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The rapid release of prepared movements by a loud acoustic stimulus capable of eliciting a startle response has been termed the StartReact effect (Valls-Solé et al., 1999), and premotor reaction times (PMTs) of <70 ms are often observed. Two explanations have been given for these short latency responses. The subcortical storage and triggering hypothesis suggests movements that can be prepared in advance of a "go" signal are stored and triggered from subcortical areas by a startling acoustic stimulus (SAS) without cortical involvement. Alternatively, it has been hypothesized that the SAS can trigger movements from cortical areas through a faster pathway ascending from subcortical structures. Two experiments were designed to examine the possible role of the primary motor cortex in the StartReact effect. In Experiment 1, we used suprathreshold transcranial magnetic stimulation (TMS) during the reaction time (RT) interval to induce a cortical silent period in the contralateral primary motor cortex (M1). Thirteen participants performed 20° wrist extension movements as fast as possible in response to either a control stimulus (82 dB) or SAS (124 dB). PMTs for startle trials were faster than for control trials, while TMS significantly delayed movement onset compared to No TMS or Sham TMS conditions. In Experiment 2, we examined the StartReact effect in a highly cortically represented action involving speech of a consonant-vowel (CV) syllable. Similar to previous work examining limb movements, a robust StartReact effect was found. Collectively, these experiments provide evidence for cortical (M1) involvement in the StartReact effect.

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Information prior to and during the acquisition of a continuous bimanual task was manipulated. Participants practiced a difficult coordination pattern, which produced circular shapes on the computer, when they moved their arms correctly. Four groups were examined, which differed in the type and amount of information provided. Either limb or circle feedback was provided in the presence or absence of instructions detailing how to move the limbs. Circle feedback facilitated learning relative to the limb feedback in which the explicit displacements of the limbs was displayed. Under circle feedback conditions, instructions hindered acquisition. Little instructional effects were observed under limb feedback conditions, despite the prediction that instructions would benefit learning when the feedback was more compatible. Findings are discussed in relation to the complexity of the feedback and processing demands.

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Reduced surface electromyogram (EMG) onsets, observed in some cases when trying to stop an earlier intended action before it begins, were taken to suggest a control process that remains open to stopping right up to the point of motor discharge. This interpretation argues against a final ballistic (involuntary) process in the control of voluntary action. That a final ballistic process may receive reduced input shortly before its manifestation as reduced output (i.e., motor discharge), however, provides for an alternative interpretation of these same data. In this study we used the Hoffmann (H) reflex to further investigate for stopping effects in the brief interval before voluntary motor discharge. Late stopping effects on the facilitated H-reflex within the time window that a final ballistic process would otherwise be expected (i.e, shortly before EMG onset) were observed in some instances. We conclude from these data good evidence against a final ballistic process in the control of voluntary action.

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Participants (N = 16) were given extensive practice (1,500 trials) on a perceptual-motor aiming task. The full-vision (FV) group practiced with vision of their response cursor, whereas the no-vision (NV) group practiced in a condition without vision. Movements were made as quickly and accurately as possible, and knowledge of results (KR) was provided. The authors tested the importance of vision early and late in practice by transferring participants to the NV condition without KR. The effects of practice differed between the two conditions. The FV group increased the speed of initial impulse to get to the target quickly, then relied on vision to make discrete error corrections. Transfer tests revealed that reliance on vision remained after extensive practice. For the NV group, practice effects were associated with a reduction in the extent to which discrete error corrections were produced.

