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Sergio L. Molina and David F. Stodden

practices of practitioners (e.g., physical educators, coaches, and other movement educators). Fitts’ law ( 1954 ) and its application, the speed-accuracy trade-off, are well-known principles that can be applied to many fundamental movements and performance ( Urbin, Stodden, Fischman, & Weimer, 2011

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Stacey L. Gorniak, Marcos Duarte, and Mark L. Latash

We explored possible effects of negative covariation among finger forces in multifinger accurate force production tasks on the classical Fitts’s speed-accuracy trade-off. Healthy subjects performed cyclic force changes between pairs of targets “as quickly and accurately as possible.” Tasks with two force amplitudes and six ratios of force amplitude to target size were performed by each of the four fingers of the right hand and four finger combinations. There was a close to linear relation between movement time and the log-transformed ratio of target amplitude to target size across all finger combinations. There was a close to linear relation between standard deviation of force amplitude and movement time. There were no differences between the performance of either of the two “radial” fingers (index and middle) and the multifinger tasks. The “ulnar” fingers (little and ring) showed higher indices of variability and longer movement times as compared with both “radial” fingers and multifinger combinations. We conclude that potential effects of the negative covariation and also of the task-sharing across a set of fingers are counterbalanced by an increase in individual finger force variability in multifinger tasks as compared with single-finger tasks. The results speak in favor of a feed-forward model of multifinger synergies. They corroborate a hypothesis that multifinger synergies are created not to improve overall accuracy, but to allow the system larger flexibility, for example to deal with unexpected perturbations and concomitant tasks.

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Elizabeth J. Bradshaw and W.A. Sparrow

The study examined adjustments to gait when positioning the foot within a narrow target area at the end of an approach or “run-up” similar to the take-off board in long jumping. In one task, participants (n = 24) sprinted toward and placed their foot within targets of four different lengths for 8-m and 12-m approach distances while “running through” the target. In a second task, participants (n = 12) sprinted toward and stopped with both feet in the target area. Infra-red timing lights were placed along the approach strip to measure movement times, with a camera positioned to view the whole approach to measure the total number of steps, and a second camera placed to view the final stride, which was analyzed using an in-house digitizing system to calculate the final stride characteristics. In the run-through task, a speed-accuracy trade-off showing a linear relationship (r = 0.976, p < .05) between target length and approach time was found for the 8-m amplitude. An accelerative sub-movement and a later targeting or “homing-in” sub-movement were found in the approach kinematics for both amplitudes. Final stride duration increased, and final stride velocity decreased with a decrease in target length.

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Marcos Duarte and Sandra M.S.F. Freitas

We investigated the speed and accuracy of fast voluntary movements performed by the whole body during standing. Adults stood on a force plate and performed rhythmic postural movements generating fore and back displacements of the center of pressure (shown as online visual feedback). We observed that for the same target distance, movement time increased with the ratio between target distance and target width, as predicted by Fitts’–type relationships. For different target distances, however, the linear regressions had different slopes. Instead, a single linear relation was observed for the effective target width versus mean movement speed. We discuss this finding as a result of the pronounced inherent variability of the postural control system and when such a source of variability is considered, the observed relationship can be explained. The results reveal that the accuracy of fast voluntary postural movements is deteriorated by the variability due to sway during standing.

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Howard N. Zelaznik

popular ( Meyer, Smith, & Wright, 1982 ) it has not been without critics ( Gentner, 1987 ; Turvey, 1977 ). For example, amodal clock-like timing is assumed in the models of Schmidt, Zelaznik, Hawkins, Frank, and Quinn ( 1979 ) and Meyer et al. ( 1982 ) for the linear speed accuracy trade-off. We began

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Janet L. Starkes and Fran Allard

Volleyball players and nonplayers were compared for speed and accuracy of performance in a task involving detection of the presence of a volleyball in rapidly presented slides of a volleyball situation. Slides depicted both game and nongame situations, and subjects performed the task in both noncompetitive and competitive conditions. For all subjects, game information was perceived more quickly and accurately than nongame information. In competition all subjects showed decreased perceptual accuracy and no change in criterion, supporting the Easterbrook (1959) notion of perceptual narrowing with stress. Very large accompanying increases in response speed, however, suggested that competition may induce adoption of a particular speed-accuracy trade-off. Cognitive flexibility in the adoption of particular speed-accuracy trade-offs is discussed with reference to volleyball.

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Andrew Chappell, Sergio L. Molina, Jonathon McKibben, and David F. Stodden

This study examined variability in kicking speed and spatial accuracy to test the impulse-variability theory prediction of an inverted-U function and the speed-accuracy trade-off. Twenty-eight 18- to 25-year-old adults kicked a playground ball at various percentages (50–100%) of their maximum speed at a wall target. Speed variability and spatial error were analyzed using repeated-measures ANOVA with built-in polynomial contrasts. Results indicated a significant inverse linear trajectory for speed variability (p < .001, η2= .345) where 50% and 60% maximum speed had significantly higher variability than the 100% condition. A significant quadratic fit was found for spatial error scores of mean radial error (p < .0001, η2 = .474) and subject-centroid radial error (p < .0001, η2 = .453). Findings suggest variability and accuracy of multijoint, ballistic skill performance may not follow the general principles of impulse-variability theory or the speed-accuracy trade-off.

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M.A. Urbin, David Stodden, Rhonda Boros, and David Shannon

The purpose of this study was to examine variability in overarm throwing velocity and spatial output error at various percentages of maximum to test the prediction of an inverted-U function as predicted by impulse-variability theory and a speed-accuracy trade-off as predicted by Fitts’ Law Thirty subjects (16 skilled, 14 unskilled) were instructed to throw a tennis ball at seven percentages of their maximum velocity (40–100%) in random order (9 trials per condition) at a target 30 feet away. Throwing velocity was measured with a radar gun and interpreted as an index of overall systemic power output. Within-subject throwing velocity variability was examined using within-subjects repeated-measures ANOVAs (7 repeated conditions) with built-in polynomial contrasts. Spatial error was analyzed using mixed model regression. Results indicated a quadratic fit with variability in throwing velocity increasing from 40% up to 60%, where it peaked, and then decreasing at each subsequent interval to maximum (p < .001, η2 = .555). There was no linear relationship between speed and accuracy. Overall, these data support the notion of an inverted-U function in overarm throwing velocity variability as both skilled and unskilled subjects approach maximum effort. However, these data do not support the notion of a speed-accuracy trade-off. The consistent demonstration of an inverted-U function associated with systemic power output variability indicates an enhanced capability to regulate aspects of force production and relative timing between segments as individuals approach maximum effort, even in a complex ballistic skill.

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Dalia Mickeviciene, Renata Rutkauskaite, Dovile Valanciene, Diana Karanauskiene, Marius Brazaitis, and Albertas Skurvydas

, one more motor control determinant becomes an important “player”: variability of motor performance. According to Harris and Wolpert ( 1998 ), minimum-variance theory accurately predicts the trajectories of movements and the speed–accuracy trade-off described by Fitts’ law. Moreover, Bertucco, Bhanpuri

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Roland van den Tillaar

affect ball velocity and accuracy. Detailed knowledge about these effects may help elucidate the underlying mechanisms of the speed–accuracy trade-off (e.g., Fitts, 1954 ). Furthermore, the findings may have practical implications regarding choosing shooting techniques in training and competition