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PubMed2004

Spatial-scale interaction in human stereoscopic vision in response to sustained and transient stimuli.

We investigated temporal properties of stereopsis at different spatial scales in dynamic random-dot stereograms (DRS) consisting of (i) the repeated presentation of two image pairs (i.e. sustained presentation) and (ii) single presentations of two image pairs (transient presentation). In dense stereograms perception of depth is possible if the levels of interocular correlation are above a certain threshold. Therefore, detection of correlation is an important step in stereopsis. Across different experiments, we varied the level of interocular correlation as a function of time by alternating correlated and un/anticorrelated random-dot stereograms. Also, we varied their spatial scale (coarse, fine and alternating between coarse and fine). The presence of stereopsis was examined using a forced-choice depth detection task. For both sustained and transient presentations of the stimuli, the results show that (i) stereopsis has similar temporal properties at coarse and fine spatial scales; (ii) interaction between spatial scales depends on their relative sizes. The results indicate a strong inhibitory influence of rivalry at a coarse scale on stereopsis at a fine scale, and just a weak inhibitory influence of rivalry at a fine scale on stereopsis at a coarse scale. This study provides experimental evidence for a hierarchical organisation of spatial scales in human stereoscopic vision based on neural interaction instead of vergence eye movements.

Adult↗
PubMed2004

The spatial window of the perceptual template and endogenous attention.

One primary function of spatial attention is to exclude external noise [e.g., Psychol. Sci. 11(2) (2000) 139], especially in the region of the target stimulus [J. Vis. 2(4) (2000) 312]. What is not known is the spatial profile of external noise exclusion in the vicinity of the target and how this depends upon attention. The spatial region around an oriented Gabor target was segmented into four concentric rings (R1-R4). Psychometric functions were measured for orientation discrimination with external random Gaussian noise in all combinations of rings (e.g., R1 alone; R1+R2; etc.). Regions with larger impact on performance are weighted more heavily in the perceptual template. In an orientation discrimination task in periphery the effective noise regions aligned closely with the high contrast regions of the target Gabor, with attention reducing the effective noise across the spatial template. The combined effects of external noise regions were well-modeled by a (non-linear) perceptual template model (PTM) [Vis. Res. 38(9) (1998) 1183]. In another experiment in attended fovea, the results were similar to those in periphery, but exhibited additional ability to selectively weight clear spatial regions.

Attention↗
PubMed2004

A unified theory of brightness contrast and assimilation incorporating oriented multiscale spatial filtering and contrast normalization.

Brightness induction includes both contrast and assimilations effects. Brightness contrast occurs when the brightness of a test region shifts away from the brightness of adjacent regions. Brightness assimilation refers to the opposite situation in which the brightness of the test region shifts toward that of the surrounding regions. Interestingly, in the White effect [Perception 8 (1979) 413] the direction of the induced brightness change does not correlate with the amount of black or white border in contact with the gray test patch. This has led some investigators to reject spatial filtering explanations not only for the White effect but for brightness perception in general. Instead, these investigators have offered explanations based on a variety of junction analyses and/or perceptual organization schemes. Here, these approaches are challenged with a critical set of new psychophysical measurements that determined the magnitude of the White effect, the shifted White effect [Perception 10 (1981) 215] and the checkerboard illusion [R.L. DeValois, K.K. DeValois, Spatial Vision, Oxford University Press, NY, 1988] as a function of inducing pattern spatial frequency and test patch height. The oriented difference-of-Gaussians (ODOG) computational model of Blakeslee and McCourt [Vision Res. 39 (1999) 4361] parsimoniously accounts for the psychophysical data, and illustrates that mechanisms based on junction analysis or perceptual inference are not required to explain them. According to the ODOG model, brightness induction results from linear spatial filtering with an incomplete basis set (the finite array of spatial filters in the human visual system). In addition, orientation selectivity of the filters and contrast normalization across orientation channels are critical for explaining some brightness effects, such as the White effect.

Computational Biology↗
PubMed2005

Long-range spatial integration across contrast signs: a probabilistic mechanism?