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The penalty shoot-out is used to break tied games in the knock-out stages of soccer competition. The shoot-out, which consists of an alternating series of penalty kicks, is won by the team with the highest goal tally after n kicks per team (n = 5). In the event of a tie after five penalty kicks each, the shoot-out progresses to 'sudden death' by increasing n in iterative fashion (i.e. n = n + 1) until one team obtains a higher goal tally than the other after an equal number of kicks per team. The team to strike first is determined at the end of extra time by the toss of a coin. As each on-field player can be awarded only a single penalty kick, the line-up order in which the penalty kicks are taken allows for the possibility of tactical influence on the final outcome. Consequently, we report a probability analysis of the penalty shoot-out in soccer from which we identify the following pre- and post-game strategies. The best five ranked penalty takers from the on-field players should be assigned to the first five penalty kicks in their reverse order of ability. That is, the fifth best penalty taker should take the first penalty kick, the fourth best penalty taker should take the second penalty kick, and so on. In the event of sudden death, the next highest ranked on-field player should be assigned to the next penalty kick until the shoot-out ends. For this tactic to be successful, players should be ranked a priori on their penalty-taking ability. Similarly, goalkeepers should be ranked a priori on their penalty-stopping ability. These findings indicate that the tactical substitution of on-field players for higher ranked penalty takers, including higher ranked penalty stoppers (i.e. goalkeepers), with a view to an impending penalty shoot-out should be given due consideration. These results are of practical importance in that they are shown to maximize the likelihood of winning the penalty shoot-out under certain initial conditions.

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Previous investigations of bilateral-unilateral reaction time (RT) differences have reported equivocal findings. Studies where bilateral RT has been found longer than unilateral RT have often emphasized movement precision, while studies reporting non-significant differences have placed little emphasis on precision. To test the hypothesis that movement precision is an important factor in the bilateral unilateral difference, we investigated the influence of changes in spatial accuracy constraints on RT for unilateral and bilateral movements. Ten self-declared right-handed subjects performed fast and accurate 45 degrees unilateral and bilateral elbow flexion movements to small (1.5 degrees) and large (12.0 degrees) targets. For bilateral movements, spatial accuracy was emphasized for only one arm (the "aiming" arm), while the contralateral ("mirroring") arm performed a simultaneous flexion movement with no emphasis on movement accuracy. We found that while changes in target size had no significant effect on movement latency, changing the hand (right vs left) for which accuracy was emphasized did. When subjects performed right-arm aiming, bilateral movements, unilateral and bilateral RT did not differ significantly. In contrast, when subjects performed left-arm aiming, bilateral movements, RT was significantly longer than for unilateral movements. We conclude that while spatial accuracy per se (i.e., target size) does not differentiate bilateral and unilateral movements, the role of the left hand (i.e., aiming vs mirroring) does. Differences in the hemispheric control of right- and left-hand aiming movements are discussed.

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Here we report two experiments that analysed sport (squash) competition as a non-linear system that transits intermittently between different behavioural states. The first experiment involved a perceptual analysis of 60 rallies in which stable behaviour and unstable behaviour, delineated by behavioural transitions (i.e. shot perturbations), were reliably (kappa = 0.930) and validly (kappa = 0.844) identified by independent observers. In addition, experts were better than non-experts at identifying the type of system behaviour (P < 0.01). These results provide for three alternative descriptions: (a) the system is multi-stable and transits between states via the mechanism of instability; (b) the system is bi-stable and abruptly transits between two states, labelled stable and unstable; or (c) the system is mono-stable and displays variability, marked by transient instability, as a result of system perturbations. The second experiment analysed squash behaviour as expressed in the phase relation between the two players from time-motion analysis. The data, from four rallies, yielded evidence of a tight anti-phase coupling with transient phase shifts, or perturbations, that were quickly damped. These data suggest a mono-stable system with a single (anti-phase) attractor onto which system fluctuations are occasionally written. However, these fluctuations failed to correspond with the short perturbations that were identified from perceptual analysis. Together, these results affirm the presence of transient behaviours in squash match-play, although the information that forms these perceptual judgements has yet to be identified.

