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At least 955 records · Page 53Linked to original sources
PubMed2001

Luminance spatial scale facilitates stereoscopic depth segmentation.

Are differences in luminance spatial frequency between surfaces that overlap in depth useful for surface segmentation? We examined this question, using a novel stimulus termed a dual-surface disparity grating. The dual-surface grating was made from Gabor micropatterns and consisted of two superimposed sinusoidal disparity gratings of identical disparity-modulation spatial frequency and orientation but of opposite spatial phase. Corrugation amplitude thresholds for discrimination of the orientation of the dual-surface grating were obtained as a function of the difference in Gabor (luminance) spatial frequency between the two surfaces. When the Gabor micropatterns on the two surfaces were identical in spatial frequency, thresholds were very high and in some instances impossible to obtain. However, with as little as a 1-octave difference in spatial frequency between the surfaces, thresholds fell sharply to near-asymptotic levels. The fall in thresholds paralleled a change in the appearance of the stimulus from one of irregular depth to stereo transparency. The most parsimonious explanation for this finding is that the introduction of a between-surface luminance spatial-frequency difference reduces the number of spurious cross-surface binocular matches, thus helping to reveal the three-dimensional structure of the stimulus.

Depth Perception↗
PubMed2002

Comparison of the spatial-frequency selectivity of local and global motion detectors.

Convergent physiological and behavioral evidence indicates that the initial receptive fields responsible for motion detection are spatially localized. Consequently, the perception of global patterns of movement (such as expansion) requires that the output of these local mechanisms be integrated across visual space. We have differentiated local and global motion processes, with mixtures of coherent and incoherent moving patterns composed of bandpass filtered dots, and have measured their spatial-frequency selectivity. We report that local motion detectors show narrow-band spatial-frequency tuning (i.e., they respond only to a narrow range of spatial frequencies) but that global motion detectors show broadband spatial-frequency tuning (i.e., they integrate across a broad range of spatial frequencies), with a preference for low spatial frequencies.

Humans↗
PubMed1986

Sampling-theory analysis of spatial vision.

Spatial-vision research has been largely concerned with measuring and understanding the consequences of receptive-field properties measured by single-unit recording. However, in order to understand spatial-information processing in the visual system, it is equally essential to know the densities and the distribution patterns of the receptive fields. If the receptive fields are not arrayed properly across the visual field, spatial information will be lost. It has been argued, on the basis of the Whittaker-Shannon sampling theorem, that the receptors of the fovea sample the retinal image at a high enough rate to preserve essentially all the available spatial information. In this paper we show how two-dimensional sampling theory can be used to determine which combinations of receptive-field shapes and sampling patterns would preserve all spatial information from the receptors. This analysis will prove useful for determining, in conjunction with electrophysiological and anatomical evidence, what spatial information is or is not being transmitted by a given stage of the visual pathway. It may also prove useful for developing and testing theories of spatial vision.

Humans↗
PubMed2006

The transcriptional regulator CBP has defined spatial associations within interphase nuclei.

It is becoming increasingly clear that nuclear macromolecules and macromolecular complexes are compartmentalized through binding interactions into an apparent three-dimensionally ordered structure. This ordering, however, does not appear to be deterministic to the extent that chromatin and nonchromatin structures maintain a strict 3-D arrangement. Rather, spatial ordering within the cell nucleus appears to conform to stochastic rather than deterministic spatial relationships. The stochastic nature of organization becomes particularly problematic when any attempt is made to describe the spatial relationship between proteins involved in the regulation of the genome. The CREB-binding protein (CBP) is one such transcriptional regulator that, when visualised by confocal microscopy, reveals a highly punctate staining pattern comprising several hundred individual foci distributed within the nuclear volume. Markers for euchromatic sequences have similar patterns. Surprisingly, in most cases, the predicted one-to-one relationship between transcription factor and chromatin sequence is not observed. Consequently, to understand whether spatial relationships that are not coincident are nonrandom and potentially biologically important, it is necessary to develop statistical approaches. In this study, we report on the development of such an approach and apply it to understanding the role of CBP in mediating chromatin modification and transcriptional regulation. We have used nearest-neighbor distance measurements and probability analyses to study the spatial relationship between CBP and other nuclear subcompartments enriched in transcription factors, chromatin, and splicing factors. Our results demonstrate that CBP has an order of spatial association with other nuclear subcompartments. We observe closer associations between CBP and RNA polymerase II-enriched foci and SC35 speckles than nascent RNA or specific acetylated histones. Furthermore, we find that CBP has a significantly higher probability of being close to its known in vivo substrate histone H4 lysine 5 compared with the closely related H4 lysine 12. This study demonstrates that complex relationships not described by colocalization exist in the interphase nucleus and can be characterized and quantified. The subnuclear distribution of CBP is difficult to reconcile with a model where chromatin organization is the sole determinant of the nuclear organization of proteins that regulate transcription but is consistent with a close link between spatial associations and nuclear functions.