It is widely assumed that the integration of orientation contrast across spatial gaps within the long-range regime is not selective to the contrast sign of the individual stimuli. Probabilistic models of perceptual integration, however, suggest that long-range spatial integration should be, if not selective, at least sensitive to local contrast signs. To clarify this issue, we tested predictions of a model based on conditional probabilistic weights of identical and opposite contrast signs in a simple spatial configuration of two co-linear lines. Contrast detection thresholds of the target line presented either by itself (control condition) or simultaneously with the co-linear inducer (test condition) were measured. The contrast sign of targets and inducers was varied so that all four possible combinations of signs were produced in the test conditions: (1) dark target with dark inducer, (2) dark target with bright inducer, (3) bright target with bright inducer and (4) bright target with dark inducer. The contrast intensity (Weber ratio) of dark and bright inducers was identical. The coaxial distance between target and inducer was constant in each of two experiments, testing for two distances that corresponded to an angular separation within the long-range domain of spatial integration as defined previously. It is found that targets and inducers with identical contrast signs produce significantly stronger facilitating effects on detection than stimuli with opposite signs. The data closely match predictions consistent with those of a probabilistic model of line contrast integration across spatial gaps and contrast signs within the long-range regime.

Adult↗
PubMed2005

Siting MSW landfills with a spatial multiple criteria analysis methodology.

The present work describes a spatial methodology which comprises several methods from different scientific fields such as multiple criteria analysis, geographic information systems, spatial analysis and spatial statistics. The final goal of the methodology is to evaluate the suitability of the study region in order to optimally site a landfill. The initial step is the formation of the multiple criteria problem's hierarchical structure. Then the methodology utilizes spatial analysis processes to create the evaluation criteria, which are mainly based on Greek and EU legislation, but are also based on international practice and practical guidelines. The relative importance weights of the evaluation criteria are estimated using the analytic hierarchy process. With the aid of the simple additive weighting method, the suitability for landfill siting of the study region is finally evaluated. The resulting land suitability is reported on a grading scale of 0-10, which is, respectively, from least to most suitable areas. The last step is a spatial clustering process, which is being performed in order to reveal the most suitable areas, allowing an initial ranking and selection of candidate landfill sites. The application of the presented methodology in the island of Lemnos in the North Aegean Sea (Greece) indicated that 9.3% of the study region is suitable for landfill siting with grading values greater than 9.

Environment↗
PubMed2005

Testing the prenatal androgen hypothesis: measuring digit ratios, sexual orientation, and spatial abilities in adults.

The present study examined whether the following variables putatively associated with prenatal androgens are inter-related in women: spatial abilities, sexual orientation, and 2nd to 4th finger (digit) length ratio (2D:4D). Participants were 99 healthy premenopausal women tested in the menstrual phase of the ovarian cycle between 0800 and 0930 hr. Women completed the Kinsey scales of sexual orientation, and were either strictly heterosexual (HS; N=79) or not-strictly heterosexual (NHS; N=20). Photocopies of the two hands were collected, and participants completed the revised Vandenberg Mental Rotations test, the Paper Folding test, and a short version of the Guilford-Zimmerman Spatial Orientation Test. Results showed that NHS women exhibited superior spatial ability relative to HS women. No significant difference was found between the HS and NHS women in the 2D:4D digit ratio. There was no association between the digit ratio and spatial performance. These results support an association between increased spatial abilities and heteroflexible sexual orientation, which may possibly be mediated by high prenatal androgens.

Adolescent↗
PubMed1999

Spatial working memory: absence of gender differences in schizophrenia patients and healthy control subjects.

BACKGROUND: Spatial working memory dysfunction has been suggested to be a cardinal feature of schizophrenia. But schizophrenia is heterogeneous in its clinical profile, course, and outcome. One fundamental contributor to this heterogeneity may be gender. No report has yet addressed gender differences in spatial working memory, as measured by the delayed-response task (DRT). METHODS: We aggregated data from three previously published studies of spatial working memory in schizophrenia and also collected DRT data from a new sample of subjects in order to examine potential gender differences in DRT performance. RESULTS: As previously reported, schizophrenia patients (n = 71) showed deficits in spatial working memory relative to normal control subjects (n = 213), however, no within-group or between-group gender differences were present. CONCLUSIONS: These findings provide evidence for the absence of gender differences in spatial working memory function.

Adult↗
PubMed1990

Theoretical description of the spatial dependence of sickle hemoglobin polymerization.

