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PubMed1976

[Dysfunctions of space perception and spatial ability in schizophrenia (author's transl)].

Thirty-seven acute schizophrenics and 25 normal subjects were investigated with regard to their spatial perception, representation, and their spatial ability, Schizophrenics showed significantly poorer performances (in terms of quantity) in those variables, which characterized the ocular apprehension of structures and wholes, the relation of parts to a whole, or the analysis of a whole in its various components as well as the availability of visual engrams, partly in the sense of spatial representation, and the practical realization of imagined spatial configurations. On the other hand, in ocular apprehension, interpretation, and when necessary the practical realization of two-dimensional represented spatial symbols and configurations and perspective abilities there was only statistical trend for quantitatively poorer performances in schizophrenics compared with healthy persons. Factor analysis of the intercorrelation matrices for 14 variables separated out the same 4 factors in each group for space perception and spatial ability. In spite of the demonstrated "quantitative" differences for the single variables between the two groups a marked similarity in a "qualitative" sense was found, when the two-factor structures were compared mathematically (similarity coefficient: 0.664). In order to specify these differences, 56 schizophrenics were classified as paranoid or nonparanoid and investigated in the above-mentioned manner. While these groups did not show any significant quantitative difference concerning their performances at variable level, they showed entirely different structures using factor analysis. Spatial perception of the paranoid schizophrenics seemed less structured and their perceptual conception less systematical. On the other hand, when factor structures from nonparanoids and healthy controls were compared mathematically, both groups showed a marked similarity (0.783). An attempt was made to relate these results to other findings of literature and to theories of cognitive and perceptual dysfunctions of schizophrenics.

Adult↗
PubMed1991

Sex differences in spatial ability in children.

There is considerable evidence that sex differences in spatial ability exist in adults, with males outperforming females at every age after puberty. It is difficult, however, to find sex differences in children younger than 13. This is due in part to the lack of adequate measures of spatial ability for use with children. We report the use of spatial tests for children that are similar to those that have shown large sex differences in adults and may be measuring ability comparable to adult spatial ability. Four tests of mental rotation and spatial visualization were given to two samples of children. The first sample consisted of 81 children (39 males and 42 females) aged 9 to 12 years. The second sample consisted of 42 children (21 males and 21 females) aged 9 to 13 years. Sex differences of .4-.6 standard deviations were found on three tests in both samples. These results indicate that sex differences in spatial ability can be found in preadolescents if appropriate tests are used. Measurement of these abilities in children facilitates the investigation of possible biological and sociocultural contributors to the sex differences in spatial ability.

Aptitude↗
PubMed1996

Spatial sampling and filtering of EEG with spline laplacians to estimate cortical potentials.

The electroencephalogram (EEG) is recorded by sensors physically separated from the cortex by resistive skull tissue that smooths the potential field recorded at the scalp. This smoothing acts as a low-pass spatial filter that determines the spatial bandwidth, and thus the required spatial sampling density, of the scalp EEG. Although it is better appreciated in the time domain, the Nyquist frequency for adequate discrete sampling is evident in the spatial domain as well. A mathematical model of the low-pass spatial filtering of scalp potentials is developed, using a four concentric spheres (brain, CSF, skull, and scalp) model of the head and plausible estimates of the conductivity of each tissue layer. The surface Laplacian estimate of radial skull current density or cortical surface potential counteracts the low-pass filtering of scalp potentials by shifting the spatial spectrum of the EEG, producing a band-passed spatial signal that emphasizes local current sources. Simulations with the four spheres model and dense sensor arrays demonstrate that progressively more detail about cortical potential distribution is obtained as sampling is increased beyond 128 channels.

Cerebral Cortex↗
PubMed1991

Attentional focussing and spatial stimulus-response compatibility.

