EXPRESS: Visually Guided Movement with Increasing Time-on-Task: Differential Effects on Movement Preparation and Movement Execution

Top-down cognitive control seems to be sensitive to the detrimental effects of fatigue induced by time-on-task (ToT). The planning and preparation of the motor responses may be especially vulnerable to ToT. Yet, effects of ToT specific to the different phases of movements have received little attention. Therefore, in three experiments, we assessed the effect of ToT on a mouse-pointing task. In Experiment 1, there were 16 possible target positions with variable movement directions. In Experiment 2, the layout of the targets was simplified. In Experiment 3, using cuing conditions we examined whether the effects of ToT on movement preparation and execution were caused by an increased orientation deficit or decreased phasic alertness. In each experiment, initiation of movement (preparatory phase) became slower, movement execution became faster and overall response time remained constant with increasing ToT. There was, however, no significant within-person association between the preparatory and execution phases. In Experiments 1 and 2, we found a decreasing movement time/movement error ratio, suggesting a more impulsive execution of the pointing movement. In addition, ToT was also accompanied with imprecise movement execution as indicated by the increased errors, mainly in Experiment 2. The results of Experiment 3 indicated that ToT did not induce orientation and phasic alerting deficits but rather was accompanied by decreased tonic alertness.

Equipment modification can enhance skill learning in young field hockey players

The aim of the study was to investigate whether performance of children can be improved by training with modified equipment that challenges movement execution. For that purpose, young field hockey players practiced with a modified and a regular hockey ball. The modified hockey ball enforces more variable movement execution during practice by rolling less predictably than a regular hockey ball and, thus, challenges the players’ stick–ball control. Two groups of 7- to 9-year old children, with 0 to 4 years of experience, participated in a crossover-design, in which they either received four training sessions with the modified ball followed by four training sessions with the regular ball or vice versa. In a pretest, intermediate test (i.e. following the first four training sessions) and a posttest, the participants dribbled an obstacle parcours with a regular ball. Results show that practice with the modified ball led to greater performance improvement than the intervention with the regular hockey ball. This performance improvement, however, was not predicted by experience and/or initial skill (i.e. pretest score). The findings indicate that by using modified equipment, sport trainers and physical education teachers can, presumably through enhancement of movement variability during practice, stimulate skill acquisition in young children.

Risky business for a juvenile marine predator? Testing the influence of foraging strategies on size and growth rate under natural conditions

Mechanisms driving selection of body size and growth rate in wild marine vertebrates are poorly understood, thus limiting knowledge of their fitness costs at ecological, physiological and genetic scales. Here, we indirectly tested whether selection for size-related traits of juvenile sharks that inhabit a nursery hosting two dichotomous habitats, protected mangroves (low predation risk) and exposed seagrass beds (high predation risk), is influenced by their foraging behaviour. Juvenile sharks displayed a continuum of foraging strategies between mangrove and seagrass areas, with some individuals preferentially feeding in one habitat over another. Foraging habitat was correlated with growth rate, whereby slower growing, smaller individuals fed predominantly in sheltered mangroves, whereas larger, faster growing animals fed over exposed seagrass. Concomitantly, tracked juveniles undertook variable movement behaviours across both the low and high predation risk habitat. These data provide supporting evidence for the hypothesis that directional selection favouring smaller size and slower growth rate, both heritable traits in this shark population, may be driven by variability in foraging behaviour and predation risk. Such evolutionary pathways may be critical to adaptation within predator-driven marine ecosystems.

Individual movement variability magnitudes are predicted by cortical neural variability

ABSTRACTHumans exhibit considerable motor variability even across trivial reaching movements. This variability can be separated into specific kinematic components such as extent and direction, which are thought to be governed by distinct neural processes. Here, we report that individual subjects exhibit different magnitudes of kinematic variability, which are consistent (within individual) across movements to different targets and regardless of which arm (right or left) was used to perform the movements. Simultaneous fMRI recordings revealed that the same subjects also exhibited different magnitudes of fMRI variability across movements in a variety of motor system areas. These fMRI variability magnitudes were also consistent across movements to different targets when performed with either arm. Cortical fMRI variability in the posterior-parietal cortex of individual subjects predicted their movement-extent variability. This relationship was apparent only in posterior-parietal cortex and not in other motor system areas, thereby suggesting that individuals with more variable movement preparation exhibit larger kinematic variability. We, therefore, propose that neural and kinematic variability are reliable and interrelated individual characteristics that may predispose individual subjects to exhibit distinct motor capabilities.

Cineradiographic Examination of Articulatory Movement of Pseudo-Tongue, Hyoid, and Mandible in Congenital Aglossia

This research examined cineradiographic films (CRF) of articulatory movements in a person with congenital aglossia (PWCA) during speech production of four phrases. Pearson correlations and a multiple regression model investigated co-variation of independent variables, positions of mandible and hyoid; and pseudo-tongue-dependent variables, positions of mylohyoid and tongue base. Results suggest that backing/fronting of the mandible assisted the mylohyoid/tongue base in making mid-antero-posterior constrictions. Co-linearity findings suggest the best predictor of tongue base movement was mandible for back sounds. Hyoid movement was highly correlated with mandibular movement horizontally, but hyoid acted independently vertically and possibly with greater phonemic specialty in the PWCA. Findings suggest hyoid was a strong determinant of vertically dependent variable movement in all phrases. The extent of hyoid activity was a unique finding and one that may begin to explain relative intelligibility in this PWCA. Observed changes in vocal tract length may have influenced F2 transitional/vowel midpoint values.

Action Decision Strategy of Simulation Robot Fish Based on Ant Colony Algorithm

In order to achieve the quick and accurate adjustment of the robot fish, there are two plans, which are based on ant-colony-algorithm movement strategy. These plans are aimed at 2D robot fish in the ant colony algorithm, and the key judgment of the robot fish relies on the branches of physic matters, together with the best match of the fish in its current speed. However, according to the dynamic algorithm project, the feedback of dynamic variable movement can process adjustment automatically. In every period, these two examples by which the 2D Simulation results show the robot fish can be adjusted on the policy path. To achieve optimal combination of speed and direction, the shortest time has a strong ability to adapt effectively to meet the simulation of robot fish or action of the action decision-making.

Dispersal and home-range dynamics of exotic, male sika deer in Maryland

Content An unknown number (n = four or five) and sex of sika deer (Cervus nippon yakushimae) were introduced to the Delmarva Peninsula, Maryland, in 1916. Since introduction, their population has grown exponentially. Aims The purpose of our study was to investigate dispersal and home-range size to enable better management of this exotic species in the presence of native white-tailed deer (Odocoileus virginianus). Methods We collected telemetry locations on 60 males (captured during their first winter) from 2008 to 2010. Animals were classified into three movement groups, including local, migratory and nomadic post-dispersal. Key results Average home-range sizes ranged from 464 to 4121 ha and were influenced by season and deer movement grouping (P = 0.0001). Of 20 deer that dispersed, 19 did so at 1 year of age. Dispersal distance and direction were random across the landscape (P = 0.899). Local deer were the most common movement group (70%; 42 of 60) and were characterised by short movements confined to a well established home range. We observed 14 deer migrations, characterised by round-trip movements associated with seasons and directionality (P = 0.003). Four deer were classified as nomadic and had long-distance movements across the landscape unassociated with seasons. Conclusions To aid managers in controlling the expansion of the population, we provide data regarding the manner, distance and direction that sika deer move. Our results show that sika deer have variable movement strategies and large home ranges. Implications Variation in movement types will influence spread of the population, confounding species interactions, management and harvest strategies. The present results may have implications to other areas that also have sika populations.