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All forms of locomotion are repetitive motor activities that require coordinated bilateral activation of muscles. The executive elements of locomotor control are networks of spinal neurons that determine gait pattern through the sequential activation of motor-neuron pools on either side of the body axis (1-4). However, little is known about the constraints that link left-right coordination to locomotor speed. Recent advances have indicated that both excitatory and inhibitory commissural neurons maybe involved in left-right coordination (5-7). But the neural underpinnings of this, and a possible causal link between these different groups of commissural neurons and left-right alternation, are lacking. Here we show, using intersectional mouse genetics, that ablation of a group of transcriptionally defined commissural neurons--the V0 population--leads to a quadrupedal hopping at all frequencies of locomotion. The selective ablation of inhibitory V0 neurons leads to a lack of left-right pattern at low frequencies, mixed coordination at medium frequencies, and alternation at high locomotor frequencies. When ablation is targeted to excitatory V0 neurons, left-right alternation is present at low frequencies, and hopping is restricted to medium and high locomotor frequencies. Therefore, the intrinsic logic of the central control of locomotion incorporates a modular organization, with two subgroups of V0 neurons required for the existence of left-right alternating modes at different speeds of locomotion. The two molecularly distinct sets of commissural neurons may constrain species-related naturally occurring frequency-dependent coordination and be involved in the evolution of different gaits., V0 neurons, characterized by the early expression of the transcription factor Dbx1 (refs 8, 9), represent a major class of commissural neurons in the ventral spinal cord, where the locomotor [...]

This study investigated the validity of Fitts' index of difficulty as a measure of task difficulty perceived by the performer. Eight subjects performed self-terminated horizontal elbow-extension movements toward targets of three indices of difficulty in two task conditions. In the target-size condition, triceps and biceps activities during acceleration and deceleration respectively decreased with increasing index of difficulty, resulting in a lower peak velocity and longer movement time. In the movement amplitude condition, however, triceps activity after movement onset and biceps activity during deceleration increased with increasing index of difficulty, resulting in a higher peak velocity. The movement time also increased as a function of the index of difficulty given increase in the distance traveled by the limb. These results suggest that Fitts' index of difficulty may not reflect the difficulty of task performance because its effect on the pattern of motor output is dependent upon the task variable manipulated in measuring the index of difficulty.

Fisher's well-known continuous method for combining independent probability values from continuous distributions is compared with an exact discrete analog of Fisher's continuous method for combining independent probability values from discrete distributions using matched-pairs t-test data. Fisher's continuous method is shown to be inadequate for combining probability values from many discrete distributions, given the continuity assumption when discrete distributions are considered. Although Fisher's continuous method does not detect a well documented effect among distributions, the exact discrete analog method clearly detects the effect.

Motor skill assessment should be a vital part of any physical education curriculum. Getting students excited about practicing motor skills and assisting them in performing correctly should be goals of [...]

The finger-tapping test is a neuropsychological test that assesses motor speed and motor control. The purpose of this study was to obtain normative data for a computerised finger-tapping instrument and [...]

This study tested 29 young Taiwanese men and 31 young Taiwanese women to examine the effects of pulling type (one handed and two-handed) and height (48 cm, 84 cm, 120 cm, and 156 cm) on maximum horizontal isometric pulling strengths. Analysis showed differences in pulling strength between one-handed and two-handed efforts were surprisingly small for free pulling postures. The pulling strength decreased significantly with pulling height. The highest pulling strength was approximately two to three fold the lowest pulling strength across the four pulling heights. The women's pulling strength was approximately 59% to 67% of men's pulling strength. The test-retest correlations for pulling strength were satisfactory. The correlations between pulling strength and subjects' anthropometry were not sufficiently high to justify the prediction of strength. Most correlations between strengths in any two different pulling conditions were high and significant.