The relative functional significance of attention shifts and attentional zooming for the coding of stimulus position in spatial compatibility tasks is demonstrated by proposing and testing experimentally a tentative explanation of the absence of a Simon effect in Experiment 3 of Umiltà and Liotti (1987). It is assumed that the neutral point of the spatial frame of reference for coding spatial position is at the position where attention is focussed immediately before exposition of the stimulus pattern. If a stimulus pattern is exposed to the right or the left of this position a spatial compatibility effect can be observed when the stimulus-response pairing is incompatible. Generalizing from this, one can say that a spatial compatibility effect will be observed if the last step in attentional focussing of the stimulus attribute specifying the response is a horizontal or a vertical attention shift. If the last step in focussing is attentional zooming (change in the representational level attended to), the stimulus pattern is localized at the horizontal and the vertical positions where the last attention shift had positioned the focus. In this case the spatial code is neutral on these dimensions and so no spatial compatibility effect should result. To test this model we conducted two experiments. Experiment 1 replicated the finding of Umiltà and Liotti that there is no Simon effect in the condition with no delay between a positional cue (two small boxes on the left or right of a fixation cross) and the imperative stimulus, whereas in the condition with a delay of 500 ms a Simon effect was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2004

Adaptive spatial filtering of multichannel surface electromyogram signals.

Spatial filtering of surface electromyography (EMG) signals can be used to enhance single motor unit action potentials (MUAPs). Traditional spatial filters for surface EMG do not take into consideration that some electrodes could have poor skin contact. In contrast to the traditional a priori defined filters, this study introduces an adaptive spatial filtering method that adapts to the signal characteristics. The adaptive filter, the maximum kurtosis filter (MKF), was obtained by using the linear combination of surrounding channels that maximises kurtosis. The MKF and conventional filters were applied to simulated EMG signals and to real EMG signals recorded with an electrode grid to evaluate their performance in detecting single motor units. The MKF was compared with conventional spatial filtering methods. Simulated signals, with different levels of spatially correlated noise, were used for comparison. The influence of one electrode with poor skin contact was also investigated. The MKF was found to be considerably better at enhancing a single MUAP than conventional methods for all levels of spatial correlation of the noise. For a spatial correlation of 0.97 of the noise, the improvement in the signal-to-noise ratio, where a MUAP could be detected, was at least 6dB. With a simulated poor skin contact for one electrode, the improvement over the other methods was at least 19 dB.

Action Potentials↗
PubMed2001

Volume conductor effects on the spatial resolution of magnetic fields and electric potentials from gastrointestinal electrical activity.

An analysis of the relative capabilities of methods for magnetic and electric detection of gastrointestinal electrical activity is presented. The model employed is the first volume conductor model for magnetic fields from GEA to appear in the literature. A mathematical model is introduced for the electric potential and magnetic field from intestinal electrical activity in terms of the spatial filters that relate the bioelectric sources with the external magnetic fields and potentials. The forward spatial filters are low-pass functions of spatial frequency, so more superficial external fields and potentials contain less spatial information than fields and potentials near the source. Inverse spatial filters, which are reciprocals of the forward filters, are high-pass functions and must be regularised by windowing. Because of the conductivity discontinuities introduced by low-conductivity fat layers in the abdomen, the electric potentials recorded outside these layers required more regularisation than the magnetic fields, and thus, the spatial resolution of the magnetic fields from intestinal electrical activity is higher than the spatial resolution of the external potentials. In this study, two smooth muscle sources separated by 5cm were adequately resolved magnetically, but not resolved electrically. Thus, sources are more accurately localized and imaged using magnetic measurements than using measurements of electric potential.

Digestive System↗
PubMed2002

Illusions in action: consequences of inconsistent processing of spatial attributes.

