Detection of long‐range dependence and estimation of fractal exponents through ARFIMA modelling

We evaluate the performance of autoregressive, fractionally integrated, moving average (ARFIMA) modelling for detecting long‐range dependence and estimating fractal exponents. More specifically, we test the procedure proposed by Wagenmakers, Farrell, and Ratcliff , and compare the results obtained with the Akaike information criterion (AIC) and the Bayes information criterion (BIC). The present studies show that ARFIMA modelling is able to adequately detect long‐range dependence in simulated fractal series. Conversely, this method tends to produce a non‐negligible rate of false detections in pure autoregressive and moving average (ARMA) series. Generally, ARFIMA modelling has a bias favouring the detection of long‐range dependence. AIC and BIC gave dissimilar results, due to the different weights attributed by the two criteria to accuracy and parsimony. Finally, ARFIMA modelling provides good estimates of fractal exponents, and could adequately complement classical methods, such as spectral analysis, detrended fluctuation analysis or rescaled range analysis.     

Fractal models for event-based and dynamical timers

Some recent papers proposed to distinguish between event-based and emergent timing. Event-based timing is conceived as prescribed by events produced by a central clock, and seems to be used in discrete tasks (e.g., finger tapping). Emergent or dynamical timing refers to the exploitation of the dynamical properties of effectors, and is typically used in continuous tasks (e.g., circle drawing). The analysis of period series suggested that both timing control processes possess fractal properties, characterized by self-similarity and long-range dependence. The aim of this article is to present two models that produce period series presenting the statistical properties previously evidenced in discrete and continuous rhythmic tasks. The first one is an adaptation of the classical activation/threshold models, including a plateau-like evolution of the threshold over time. The second one is a hybrid limit-cycle model, including a time-dependent linear stiffness parameter. Both models reproduced satisfactorily the spectral signatures of event-based and dynamical timing processes, respectively. The models also produced auto-correlation functions similar to those experimentally observed. Using ARFIMA modeling we show that these simulated series possess fractal properties. We suggest in conclusion some possible extensions of this modeling approach, to account for the effects of metronomic pacing, or to analyze bimanual coordination.     

Fractal 1/ƒ dynamics suggest entanglement of measurement and human performance

Variability of repeated measurements in human performances exhibits fractal 1/? noise. Yet the relative strength of this fractal pattern varies widely across conditions, tasks, and individuals. Four experiments illustrate how subtle details of the conditions of measurement change the fractal patterns observed across task conditions. The results call into question whether measurement noise and measured signal can be distinguished in human performance, suggesting that human performance is inextricably entangled with measurement context. Perhaps, though, a hypothesis of soft assembly of human performance can circumvent the conundrum (e.g., Turvey, 2007).     

Fractal properties and short-term correlations in motor control in cycling: influence of a cognitive challenge

Fluctuations in cyclic tasks periods is a known characteristic of human motor control. Specifically, long-range fractal fluctuations have been evidenced in the temporal structure of these variations in human locomotion and thought to be the outcome of a multicomponent physiologic system in which control is distributed across intricate cortical, spinal and neuromuscular regulation loops.Combined with long-range correlation analyses, short-range autocorrelations have proven their use to describe control distribution across central and motor components.We used relevant tools to characterize long- and short-range correlations in revolution time series during cycling on an ergometer in 19 healthy young adults. We evaluated the impact of introducing a cognitive task (PASAT) to assess the role of central structures in control organization.Autocorrelation function and detrending fluctuation analysis (DFA) demonstrated the presence of fractal scaling. PSD in the short range revealed a singular behavior which cannot be explained by the usual models of even-based and emergent timing.The main outcomes are that (1) timing in cycling is a fractal process, (2) this long-range fractal behavior increases in persistence with dual-task condition, which has not been previously observed, (3) short-range behavior is highly persistent and unaffected by dual-task.Relying on the inertia of the oscillator may be a way to distribute more control to the periphery, thereby allocating less resources to central process and better managing additional cognitive demands. This original behavior in cycling may explain the high short-range persistence unaffected by dual-task, and the increase in long-range persistence with dual-task.     