Inhibition of return (IOR) occurs when people are slower to detect a target that appeared at a previously cued location. Prior research has shown that younger and older adults display similar amounts of IOR, but this research has not examined the time course of the process. Because elderly people may be slower to engage or disengage spatially based attention, the present experiment examined age differences in IOR at stimulus-onset asynchronies ranging from 50 ms to 3,000 ms. The results show that the peak magnitude of IOR was similar for younger and older adults, but the onset of IOR occurred approximately 300 ms later in elderly persons. Older adults also showed a greater degree of facilitation at shorter stimulus-onset asynchronies. The results suggest that there is a change in the temporal dynamics of inhibition that occurs with age.

The purpose of this study was to make a preliminary evaluation of the test-retest reliability of the Groningen Functional Capacity Test, a test developed to assess the functional capacity of people with a chronic disease and/or physical handicap and participating in a recreational sports stimulation program called SCALA, as a way to create homogeneous sport groups. The test includes motor actions typical for the SCALA sports program and has eight subtests, reaching, balancing, ball-catching, picking up objects, ball-kicking, ball-throwing accuracy, tennis, and walking. The subjects were 52 adults aged 46-71 years, randomly selected from the SCALA project. Intraclass correlations ranged from .96 to .58. Two subtests showed significant improvements on retest for walking (total sample and men) and picking up (total sample, men, and women). For most subtests, test-retest reliability was satisfactory and therefore worth being implemented in the SCALA program.

The purpose of this study was to examine the test-retest reliability of the Eurofit motor fitness tests performed by university students. A total of 98 undergraduate students who were enrolled in physical education departments in Greece participated (29 men aged 19.5 [+ or -] 2.7 hr. and 66 women aged 19.4 [+ or -] 2.7 yr.). All Eurofit motor fitness tests and anthropometric measurements were obtained twice with one week between the two measurements. Intraclass correlation coefficient indicated satisfactory coefficients above .70 for most tests. The only exception was the plate-tapping test, which yielded a low value (R = .57). Further, the majority of the Eurofit test battery fitted well within the 95% confidence interval, and only three Eurofit motor fitness test items (flamingo balance, plate tapping, and sit-ups) presented a confidence limit below the value of .70. These findings indicated that the Eurofit test battery yielded reliable data for undergraduate students. However, modifications should be considered to improve the reliability of certain test items, for application to undergraduates.

ABSTRACT. In recent experiments (Q. Lai, C. H. Shea, & M. Little, 2000; C. H. Shea, G. Wulf, J. Park, & B. Gaunt, 2001), auditory models were found to be [...]

ABSTRACT. In rapid limb oscillations, bursts of muscle activity occur during certain phases of the movement. The authors examined phase stabilization in rapid oscillations of the index finger in a [...]

ABSTRACT. Although effector independence is predicted in a number of theoretical perspectives, it has received only moderate empirical support. The authors conducted 3 experiments to determine the extent to which [...]

ABSTRACT. 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 [...]

ABSTRACT. In the present study, the authors explored the effect of manipulating the distance between footfalls (pace length) in level walking in 3 men. The translational kinetic energy to gravitational [...]

ABSTRACT. The problem of constancy of perception over variations in sensory input applies as much to proprioception as it does to vision and audition. The authors conducted an experiment in [...]

ABSTRACT. In models of sensorimotor synchronization, it is generally assumed that phase correction occurs in response to information about sensorimotor asynchrony or relative phase. Without such feedback, a phase perturbation [...]

ABSTRACT. The authors investigated how precues about the location of an upcoming target are used by the sensorimotor system to reduce manual reaction time. In 4 experiments, participants (N = [...]