Many authors have performed experiments in which subjects grasp objects in illusory surroundings. The vast majority of these studies report that illusions affect the maximum grip aperture less than they affect the perceived size. This observation has frequently been regarded as experimental evidence for separate visual systems for perception and action. In order to make this conclusion, one assumes that the grip aperture is based on a visual estimate of the object's size. We believe that it is not, and that this is why size illusions fail to influence grip aperture. Illusions generally do not affect all aspects of space perception in a consistent way, but mainly affect the perception of specific spatial attributes. This applies not only to object size, but also to other spatial attributes such as position, orientation, displacement, speed, and direction of motion. Whether an illusion influences the execution of a task will therefore depend on which spatial attributes are used rather than on whether the task is perceptual or motor. To evaluate whether illusions affect actions when they influence the relevant spatial attributes we review experimental results on various tasks with inconsistent spatial processing in mind. Doing so shows that many actions are susceptible to visual illusions. We argue that the frequently reported differential effect of illusions on perceptual judgements and goal-directed action is caused by failures to ensure that the same spatial attributes are used in the two tasks. Illusions only affect those aspects of a task that are based on the spatial attributes that are affected by the illusion.

Cues↗
PubMed2003

Spatial and temporal visual properties of single neurons in the feline anterior ectosylvian visual area.

The spatial and temporal visual sensitivity to drifting sinusoidal gratings was studied in 75 neurons of the feline anterior ectosylvian visual area (AEV). Extracellular single-unit recordings were performed in halothane-anesthetized (0.6%), immobilized, artificially ventilated cats. Most cells were strongly sensitive to the direction of drifting gratings. The mean value of the direction tuning widths was approximately 90 deg. Most of the cells (69 of the 75 cases) displayed rather narrowly tuned band-pass characteristics in the low spatial frequency range, with a mean optimal spatial frequency of 0.2 cycles/degree (c/deg). The mean spatial bandwidth was 1.4 octaves. The remainder of the units was low-pass tuned. A majority of the units responded optimally to high temporal frequencies (mean 6.3 Hz), although some cells did exhibit preferences for every examined temporal frequency between 0.6 Hz and 10.8 Hz. The temporal frequency-tuning functions mostly revealed a band-pass character with a mean temporal bandwidth of 1.1 octaves. Our results demonstrate that the neurons along the anterior ectosylvian sulcus display particular spatial and temporal characteristics. The AEV neurons, with their preference for low spatial frequencies and with their fine spatial and temporal tuning properties, seem to be candidates for special tasks in motion perception.

Animals↗
PubMed2001

Multimodal mechanisms of attention related to rates of spatial shifting in vision and touch.

Covert attention can be directed spatially in several different sensory modalities (e.g. vision and touch). Recent psychological experiments indicate the existence of crossmodal links in spatial attention, but their neural basis in humans remains underspecified. We used positron emission tomography (PET) to assess the role of stimulus modality in the activity of brain regions involved in different rates of spatial attention shifting. A 2 x 2 factorial design manipulated the rate (high versus low) of spatial attention shifts between left and right hemifields, plus the sensory modality (vision versus touch) of stimulation. Two brain regions showed activations related to attentional shift-rate, independent of the stimulated modality: these were the right frontopolar gyrus, and the right posterior superior temporal sulcus (STS). The anterior area showed higher blood flow with the high rate of shifts in spatial attention, while the posterior area showed higher flow during the low rate conditions, where attention was sustained for longer on one side. No area showed a significant rate effect in one modality without an effect in the second modality. These results demonstrate multimodal roles for the activated brain regions in relation to the rate of spatial attention shifting, plus right-hemisphere dominance for this. They also suggest that anterior and posterior regions of the spatial-attention network play different roles in attention shifting.

Adult↗
PubMed2000

Effects of stimulus orientation on spatial frequency function of the visual evoked potential.