Calibration processes in a serial talent test

ObjectivesIn the beginning of serial evaluations, raters assess performances without knowledge about following performances. We assume that judges must observe a certain number of performances to calibrate their judgment scale, leading to systematic biases (avoidance of extreme judgments) in the beginning of judgment series. The present experiment investigates how many performance observations are necessary to calibrate internal judgment scales, leading to consistent judgments.DesignA between-group design was used.MethodVideos of a talent-test were presented in different orders. Every performance was presented in early, medium, and late positions. Thirty participants rated these series and we assessed the effect of performance position on performance evaluations.ResultsWe found calibration biases within the first nine performances; after that, evaluations remained stable and consistent.ConclusionCalibration processes are completed after a specific number of judgments; this implies interesting interventions for consistent judgments independent of the position in a series.     

Testing for the presence of 1/f noise in continuation tapping data.

A number of recent papers have suggested that the series of time intervals produced in continuation tapping may have fractal properties. This proposition, nevertheless, was only based on the visual appraisal of graphical results, and was not statistically supported. In the present study, we applied the ARMA/ARFIMA modeling procedures proposed by Wagenmakers, Farrell, and Ratcliff (2005) to test for the presence of long-range dependencies in continuation tapping data. Our results demonstrate the presence of long-range dependencies in most series and offer strong support for the hypothesis that fluctuations in tapping series are fractal in nature.     

Rapports au travail, contrôle et santé dans les centres de gestion de la relation-client

The main objective of the present research was to analysis the organizational work and health in call centre. In facts, it proves that this specific professional activity produces so much effects on the level call centre agents (violence, perceived stress, perceived health, musculoskeletal disorder symptoms, intention to quit, satisfaction), that at the organizational level (turnover, lower quality, lowers performances). So, the evolution of the career, the organizational support, the participation in the decisions or the type of management produce a positive effects at the same time, on the worker and the organization (job satisfaction, implication, better real or perceived performances well-being, job involvement, better quality of life, lower turnover or absenteeism…). Lastly, we propose a model of analysis of strain at the work which integrates emotional exhaustion and the depersonalization.     

Small-angle X-ray scattering study on the fractal structure of solid products of bituminous coal at different carbonization temperatures

Carbonization is one of the main methods for comprehensive utilization of bituminous coal. Bituminous coal and its solid products from carbonization, namely char and coke, have complex pore structures, which can be characterized by fractals. We performed a study on the fractal structure of the solid products prepared from the bituminous coal of Shuiyu mine in Shanxi Province, China, at different carbonization temperatures (25°C～1000°C) by synchrotron radiation small-angle X-ray scattering (SAXS). The results show that the bituminous coal has a surface fractal structure during the whole carbonization process. The variation of fractal dimension with carbonization temperature illustrates the different stages of the carbonization process.     

Habiletés phonologiques chez des enfants dysphasiques de GS et CP : étude comparative avec des enfants au développement langagier normal

The aim of this study was to investigate the deficit in phonological skills of pre-reader and beginning reader children with Specific Language Impairment (SLI). We compared their performances in different metaphonological tasks (a common unit detection task (syllable vs phoneme) and a phoneme deletion task) with those of children with Normal Language Development (NLD) of the same school level. Phoneme detection task is very difficult for all children in kindergarten. The performances of SLI children are poorer than those of NLD children for syllables and phonemes in first grade. The forced choice phoneme deletion tasks point out a specific difficulty for children with SLI to focus on the phonological properties of words when their attention must shift from content to form.     

Classroom applications of stimulus equivalence technology

We review basic concepts and methods of stimulus equivalence research and suggest applications in teaching rudimentary language arts skills in the classroom. We describe methods of establishing equivalence-based networks of matching-to-sample, writing, and naming performances. The methods may be used as a supplement to classroom instruction to assess whether standard curriculum-based approaches establish such integrated networks. Methods derived from equivalence research may be useful for remediation when traditional teaching approaches fail. Recent research suggests that direct focus on spelling performances may be required if entire networks of language arts skills are to be acquired. In addition, the equivalence relations themselves may require concentrated teaching in some children.     

