João Barreiros

Contemporary theories of 1/f noise in motor control

1/f noise has been discovered in a number of time series collected in psychological and behavioral experiments. This ubiquitous phenomenon has been ignored for a long time and classical models were not designed for accounting for these long-range correlations. The aim of this paper is to present and discuss contrasted theoretical perspectives on 1/f noise, in order to provide a comprehensive overview of current debates in this domain. In a first part, we propose a formal definition of the phenomenon of 1/f noise, and we present some commonly used methods for measuring long-range correlations in time series. In a second part, we develop a theoretical position that considers 1/f noise as the hallmark of system complexity. From this point of view, 1/f noise emerges from the coordination of the many elements that compose the system. In a third part, we present a theoretical counterpoint suggesting that 1/f noise could emerge from localized sources within the system. In conclusion, we try to draw some lines of reasoning for going beyond the opposition between these two approaches.

The contextual interference effect in applied settings

This paper analyses the research literature that approaches the contextual interference effect in applied settings. In contrast to the laboratory settings, in which high interference conditions depress acquisition and promote learning evaluated in retention and transfer tests, in applied settings most of the studies (60%) fail to observe positive effects after manipulation of the contextual interference. Some possible explanations for the fact are hypothesized regarding the characteristics of the task, with serial tasks doing best, shor t inter trial intervals rare in applied settings, interference produced by the use of different motor programmes and the possible interference of concurrent feedback in slow tasks in contrast to ballistic skills. It seems that there is a more evident contextual interference effect in an applied setting, when subject learns a serial task with high degree of complexity.

Does the brake response time of the right leg change after left total knee arthroplasty? A prospective study

Patients undergoing total knee arthroplasty often ask when they can safely resume car driving. There is little evidence available on which physicians can rely when advising patients on this issue. In a prospective study we assessed the brake response time of 24 patients admitted to the clinic for left total knee arthroplasty preoperatively and then 10 days after surgery. On each measurement day the patients performed two tasks, a simple and a complex brake response time task in a car simulator. Ten days after left TKA the brake response time for the simple task had decreased by 3.6% (p=0.24), the reaction time by 3.1% (p=0.34) and the movement time by 6.6% (p=0.07). However, the performance improvement was not statistically significant. Task complexity increased brake response time at both time points. A 5.8% increase was significant (p=0.01) at 10 days after surgery. Based on our results, we suggest that patients who have undergone left total knee arthroplasty may resume car driving 10 days after surgery as long as they drive a car with automatic transmission.

Golf-related injuries: A systematic review

Abstract A review was undertaken to assess the prevalence of musculoskeletal injuries in golf and to stimulate the discussion on possible injury mechanisms. The main conclusion of most published studies is that although professional and amateur golfers show a similar anatomical distribution of injuries by body segment, differences tend to be seen in the ranking of injury occurrence by anatomical site. This could be due to many things, including the players handicap, age, golf swing biomechanics, and training or playing habits. The impact of golf injuries deserves special attention due to the interaction of the nature of the injury, practice routines, amount of practice, handicap, and frequency of activity. Individual differences and clinical and coaching procedures deserve investigation. Other epidemiological information should be regarded as insufficient with respect to a full understanding of injury mechanisms, which can give us a better insight into the evolutionary nature of the injury. Also, a better understanding of golf swing mechanisms and individual neuromuscular aspects can help explain why some individuals are more injury-prone than others.

The Effects of Task Complexity on Brake Response Time Before and After Primary Right Total Knee Arthroplasty

OBJECTIVE To study the effects of an increase in task complexity on brake response time (BRT) in patients undergoing total knee arthroplasty (TKA). DESIGN A prospective repeated-measures design was used. The measurements took place 1 day before and 10 and 30 days after surgery. SETTING Clinic. PARTICIPANTS The data of patients (N=21) who were admitted for primary total arthroplasty of the right knee were pooled for analysis. INTERVENTIONS On each measurement day patients performed 5 practice and 10 test trials for 2 tasks (1 simple, 1 complex) in a car simulator. Task complexity was increased by adding a second movement to the first task performed. MAIN OUTCOME MEASURES BRT, reaction time (RT), and movement time were assessed. RESULTS An increase in task complexity increased BRT, RT, and movement time at all measurement times. Right TKA increased BRT by increasing movement time. Thirty days after surgery BRT was no longer increased compared with preoperative values in both tasks. CONCLUSIONS Task complexity consistently increased BRT and its components. The effects of task complexity remained constant throughout the 3 measurements. After right TKA, we suggest patients should be advised to wait 30 days after surgery before resuming driving.

The influence of instructions and body-scaling as constraints on decision-making processes in team sports.

Abstract Team games conceptualized as dynamical systems engender a view of emergent decision-making behaviour under constraints, although specific effects of instructional and body-scaling constraints have yet to be verified empirically. For this purpose, we studied the effects of task and individual constraints on decision-making processes in basketball. Eleven experienced female players performed 350 trials in 1 vs. 1 sub-phases of basketball in which an attacker tried to perturb the stable state of a dyad formed with a defender (i.e. break the symmetry). In Experiment 1, specific instructions (neutral, risk taking or conservative) were manipulated to observe effects on emergent behaviour of the dyadic system. When attacking players were given conservative instructions, time to cross court mid-line and variability of the attackers trajectory were significantly greater. In Experiment 2, body-scaling of participants was manipulated by creating dyads with different height relations. When attackers were considerably taller than defenders, there were fewer occurrences of symmetry-breaking. When attackers were considerably shorter than defenders, time to cross court mid-line was significantly shorter than when dyads were composed of athletes of similar height or when attackers were considerably taller than defenders. The data exemplify how interacting task and individual constraints can influence emergent decision-making processes in team ball games.

