The Organization of Multisegmental Pulls Made by Standing Humans: II. Submaximal Pulls

Previously, an autonomous oscillator model with three parameters was derived that describes the relationship between anterior-posterior center of mass motions and pulling force for near-maximal, bimanual pulls made by standing subjects (Michaels, Lee, & Pai, 1993). The present study evaluated the extent to which a full range of pulling forces could be fit by the model and how the model's three parameters changed with intended pulling force. How much variation in force each parameter could contribute was determined by simulating the model. Qualitative and quantitative analyses of pulls made by 6 well-practiced subjects at 5%, 10%, 20%, 40%, 60%, 80%, and 95% of their maximum pulling force revealed that the model holds well, except for the least forceful pulls of some subjects. Two parameters appeared to be controlled; one, related to the position of the center of pressure, varied most among less forceful pulls; the second, related to the position of the center of mass at the time of handle-force onset, varied most among more forceful pulls. How these parameters might be set is discussed.     

Postintentional Neglect

F. Mechsner (2004) seems to deny a functional importance of postintentional processes, except that their characteristics can be taken into account at the perceptual-cognitive level of control. In that perspective, processes that are critical for the understanding of motor control and its limitations are neglected. On the other hand, the functional importance of task conceptions or task sets, which can vary and affect performance even for tasks that appear identical to an observer, is emphasized.     

On the Hand Transport Component of Prehensile Movements

Jeannerod (1981) proposed that prehensile movements involve two independent visuomotor channels that are responsible for hand transport and hand aperture. In many studies, the movement of a marker placed on the wrist has been used as an index of hand transport because wrist movement is unaffected by the movements of the digits responsible for hand aperture. In the present study, the spatial paths of the wrist, index finger, and thumb of 5 adults, each performing 50 reaching movements, were measured with a WATSMART movement tracking system, and their variability was analyzed. The measures of movement variability suggest that the motor system is more concerned with thumb position than with wrist position during hand transport. Although the wrist is a technically convenient index of hand transport, the thumb may be a more appropriate index from the point of view of motor control.     

Perturbations in Action Goal Influence Bimanual Grasp Posture Planning

The authors examined the effects of perturbations in action goal on bimanual grasp posture planning. Sixteen participants simultaneously reached for 2 cylinders and placed either the left or the right end of the cylinders into targets. As soon as the participants began their reaching movements, a secondary stimulus was triggered, which indicated whether the intended action goal for the left or right hand had changed. Overall, the tendency for a single hand to select end-state comfort compliant grasp postures was higher for the nonperturbed condition compared to both the perturbed left and perturbed right conditions. Furthermore, participants were more likely to plan their movements to ensure end-state comfort for both hands during nonperturbed trials, than perturbed trials, especially object end-orientation conditions that required the adoption of at least one underhand grasp posture to satisfy bimanual end-state comfort. Results indicated that when the action goal of a single object was perturbed, participants attempted to reduce the cognitive costs associated with grasp posture replanning by maintaining the original grasp posture plan, and tolerating grasp postures that result in less controllable final postures.     

Moving memories: Behavioral synchrony and memory for self and others

Establishing and maintaining connections with others is central to a fulfilling social life. In this respect, behavioral coordination provides one avenue by which interpersonal linkages can be formed. Drawing from the dynamical systems approach, the present research explored whether temporary interpersonal connections founded on coordinated behavior influence memory for self and others. To do so, we measured participants’ incidental recall of self and other-relevant information after a period of either in-phase or anti-phase interpersonal coordination. While participants in the less stable anti-phase condition demonstrated the typical memory advantage for self-related compared to other-related information, this effect was eliminated when participant and confederate movements displayed in-phase coordination. These results are discussed with respect to the interplay between the systems that support interpersonal synchrony and basic social-cognitive processing.     

Practice Effects in Bimanual Force Control: Does Age Matter?

