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Period Variability (period + variability)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Development of dynamic stability in children's rhythmic movement

DEVELOPMENTAL PSYCHOBIOLOGY, Issue 6 2009
Eric G. James
Abstract This study examined the hypothesis that the stability of rhythmic motor patterns increases with developmental age in children. Children aged 6 and 10 years and adults (18- to 23-year-olds) rocked back and forth at their preferred amplitude and frequency while seated on a wooden box placed atop a force platform. Participants performed the seated rocking task with their feet supported and unsupported. There was an age-related decrease in rocking frequency and variability of the rocking cycle period, while the stability of the rocking dynamics increased, as indexed by the standard deviation of the phase angle of center of pressure motion. The presence of foot support decreased the stability of the rocking dynamics and reduced cycle period variability in the children, but not the adults. The results revealed that increments of age are associated with an increase in the stability of rhythmic motor patterns even when environmental conditions are altered. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 465,473, 2009 [source]

Individual Differences in Infants' Recognition of Briefly Presented Visual Stimuli

INFANCY, Issue 3 2001
Janet E. Frick
Infants' recognition memory has been shown to be related to individual differences in look duration and level of heart period variability. This study examined the effect of individual differences in these 2 measures on infants' recognition of briefly presented visual stimuli using a paired-comparison recognition-memory paradigm. A sample of 35 full-term infants was studied longitudinally at 14, 20, and 26 weeks of age. Recognition memory for briefly presented stimuli was tested in 6 experimental conditions, with delays corresponding to different heart-rate-defined phases of attention. The 20-and 26-week-old infants, and infants with high levels of heart period variability, generally showed more evidence of recognition memory for briefly presented visual stimuli. Greater evidence of recognition memory was observed when stimuli were presented during sustained attention. Infants with more mature baseline physiological responses show greater evidence of recognition memory, and stimulus and procedural factors may be more important for the study of individual differences in infant visual attention than has previously been suggested. [source]

Variability in red supergiant stars: pulsations, long secondary periods and convection noise

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
L. L. Kiss
ABSTRACT We study the brightness variations of galactic red supergiant stars using long-term visual light curves collected by the American Association of Variable Star Observers over the last century. The full sample contains 48 red semiregular or irregular variable stars, with a mean time-span of observations of 61 yr. We determine periods and period variability from analyses of power density spectra and time,frequency distributions. We find two significant periods in 18 stars. Most of these periods fall into two distinct groups, ranging from a few hundred to a few thousand days. Theoretical models imply fundamental, first and possibly second overtone mode pulsations for the shorter periods. Periods greater than 1000 d form a parallel period,luminosity relation that is similar to the long secondary periods of the asymptotic giant branch stars. A number of individual power spectra shows a single mode resolved into multiple peaks under a Lorentzian envelope, which we interpret as evidence for stochastic oscillations, presumably caused by the interplay of convection and pulsations. We find a strong 1/f noise component in the power spectra that is remarkably similar in almost all stars of the sample. This behaviour fits the picture of irregular photometric variability caused by large convection cells, analogous to the granulation background seen in the Sun. [source]

Cardiorespiratory measures before and after feeding challenge in term infants are related to birth weight

ACTA PAEDIATRICA, Issue 7 2009
M Cohen
Abstract Aim:, This study tested the hypothesis that, within a few hours of delivery, cardiorespiratory measure taken during feeding provides markers of group differences related to birth weight. A secondary hypothesis was that high-frequency heart period variability would be related to underlying differences in autonomic control associated with birth weight. Methods and Subjects:, One hundred four term infants in the lowest, middle, and highest birth weight quintiles were enrolled. Exclusion criteria were evidence of drug abuse, congenital anomalies, Apgar scores less than 7 or admission to the neonatal intensive care unit. Within 96 h of delivery, heart and respiratory rates, blood pressures and heart period variability were measured before, during and after feeding. Results:, Term babies in the lowest quintile of birth weights have lower heart rates prior to feeding but greater increases in heart rate during the early postprandial period. Assessments of high-frequency heart period variability suggest that small term infants have greater parasympathetic tone before feeding and more sustained parasympathetic withdrawal following feeding. Conclusion:, Measurements of cardiorespiratory functions before and after feeding are related to birth weight and may provide markers that can help identify the most vulnerable of infants with small size at birth. [source]