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Two experiments are reported that investigated the effects of target size and inertial load on the control of rapid aiming movements. Based on kinematic profiles, movements were partitioned into their preprogrammed initial impulse- and feedback-based error correction phases. Electromyographic (EMG) rise rates were examined to investigate whether participants used a speed-sensitive or speed-insensitive control strategy. The results from both experiments showed that initial impulse velocity and EMG rise rates varied as a function of target size, i.e., a speed-sensitive strategy. This was the case whether participants were allowed to make error corrections to their movements (experiment 1) or were instructed to produce initial impulses that hit the target (experiment 2). Both experiments also showed that initial impulse velocity and endpoint variability were inversely related to inertial load. The results from experiment 2 indicated that, while the manipulation of inertial load had no effect on EMG rise rates for movements to a large target, EMG slopes were modulated between inertial load conditions when the target was small.

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Two experiments investigated the response complexity effect using elbow extension/flexion movements. In the first experiment, RT for an extension movement was significantly less than RT for an extension/flexion movement. However, this difference in RT was not evident when participants were asked to pause at the reversal of the extension/flexion for approximately 260 ms. The second experiment manipulated the duration of the pause between these movements and also measured the electromyographical (EMG) activity of the triceps and biceps muscles. When the pause was reduced to 75 ms participants were not able to program the flexion portion of the movement at the reversal, forcing them to preprogram this movement; hence, increasing their premotor reaction time.

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Electromyographic (EMG) data show that a speeded elbow extension response can be interrupted at any time after its execution. Submaximal, or partial, EMG data are also observed in some cases, from which 2 alternatives were considered. The partial response might in fact be interrupted early in response production or, alternately, it might arise from stopping processes that incompletely suppress the response production processes prior to their execution. An interrupted response is easily accounted for by a horse race between independent response production and stopping processes, whereas a partial response can only be reconciled if leakage between the two processes is allowed for. If the distinction between an interrupted and a partial response is correct, then the data yielded evidence for a phantom point of no return that locates late in the premotor component of the response and, thus, prior to the onset of EMG activity.

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This study tested a computer-aided coaching analysis instrument (CAI) as part of an intervention strategy designed to modify verbal coaching behaviour. Four coaches were observed and analysed over 12 practice sessions. Coaches A, B and C received intervention feedback through CAI data, where selected behaviours were highlighted for discussion, and videotape images were used to illustrate discussion points. Coach D was provided with videotapes of his own performance and told to formulate and implement any of his own recommendations. The CAI data are primarily quantitative, so target values were created for the different dimensions of verbal behaviour. This benefited the coaches in interpreting their effectiveness and provided a reference to evaluate the magnitude of change. Written journals and audiotape recordings were also used to promote insight into the complexity of verbal behaviour and the "human factors' (e.g. relationship with players, attitude to researcher) that affect behaviour modification. Instructional effectiveness was assessed by time-series analysis. There was evidence from each behaviour dimension that change can occur and be maintained as a result of exposure to the CAI intervention strategy. However, this is clearly contingent upon the coach understanding what is asked of him or her, and remains focused and committed to changing these particular behaviours. The analysis of Coach D's behavioural change suggests there are limitations to the sensitivity of discretionary viewing, as only two dimensions of behaviour were identified for, and resulted in, positive change. The results of this study provide support for Locke's (1984) contention that behaviour modification can occur by using data as direct feedback, as reinforcement and as information in the form of recommendations. However, the study also illuminates several factors that can negate the modification and maintenance of verbal coaching behaviour.

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This study reports a stochastic (Markov) model for squash which uses empirical data to transit event states on a shot by shot basis. This offers more information than traditional models with regard to how points were won or lost and the potential for predicting future athletic performance from a priori observation. The predictive capacity of the model, however, is presently restricted because the observed behaviors (shots) and associated outcomes (winners, errors and lets) are statistically variant (p < .25). A player does not produce a consistent athletic response to the same preceding condition when competing against different opponents, although it is unclear at present whether this observation is a function of the particular analysis employed. Nevertheless, the modeling of athletic behavior is a way to search for critical data which underpin competitive sport performance.