What mechanisms underlie the flexible formation, adaptation, synchronization, and dissolution of large-scale neural assemblies from the [10.sup.10] densely interconnected, continuously active neurons of the human brain? Nonlinear dynamics provides a unifying perspective on self-organization. It shows that the emergence of patterns in open, nonequilibrium systems is governed by their stability in response to small disturbances and predicts macroscopic transitions between patterns of differing stability. Here, we directly demonstrate that such transitions can be elicited in the human brain by interference at the neural level. As a probe, we used a classic motor coordination paradigm exhibiting well described movement states of differing stability. Functional neuro-imaging identified premotor (PMA) and supplementary motor (SMA) cortices as having neural activity linked to the degree of behavioral instability. These regions then were transiently disturbed with graded transcranial magnetic stimulation, which caused sustained and macroscopic behavioral transitions from the less stable out-of-phase to the stable in-phase movement, whereas the stable pattern could not be affected. Moreover, the strength of the disturbance needed (a measure of neural stability) was linked to the degree of behavioral stability, demonstrating the applicability of nonlinear system theory as a powerful predictor of the dynamical repertoire of the human brain.

People's activities vary dynamically from moment to moment, and analysis of level of skill complexity in successive activities provides a tool to portray and analyze variation as skills are learned. Systematic examination of these variations is crucial for illuminating the dynamic nature of learning and development- the ways that people construct activities under the influence of multiple factors interacting in complex ways, in context, over time. A study of adults learning to use a computer program illustrates three important patterns in the dynamic variation of adult cognitive microdevelopment: (1) each person's performance levels vary within a range between upper and lower attractor during dynamic construction of a skill. (2) Performance moves through different pathways from a novice pattern to a transitional pattern characterized by scalloping (repeated building up and collapse of complex performance) to an expert pattern. Social scaffolding plays an important role in moving a learner toward the upper attractor. (3) Each person functions at diverse levels depending on demands of the task, domain, background, scaffolding, and capacity and thus shows asynchrony in level, not simple consistency. Tasks and situations attract specific skill levels that are often below people's highest capacities.

This field study investigated the effect of retaking identical selection tests on subsequent test scores of 4,726 candidates for law enforcement positions. For both cognitive ability and oral communication ability selection tests, candidates produced significant score increases between the 1st and 2nd and the 2nd and 3rd test administrations. Furthermore, the repeat testing relationships with posthire training performance and turnover were examined in a sample of 1,515 candidates eventually selected into the organization. As predicted from persistence and continuance commitment rationales, the number of tests necessary to gain entry into the organization was positively associated with training performance and negatively associated with turnover probability.

ABSTRACT. Two experiments were conducted in which participants (N = 12, Experiment 1; N = 12, Experiment 2) performed rapid aiming movements with and without visual feedback under blocked, random, [...]

The purpose of this study was to examine the contributions of 3 predictor variables (age, sex, and body mass index) to performance of 7 fundamental movement skills (locomotor; run, gallop, hop, leap, jump, skip, and slide) and 4 fitness tasks (grip strength, step test, sit and reach, and timed sit-ups) by 65 children in Grades K-2 (M=6 yr.). A multiple regression analysis indicated that running, leaping, and skipping improved with age. No sex differences were observed on any of the seven skills. In terms of the four fitness tasks, age was positively associated with timed sit-ups and grip strength and inversely associated with step-test performance. Sex was associated with step-test and sit and reach performance (girls performed better on both). Finally, body mass index was related to increased grip strength and fewer timed sit-ups.

