Optic variables used to judge future ball arrival position in expert and novice soccer players

Although many studies have looked at the perceptual-cognitive strategies used to make anticipatory judgments in sport, few have examined the informational invariants that our visual system may be attuned to. Using immersive interactive virtual reality to simulate the aerodynamics of the trajectory of a ball with and without sidespin, the present study examined the ability of expert and novice soccer players to make judgments about the ball's future arrival position. An analysis of their judgment responses showed how participants were strongly influenced by the ball's trajectory. The changes in trajectory caused by sidespin led to erroneous predictions about the ball's future arrival position. An analysis of potential informational variables that could explain these results points to the use of a first-order compound variable combining optical expansion and optical displacement.

Cumulative or sequential assessment during hermit crab shell fights: effects of oxygen on decision rules

Agonistic interactions between animals are often settled by the use of repeated signals which advertise the resource-holding potential of the sender. According to the sequential assessment game this repetition increases the accuracy with which receivers may assess the signal, but under the cumulative assessment model the repeated performances accumulate to give a signal of stamina. These models may be distinguished by the temporal pattern of signalling they predict and by the decision rules used by the contestants. Hermit crabs engage in shell fights over possession of the gastropod shells that they inhabit. During these interactions the two roles of signaller and receiver may be examined separately because they are fixed for the duration of the encounter. Attackers rap their shell against that of the defender in a series of bouts whereas defenders remain tightly withdrawn into their shells for the duration of the contest. At the end of a fight the attacker may evict the defender from its shell or decide to give up without first effecting an eviction; the decision for defenders is either to maintain a grip on its shell or to release the shell and allow itself to be evicted. We manipulated fatigue levels separately for attackers and defenders, by varying the oxygen concentration of the water that they are held in prior to fighting, and examined the effects that this has on the likelihood of each decision and on the temporal pattern of rapping. We show that the vigour of rapping and the likelihood of eviction are reduced when the attacker is subjected to low oxygen but that this treatment has no effect on rates of eviction when applied to defenders. We conclude that defenders compare the vigour of rapping with an absolute threshold rather than with a relative threshold when making their decision. The data are compatible with the cumulative assessment model and with the idea that shell rapping signals the stamina of attackers, but do not fit the predictions of the sequential assessment game.

How information guides movement: Intercepting curved free kicks in soccer

Previous studies have shown that balls subjected to spin induce large errors in perceptual judgements (Craig et al, 2006; Craig et al 2009) due to the additional accelerative force that causes the ball’s flight path to deviate from a standard parabolic trajectory. A recent review however, has suggested that the findings from such experiments may be imprecise due to the decoupling of perception and action and the reliance on the ventral system (Van der Kamp et al, 2008). The aim of this study was to present the same curved free kick trajectory simulations from the perception only studies (Craig et al, 2006; Craig et al, 2009) but this time allow participants to move to intercept the ball. By using immersive, interactive virtual reality technology participants were asked to control the movement of a virtual effector presented in a virtual soccer stadium so that it would make contact with a virtual soccer ball as it crossed the goal-line. As in the perception only studies the direction of spin had a significant effect on the participants’ responses (F(2,12)=222.340; p

Purchasing power parity versus fixed exchange rate rules: A stability and welfare analysis

This paper evaluates the desirability of PPP rules vis-á-vis fixed exchange rates both in terms of welfare and stability properties. The analysis is conducted within a small open-economy New Keynesian framework extended to include a cost channel. In terms of stability, we find that while the equilibrium is always unique under fixed exchange rates its uniqueness critically depends upon the presence/absence of the cost channel under a PPP rule. Overall, then, in terms of welfare a fixed exchange rate always outperforms a PPP rule.

Measuring inconsistency in network intrusion rules

In this preliminary case study, we investigate how inconsistency in a network intrusion detection rule set can be measured. To achieve this, we first examine the structure of these rules which incorporate regular expression (Regex) pattern matching. We then identify primitive elements in these rules in order to translate the rules into their (equivalent) logical forms and to establish connections between them. Additional rules from background knowledge are also introduced to make the correlations among rules more explicit. Finally, we measure the degree of inconsistency in formulae of such a rule set (using the Scoring function, Shapley inconsistency values and Blame measure for prioritized knowledge) and compare the informativeness of these measures. We conclude that such measures are useful for the network intrusion domain assuming that incorporating domain knowledge for correlation of rules is feasible.

WTO government procurement rules and the local dynamics of procurement policies: A malaysian case study

This article examines efforts to create binding international rules regulating public procurement and considers, in particular, the failure to reach a WTO agreement oil transparency in government procurement. The particular focus of the discussion is the approach taken by Malaysia to these international procurement rules and to the negotiation of an agreement on transparency. Rules governing public procurement directly implicate fundamental arrangements of authority amongst and between different parts of government, its citizens and non-citizens. At the same time, the rules touch upon areas that are particularly sensitive for some developing countries. Many governments use preferences in public procurement to accomplish important redistributive and developmental goals. Malaysia has long used significant preferences in public procurement to further sensitive developmental policies targeted at improving the economic strength of native Malays. Malaysia also has political and legal arrangements substantially at odds with fundamental elements of proposed global public procurement rules. Malaysia has, therefore, been forceful in resisting being bound by international public procurement rules, and has played all important role in defeating the proposed agreement oil transparency. We suggest that our case study has implications beyond procurement. The development of international public procurement rules appears to be guided by many of the same values that guide the broader effort to create a global administrative law. This case study, therefore, has implications for the broader exploration of these efforts to develop a global administrative law, in particular the relationship between such efforts and the interests of developing countries.