Acetylation↗
PubMed2006

Spatial ability subfactors and their influences on a computer-based information search task.

OBJECTIVE: The present study examined the relationship between two distinct subfactors of spatial ability and performance in an information search task modeled on browsing the Web. BACKGROUND: Previous studies have found relationships between various measures of spatial ability and performance in a wide variety of computer-based tasks. METHOD: In the search task 101 participants (18-29 years of age) searched for the answer to a question by navigating the system. They completed the experimental task as well as a battery of cognitive ability measures that included two different measures of spatial ability. RESULTS: The results indicate that spatial orientation ability was related to performance with tasks that were high in their navigational requirement (engendered by the use of a novel aid), whereas spatial visualization was unrelated to performance in any task condition. CONCLUSION: A closer inspection of the cognitive requirements of a task may reveal what interventions could be most useful when designing computer systems or developing training programs. APPLICATION: Given the unique differences between the different spatial abilities, the current results suggest the design of navigational aids that place less demand on spatial orientation ability.

Adolescent↗
PubMed2005

Synergistic effect of combined temporal and spatial expectations on visual attention.

We developed a naturalistic behavioral task to investigate the influence of spatial and temporal expectations on attentional orienting to moving targets. In this task, the movement of an object before its disappearance under an occluding barrier generated expectations concerning the location and/or time of its reappearance. Four different trial types were intermixed, each inducing a different state of expectation: no expectation, only spatial expectation about the location of reappearance, only temporal expectation about the moment of reappearance, and combined spatial and temporal expectation. The behavioral validity of the task was shown by the fact that all expectation conditions produced significantly shorter reaction times than the control state of no expectation. Spatial attention modulated early perceptual analysis in extrastriate areas, as demonstrated by significant enhancement of the visual P1 component. Temporal attention alone had no effect on P1 but instead modulated response-specific components. However, when spatial and temporal attention were combined, the enhancement of perceptual processing was significantly augmented, leading to a greater enhancement of the P1 component than by spatial attention alone. Perceptual analysis reflected by the P1 component correlated significantly with reaction times. In summary, event-related potentials revealed the presence of individual modulatory effects attributable to spatial and temporal expectation as well as synergistic effects indicative of an interaction of the two. This synergistic effect is likely to play a critical role in directing attention to the reappearance of a temporarily occluded moving target, a process of obvious importance in everyday situations.

Adult↗
PubMed2006

Density dependence in marine fish populations revealed at small and large spatial scales.

Experimental manipulation of population density has frequently been used to demonstrate demographic density dependence. However, such studies are usually small scale and typically provide evidence of spatial (within-generation) density dependence. It is often unclear whether small-scale, experimental tests of spatial density dependence will accurately describe temporal (between-generation) density dependence required for population regulation. Understanding the mechanisms generating density dependence may provide a link between spatial experiments and temporal regulation of populations. In this study, I manipulated the density of recently settled kelp rockfish (Sebastes atrovirens) in both the presence and absence of predators to test for density-dependent mortality and whether predation was the mechanism responsible. I also examined mortality of rockfish cohorts within kelp beds throughout central California to evaluate temporal (between-generation) density dependence in mortality. Experiments suggested that short-term behavioral responses of predators and/or a shortage of prey refuges caused spatial density dependence. Temporal density dependence in mortality was also detected at larger spatial scales for several species of rockfish. It is likely that short-term responses of predators generated both spatial and temporal density dependence in mortality. Spatial experiments that describe the causal mechanisms generating density dependence may therefore be valuable in describing temporal density dependence and population regulation.

