Constraints on movement variability during a discrete multi-articular action

The aim of this programme of work was to examine how the manipulation of organismic and task constraints affected movement variability during a basketball shooting task. The specific constraints that were manipulated included task expertise, state anxiety and dioptric blur (organismic constraints), and, shooting distance and attentional focus instruction (task constraints). The aim of Study 1 was to investigate the effect of shooting distance and task expertise on movement variability. Task expertise was characterised by decreased coordination variability and heightened compensatory variability between wrist, elbow and shoulder joints. However, no significant difference was found in joint angle variability at release as a function of task expertise. There was no significant change in movement variability with shooting distance, a finding that was consistent across all expertise groups. In Study 2, the aims were to examine the effect of induced dioptric blur on shooting performance and movement variability during basketball free-throw shooting, and, to ascertain whether task expertise plays a mediating role in the capacity to stabilise performance against impaired visual information. Significant improvements in shooting performance were noted with the introduction of moderate visual blur (+1.00 and +2.00 D). This performance change was evident in both expert and novice performers. Only with the onset of substantial dioptric blur (+3.00 D), equivalent to the legal blindness limit, was there a significant decrease in coordination variability. Despite the change in coordination variability at +3.00 D, there was no significant difference in shooting performance when compared to the baseline condition. The aims of Study 3 were to examine the effect of elevated anxiety on shooting performance and movement variability and, again, to determine whether task expertise plays a mediating role in stabilising performance and movement kinematics against perturbation from emotional fluctuations. Commensurate with the results of Study 2, both expert and novice performers were able to stabilise performance and movement kinematics, this time with elevated anxiety. Stabilisation was achieved through the allocation of additional attentional resources to the task. Study 4, had two aims. The first was to examine the interactive effects of practice and focus of attention on both performance and learning of an accuracy-based, discrete multi-articular action. The second was to identify potential focus-dependent changes on joint kinematics, intra-limb coordination and coordination variability. Support was found for the role of an external focus of attention on shooting performance during both acquisition and retention. However, there was evidence to suggest that internal focus instruction could play a pivotal role in shaping emerging patterns of intra-limb coordination and channelling the learners‟ search towards a smaller range of kinematic solutions within the perceptual-motor workspace. Collectively, this programme of work consistently highlighted the fundamental role that constraints play in governing shooting performance, movement variability and, more broadly, perceptual-motor organisation. For instance, task expertise was characterised by decreased coordination variability and heightened compensatory control. However, in light of the data pertaining to joint angle variability at release, general assumptions about expertise-variability relations cannot be made and should be viewed with caution. In addition, there is strong evidence to suggest that adaptation to constraints is, perhaps, a universal human response, and consequently not mediated by task expertise. Further research is needed to fully elucidate this proposition

CO-ORDINATION ANALYSIS OF LANDING STRATEGIES IN BEAM DISMOUNTS

INTRODUCTION: Landing strategies selected by female gymnasts performing somersault dismounts from the beam may be related to the availability of feedback (McNitt-Gray et al., 2001). This study aims to employ co-ordination analysis to examine how female gymnasts control dropping and landing from forward and backward somersault beam dismounts

Semiclassical limits to the linewidth of an atom laser

We investigate the linewidth of a quasi-continuous atom laser within a semiclassical framework. In the high flux regime, the lasing mode can exhibit a number of undesirable features such as density fluctuations. We show that the output therefore has a complicated structure that can be somewhat simplified using Raman outcoupling methods and energy-momentum selection rules. In the weak outcoupling limit, we find that the linewidth of an atom laser is instantaneously Fourier limited, but, due to the energy `chirp' associated with the draining of a condensate, the long-term linewidth of an atom laser is equivalent to the chemical potential of the condensate source. We show that correctly sweeping the outcoupling frequency can recover the Fourier-limited linewidth.Comment: 9 Figure

