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PubMed1997

Pitfalls in estimating motion detector receptive field geometry.

A number of psychophysical investigations have used spatial-summation methods to estimate the receptive field (RF) geometry of motion detectors by exploring how psychophysical thresholds change with stimulus height and/or width. This approach is based on the idea that an observer's ability to detect motion direction is strongly determined by the relationship between the stimulus geometry (height and width) and the RF of the activated motion detectors. Our results show that previous estimates of RF geometry can depend significantly on stimulus position in the visual field as well as on the stimulus height-to-width ratio. The data further show that RF estimates depend on the stimulus in a manner that is inconsistent with basic predictions derived from current motion detector models. Hence previous estimates of height, width, and height-to-width ratios of motion detector RFs are inaccurate and unreliable. This inaccuracy/unreliability is attributed to a number of sources. These include incorrect fixed-parameter values in model fits, as well as the confounding of physiological spatial summation area through combined use of contrast thresholds and Gaussian-windowed stimuli. A third source of error is an asymmetric variation of spatiotemporal correlation in the stimulus as either its height or width is varied (and the other dimension held constant). Most importantly, a fourth source of unreliability is attributed to the existence of a nonlinear, nonmonotonic distribution of motion detectors in the visual field that has been previously described and is a natural result of visual anatomy.

Contrast Sensitivity↗
PubMed2002

Numerical characterization of high harmonic attosecond pulses.

A numerical simulation of attosecond harmonic pulse generation in a three-dimensional field-ionizing gas is presented. Calculated harmonic efficiencies quantitatively reproduce experimental findings. This allows a quantitative characterization of attosecond pulse generation revealing information currently not accessible by experiment. The rapid phase variation and spatiotemporal distortions of harmonics are smaller than anticipated, allowing focusing of 30-nm, 750-as pulses to intensities in excess of 10(13) W/cm(2). Feasibility of such pulses brings novel applications such as extreme ultraviolet nonlinear optics and attosecond pump probe spectroscopy within reach.

Journal Article↗
PubMed2000

High resolution spatiotemporal analysis of the contingent negative variation in simple or complex motor tasks and a non-motor task.

OBJECTIVES: Since the characteristics of the Bereitschaftspotential (BP) - voluntary movement paradigm of internally-driven movements - have been established recently by our group using high resolution DC-EEG techniques, it was of great interest to apply similar techniques to the other slow brain potential--contingent negative variation (CNV) of externally-cued movements--with the same motor tasks using the same subjects. METHODS: The CNV for simple bimanual sequential movements (task 1), complex bimanual sequential movements (task 2) and a non-motor condition (task 3) was recorded on the scalp using a 64 channel DC-EEG in 16 healthy subjects, and the data were analyzed with high resolution spatiotemporal statistics and current source density (CSD). RESULTS: (1) The CNV was distributed over frontal, frontocentral, central and centroparietal regions; a negative potential was found at the frontal pole and a positive potential was found over occipital regions. (2) CNV amplitudes were higher for task 2 than for task 1, and there was no late CNV for task 3. (3) A high resolution spatiotemporal analysis revealed that during the early CNV component, statistical differences existed between the motor tasks (tasks 1 and 2) and the non-motor task (task 3), which occurred at frontocentral, central, centroparietal, parietal and parieto-occipital regions. During the late CNV component, additional significant differences were found not only between the motor tasks and the non-motor task but also between motor task 1 and task 2 at frontocentral, central and centroparietal regions. (4) Comparison of the CNV between the frontomesial cortex (situated over the supplementary/cingulate areas, SCMA) and both lateral pre-central areas (situated over the primary motor areas, MIs) showed that there was no statistically significant difference between the two cortical motor areas except for the early CNV. (5) Comparison of the CNV between the 3 tasks over the cortical motor areas showed that there were significant differences between the motor tasks and the non-motor task regarding the auditory evoked potential (AEP) and the early CNV component, and between all 3 tasks in the late CNV, the visual evoked potential (VEP(2)) and the N-P component. (6) The ranges and the densities of the CSD maps were larger and higher for complex than for simple tasks. The current sinks of the AEP and the early CNV were located at Fz, the late CNV at FCz and surrounding regions. As to be expected, current sources of the VEPs were located at the occipital lobes. The CNV was a current sink (negative) except for the VEP's main component which was a current source (positive). CONCLUSIONS: (1) The CNV topography over the scalp varied with the complexity of motor tasks and between motor and non-motor conditions. (2) The origin of the early CNV may rest in the frontal lobes, while the late CNV may stem from more extensive cortical areas including SCMA, MIs, etc. (3) The late CNV component is not identical with the BP.