Animals↗
PubMedDate not supplied

A spatially explicit investigation of phosphorus sorption and related soil properties in two riparian wetlands.

Soils of riparian wetlands are highly effective at phosphorus (P) sorption. However, these soils exhibit extreme spatial variability across riparian zones. We used a spatially explicit sampling design in two riparian wetlands in North Carolina to better understand the relationships among P sorption, soil properties, and spatial variability. Our objectives were to quantify patterns of spatial variability of P sorption and related soil properties, and to determine which soil properties best explained the variability in P sorption after accounting for the effects of spatial autocorrelation. We measured bulk density, moisture, pH, soil organic matter (SOM), texture (percent clay, silt, and sand), oxalate-extractable aluminum (Al(ox)), iron (Fe(ox)), and the phosphorus sorption index (PSI). Due to differences in texture, Al(ox), and Fe(ox), the two sites had substantially different mean PSIs. At each site, we found considerable differences in the spatial variability of soil properties. For example, semivariance analysis and kriging illustrated that soil properties at Site 1 varied at smaller scales than those at Site 2. At both sites, after accounting for the effects of spatial autocorrelation and all other soil properties, we determined that Al(ox) had the highest Mantel correlation with PSI. We believe this geostatistic and Mantel approach is robust and could serve as a model for research on other biogeochemical processes such as denitrification.

Adsorption↗
PubMed2006

Spatial patterns of labile forms of phosphorus in a subtropical wetland.

Phosphorus (P) has been identified as the key constituent defining wetland productivity, structure, and function. Our goal was to investigate the spatial patterns of total P and three labile forms of P (labile organic, inorganic, and microbial biomass P) across a subtropical wetland located in east-central Florida, the Blue Cypress Marsh Conservation Area (BCMCA), and link spatial patterns to ecosystem processes. The wetland received a continual input of nutrients primarily from the south and intermittently from the west and east, respectively, which ceased in the mid-1990s. Since then the marsh system has been undergoing natural succession. We used (i) ordinary kriging to characterize the spatial patterns of total P and labile P forms across the wetland, (ii) local, moving spatial correlations to investigate relationships between total P and labile P forms, and (iii) a clustering technique to link the identified spatial patterns to biogeochemical processes. The spatially explicit analyses revealed patterns of total P and labile P forms as well as changing relationships between variables across the marsh. We were able to distinguish P-enriched areas from unaffected ("natural") areas and intermediate zones that are currently undergoing change as P is mobilized and translocated. We also identified areas that are at risk, showing a shift toward a more P-enriched status. Our results improve our understanding of P and its labile components within a spatially explicit context.

Ecosystem↗
PubMed2001

Compound spatial sonography of the thyroid gland: evaluation of freedom from artifacts and of nodule conspicuity.

OBJECTIVE: The purpose of this study was to compare compound spatial sonography with conventional sonography of the thyroid gland with respect to freedom from sonographic artifacts and conspicuity of thyroid nodules. SUBJECTS AND METHODS: A prospective study was performed on 50 thyroid nodules (in 43 patients). Each nodule was examined using compound spatial sonography and conventional sonography. The sonographic techniques were then compared with respect to freedom from sonographic artifacts and thyroid nodule conspicuity. RESULTS: For freedom from artifacts, compound spatial sonography was superior in 45 cases (90%), and conventional sonography was superior in five cases (10%). Statistical analysis showed that compound spatial sonography was superior to conventional sonography for freedom from artifacts (p < 0.001). For thyroid nodule conspicuity, compound spatial sonography was superior in 37 cases (74%), and conventional sonography was superior in 13 cases (26%). Statistical analysis showed that compound spatial sonography was superior to conventional sonography for thyroid nodule conspicuity (p < 0.001). CONCLUSION: Compound spatial sonography of the thyroid displays greater freedom from artifacts and better nodule conspicuity than does conventional sonography.