EXPERTISE AND DISTANCE AS CONSTRAINTS ON COORDINATION STABILITY DURING A DISCRETE MULTI-ARTICULAR ACTION

The purpose of this study was to identify how coordination variability of the shooting arm varied as a function of interacting task constraints of expertise and shooting distance. Skilled, intermediate and novice male basketball players (n=9 in each group) performed 30 shots from three distances (4.25, 5.25 and 6.25 metres). The dependent variables included shooting performance scores and measures of coordination variability in three joint couplings: wrist-elbow, elbow-shoulder and wrist-shoulder. A main effect for distance was observed for shooting performance, with a reduction in score occurring with increasing distance. Significant main effects for expertise were also apparent for shooting performance together with coordination variability for all three joint couplings. Regression analyses revealed significant, negative relationships between shooting performance and coordination variability for all three joint couplings irrespective of shooting distance. The findings corroborated extant data on changes in movement variability with practice, demonstrating how skilled performers assemble stable movement solutions to satisfy changing task constraints, in contrast to novices and intermediates

EFFECTS OF ATTENTIONAL STRATEGIES, TASK EXPERTISE AND ANXIETY ON COORDINATION OF A DISCRETE MULTI-ARTICULAR ACTION

The purpose of this study was to determine whether anxiety effects on performance of a discrete multi-articular action could be alleviated by attentional strategies and task expertise. 10 expert and 9 novice male basketball players performed 30 freethrows under both control and anxiety conditions. The dependent variables of interest included shooting performance, reaction time, joint amplitude of the wrist, elbow and shoulder, and coordination variability of the shooting arm using the normalised root mean squared difference technique. A significant main effect for condition was observed for reaction time, indicating the implementation of attentional strategies in both groups. In relation to this observation, no significant main effects for condition were found for shooting performance or any of the kinematic variables. Under conditions of elevated emotions, the allocation of additional attention to the primary shooting task seemed to attenuate the effects of anxiety, regardless of expertise. The findings are harmonious with existing data on attention and anxiety effects on coordination of rhythmical actions. They specifically demonstrated how participants, differing in expertise, used attentional strategies to stabilise performance of a discrete multi-articular action against emotional fluctuations

Sensitivity of estuaries to compound flooding.

Fluvial and surge-tide extremes can occur synchronously resulting in compound flooding in estuaries, greatly intensifying the hazard. This flood risk has the potential to increase in the future as the frequency, phasing and/or intensity of these drivers change. Improved understanding of how extreme fluvial discharge and surge-tides interact will help inform future flood mitigation methodology. In this paper, therefore, we resolve for the first time intra-estuary sensitivities to fluvial and surge-tide extremes, for two contrasting UK estuaries (Humber and Dyfi). Model simulations at hyper-spatial resolution (< 50 m) using a 2D hydrodynamic model predicted compound flooding hazards based on: (1) present-day extreme events (worst on record); (2) present-day extreme events with shifted timings of the drivers to maximise flooding; and (3) modified drivers representing projected climate change. We found that in a small estuary with short-duration, high-intensity fluvial inputs (Dyfi), flood extent is sensitive to the relative timing of the fluvial and surge-tide drivers. In contrast, the relative timing of these drivers did not affect flooding in a larger estuary with a slower fluvial response to rainfall (Humber). In the Humber, extreme fluvial inputs during a compound hazard actually reduced maximum water depths in the outer estuary, compared with a surge-tide-only event. Projected future changes in these drivers by 2100 will increase compound flooding hazards: simulated sea-level rise scenarios predicted substantial and widespread flooding in both estuaries. However, projected increases in surge-tide behaved differently to sea-level rise of the same magnitude, resulting in a greater seawater influx and more flooding. Increased fluvial volumes were the weakest driver of estuarine flooding. In this paper we show how these interactions are complex and how the hydrodynamics vary considerably between different estuaries and sites within estuaries, making it difficult to generalise, use probabilistic or use 1D approaches for assessing compound flooding hazards. Hence, we contribute new knowledge and methods for catchment-to-coast impact modelling used for flood mitigation strategies