Fractal Structure of Event Segmentation: Lessons From Reel and Real Events

We investigated fractality in the segmentation of cinematic and live events. Four movies from distinct genres were first analyzed and found to be fractal, albeit in different regions of the fractal range. In Experiment 1, viewers parsed the films' events, attending to short or long timescales, using a button box to indicate break points. The temporal structure of film viewing was found to be fractal regardless of the scale of attention and to reflect the differing fractal editing structure of the films. Experiment 2 found event segmentation to be fractal in a natural setting, a basketball game, as well. An additional parallel between reel and real events was uncovered: fractal indices were at the higher end of the range for both the film genre intended to be anxiogenic and the more suspenseful portion of the basketball game. We argue that the fractal structure of perception reflects the fractal structure of events whether the events are in film or in nature. We speculate that fractal structure has implications for understanding subjective experience and, ultimately, the correspondence between films and the world.     

The effects of expertise and age on rhythm production: adaptations to timing and sequencing constraints.

We investigate age- and expertise-related individual differences in component processes of rhythmic timing. To this end we apply analysis of covariance structure and symbolic dynamics to time series obtained from performances of two bimanual rhythm tasks at different tempos. Results show similar effects for peripheral motor implementation and timekeeper execution in young and older amateur pianists. Older participants show specific problems with temporal sequencing processes (specification of different target intervals). Expert pianists show lower variability in both motor implementation and timekeeper execution and they accommodate to the sequencing demands of different tempos by selectively relying on integrated or parallel timing. We argue that the observed timing control characteristics reflect individuals' adaptations to internal processing limitations and performance constraints.     

Quantifying false positives in simulated events using partial interval recording and momentary time sampling with dual‐criteria methods

The dual‐criteria (DC) and conservative dual‐criteria (CDC) methods allow clinicians and researchers to quantify the occurrence of false‐positive outcomes within single‐case experimental designs. The purpose of the current study was to use these DC and CDC methods to measure the incidence of false positives with simulated data collected via discontinuous interval methods (i.e., momentary time sampling, partial‐interval recording) as a function of data series length. We generated event data to create 316,800 unique simulated data series for analysis. In Experiment 1, we evaluated how changes in relevant parameters (i.e., interval sizes, event durations, IRT‐to‐event‐run ratios) produced false positives with momentary time sampling procedures. We also assessed the degree that the CDC method produced fewer false positives than the DC method with simulated interval data. In Experiment 2, we used similar procedures to quantify the occurrence of false positives with partial‐interval recording data. We successfully replicated outcomes from previous research in the current study, though such results only highlight the generality of the procedures relating to false positive (and not false negative) outcomes. That is, these results indicate MTS and PIR may adequately control for false positives, but our conclusions are limited by a lack of data on power.     

Quality at the Point of Service: Profiles of Practice in After-School Settings

A unique observational data set was used to explore quality at the point of service in after-school programs. Staff practices in after-school settings were represented on a series of unidimensional scales closely indexed to staff behavior. In order to account for heterogeneity of staff performances, pattern-centered methods were used to construct profiles of common staff practices. Results revealed six pedagogy profiles that were classified in terms of three broad types of performances delivered by after-school staff: (1) positive youth development, (2) staff-centered, and (3) low-quality. Staff membership in these profiles was not related to youth-staff ratio. However, results revealed significant differences between the profiles on the content of the offering and the age of youth in the setting.     

Rotated Drawing: The Range of Performance and Anatomical Correlates in a Series of 16 Patients

Recently there has been interest in an unusual neuropsychological disorder in which the patient copies a complex drawing in a position which is grossly rotated relative to the original. This disorder is of interest partly because of its relationship to current theories of the process of object recognition, but the range of performances typically seen, as well as its anatomical correlates, remain obscure. We report 16 cases who produced grossly rotated drawings of the Rey and Taylor Complex Figures. These patients were drawn from an unselected series of 240 cases, with a wide variety of lesion types and sites. The performances of the 16 patients displayed striking similarities. We describe the formal features of these drawings and plot their anatomical correlates.     