We have generalized the double nucleation mechanism of Ferrone et al. (Ferrone, F. A., J. Hofrichter, H. Sunshine, and W. A. Eaton. 1980. Biophys. J. 32:361-377; Ferrone, F. A., J. Hofrichter, and W. A. Eaton. 1985. J. Mol. Biol. 183:611-631) to describe the spatial dependence of the radial growth of polymer domains of sickle hemoglobin. Although this extended model requires the consideration of effects such as monomer diffusion, which are irrelevant to a spatially uniform description, no new adjustable parameters are required because diffusion constants are known independently. We find that monomer diffusion into the growing domain can keep the net unpolymerized monomer concentration approximately constant, and in that limit we present an analytic solution of the model. The model shows the features reported by Basak, S., F. A. Ferrone, and J. T. Wang (1988. Biophys J. 54:829-843) and provides a new means of determining the rate of polymer growth. When spatially integrated, the model exhibits the exponential growth seen in previous studies, although molecular parameters derived from analysis of the kinetics assuming uniformity must be modified in some cases to account for the spatially nonuniform growth. The model developed here can be easily adapted to any spatially dependent polymerization process.

Hemoglobin, Sickle↗
PubMed1994

Spatial non-uniformities in [Ca2+]i during excitation-contraction coupling in cardiac myocytes.

The intracellular calcium ([Ca2+]i) transient in adult rat heart cells was examined using the fluorescent calcium indicator fluo-3 and a laser scanning confocal microscope. We find that the electrically evoked [Ca2+]i transient does not rise at a uniform rate at all points within the cell during the [Ca2+]i transient. These spatial non-uniformities in [Ca2+]i are observed immediately upon depolarization and largely disappear by the time the peak of the [Ca2+]i transient occurs. Importantly, some of the spatial non-uniformity in [Ca2+]i varies randomly in location from beat to beat. Analysis of the spatial character of the non-uniformities suggests that they arise from the stochastic nature of the activation of SR calcium-release channels. The non-uniformities in [Ca2+]i are markedly enhanced by low concentrations of Cd2+, suggesting that activation of L-type calcium channels is the primary source of activator calcium for the calcium transient. In addition, the pattern of calcium release in these conditions was very similar to the spontaneous calcium sparks that are observed under resting conditions and which are due to spontaneous calcium release from the SR. The spatial non-uniformity in the evoked [Ca2+]i transient under normal conditions can be explained by the temporal and spatial summation of a large number of calcium sparks whose activation is a stochastic process. The results are discussed with respect to a stochastic local control model for excitation-contraction (E-C) coupling, and it is proposed that the fundamental unit of E-C coupling consists of one dihydropyridine receptor activating a small group of ryanodine receptors (possibly four) in a square packing model.

Animals↗
PubMed2003

Ethanol-induced impairment of spatial memory and brain matrix metalloproteinases.

The formation of spatial memory appears to be dependent upon an intact hippocampus capable of the specific biochemical changes associated with synaptic remodeling. Hippocampal damage results in the disruption of synaptic remodeling and the acquisition of spatial memory tasks. Ethanol also disrupts normal hippocampal functioning and spatial memory. The present investigation established a dose-response relationship between ethanol treatment and impairment of spatial memory as measured using the circular water maze task. Intraperitoneal ethanol doses of 1.5 and 2 g/kg significantly increased the latency and distance swam to find the submerged pedestal as compared with a 1 g/kg dose, and 0.15 M NaCl vehicle control treatments. On days 2, 4, and 6 of acquisition animals were sacrificed and brain tissues were retained from the hippocampus, prefrontal neocortex, and cerebellum for measurement of matrix metalloproteinases (MMPs). The results indicated that ethanol treatment interfered with MMP-9, but not MMP-2, activity in the hippocampus, and to a lesser degree in the prefrontal cortex. No changes in the cerebellum were measured. Elevations in MMP activity appear to be a prerequisite to reconfiguration of extracellular matrix cell adhesion molecules thought to be important in the process of synaptic plasticity, which in turn appears to be necessary for memory consolidation. Thus, ethanol-induced impairment in the acquisition of spatial memory tasks may, in part, be due to disruption of brain MMP activity.

Animals↗
PubMed1997

The effects of type I and type II corticosteroid receptor agonists on exploratory behavior and spatial memory in the Y-maze.