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Analysis of competitive sport performance from a priori observation is frequently used to prepare an athlete for a future contest. This practice necessarily assumes that the observed athletic behaviours are invariant, in that the data from an earlier contest apply to the next. We report different analyses of championship squash matches from 1987 and 1988 in search of such invariance and thus a general signature of athletic behaviour. The results show that once the preceding condition to an athletic response (shot) becomes more detailed, by either accounting for where on court the previous shot was played to, or by pairing the previous shot with its own antecedent, the corresponding response becomes more predictable (P > 0.25). This is especially the case for a squash champion when the forehand and backhand characteristics of his shot response are accounted for. The finding that the champion is more consistent if his forehand and backhand shot responses to a preceding shot are analysed separately, shows that the level of analytic detail is an important consideration if the derived information from sport analysis is to prepare an athlete reliably for future sport competition. Finally, we consider sport competition from an ecological perspective with regard to the natural organization and stability of non-linear systems in an attempt to explain the empirical data.

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Evidence for a point of no return in a motor act has been reported to occur very late in its preparation and even to the point at which the response is executed. We report a qualitative example from electromyographic (EMG) data of an elbow-extension movement from 1 of 12 adults which suggests that the response can be stopped at any time up to its production, from which we conclude that the response is subject to on-line control at all times.

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Modelling sport competition is an informative analytic technique for the investigation of athletic behaviour because it focuses attention on the critical aspects of data which characterize sporting success. A stochastic (Markov) model of championship squash match-play is reported which infers prospective behaviour from previous sport performance through forecasting shot response and associated outcome from the preceding shot. The results presently restrict the model to the competing players already analysed because, while a consistent athletic response was established when competing against the same opponent (P > 0.25), an inconsistent response was found when competing against different opponents (P < 0.25). These results may impact the information value traditionally drawn from previous sport analysis. The hypothesis that future squash match-play can be successfully predicted from previous sport performance requires further investigation, since it remains unclear whether the present analysis failed to identify the preceding condition(s) which elicit a reasonably stable behavioural response, or indeed whether athletic behaviour in championship squash is more variant than initially believed. Alternative modelling considerations are discussed and a refinement to the present model is proposed in an effort to improve future model utility and application.

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The aim of this work was to analyse and compare the dynamic motions of squash players of varying technical abilities, and link these to the tactics that the different standard players adopt. A computerized tracking system utilized mixed images on the VDU of both the tracking surface, and the subject during competitive matchplay. Four groups of squash players were categorized Elite (international); Provincial (provincial representatives); Club A/B (players at either the A or B level in the inter-club leagues in British Columbia); and Club C/D (players at the C or D level in the inter-club leagues in British Columbia). Six competitive matches of different players were analysed for each group. Each game in each match was analysed separately and means-per-rally calculated for: positional data, X and Y; lateral and longitudinal velocities, Vx and Vy; average velocities, V; distances travelled, D; and accelerations, A. The longitudinal position in the winning rallies for all groups was closer to the front wall than that in the losing rallies (p < 0.10), supporting previous research and demonstrating the operational validity of this methodology. The Elite and Provincial groups had significant differences in all the velocities and the accelerations between the winning rallies and losing rallies (p < 0.10), confirming the hypothesis that their tactic was to attempt to reduce their opponents' playing time by taking the ball as early as possible and use all of the court.(ABSTRACT TRUNCATED AT 250 WORDS)

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The concept of invariant relative timing has typically been associated with the concept of a generalized motor programme. The present study approaches the phenomenon of invariant relative timing from the perspective of learning. The underlying question of concern for this study was, "What is learned." The specific question was whether relative timing is one of the essential properties of movement that is learned during skill acquisition. In the present experiment, subjects were given extensive practice in learning to track and reproduce a criterion waveform using a joystick control for their response. In order to test whether subjects learn the relative timing of a movement, they were transferred to tracking waveforms that were identical to the criterion in terms of relative timing, but different in terms of absolute timing. Measurements were taken on all waveforms in two conditions: (a) in a pursuit tracking condition where subjects were temporally constrained by the stimulus, and (b) in a reproduction condition where subjects' timing was not constrained. The outcome from both conditions gives support to the idea that humans learn invariant relative timing during the acquisition of a motor skill.

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