Fractal dynamics of heart beat interval fluctuations in corticotropin-releasing factor receptor subtype 2 deficient mice

Non-linear fractal analysis of cardiac interbeat time series was performed in corticotropin-releasing factor receptor subtype 2 (CRFR2) deficient mice. Heart rate dynamics in mice constitutes a self-similar, scale-invariant, random fractal process with persistent intrinsic long-range correlations and inverse power-law properties. We hypothesized that the sustained tachycardic response elicited by intraperitoneal (ip) injection of human/rat CRF (h/rCRF) is mediated by CRFR2. In wildtype control animals, heart rate was increased to about maximum levels (~ 750 bpm) while in CRFR2-deficient animals baseline values were retained (~ 580 bpm). The tachycardic response elicited by ip-application is mediated by CRFR2 and is interpreted to result from sympathetic stimulation. However, the functional integrity of CRFR2 would not present a prerequisite to maintaining the responsiveness and resiliency of cardiac control to external environmental perturbations experimentally induced by extrinsic ip-application of h/rCRF or under physiological conditions that may be associated with an increased peripheral release of CRF. Under stressful physiological conditions achieved by novelty exposure, CRFR2 is not involved in the cardiodynamic regulation to external short-term stress. While the hypothesis of involvement of CRFR2 in cardiac regulation upon pharmacological stimulation cannot be rejected, the present findings suggest that the mechanism of action is by sympathetic stimulation, but would not unambiguously allow to draw any conclusions as to the physiological role of CRFR2 in the control of cardiac dynamics.     

Fractal Dynamics of Heart Beat Interval Fluctuations in Corticotropin-Releasing Factor Receptor Subtype 2 Deficient Mice

Non-linear fractal analysis of cardiac interbeat time series was performed in corticotropin-releasing factor receptor subtype 2 (CRFR2) deficient mice. Heart rate dynamics in mice constitutes a self-similar, scale-invariant, random fractal process with persistent intrinsic long-range correlations and inverse power-law properties. We hypothesized that the sustained tachycardic response elicited by intraperitoneal (ip) injection of human/rat CRF (h/rCRF) is mediated by CRFR2. In wildtype control animals, heart rate was increased to about maximum levels (approximately 750 bpm) while in CRFR2-deficient animals baseline values were retained (approximately 580 bpm). The tachycardic response elicited by ip-application is mediated by CRFR2 and is interpreted to result from sympathetic stimulation. However, the functional integrity of CRFR2 would not present a prerequisite to maintaining the responsiveness and resiliency of cardiac control to external environmental perturbations experimentally induced by extrinsic ip-application of h/rCRF or under physiological conditions that may be associated with an increased peripheral release of CRF. Under stressful physiological conditions achieved by novelty exposure, CRFR2 is not involved in the cardiodynamic regulation to external short-term stress. While the hypothesis of involvement of CRFR2 in cardiac regulation upon pharmacological stimulation cannot be rejected, the present findings suggest that the mechanism of action is by sympathetic stimulation, but would not unambiguously allow to draw any conclusions as to the physiological role of CRFR2 in the control of cardiac dynamics.     

Simple geometric fractals

Recently, vision scientists have begun to explore fractals. This paper describes a set of programs that can be used to create fractal and fractal-like drawings. The programs were implemented on the Apple II series of computers. The programs were primarily designed to create deterministic and random fractal-like patterns with fractal dimensionality between 1 and 2. A supplementary program computes the box dimensionality, a measure of dimensionality that does not assume an infinite recursive process. The advantages of this measure of dimensionality over the more typical self-similar measure are discussed.     

Développement de la mémoire de travail : relations du centre exécutif avec la boucle phonologique et le calepin visuospatial chez des enfants de CE1 et de CM2

The aim of this study was to examine the development of working memory's components and their relationships. Phonological loop's, visuospatial sketchpad's and central executive's efficiencies were assessed by simple and complex span tasks and executive tasks with verbal and visuospatial material. The analyses were performed on 64 second-grade and 55 fifth-grade children's data. Developmental performances improvement was examined according to tasks and material. Analyses of variance revealed performances improvement according to age and type of material (verbal > non verbal) for the slave system tasks and for a part of central executive's tasks. Correlation analysis and exploratory factorial analysis suggested that slave systems would become progressively more specific and that central executive's efficiency would be dependent on this specialization.