We investigated the effects of two adrenal steroid agonists on adrenalectomized (ADX) rats' performance on the Y-maze. The Y-maze was chosen because memory can be assessed quickly and because it is sensitive to various parameters of exploratory behavior and spatial memory performance. Four days after surgery, ADX rats were injected with aldosterone (ALDO, a selective Type I receptor agonist), RU362 (a selective Type II receptor agonist) or sesame vehicle at three different time points (120 min prior to Trial 1, immediately after Trial 1 or 120 min after Trial 1). SHAM-operated rats injected with vehicle were also tested. The results indicate that vehicle-treated ADX rats were impaired on spatial recognition memory compared to SHAM rats. Treatment with ALDO restored spatial recognition memory performance of ADX rats to a level comparable to SHAM-treated rats by acting on acquisition and consolidation, whereas treatment with RU362 did not change the poor spatial recognition memory performance of ADX rats. Discrimination memory was improved only when either agonist was injected prior to the first trial, strongly suggesting a non-selective effect of corticosteroids on discrimination memory such as increasing arousal. A detailed analysis of exploratory behavior showed that both the ALDO- and RU362-treated rats explored the Y-maze more than the ADX and SHAM groups at all periods of the experiment. These results show that the non-specific increase in exploratory behavior induced by replacing corticosteroids targeted at Type I and Type II receptors was used differentially with the ALDO-treated rats learning and consolidating spatial information better than the RU362-treated rats. These data are discussed along with other evidence to suggest that Type II receptors may require the simultaneous occupancy of Type I receptors to affect learning and memory processes.

Adrenalectomy↗
PubMed2002

Returning the tables: language affects spatial reasoning.

Li and Gleitman (Turning the tables: language and spatial reasoning. Cognition, in press) seek to undermine a large-scale cross-cultural comparison of spatial language and cognition which claims to have demonstrated that language and conceptual coding in the spatial domain covary (see, for example, Space in language and cognition: explorations in linguistic diversity. Cambridge: Cambridge University Press, in press; Language 74 (1998) 557): the most plausible interpretation is that different languages induce distinct conceptual codings. Arguing against this, Li and Gleitman attempt to show that in an American student population they can obtain any of the relevant conceptual codings just by varying spatial cues, holding language constant. They then argue that our findings are better interpreted in terms of ecologically-induced distinct cognitive styles reflected in language. Linguistic coding, they argue, has no causal effects on non-linguistic thinking--it simply reflects antecedently existing conceptual distinctions. We here show that Li and Gleitman did not make a crucial distinction between frames of spatial reference relevant to our line of research. We report a series of experiments designed to show that they have, as a consequence, misinterpreted the results of their own experiments, which are in fact in line with our hypothesis. Their attempts to reinterpret the large cross-cultural study, and to enlist support from animal and infant studies, fail for the same reasons. We further try to discern exactly what theory drives their presumption that language can have no cognitive efficacy, and conclude that their position is undermined by a wide range of considerations.

Cognition↗
PubMed2003

The mental representation of ordinal sequences is spatially organized.

In the domain of numbers the existence of spatial components in the representation of numerical magnitude has been convincingly demonstrated by an association between number magnitude and response preference with faster left- than right-hand responses for small numbers and faster right- than left-hand responses for large numbers (Dehaene, S., Bossini, S., & Giraux, P. (1993) The mental representation of parity and number magnitude. Journal of Experimental Psychology: General, 122, 371-396). Because numbers convey not only real or integer meaning but also ordinal meaning, the question of whether non-numerical ordinal information is spatially coded naturally follows. While previous research failed to show an association between ordinal position and spatial response preference, we present two experiments involving months (Experiment 1) and letters (Experiment 2) in which spatial coding is demonstrated. Furthermore, the response-side effect was obtained with two different stimulus-response mappings. The association occurred both when ordinal information was relevant and when it was irrelevant to the task, showing that the spatial component of the ordinal representation can be automatically activated.

Adult↗
PubMed2006

Visual spatial neglect in multiple sclerosis.

Neuropsychological dysfunction in multiple sclerosis (MS) patients is now a well-established clinical finding. We examined the entity of visual spatial neglect in demyelinating disease and its correlation to the functional and neuroradiological parameters. The phenomenon of visual spatial neglect was examined in 20 (5 male and 15 female) MS patients. Two different examination methods were used--the line bisection test and the random shape cancellation test. The results were compared with 20 aged matched control individuals. The correlation of the visual spatial neglects to neurological deficits and handicaps, using Kurtzke's Expanded Disability Status Scale (EDSS), as well as with the MRI's neuroradiological findings, was analyzed. A highly significant different result on the line bisection test for three various line lengths (p = .006, p < .0001, p < .001) with displacement towards the right side was found. In all the cancellation subtests, a significant difference in error rate was found in comparing patients to controls toward a higher one on the left side of the MS patients (p = .005, p < .002, p < .0001 and p = .02 in the left side subtest, and p = n.s. in the right side subtest). There was no significant correlation between the cancellation tests and bisection results and the EDSS scale data, as well as with the neuroradiological findings. The present results demonstrate the presence of visual spatial neglect among MS patients, even without the demonstration of a characteristic neuroanatomical lesion. The hypotheses for this finding are discussed with a stress on the possibility of disruption of multiple intrahemispheric connections, especially under the condition of asymmetry of dominance regarding spatial attention.