Adult↗
PubMed2001

Synapse-specific contribution of the variation of transmitter concentration to the decay of inhibitory postsynaptic currents.

Synaptic transmission is characterized by a remarkable trial-to-trial variability in the postsynaptic response, influencing the way in which information is processed in neuronal networks. This variability may originate from the probabilistic nature of quantal transmitter release, from the stochastic behavior of the receptors, or from the fluctuation of the transmitter concentration in the cleft. We combined nonstationary noise analysis and modeling techniques to estimate the contribution of transmitter fluctuation to miniature inhibitory postsynaptic current (mIPSC) variability. A substantial variability (approximately 30%) in mIPSC decay was found in all cell types studied (neocortical layer2/3 pyramidal cells, granule cells of the olfactory bulb, and interneurons of the cerebellar molecular layer). This large variability was not solely the consequence of the expression of multiple types of GABA(A) receptors, as a similar mIPSC decay variability was observed in cerebellar interneurons that express only a single type (alpha(1)beta(2)gamma(2)) of GABA(A) receptor. At large synapses on these cells, all variance in mIPSC decay could be accounted for by the stochastic behavior of approximately 36 pS channels, consistent with the conductance of alpha(1)beta(2)gamma(2) GABA(A) receptors at physiological temperatures. In contrast, at small synapses, a significant amount of variability in the synaptic cleft GABA transient had to be present to account for the additional variance in IPSC decay over that produced by stochastic channel openings. Thus, our results suggest a synapse-specific contribution of the variation of the spatiotemporal profile of GABA to the decay of IPSCs.

Animals↗
PubMed1988

The development of grooming and its expression in adult animals.

We have seen that grooming is a class of heterogeneous activities, widely represented in animal taxa, yet sufficiently homogeneous within some phyletic groups to generate and test phylogenetic hypotheses. In the life of the grooming animal, the functions served by these activities are also diverse. Similar acts of grooming may serve different functions in different species or in different contexts. Sometimes these different functions can be discovered by careful attention to variations in the spatiotemporal patterning or sequencing of grooming elements. In several species a general cephalocaudal progression has been noted during both the ontogeny of grooming and during its expression in adults. During early development and in adulthood, the components or functional units of grooming appear to be hierarchically organized. Scratching with the hindpaw, for example, appears in rodents to be separate from the hierarchical branches in which one finds licking and face wiping. At least some transitions between functional units can be predicted from changes in the temporal patterning of one grooming unit (e.g., eye wipe) just prior to the onset of another unit (e.g., ear wipe). Analyses of genital and other types of grooming during two forms of sexual activity (copulation and the display of penile erections ex copula) were used to demonstrate once again that the stimulus regulation of grooming is context dependent. Among the implications of this review for the physiological study of grooming are the following: 1. Careful attention should be given to the spatiotemporal patterning of grooming, in order to reduce errors of "lumping" and "splitting" in classifying grooming acts, and also to detect alterations in the patterning when they occur. Such changes in patterning may be assumed to reflect changes in the physiological state of the animal. 2. Grooming acts that appear formally similar in different contexts may operate under rather different physiological systems. 3. Experimental manipulations may affect grooming directly, that is, by generating grooming efference without changing afference, or indirectly, by altering the "motivational state" or by creating stimulation that potentiates grooming, as from itching or from reafference due to provoking other behavior patterns.

Aging↗
PubMed2004

Evaluating the disparity of female breast cancer mortality among racial groups - a spatiotemporal analysis.