Nutritive sucking pattern - from very low birth weight preterm to term newborn.

UNLABELLED The contribution of maturation and stimulation to the development of oral feeding was investigated, with two main objectives: (1) to analyze the nutritive sucking pattern of very-low-birth-weight newborns from their first oral feeding to the acquisition of independent oral feeding, and (2) to compare the nutritive sucking patterns of these babies, after feeding autonomy, with healthy term newborns. METHODS Two groups were considered for analysis. Group 1: N=15 Very-Low-Birth-Weight (VLBW), gestacional age (GA)=28.15+/-1.5, birth weight (BW)=1178.3+/-174.4. The intervention program began at 30.19+/-1.52 weeks GA. Group 2: N=25 term newborns, healthy, GA=39.04+/-1.2, BW=3370.42+/-310.76. Repeated measures of the following variables were taken (weekly for group 1): suction efficacy (SEF), rhythm of milk transfer (RMT), suctions, bursts and pauses. Group 2 was analysed only once between the 2nd and 5th day of life. RESULTS Group 1 has revealed a minimal suction number at 32 GA weeks (82+/-77.6) and maximal suction number at 36-37 GA weeks (162.7+/-60.7). The number of sucks seemed to be dependent of weight (p=0.005), duration of intervention (p=0.001) and chronological age (p=0.000). Significant statistical effects of gestational age were not observed (p=0.904). Sucks in bursts represented 77% at the beginning of oral feeding (32 weeks GA), and 96% at 33 weeks GA, remaining constant thereafter. The number of sucks and bursts increased with GA and weeks of feeding. The mean duration of the pauses decreased from first to fourth week of feeding (week1=14.1+/-9.1 and week4=6.4+/-1.4 s). The sucking efficacy (SEF) was better explained by weight (p=0.000), number of sucks in 5 min (p=0.025) and chronological age (p=0.044). Gestational age (p=0.051) and nutritive intervention duration (NDI) (p=0.110) did not contribute to explain SEF. Despite the observation of significant statistical differences between groups regarding GA (35.9/39.08; p=0.00), chronological age (53.3/2.5; p=0.00) and weight (1875/3360; p=0.00), the nutritive suction pattern was not statistically different between groups after feeding autonomy. CONCLUSION in VLBW oral feeding before 32 weeks GA allows the attainment of a mature nutritive suction pattern before term (37-40 weeks). Experience seems to be one of the influencing factors in the change of the nutritive suction pattern.

Lateral Manual Asymmetries: A Longitudinal Study From Birth to 24 Months

Longitudinal studies tracking the early development of manual asymmetries are fairly rare compared to the large number of studies assessing hand preference in infancy. Moreover, most prior longitudinal studies have performed behavioral observation over relatively short-time spans considering the celerity of early development. This study aims (i) to investigate the direction and consistency of manual lateral asymmetries over a longer period, from birth to 24 months of age, and (ii) to compare individual and group trajectories to better understand discrepancies between prior studies. Nineteen healthy infants were observed eight times in tasks that were adjusted progressively as infants manual skills developed. Results suggested two distinct periods in terms of the direction, strength, and consistency of manual preference. First, infants went through an initial phase characterized by a lack of lateral manual asymmetries. From 9 months of age, however, group analyses revealed an emerging and steadily growing right lateral bias over time, while individual trajectories revealed that the group-level right-bias formed progressively from a background of highly fluctuating and highly variable developmental trajectories.

Influence of age, sex and somatic variables on the motor performance of pre-school children

Abstract Background: Biological factors can affect the motor development process of children. However, the magnitude of these effects throughout the developmental process remains fairly unknown. Aim: To determine the influence of age, sex and selected somatic measures on the motor performance of pre-school children. Subjects and methods: Three hundred and sixty-seven pre-schoolers (172 boys and 195 girls), aged from 3–5 years old, were recruited from 10 public pre-schools located in the district of Viana do Castelo, Portugal. The children’s motor performance was assessed by five motor sub-tests of Peabody Developmental Motor Scales-2: grasping, visuo-motor integration, stationary, locomotion and object manipulation sub-tests. Age, sex, height, weight and BMI were considered as hypothetical predictors of motor performance. Pearson’s correlation test and multiple linear regression analysis were used to explore the magnitude of the relationship between motor sub-tests and the hypothetical predictors. Results: Depending on the motor sub-test and age group, the models predicted motor performance from a minimum of 3.6% to a maximum of 34.4%. Age in months and sex stood out as the main predictors of motor performance. Conclusions: The relationship between motor performance and selected biological factors varied with age and with the specificity of the motor test.

Perceiving affordances in rugby union

Abstract To succeed in competitive environments, players need to continuously adjust their decisions and actions to the behaviour of relevant others. Players’ interactions demand ongoing decisions that are constrained by what is previously defined (e.g., coaches’ prescriptions that establish ‘what’ to do) and by information that is available in the context and specifies not only ‘what’ the player should do, but also ‘how’, ‘when’ and ‘where’ . We describe what affordances emerge to the ball carrier as a consequence of changes in kinematic variables, such as interpersonal distances or distances to the nearest sideline. Changes in these variables determine whether and when different actions are possible. The ball carrier tended to perform a pass when the tackler was farthest from the sideline and the velocity of approach to the tackler did not seem to effect the ball carriers decision. In the few episodes where the ball carrier moved forward instead of passing the ball, he was mainly influenced by contextual information, such as the variability of the players’ distance to the nearest sideline. In sum, actors must be aware of the affordances of others that are specified by particular variables that become available just before decision-making.