Adult↗
PubMed2000

Spatial associations among density of cattle, abundance of wild canids, and seroprevalence to Neospora caninum in a population of beef calves.

OBJECTIVE: To determine the epidemiologic plausibility of a sylvatic transmission cycle for Neospora caninum between wild canids and beef cattle. DESIGN: Spatial analysis study. ANIMALS: 1,009 weaned beef steers from 94 beef herds in Texas. PROCEDURE: Calves were grouped on the basis of seroprevalence for N caninum and ecologic region in Texas. The Morans I test was used to evaluate spatial interdependence for adjusted seroprevalence by ecologic region. Cattle density (Number of cattle/259 km2 [Number of cattle/100 mile2] of each ecologic region) and abundance indices for gray foxes and coyotes (Number of animals/161 spotlight-transect [census] km [Number of animals/100 census miles] of each ecologic region) were used as covariates in spatial regression models, with adjusted seroprevalence as the outcome variable. A geographic information system (GIS) that used similar covariate information for each county was used to validate spatial regression models. Results-Spatial interdependence was not detected for ecologic regions. Three spatial regression models were tested. Each model contained a variable for cattle density for the ecologic regions. Results for the 3 models revealed that seroprevalence was associated with cattle density and abundances of gray foxes, coyotes, or both. Abundances of gray foxes and coyotes were collinear. Results of a GIS-generated model validated these spatial models. CONCLUSIONS AND CLINICAL RELEVANCE: In Texas, beef cattle are at increased risk of exposure to N caninum as a result of the abundance of wild canids and the density of beef cattle. It is plausible that a sylvatic transmission cycle for neosporosis exists.

Animals↗
PubMed1986

Effects of menstrual cycle on spatial information-processes.

The present study examined effects of menstrual cycle (i.e., ovulatory vs menstrual phase) on performance on spatial information-processes. Participants included 20 spontaneously cycling women (with regular 28- to 30-day menstrual cycles) who were tested on a reaction-time task developed to assess specific spatial information-processes and the Spatial Relations subtest of the PMA battery. For the spatial information-processing task, women responded faster and applied relatively less stringent criteria in the decision process during the ovulatory phase. No effects of cycle changes were found for accuracy of performance on either of the spatial tasks. It is suggested that studies examining effects of menstrual cycle on spatial ability consider an information-processing approach in measuring spatial performance and an application of signal-detection theory to separate components (strategy vs aptitude) of problem solving.

Achievement↗
PubMed2006

Spatial pattern learning in the radial arm maze.

Rats experienced a spatial pattern of baited and unbaited arms in an eight-arm radial maze. The spatial pattern remained constant over trials, but the spatial locations that were baited varied unpredictably. Although there was no evidence of control by the spatial pattern during free choice training trials, the rats' ability to locate baited arms in forced choice test trials was superior to that of animals in a control condition for which maze arms were not baited in a consistent spatial pattern. This is consistent with the results of experiments showing that spatial choices by rats in a pole box maze are controlled by abstract spatial patterns.

Animals↗
PubMed2001

A comparison of tactile spatial sensitivity on the palm and fingerpad.

Studies of tactile spatial pattern perception have, for the most part, been carried out using the fingerpad. On the basis of these studies, models have been developed linking spatial pattern identification and resolution with underlying neural structures. It has been suggested that with appropriate scaling, these models would apply to the processing of spatial patterns presented to other sites on the body. Spatial sensitivity was examined on another site on the body, the palm, using two measures, letter identification and grating orientation. The results from these measures were compared with results from similar studies conducted on the fingerpad and with estimates of the density of innervation of the fingerpad and palm. To produce levels of performance similar to those on the fingerpad required letters on the palm 50 mm in height, seven to nine times larger than those used on the fingerpad. Gratings had to be six to more than seven times larger on the palm to produce the same levels of performance achieved on the fingerpad. For the two types of receptor systems sensitive to spatial information, the ratio of density of innervation between the fingerpad and the palm is estimated to be 5.7:1 and 8.8:1. Performance of spatial tasks on the palm can be predicted quantitatively from fingerpad data with a moderate degree of accuracy. Qualitative comparisons between the palm and fingerpad data indicate that spatial patterns are processed similarly at the two sites.