BACKGROUND: The literature suggests that the distribution of female breast cancer mortality demonstrates spatial concentration. There remains a lack of studies on how the mortality burden may impact racial groups across space and over time. The present study evaluated the geographic variations in breast cancer mortality in Texas females according to three predominant racial groups (non-Hispanic White, Black, and Hispanic females) over a twelve-year period. It sought to clarify whether the spatiotemporal trend might place an uneven burden on particular racial groups, and whether the excess trend has persisted into the current decade. METHODS: The Spatial Scan Statistic was employed to examine the geographic excess of breast cancer mortality by race in Texas counties between 1990 and 2001. The statistic was conducted with a scan window of a maximum of 90% of the study period and a spatial cluster size of 50% of the population at risk. The next scan was conducted with a purely spatial option to verify whether the excess mortality persisted further. Spatial queries were performed to locate the regions of excess mortality affecting multiple racial groups. RESULTS: The first scan identified 4 regions with breast cancer mortality excess in both non-Hispanic White and Hispanic female populations. The most likely excess mortality with a relative risk of 1.12 (p = 0.001) occurred between 1990 and 1996 for non-Hispanic Whites, including 42 Texas counties along Gulf Coast and Central Texas. For Hispanics, West Texas with a relative risk of 1.18 was the most probable region of excess mortality (p = 0.001). Results of the second scan were identical to the first. This suggested that the excess mortality might not persist to the present decade. Spatial queries found that 3 counties in Southeast and 9 counties in Central Texas had excess mortality involving multiple racial groups. CONCLUSION: Spatiotemporal variations in breast cancer mortality affected racial groups at varying levels. There was neither evidence of hot-spot clusters nor persistent spatiotemporal trends of excess mortality into the present decade. Non-Hispanic Whites in the Gulf Coast and Hispanics in West Texas carried the highest burden of mortality, as evidenced by spatial concentration and temporal persistence.

Journal Article↗
PubMed2004

Detecting spatiotemporal clusters of accidental poisoning mortality among Texas counties, U.S., 1980 - 2001.

BACKGROUND: Accidental poisoning is one of the leading causes of injury in the United States, second only to motor vehicle accidents. According to the Centers for Disease Control and Prevention, the rates of accidental poisoning mortality have been increasing in the past fourteen years nationally. In Texas, mortality rates from accidental poisoning have mirrored national trends, increasing linearly from 1981 to 2001. The purpose of this study was to determine if there are spatiotemporal clusters of accidental poisoning mortality among Texas counties, and if so, whether there are variations in clustering and risk according to gender and race/ethnicity. The Spatial Scan Statistic in combination with GIS software was used to identify potential clusters between 1980 and 2001 among Texas counties, and Poisson regression was used to evaluate risk differences. RESULTS: Several significant (p < 0.05) accidental poisoning mortality clusters were identified in different regions of Texas. The geographic and temporal persistence of clusters was found to vary by racial group, gender, and race/gender combinations, and most of the clusters persisted into the present decade. Poisson regression revealed significant differences in risk according to race and gender. The Black population was found to be at greatest risk of accidental poisoning mortality relative to other race/ethnic groups (Relative Risk (RR) = 1.25, 95% Confidence Interval (CI) = 1.24 - 1.27), and the male population was found to be at elevated risk (RR = 2.47, 95% CI = 2.45 - 2.50) when the female population was used as a reference. CONCLUSION: The findings of the present study provide evidence for the existence of accidental poisoning mortality clusters in Texas, demonstrate the persistence of these clusters into the present decade, and show the spatiotemporal variations in risk and clustering of accidental poisoning deaths by gender and race/ethnicity. By quantifying disparities in accidental poisoning mortality by place, time and person, this study demonstrates the utility of the spatial scan statistic combined with GIS and regression methods in identifying priority areas for public health planning and resource allocation.

Journal Article↗
PubMed1999

Spatiotemporal heterogeneity in the induction of ventricular fibrillation by rapid pacing: importance of cardiac restitution properties.