Adult↗
PubMed2001

Remembering what but not where: independence of spatial and visual working memory in the human brain.

We report the neuropsychological and MRI investigation of a patient (MV) who developed a selective impairment of visual-spatial working memory (WM) with preservation not only of verbal, but also of visual shape WM, following an ischemic lesion in the cerebral territory supplied by one of the terminal branches of the right anterior cerebral artery. MV was defective in visual-spatial WM whether the experimental procedure involved arm movement for target pointing or not. Also, in agreement with the role generally assigned to visual-spatial WM in visual imagery, MV was extremely slow in the mental rotation of visually and verbally presented objects. In striking contrast with the WM deficit, MV's visual-spatial long-term memory was intact. The behavioral and neuroanatomical investigation of MV provides support for the hypothesis that the superior frontal gyrus (BA 6) and the dorsomedial cortex of the parietal lobe (BA 7) are part of the neural circuitry underlying visual-spatial WM in humans.

Brain↗
PubMed2002

Visuomotor adaptation to optical prisms: a new cure for spatial neglect?

In this issue, McIntosh and colleagues show that visual and haptic deficits in spatial neglect can be improved following a brief period of visuomotor adaptation to rightward displacing optical prisms. Their paper is the latest in a series of recent studies that have demonstrated the utility of prismatic adaptation in reducing the clinical symptoms of unilateral spatial neglect (Pisella et al., 2002; Rode et al., 1999; Rossetti et al., 1998; Rossetti et al., 1999). The technique has great promise as a rehabilitative tool, and may provide unique insights into the underlying mechanisms of spatial perception and action in normality and pathology. In this article I provide an introduction to the neuropsychological syndrome of spatial neglect, highlighting the significant rehabilitative challenges it poses for clinicians. I then outline the prism adaptation procedure, and consider the possible reasons for its beneficial effects in patients with spatial neglect. I conclude with some open questions and suggestions for future research.

Adaptation, Psychological↗
PubMed1999

Spatial cognition in males with Fragile-X syndrome: evidence for a neuropsychological phenotype.

Spatial performance in a group of young Fragile-X syndrome males with FMR-1 full mutation was compared to a learning disabled control group comprising young Down's syndrome males and two control groups of mainstream schoolchildren. Performance was assessed across a wide range of spatial tasks including visuo-construction, visuo-spatial memory, visuo-motor, and visuo-perception. The findings indicate a task-specific rather than global deficit in spatial performance in Fragile-X males with visuo-constructive and visuo-motor skills most vulnerable. Molecular analysis of the lymphocyte DNA found minimal evidence for a correlation between CGG expansion size and spatial performance, although tasks with a visuo-perceptual component correlated negatively with expansion size indicating that the further away the number of repeats are from the 200 threshold the poorer the performance.

Adolescent↗
PubMed1999

A comparison of egocentric and allocentric spatial memory in medial temporal lobe and Korsakoff amnesics.

Two patients with medial temporal lobe damage, seven Korsakoff amnesics and fourteen healthy control subjects were tested on three conditions of a spatial memory test ('short delay', 'allocentric' and 'egocentric'). The task required subjects to recall the position of a single spot of light presented on a board after various delays. The 'short delay' condition tested memory over very short, unfilled intervals. The other two conditions used longer, filled delays. The allocentric condition required subjects to move to a different place around the board before recalling the position of the light. In the egocentric condition stimuli were presented in darkness, which eliminated allocentric cues. The Korsakoff amnesics were impaired at all delays of the short delay tasks, suggesting poor encoding. On the allocentric and egocentric tasks the Korsakoff amnesics showed a comparable impairment in the two conditions, which worsened with delay. This accelerated forgetting suggested that the Korsakoff amnesics also had impaired memory for allocentric and egocentric information. The patients with medial temporal lobe damage were unimpaired in the 'short delay' condition suggesting intact encoding and short-term memory of spatial information. However, they were impaired in the allocentric condition and showed accelerated loss of allocentric spatial information. In the egocentric condition, while the performance of one patient was impaired, the performance of the other was as good as controls. This result suggests that, in contrast to allocentric spatial memory, which is sensitive to medial temporal lobe damage, an intact medial temporal lobe need not be necessary for successful performance on an egocentric spatial memory task.

Aged↗