ABSTRACT

The authors examined age-related differences in fine motor control during a bimanual coordination task. The task required the modulation of fingertip forces in the precision grip according to a visually presented sinusoidal antiphase pattern (force range 2–12 N; frequency 0.2 Hz). Thirty-four right-handed participants of three age groups (young, early middle-aged, and late middle-aged) practiced 30 trials of the task. Accuracy and variability of relative timing and relative forces at minima and maxima of the sine wave were analyzed for hand–hand and hand–stimulus couplings and compared between age groups. Analysis showed for relative timing and force weaker hand–hand than hand–stimulus coupling as well as lower accuracy and higher variability for minima as compared to maxima. Further, we analyzed practice effects by comparing the first and last trials and characterized the course of practice by detecting the transition of a steeper to a shallower acquisition slope for the different age groups. Late middle-aged participants demonstrated poorer performance than both other groups for all parameters. All groups improved performance to a similar amount. However, an age-related difference in acquisition strategy is visible. Late middle-aged participants seemed to have focused on improvement of force amplitude, whereas young and early middle-aged focused on timing.     

Reprint of “Relationship between BMI,waist circumference,physical activity and probable developmental coordination disorder over time”

BackgroundCross-sectional studies have shown that children with developmental coordination disorder (DCD) are less likely to be physically active and have excess weight gain. However, longitudinal studies examining the relationship between DCD and measures of body composition (BMI and waist circumference) over time are lacking. It is not known if sex and physical activity affect the relationship between DCD and measures of body composition over time.Objective(1) To examine if BMI and waist circumference in children with and without probable DCD (pDCD) remain constant over time or change as children age, and whether this relationship varies by sex. (2) To examine if differences in physical activity between children with and without pDCD account for differences in BMI and waist circumference over time.MethodsPhysical Health Activity Study Team (PHAST) data were used for this longitudinal analysis. At baseline, a total of 2,278 (pDCD = 103) children aged 9–10 years were included in the analysis. The total follow-up period was five years. Mixed-effects modeling was used to estimate change in body composition measures in children over time.ResultsChildren with pDCD have higher BMI and waist circumference compared to typically developing children, and this difference increased over the study period. The relationship between pDCD and BMI over time also varied by sex. A similar trend was observed for waist circumference. Boys with pDCD were found to have a more rapid increase in BMI and waist circumference compared to girls with pDCD. Physical activity had neither a mediating nor a moderating effect on the relationship between pDCD and measures of body composition. However, physical activity was independently and negatively associated with measures of body composition.ConclusionspDCD is associated with higher body mass and waist circumference, both important risk factors for cardiovascular disease, type 2 diabetes, and psychological problems and other health conditions.     

Strength Recovery Patterns Following Isometric and Isotonic Exercise

In 3 experiments, the author tested the hypothesis that coordination dynamics is the content of a generalized motor program (GMP) for rhythmic interlimb coordination. In Experiment 1, learners (N = 14) practiced a ?90° movement with either identically timed or differently timed limbs. Both acquisition and transfer to novel (effector and pattern) timings were unaffected by the learning condition and were suggestive of the intrinsic dynamics for in-phase and antiphase. In Experiment 2, learners' (N = 13) acquisition of 2 different phase relations (?90° and ?45°) was qualitatively identical. Attractor reconstruction revealed an increase in the predictability of individual movement trajectories and a decrease in attractor dimensionality over learning. Transfer for both ?90° and ?45° was again suggestive of the intrinsic dynamics. In Experiment 3, learning altered participants' (N = 8) performance of in-phase and antiphase relations. Together, the results suggested a single continuum of phase relations, called an attractor landscape, that produces similar patterns of CE and VE for both previously stable and learned coordinations.     

The Effects of Initial Habit Strength Differences Upon Performance in a Coaction Situation

The present investigation examined the effects of initial habit strength differences upon performance in a coaction situation. During a training session, a habit-strength hierarchy was developed in each of three groups through the establishment of a differential response expectancy for each of four alternative responses. In a subsequent test session, both performance and consistency of performance were affected by the pretraining on the correct habit. However, there was no statistical support for the hypothesis that coaction would interact with the habit-strength condition resulting in an improvement in the coaction/habit-correct group and a decrement in the coaction/habit-incorrect group. Similarly, no differences were found between the coaction and alone conditions.     

Influence of Response Similarity on Interference in Perceptual Motor Learning

Motor interference was measured in terms of average response time in sorting 15 pairs of cards, each pair containing words which were either unrelated or identical but printed in different colors. The two words of each pair were used in labeling two cubicles in such a way that they were apart by 0, 1, 2, or 3 intervening cubicles in quasirandomly chosen directions. Interference was inversely related to response similarity, but this relationship may not appear in the absence of sufficient stimulus similarity. The findings are interpreted in the light of a hypothesis which views motor interference as a tendency for responses to deflect from their own courses and be pulled towards those of other responses with which they are at conflict.