Visual performance is better in response to vertical and horizontal stimuli than oblique ones in many visual tasks; this is called the orientation effect. In order to elucidate the electrophysiological basis of this psychophysical effect, we studied the effects of stimulus orientation on the amplitudes and latencies of visual evoked potentials (VEPs) over different spatial frequencies of the visual stimulation. VEPs to sinusoidal gratings at four orientations (vertical, horizontal, and oblique at 45 degrees and 135 degrees) with eight spatial frequencies (0.5-10.7 cycles/deg) at reversal rates of 1 Hz and 4 Hz were recorded in nine subjects. At 1-Hz stimulation, the amplitude and latency of P100 were measured. At 4-Hz stimulation, VEPs were Fourier-analyzed to obtain phase and amplitude of the second harmonic response (2F). At 1-Hz stimulation, P100 latencies were decreased for oblique stimuli compared with those for horizontal and vertical stimuli at lower spatial frequencies. Conversely, those for oblique stimuli were increased compared with those for horizontal and vertical stimuli at higher spatial frequencies. At 4-Hz stimulation, spatial tuning observed in 2F amplitude of the oblique gratings shifted to lower spatial frequencies when compared with those of vertical stimulation. The alteration of the VEP spatial frequency function caused by the oblique stimuli was in good agreement with the orientation effect observed in psychophysical studies. Our study may have a clinical implication in that VEP testing with stimuli in more than one orientation at slow and fast temporal modulations can be useful in evaluating neurological disease affecting the visual system.

Adult↗
PubMed2006

Testing for spatial clustering of amino acid replacements within protein tertiary structure.

Widely used models of protein evolution ignore protein structure. Therefore, these models do not predict spatial clustering of amino acid replacements with respect to tertiary structure. One formal and biologically implausible possibility is that there is no tendency for amino acid replacements to be spatially clustered during evolution. An alternative to this is that amino acid replacements are spatially clustered and this spatial clustering can be fully explained by a tendency for similar rates of amino acid replacement at sites that are nearby in protein tertiary structure. A third possibility is that the amount of clustering exceeds that which can be explained solely on the basis of independently evolving protein sites with spatially clustered replacement rates. We introduce two simple and not very parametric hypothesis tests that help distinguish these three possibilities. We then apply these tests to 273 homologous protein families. The null hypothesis of no spatial clustering is rejected for 102 of 273 families. The explanation of spatially clustered rates but independent change among sites is rejected for 43 families. These findings need to be reconciled with the common practice of basing evolutionary inferences on models that assume independent change among sites.

Amino Acid Substitution↗
PubMed2003

Spatial pattern of ecosystem function and ecosystem conservation.

The spatial pattern of ecosystem function can affect ecosystem conservation. Ecosystem functions are often heterogeneous spatially due to physical and biological factors. We can influence ecosystem functions by changing the spatial patterns of the physical and biological elements of an ecosystem and regulating their combinations. The variation-position effect highlights a phenomenon resulting from the spatial pattern of ecosystem function. The effect shows that the identical variation of a factor may produce different effects on the over-all situation when this variation occurs in a different spatial position. In a watershed of the Yangtze River, water retention is a primary ecosystem function. The variation-position effect for water retention capacity occurs in the watershed because of the spatial heterogeneity in vegetation, soil, and slope. The change of vegetation that occurs in a complex can affect the overall situation of water retention, and the effect can be different due to the change occurring in the position holding different vegetation-soil-slope complex. To improve the ecosystem in the watershed and to meet the social needs for the ecosystem function of water retention, a strategy called "ecosystem function and spatial pattern-based forest extension" was proposed to conserve forests. The implementation of the strategy enables the watershed to attain the maximum effective increase in water retention capacity.

Conservation of Natural Resources↗
PubMed2006

A comparison of spatial and spectral image resolution for mapping invasive plants in coastal california.