Adult↗
PubMed2000

Functionality and spatial relations in memory and language.

We examined whether the functionality of spatial relations affects the construction and memory of information in situation models. A functional relationship involves the interaction of entities that is implied by either typical use or contextual demands. Previous research has shown that spatial relations are less likely to be encoded during comprehension unless there is extensive prior knowledge, explicit instructions to attend to spatial information, or a clear emphasis on spatial information. If the construction of a situation model is guided by a need to understand the functional structure of a situation, then functional spatial relations should be more likely to be encoded. The results of our study showed that sentences with functional spatial relations were read faster and remembered better in both recall and recognition tests than sentences with nonfunctional spatial relations.

Adult↗
PubMed2000

Spatial frequencies in short-term memory for faces: a test of three frequency-dependent hypotheses.

Spatial frequency manipulations have been shown to have significant utility in ascertaining the various types of information that might be important in object identification and recognition tasks. This utility suggests that, given some mapping between ranges of spatial frequencies and different types of psychological information, it should be possible to examine the roles of these different types of psychological information by way of spatial frequency manipulations. One potential problem, however, is that there is no well-specified, unambiguous mapping between the distinctions in the frequency domain and the distinctions in the informational domain. Three experiments provide tests of three general hypotheses regarding the ways in which different spatial frequencies might map to different information in facial perception and memory tasks: (1) the low-frequency dominance hypothesis, which proposes that low-frequency information should be superior (to high-frequency information) as a cue to perception and memory; (2) the distinct informational roles hypothesis, which holds that high spatial frequencies should carry featural information while low spatial frequencies should carry information about the configuration of those features; and (3) the task-dependent information hypothesis, which suggests that high-frequency information should be best suited to discrimination tasks while low-frequency information should be best suited for recognition tasks. Results generally contradict the first two of these hypotheses, while providing support for the third. Implications with regard to the various issues related to the mapping between spatial frequencies and the informational content of faces, as well as the need to consider important interactions among perceptual and memory processes, are discussed.

Adult↗
PubMed1990

Visual space-time interactions: effects of adapting to spatial frequencies on temporal sensitivity.

To study how adaptation to spatial frequency patterns affects temporal sensitivity in vision, observers were selectively adapted for 4 min to either a high- or a low-spatial-frequency sinusoidal grating (12 and 2 cpd, respectively). Their sensitivities to modulation of a blurred patch at high or low temporal frequencies (12 Hz and 2 Hz, respectively) were measured, before and after the adaptation period, by using the yes/no task of signal detection theory. The data consistently indicated that spatial adaptation differentially affected the observers' sensitivities to temporal signals. Specifically, when the observers were adapted to low spatial frequencies, their sensitivity to low temporal frequencies was reduced; when they were adapted to high spatial frequencies, their sensitivity to high temporal frequencies was increased. These results have implications for the psychophysical measurements of temporal and spatial sensitivity, as well as for the issue of the separability of spatial and temporal properties of individual channels.

Attention↗
PubMed1993

The role of spatial frequency in the processing of hierarchically organized stimuli.

Can spatial frequency differences between local and global forms account for differences in the way different levels of structure are analyzed? We examined this question by having subjects identify local or global forms of hierarchical stimuli that had been contrast balanced. Contrast balancing eliminates low spatial frequencies, so that both local and global forms must be identified on the basis of high spatial frequency information. Response times (RTs) to global (but not local) forms were slowed for contrast-balanced stimuli, suggesting that low spatial frequencies mediate the global RT advantage typically found. In contrast, interference between local and global forms was little affected by contrast balancing or by shifts of attention between local and global forms, suggesting that it does not result from inhibitory interactions between spatial frequency channels or from temporal precedence of low versus high spatial frequency information. Finally, shifts of attention between local and global forms were also little affected by contrast balancing, suggesting that they were not based on spatial frequency.

Adolescent↗