The mechanism by which rapid pacing induces ventricular fibrillation (VF) is unclear. We performed computerized epicardial mapping studies in 10 dogs, using 19-beat pacing trains. The pacing interval (PI) of the first train was 300 ms and then was progressively shortened until VF was induced. For each PI, we constructed restitution curves for the effective refractory period (ERP). When the PI was long, the activation cycle length (CL) was constant throughout the mapped region. However, as the PI shortened, there was an increase in the spatiotemporal complexity of the CL variations and an increase in the slope of the ERP restitution curve. In 5 dogs, we documented the initiation of VF by wavebreak at the site of long-short CL variations. Computer simulation studies using the Luo-Rudy I ventricular action potential model in simulated 2-dimensional tissue reproduced the experimental results when normal ERP and conduction velocity (CV) restitution properties were intact. By altering CV and ERP restitutions in this model, we found that CV restitution creates spatial CL variations, whereas ERP restitution underlies temporal, beat-to-beat variations in refractoriness during rapid pacing. Together, the interaction of CV and ERP restitutions produces spatiotemporal oscillations in cardiac activation that increase in amplitude as the PI decreases, ultimately causing wavebreak at the site of intrinsic heterogeneity. This initial wavebreak then leads to the formation of spiral waves and VF. These findings support a key role for both CV and ERP restitutions in the initiation of VF by rapid pacing.

Action Potentials↗
PubMed1995

Articulatory organization of mandibular, labial, and velar movements during speech.

It has been shown that articulator movements during speech are adjusted along a number of spatiotemporal dimensions. For example, variations in the extent of lip, jaw, or tongue motion are associated with proportional changes in the respective articulators' peak velocity. Modifications in the timing of lip and jaw actions are apparently constrained, exhibiting relative timing covariation. Syllable prominence systematically affects some combination of the articular motion parameters, i.e., extent, speed, and duration. The present investigation is an attempt to extend observations of the spatiotemporal properties of articulator movement to include the velum. Lip, jaw, and velar kinematics were recorded optoelectronically and simultaneously with the acoustic signal during productions of the utterance/mabnab/. The spatial and temporal relations between the lips, the jaw, and the velum were examined and compared across articulators. For movements associated with each syllable, the velum displayed scaling pattern qualitatively similar to those of the lips and jaw. Moreover, velocity-displacement relations were more robust for the lowering than for the raising movements of the velum. There was evidence of interarticulator coupling between the velum and the jaw, and between the velum and the upper lip, although this coupling was not as strong as that observed among the oral articulators. Articulator specific differences in velocity-displacement correlations and degree of interarticulator cohesion for the various movement phases may be related to a combination of aerodynamic and phonetic factors, such as the phonologically noncontrastive nature of nasalization in English.

Adult↗
PubMedDate not supplied

A study of the spatiotemporal health impacts of ozone exposure.

Exposure analysis and mapping of spatiotemporal pollutants in relation to their health effects are important challenges facing environmental health scientists and integrated assessment modellers. In this work, a methodological framework is discussed to study the impact of spatiotemporal ozone (O3) exposure distributions on the health of human populations. The framework, however, is very general and can be used to study various other pollutants. The spatiotemporal analysis starts with exposure distributions producing the input to pollutokinetic (or toxicokinetic) laws which are linked to effect models which, in turn, are integrated with relationships that describe how effects are distributed across populations. Important characteristics of the environmental health framework are holisticity and stochasticity. Holisticity emphasizes the functional relationships between composite space/time O3 maps, pollutokinetic models of burden on target organs and tissues, and health effects. These relationships offer a meaningful physical interpretation of the exposure and biological processes that affect human exposure. Stochasticity involves the rigorous representation of natural uncertainties and biological variations in terms of spatiotemporal random fields. The stochastic perspective introduces a deeper epistemological understanding in the development of improved models of spatiotemporal human exposure analysis and mapping. Also, it explicitly determines the knowledge bases available and develops logically plausible rules and standards for data processing and human exposure map construction. The proposed approach allows the horizontal integration among sciences related to the human exposure problem that leads to accurate and informative spatiotemporal maps of O3 exposure and effect distributions and an integrative analysis of the whole risk case. By processing a variety of knowledge bases, the spatiotemporal analysis can bring together several sciences which are all relevant to the aspect of human exposure reality that is examined.

