding in the middle of the movement than the longer (50-cm) movements, but movement time had no effect.