We explored the potential of detecting three target invasive species: iceplant (Carpobrotus edulis), jubata grass (Cortaderia jubata), and blue gum (Eucalyptus globulus) at Vandenberg Air Force Base, California. We compared the accuracy of mapping six communities (intact coastal scrub, iceplant invaded coastal scrub, iceplant invaded chaparral, jubata grass invaded chaparral, blue gum invaded chaparral, and intact chaparral) using four images with different combinations of spatial and spectral resolution: hyperspectral AVIRIS imagery (174 wavebands, 4 m spatial resolution), spatially degraded AVIRIS (174 bands, 30 m), spectrally degraded AVIRIS (6 bands, 4 m), and both spatially and spectrally degraded AVIRIS (6 bands, 30 m, i.e., simulated Landsat ETM data). Overall success rates for classifying the six classes was 75% (kappa 0.7) using full resolution AVIRIS, 58% (kappa 0.5) for the spatially degraded AVIRIS, 42% (kappa 0.3) for the spectrally degraded AVIRIS, and 37% (kappa 0.3) for the spatially and spectrally degraded AVIRIS. A true Landsat ETM image was also classified to illustrate that the results from the simulated ETM data were representative, which provided an accuracy of 50% (kappa 0.4). Mapping accuracies using different resolution images are evaluated in the context of community heterogeneity (species richness, diversity, and percent species cover). Findings illustrate that higher mapping accuracies are achieved with images possessing high spectral resolution, thus capturing information across the visible and reflected infrared solar spectrum. Understanding the tradeoffs in spectral and spatial resolution can assist land managers in deciding the most appropriate imagery with respect to target invasives and community characteristics.

California↗
PubMed1998

A Knowledge-Based Systems Approach to Design of Spatial Decision Support Systems for Environmental Management

/ This paper describes a framework for designing spatial decision support systems for environmental management using a knowledge-based systems approach. An architecture for knowledge-based spatial decision supportsystems (KBSDSS) is presented that integrates knowledge-based systems with geographical information systems (GIS) and other problem-solving techniques. A method based on spatial influence diagrams is developed for representation of environmental problems. The spatial influence diagram provides an interface through which knowledge-based systems techniques can be applied to build capabilities for problem formulation, automated design, and execution of a solution process. In addition to the flexibility and developmental advantages of knowledge-based systems, the KBSDSS incorporates expert knowledge to provide assistance for structuring spatial influence diagrams and executing a solution process that automatically integrates the GIS, data base, knowledge base, and different types of models. The framework is illustrated with a system, known as the Islay Land Use Decision Support System (ILUDSS), designed to assist planners in strategic planning of land use for the development of the island of Islay, off the west coast of Scotland.KEY WORDS: Geographical information systems; Spatial decision support systems; Knowledge-based systems; Spatial influence diagrams; Environmental management

Journal Article↗
PubMed2003

Spatial analysis of stable isotope data to determine primary sources of nutrition for fish.

Carbon and nitrogen stable isotopes were used to determine the ultimate autotrophic sources supporting production of three commercially important fish species over unvegetated mudflats in a subtropical estuary. Mean isotope values over the whole estuary for fish and autotroph sources were modeled to indicate feasible combinations of sources. Variability in isotope values among nine locations (separated by 3-10 km) was then used as a further test of the likelihood that sources were involved in fish nutrition. A positive spatial correlation between isotope values of a fish species and an autotroph indicates a substantial contribution from the autotroph. Spatial correlations were tested with a newly developed randomization procedure using differences between fish and autotroph values at each location, based on carbon and nitrogen isotopes combined in two-dimensional space. Both whole estuary modeling and spatial analysis showed that seagrass, epiphytic algae and particulate organic matter in the water column, including phytoplankton, are likely contributors to bream (Acanthopagrus australis) nutrition. However, spatial analysis also showed that mangroves were involved (up to 33% contribution), despite a very low contribution from whole estuary modeling. Spatial analysis on sand whiting (Sillago ciliata) demonstrated the importance of two sources, mangroves (up to 25%) and microalgae on the mudflats, considered unimportant based on whole estuary modeling. No spatial correlations were found between winter whiting (Sillago maculata) and autotrophs, either because fish moved among locations or relied on different autotrophs at different locations. Spatial correlations between consumer and source isotope values provide a useful analytical tool for identifying the role of autotrophs in foodwebs, and demonstrated here that both in situ production of microalgae and organic matter from adjacent habitats were important to fish over mudflats.

Animals↗
PubMed2004

Scale-dependent relationships between the spatial distribution of a limiting resource and plant species diversity in an African grassland ecosystem.

