Constrained-Realization Monte-Carlo Method for Hypothesis Testing

We compare two theoretically distinct approaches to generating artificial (or ``surrogate'') data for testing hypotheses about a given data set. The first and more straightforward approach is to fit a single ``best'' model to the original data, and then to generate surrogate data sets that are ``typical realizations'' of that model. The second approach concentrates not on the model but directly on the original data; it attempts to constrain the surrogate data sets so that they exactly agree with the original data for a specified set of sample statistics. Examples of these two approaches are provided for two simple cases: a test for deviations from a gaussian distribution, and a test for serial dependence in a time series. Additionally, we consider tests for nonlinearity in time series based on a Fourier transform (FT) method and on more conventional autoregressive moving-average (ARMA) fits to the data. The comparative performance of hypothesis testing schemes based on these two approaches is found to depend on whether or not the discriminating statistic is pivotal. A statistic is ``pivotal'' if its distribution is the same for all processes consistent with the null hypothesis. The typical-realization method requires that the discriminating statistic satisfy this property. The constrained-realization approach, on the other hand, does not share this requirement, and can provide an accurate and powerful test without having to sacrifice flexibility in the choice of discriminating statistic.Comment: 19 pages, single spaced, all in one postscript file, figs included. Uncompressed .ps file is 425kB (sorry, it's over the 300kB recommendation). Also available on the WWW at http://nis-www.lanl.gov/~jt/Papers/ To appear in Physica

Coarse-grained entropy rates for characterization of complex time series

A method for classification of complex time series using coarse-grained entropy rates (CER's) is presented. The CER's, which are computed from information-theoretic functionals -- redundancies, are relative measures of regularity and predictability, and for data generated by dynamical systems they are related to Kolmogorov-Sinai entropy. A deterministic dynamical origin of the data under study, however, is not a necessary condition for the use of the CER's, since the entropy rates can be defined for stochastic processes as well. Sensitivity of the CER's to changes in data dynamics and their robustness with respect to noise are tested by using numerically generated time series resulted from both deterministic -- chaotic and stochastic processes. Potential application of the CER's in analysis of physiological signals or other complex time series is demonstrated by using examples from pharmaco-EEG and tremor classification.Comment: 15 pages, uuencoded compressed postscript file, figures embedded in the text, , <[email protected]

The Effect of Internal vs. External Focus of Attention Instructions on Countermovement Jump Variables in NCAA Division I Baseball Players

INTRODUCTION: Coaches utilize verbal instruction to focus an athlete’s attention on pertinent aspects of a skill. Focus of attention can be classified as either internal or external (13). An internal instruction directs focus to bodily movements or the action itself whereas an external instruction pertains to the desired movement outcome, an implement (golf club, ball, etc.) or the environment (87, 13). PURPOSE: To compare the effect of internal and external focus of attention instructions on force-time characteristics of the countermovement jump (CMJ) in collegiate baseball players. METHODS: Forty-three resistance trained men ( ± SD; age = 20 ± 1.5 years; height = 186.4 ± 6.6 cm; body mass = 88.9 ± 8.8 kg) on an NCAA Division I baseball team volunteered to participate in this study. Each participant performed a total of 16 CMJs (2x4 jumps in both an internal and external focus condition). Jump height (JH), peak velocity (PV), mean concentric velocity (MCV), peak force (PF), mean concentric force (MCF), peak power (PP), mean concentric power (MCP), average eccentric rate of force development (ECC-RFD), relative mean concentric force (rCON) and relative net concentric impulse (rCON Impulse) were calculated from force-time and position data. Paired samples t-tests and Cohen’s d effect sizes were used to examine differences between conditions. Subjects also completed manipulation check surveys following each set of jumps. RESULTS: When subjects were instructed using an external focus they demonstrated significantly (p < 0.05) greater JH (48.0 ± 5.6 cm), PV (3.6 ± 0.3 m·s-1), MCV (2.31 ± 0.22 m·s-1), MCP (4,442.41 ± 716.35 W), ECC RFD (1,512.5 ± 249.1 N·s-1), and rCON impulse (3.4 ± 0.3 Ns·kg-1) as compared to jumps performed with the internal focus (46.4 ± 5.4 cm; 3.5 ± 0.3 m·s-1; 2.25 ± 0.23 m·s-1; 4,350.85 ± 729.79 W; 1,461. 2 ± 252. 8 N·s-1; 3.3 ± 0.3 Ns·kg-1).  According to the manipulation checks, subjects adopted the desired focus of attention in 73.8% of the internal trials, and 66.6% in external trials. CONCLUSIONS: Trials in which subjects were instructed with an external focus of attention displayed significantly greater JH, PV, MCV, MCP, ECC-RFD, and rCON impulse. These results support the Constrained Action Hypothesis and related literature which state that external focus of attention enhances automaticity and subconscious control of motor patterns (101). It is interesting to note that there was superior recall of the internal instructions during the manipulation checks. This may suggest that the subjects thought about or consciously processed these instructions to a greater extent. Conscious processing may also explain the reduced internal condition performance. PRACTICAL APPLICATION: The present study demonstrates that several CMJ jump variables were significantly influenced by the stipulated instructions. These results indicate that instructions can alter the efficiency and performance of a skill and should be designed and applied appropriately. According to the literature and the present study, if an optimum performance metric (jump height, peak velocity) is desired, external focus of attention instructions should be used

Validierung klinischer Tests zur Vereinfachung der Differenzialdiagnose des Parkinsontremors