Body Burden↗
PubMed2005

The detection of motion in chromatic stimuli: first-order and second-order spatial structure.

This study provides evidence for the existence of a low-level chromatic motion mechanism and further elucidates the conditions under which its operation becomes measurable in an experimental stimulus. Observers discriminated the direction of motion of amplitude modulated (AM) gratings that were defined by luminance or chromatic variation and masked with spatiotemporally broadband luminance or chromatic noise. The size and retinal location of the stimuli were varied and the effects of broadband noise and grating masks were both compared with the cohort of stimuli. Some significant disparities in the published literature were well explained by the results. In conclusion, evidence for a chromatically sensitive motion mechanism that evades the, detrimental effects of a luminance mask was found only at the fovea and only when the stimulus was small and centrally placed.

Color Perception↗
PubMed2002

Phase transitions and volunteering in spatial public goods games.

We present a simple yet effective mechanism promoting cooperation under full anonymity by allowing for voluntary participation in public goods games. This natural extension leads to "rock-scissors-paper"-type cyclic dominance of the three strategies, cooperate, defect, and loner. In spatial settings with players arranged on a regular lattice, this results in interesting dynamical properties and intriguing spatiotemporal patterns. In particular, variations of the value of the public good leads to transitions between one-, two-, and three-strategy states which either are in the class of directed percolation or show interesting analogies to Ising-type models. Although volunteering is incapable of stabilizing cooperation, it efficiently prevents successful spreading of selfish behavior.

Economics↗
PubMed2003

Hemodynamics is a key epigenetic factor in development of the cardiac conduction system.

The His-Purkinje system (HPS) is a network of conduction cells responsible for coordinating the contraction of the ventricles. Earlier studies using bipolar electrodes indicated that the functional maturation of the HPS in the chick embryo is marked by a topological shift in the sequence of activation of the ventricle. Namely, at around the completion of septation, an immature base-to-apex sequence of ventricular activation was reported to convert to the apex-to-base pattern characteristic of the mature heart. Previously, we have proposed that hemodynamics and/or mechanical conditioning may be key epigenetic factors in development of the HPS. We thus hypothesized that the timing of the topological shift marking maturation of the conduction system is sensitive to variation in hemodynamic load. Spatiotemporal patterns of ventricular activation (as revealed by high-speed imaging of fluorescent voltage-sensitive dye) were mapped in chick hearts over normal development, and following procedures previously characterized as causing increased (conotruncal banding, CTB) or reduced (left atrial ligation, LAL) hemodynamic loading of the embryonic heart. The results revealed that the timing of the shift to mature activation displays striking plasticity. CTB led to precocious emergence of mature HPS function relative to controls whereas LAL was associated with delayed conversion to apical initiation. The results from our study indicate a critical role for biophysical factors in differentiation of specialized cardiac tissues and provide the basis of a new model for studies of the molecular mechanisms involved in induction and patterning of the HPS in vivo.

Animals↗
PubMed1992

Spatiotemporal irregularities of spiral wave activity in isolated ventricular muscle.

Voltage-sensitive dyes and high resolution optical mapping were used to analyze the characteristics of spiral waves of excitation in isolated ventricular myocardium. In addition, analytical techniques, which have been previously used in the study of the characteristics of spiral waves in chemical reactions, were applied to determine the voltage structure of the center of the rotating activity (ie, the core). During stable spiral wave activity local activation occurs in a periodic fashion (ie, 1:1 stimulus: response activation ratio) throughout the preparation, except at the core, which is a small elongated area where the activity is of low voltage and the activation ratio is 1:0. The voltage amplitude increases gradually from the center of the core to the periphery. In some cases, however, regular activation patterns at the periphery may coexist with irregular local activation patterns near the core. Such a spatiotemporal irregularity is attended by variations in the core size and shape and results from changes in the core position. The authors conclude that functionally determined reentrant activity in the heart may be the result of spiral waves of propagation and that local spatiotemporal irregularities in the activation pattern are the result of changes in the core position.