One cornerstone of ecological theory is that nutrient availability limits the number of species that can inhabit a community. However, the relationship between the spatial distribution of limiting nutrients and species diversity is not well established because there is no single scale appropriate for measuring variation in resource distribution. Instead, the correct scale for analyzing resource variation depends on the range of species sizes within the community. To quantify the relationship between nutrient distribution and plant species diversity, we measured NO(3)(-) distribution and plant species diversity in 16 paired, modified Whittaker grassland plots in Serengeti National Park, Tanzania. Semivariograms were used to quantify the spatial structure of NO(3)(-) from scales of 0.4-26 m. Plant species diversity (Shannon-Weiner diversity index; H ') was quantified in 1-m(2) plots, while plant species richness was measured at multiple spatial scales between 1 and 1000 m(2). Small-scale variation in NO(3)(-) (<0.4 m) was positively correlated with 1-m(2) H ', while 1000-m(2) species richness was a log-normal function of average NO(3)(-) patch size. Nine of the 16 grassland plots had a fractal (self-similar across scales) NO(3)(-) spatial distribution; of the nine fractal plots, five were adjacent to plots that had a non-fractal distribution of NO(3)(-). This finding offered the unique opportunity to test predictions of Ritchie and Olff (1999): when the spatial distribution of limiting resources is fractal, communities should display a left-skewed log-size distribution and a log-normal relationship between net primary production and species richness. These predictions were supported by comparisons of plant size distributions and biomass-richness relationships in paired plots, one with a fractal and one with a non-fractal distribution of NO(3)(-). In addition, fractal plots had greater large-scale richness than paired non-fractal plots (1,0-1000 m(2)), but neither species diversity ( H') nor richness was significantly different at small scales (1 m(2)). This result is most likely explained by differences in the scale of resource variation among plots: fractal and non-fractal plots had equivalent NO(3)(-) variation at small scales but differed in NO(3)(-) variation at large scales (as measured by the fractal dimension). We propose that small-scale variation in NO(3)(-) is largely due to the direct effects of plants on soil, while patterns of species richness at large scales is controlled by the patch size and fractal dimension of NO(3)(-) in the landscape. This study provides an important empirical step in understanding the relationship between the spatial distribution of resources and patterns of species diversity across multiple spatial scales.

Africa↗
PubMed2006

Multiscale spatial and small-scale temporal variation in the composition of Riverine fish communities.

We studied the multiscale (sites, river reaches and rivers) and short-term temporal (monthly) variability in a freshwater fish assemblage. We found that small-scale spatial variation and short-term temporal variability significantly influenced fish community structure in the Macquarie and Namoi Rivers. However, larger scale spatial differences between rivers were the largest source of variation in the data. The interaction between temporal change and spatial variation in fish community structure, whilst statistically significant, was smaller than the variation between rivers. This suggests that although the fish communities within each river changed between sampling occasions, the underlying differences between rivers were maintained. In contrast, the strongest interaction between temporal and spatial effects occurred at the smallest spatial scale, at the level of individual sites. This means whilst the composition of the fish assemblage at a given site may fluctuate, the magnitude of these changes is unlikely to affect larger scale differences between reaches within rivers or between rivers. These results suggest that sampling at any time within a single season will be sufficient to show spatial differences that occur over large spatial scales, such as comparisons between rivers or between biogeographical regions.

Animals↗
PubMed1992

Visual scanning with or without spatial uncertainty and divided and selective attention.

An experiment was conducted to address the relation between theories of selective attention and theories of divided attention by examining the pattern of task interference between visual scanning as a sequential and selective attention process and other concurrent spatial or verbal processing tasks. A distinction is proposed between visual scanning with or without spatial uncertainty regarding their possible differential effects on interference with other concurrent processes. The experiment required the subjects to perform a primary tracking task, which was concurrently performed with a secondary spatial or verbal decision task. The relevant information that was needed to perform the decision tasks was displayed with or without spatial uncertainty. The results provide evidence that visual scanning as a spatial exploratory activity produces greater task interference with concurrent spatial tasks than with verbal tasks. Furthermore, spatial uncertainty in scanning is identified to be the crucial factor in producing this differential effect.

Adult↗