Ziel dieser Studie war es einfache klinische Tests zur Differenzialdiagnose des Parkinsontremors (PT) zu entwickeln und zu validieren, um die Rate der Fehldiagnosen zu senken. Tremores werden in der Regel klinisch diagnostiziert. Es wurden zwei klinische Testverfahren untersucht, die auf dem propagierten Phänomen beruhen, dass der Ruhetremor nur beim Morbus Parkinson bei Bewegungsbeginn supprimiert wird. In die Studie eingeschlossen wurden 46 Patienten mit PT und 45 Patienten mit anderen Tremores, darunter 31 ET. Es wurden die folgenden Videosequenzen angefertigt: Nach Provokation eines Ruhetremors wurde im ersten Test ein Anhebemanöver des tremordominanten Arms durchgeführt, während im zweiten Test eine kombinierte Anhebe- und Zeigebewegung vollzogen wurde. Die Beurteilung der Tremorsuppression erfolgte anhand einer 5-Punkte-Skala durch einen (unverblindeten) erfahrenen Neurologen. Diese stellte auch die Referenz für die folgende Validitätsprüfung per Video durch vier verblindete Neurologen, darunter 2 Bewegungsstörungsexperten, dar. In der klinischen Untersuchung zeigten zwischen 85- 89 % der Parkinson-Patienten je nach Verfahren eine Tremorsuppression, und nur jeweils 3 Patienten aus der Vergleichsgruppe, darunter 2 ET. Die im Videorating erzielten Sensitivitäten (0,93 - 1,00) und Spezifitäten (0,84 - 0,96) waren jeweils sehr hoch. Die Interrater-Reliabilität zwischen den Videoratern war in beiden Testverfahren fast perfekt(kappa = 0,85 - 0,93). Durch die Beurteilung von Videosequenzen und der damit verbundenen Störanfälligkeit verloren die Testverfahren jedoch insgesamt an Genauigkeit. Die Beurteilung der Tremorsuppression ist somit ein einfacher, valider, reliabler und vor allem kostenneutraler klinischer Test, mit dessen Hilfe die Diagnose des Parkinsontremors vereinfacht wird. Besondere Kenntnisse sind zur Durchführung und Beurteilung des Tests nicht erforderlich. Eine Nativ-Beurteilung ist einer Videobeurteilung allerdings vorzuziehen. Das Ergebnis, dass die Tremorsuppression fast ausschließlich bei Parkinson-Patienten zu beobachten ist, legt den Schluß nahe, dass der PT und der ET trotz vieler Parallelen verschiedenen Pathophysiologien unterliegen könnten

The effects of internally and externally directed attention during motor skill execution and learning

Focusing attention onto the intended outcome or goal of a movement (an External focus of attention) has been shown to be more beneficial to the learning and performance of movements than focusing onto the components of the movement being carried out (an Internal focus of attention). In this thesis, four studies assessed the effects of attentional focusing strategies on the learning and execution of motor skills during different situations. Study 1 demonstrated that an internal focus of attention during a suprapostural pointing task resulted in degraded postural control as well as larger movements of the hand and arm. In Study 2 novices using an external focus were more accurate in a dart throwing task than those using an internal focus, but no different from a control condition. In Study 3 two experiments investigated the effects of attentional focuses on postural control at rest and whilst fatigued. Postural control was no better using external focus when compared to an internal focus at rest, but was better than baseline. When fatigued (localised and generalised), balance was significantly deteriorated using an external focus, but not when an internal focus was used. In two experiments during Study 4 novices carrying out a dart throwing task used different attentional focusing instructions during practice and later performance. During practice sessions in Experiment 4.1 and 4.2 accuracy was not affected by attentional focusing instructions. Using an external focus during performance resulted in significantly better accuracy than using an internal focus. In Experiment 4.2, novices who preferred an internal focus but used an external focus during performance performed less accurately than participants who preferred the external focus. Findings demonstrate that the benefits of an external focus of attention is evident in performance situations, whereas an internal focus may be beneficial whilst fatigued and is not detrimental during practice

Estudo do comportamento postural em doentes com doença de Parkinson : caracterização e análise segundo metodologias tradicionais e não lineares.

Doutoramento em Motricidade Humana na especialidade de Ciências da MotricidadeEste trabalho analisa o comportamento postural de doentes com Doença de Parkinson (DP) centrando-se essencialmente na avaliação e análise do comportamento do centro de pressão (CP) e do centro de gravidade (CG). Foi utilizada a Posturografia Dinâmica Computorizada e métodos de análise tradicionais (lineares) e não lineares. O objetivo deste estudo foi fornecer informação que possibilitasse uma maior sustentabilidade clínica e científica relativamente à dinâmica de controlo motor destes doentes. A análise compreendeu: a) a caracterização quantitativa do comportamento postural dos doentes com DP, através de métodos tradicionais, nas diferentes fases de evolução da doença (segundo a escala de Hoehn & Yahr - H&Y); b) a caracterização do comportamento postural destes doentes segundo uma metodologia de análise não linear; c) a quantificação da instabilidade postural e do risco de quedas destes doentes com base nos resultados de escalas clínicas (Pulltest) e de variáveis posturográficas. Os resultados permitem concluir que é possível identificar diferenças entre os estadios de severidade da doença, com base numa abordagem quantitativa definida por variáveis associadas ao controlo postural. Em geral, as dimensões independentes que permitem discriminar os estadios da escala de H&Y também permitem discriminar os grupos definidos pelo nível de instabilidade postural (Pulltest)