Our goal is to develop a direct brain interface (DBI) that will provide communication and environmental control to persons who are 'locked-in' (or nearly so) as a consequence of brainstem stroke, amyotrophic lateral sclerosis (ALS), or other etiologies. Previously we demonstrated that templates constructed from trigger averaged event-related potentials (ERPs) can be cross-correlated with ongoing electrocorticograms (ECoGs) to detect ERPs associated with the performance of simple motor actions. However, it was difficult to predict a priori which of many candidate ECoG recording site(s) could provide signals that would provide adequate motor action detection. We present here a measure of ERP quality based on an estimate of the signal to noise ratio (SNR) associated with the formation of an ERP template from the performance of consecutive voluntary actions. Detection-theory-based receiver operator characteristics (ROCs) and a database of ECoGs (6000+) recorded from the cortical surface of awake human subjects were used to assess the usefulness of the SNR technique. The SNR method was found to predict the detection efficacy of ERPs when characterized over a wide parameter range, with the majority of ROC curve areas greater than 90%. This method was compared with our previously developed quality measure (the peak-to-baseline ratio) and found to provide significantly better performance (ROC area differences from 4.4% to 13.7%). Thus, the SNR estimate of the ERP is a useful tool to predict the efficacy of ERP templates for cross-correlation-based detection and assist in the selection of viable ERP templates for DBI applications. Index Terms--Assistive technology, brain-computer interface (BCI), detection, direct brain interface, electrocorticogram (ECoG), event-related potential (ERP), signal-to-noise ratio.

A subgroup classification of handedness, ordered for degrees of relative hand skill, was linearly related to the probability of nonright preference for foot and eye in a volunteer sample of 263 people from the general public. Percentages of people with a nonright-handed parent also differed over groups as expected but not significantly.

This article explores the relationship between the development of interhemispheric communication and age-related bimanual coordination. The authors, conducting two experiments on children between the ages of 5-10 years old and 3-7 years old, conclude that improved interhemispheric communication has a positive influence on the progress of bimanual coordination.

The authors examine the development of serial reaction in test groups consisting of children from 4- to -10 years-old and 7- to -10 years-old. Topics include explicit and implicit motor skills, learning skills and, serial reaction time.

The goal of the present research programme was to find out how common driver fatigue is among New Zealand truck drivers and the degree to which they suffer from fatigue-related [...]

The relationship between attention, performance, and motor difficulty versus cognitive difficulty of a task has been examined in a series of experiments. Motor difficulty is associated with enhanced attention and performance, while greater cognitive difficulty slows response time and decreases accuracy.

Research indicates that expansion velocity, or looming, is the optical variable an individual uses to begin and guide body movement in hitting a ball, rather than the variable of rate of change of optical expansion. Tests involved seated subjects, whose elbow joint angles were observed for flexion initiation in striking a dropped ball.

We studied spatial stimulus response compatibility in the somatosensory modality by instructing 16 men and 16 women to press a key using the left or the right thumb in response to a nonnoxious electric stimulation delivered either to the left or to the right little finger or, in different blocks, to the left or to the right malleolar region. The task was performed in compatible (stimulus and key-response on the same side of the corporeal midline) and in incompatible conditions (stimulus and key-response on opposite sides of the corporeal midline). In Exp. 1 subjects were tested while keeping their limbs in anatomic position; in Exp. 2 subjects performed the task while keeping the left upper and lower limbs on the right side and the right limbs on the left side of the bodily midline (crossed position). The compatibility effect was observed in both experiments and was higher for stimuli delivered to the little finger than to the malleolar region. This suggests that the cost of inhibiting compatible responses is maximal when stimulated and responding body parts are contiguous. Moreover, in the spatially most demanding task (Exp. 2) men outperformed women for both speed and accuracy suggesting a sex-related specialisation in the spatial processing of somatosensory information.

This study evaluated norms for fine motor dexterity skills on elementary school children of ages 5 through 10 and conducted reliability and validity studies utilizing the Nine-hole Peg Test. The sample included 826 students in 10 elementary schools. Moderately high test-retest reliability (rs = .81 and .79) and high interrater agreement (rs > .99) were obtained. Older students had shorter completion time that measured fine motor dexterity than younger students. Significant sex differences were found in completion time, but only for the dominant hand. Correlations of - .80 and -.74 between the scores on the Nine-hole Peg Test and Purdue Pegboard Test at all tested ages indicated adequate concurrent validity of the measures and a significant difference in test scores between regular and special education groups provided further evidence of construct validity. The findings supported the Nine-hole Peg Test as an effective screening tool for fine motor dexterity of school-age children.