A Note on the Conscious Controls of Motor Units by Children Under Six

A simple form of training the conscious control of motor units in skeletal muscle has been demonstrated in a series of children under age 6. Easy boredom is the chief deterrent in the very young. So long as a child understands and cooperates, he can learn to isolate single units in a period of about 30 min.     

Visual and Kinesthetic Components of Pursuit-Tracking Performance

Ss (N=75) were trained on a pursuit rotor for 10 trials with ambient illumination from a strobe light flashing at frequencies of either 2, 5, 10, 15, or 20/sec. A transfer trial followed, with a strobe flashing frequency of 10/sec for all Ss. Results supported hypotheses derived from Adams’ (1971) closed-loop theory of motor learning that (a) performance would improve during training as a function of amount of visual feedback available, and that (b) if after training visual feedback was reduced, performance would be maintained to the extent that reliance upon kinesthetic feedback had been learned as an alternate compensatory feedback loop.     

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.     

Dissociation of Bimanual Responses With the Simon Effect: On the Nonunitization of Bimanual Responses

The authors examined whether responses of the 2 hands were completely unitized when participants (N = 36) produced bimanual responses to lateralized targets in a Simon-type paradigm. Their primary aim was to investigate whether lateralized stimuli differentially influence the response dynamics of the 2 hands. Simon effects were obtained in reaction time and force; components of the bimanual response by the hand on the same side as the lateralized stimulus were more forceful than were those of the other hand. Also, Simon effects were larger when the lateralized target appeared alone than when it was accompanied by a distractor on the other side of the display. Finally, responses of the 2 hands were correlated most strongly when stimulus displays were symmetrical. The authors conclude that bimanual responses are strongly coupled, but not perfectly so.     

Changes in children’s perception-action tuning over short time scales: Bicycling across traffic-filled intersections in a virtual environment

This investigation examined short-term changes in child and adult cyclists’ gap decisions and movement timing in response to general and specific road-crossing experiences. Children (10- and 12-year-olds) and adults rode a bicycle through a virtual environment with 12 intersections. Participants faced continuous cross traffic and waited for gaps they judged were adequate for crossing. In the control condition, participants encountered randomly ordered gaps ranging from 1.5 to 5.0 s at all intersections. In the high-density condition, participants encountered high-density intersections sandwiched between sets of control intersections. These high-density intersections were designed to push participants toward taking tighter gaps. Participants in both conditions were more likely to accept 3.5-, 4.0-, 4.5-, and 5.0-s gaps at the last set of intersections than at the first set of intersections, whereas participants in the high-density condition were also more likely to accept very tight 3.0-s gaps at the last intersections than at the first intersections. Moreover, individuals in the high-density condition who waited less and took shorter gaps at the middle intersections were also more likely to take very tight 3.0-s gaps at the last intersections. The 10-year-olds in both conditions had more time to spare when they cleared the path of the oncoming car at the last intersections, whereas the 12-year-olds and adults showed no change in time to spare across intersections. The discussion focuses on linking short-term change in perceptual-motor functioning to longer term perceptual-motor development.     

Information–movement coupling in developing cricketers under changing ecological practice constraints

Changing informational constraints of practice, such as when using ball projection machines, has been shown to significantly affect movement coordination of skilled cricketers. To date, there has been no similar research on movement responses of developing batters, an important issue since ball projection machines are used heavily in cricket development programmes. Timing and coordination of young cricketers (n = 12, age = 15.6 ± 0.7 years) were analyzed during the forward defensive and forward drive strokes when facing a bowling machine and bowler (both with a delivery velocity of 28.14 ± 0.56 m s⁻¹). Significant group performance differences were observed between the practice task constraints, with earlier initiation of the backswing, front foot movement, downswing, and front foot placement when facing the bowler compared to the bowling machine. Peak height of the backswing was higher when facing the bowler, along with a significantly larger step length. Altering the informational constraints of practice caused major changes to the information–movement couplings of developing cricketers. Data from this study were interpreted to emanate from differences in available specifying variables under the distinct practice task constraints. Considered with previous findings, results confirmed the need to ensure representative batting task constraints in practice, cautioning against an over-reliance on ball projection machines in cricket development programmes.