Animals↗
PubMed2001

Spatiotemporal tuning of directional neurons in mammalian and avian pretectum: a comparison of physiological properties.

Responses were recorded from 72 neurons in the wallaby's nucleus of the optic tract (NOT) during stimulation with drifting sinusoidal gratings at a range of temporal and spatial frequencies (TF and SF). Most cells (70/72) were TF tuned, but two were velocity tuned. The neurons are placed into two descriptive groups: fast and slow cells, which prefer SF/TFs of 0.06-0.6 cpd/0.4-20 Hz and 0.13-1 cpd/<1 Hz, respectively. The peak spatiotemporal tunings of the neurons are compared for motion in preferred and anti-preferred directions with little variation observed in most cases. The spatiotemporal properties of wallaby NOT are compared with those of pigeon lentiformis mesencephali: the avian homologue of NOT. The neurons in the pigeon and wallaby nuclei segregate into fast and slow cells that operate in similar spatiotemporal domains. The fast and slow cells segregate largely on the basis of TF in wallabies and SF in pigeons, but their respective velocity tuning properties are very similar. In both species, the mean velocity tuning for fast and slow cells is approximately 50 degrees/s and 1 degrees/s, respectively.

Animals↗
PubMed2004

[Influence of speed variation and age on the intrasubject variability of ground reaction forces and spatiotemporal parameters of children's normal gait].

OBJECTIVE: To assess the effect of age and speed on the variability of ground reaction forces (GRF) and stride parameters of gait in normal children. MATERIAL AND METHOD: Forty-seven children aged 4-10 years were split into three age groups. Each child walked at three constant speeds on a treadmill. Thirty consecutive steps of each leg were recorded. For each child, the mean parameters of the 30 steps were calculated. The mean parameter of each child was taken to calculate the mean parameters of the group. The variability was evaluated by the coefficient of variation (CV). The influence of both age and speed on the variability was examined with a to-way analysis of variance. RESULTS: The cross effect of age and speed on the variability was not significant. The variability of the parameters decreased significantly with age between 4 and 8 years. The variability of vertical forces increased significantly with speed (between 2.7 and 4.5 km/h), while the variability of antero-posterior forces, the stride and the stance decreased between 2.7 and 3.6 km/h. However, the variability of double stance was not influenced by walking speed between 2.7 and 4.5 km/h. Except the time of production of the vertical force of propulsion (Tz3), the variability of temporal vertical parameters decreased significantly with speed between 2.7 and 4.5 km/h and the variability of temporal antero-posterior parameters decreased significantly between 2.7 and 3.6 km/h. DISCUSSION-CONCLUSION: The variability of the GRF and spatio-temporal parameters in children was influenced by age between 4 and 8 years old and by speed between 2.7 and 3.6 km/h. Moreover, the effect of age on the GRF persists up to 8 years. The variabilities of the time of production of the antero-posterior force of propulsion (Ty2) and stance duration were lower than the variabilities of the others parameters. These two variables could be the most reliable parameters when assessing gait in children aged 4-10 years, walking at speeds between 2.7 and 4.5 km/h.

Age Factors↗
PubMed1983

Suprathreshold spatiotemporal response characteristics of the human visual system.

The apparent contrasts of suprathreshold stationary gratings, countermodulated gratings, and homogeneous flickering fields were assessed with a contrast-matching procedure. Results show that, as stimulus amplitude is increased relative to threshold, variations in apparent contrast with spatiotemporal-frequency content become much less pronounced. In other words, the contrast-matching functions are more uniform across both spatial and temporal frequency at levels of contrast well above threshold. These data are interpreted in terms of a compensatory stage in the visual system that varies its gain characteristics according to the detectability of the stimulus.

Differential Threshold↗