Representation Of Spatial Information Research Articles

An SVG-based method to support spatial analysis in XML/GML/SVG-based WebGIS

XML/GML/SVG-based approaches are promising for building Web-based geographic information systems (WebGIS). However, current XML/GML/SVG-based WebGISs are lacking in spatial analysis. Some of them are designed for web mapping only. Others adopt a server-side solution for spatial analysis, which suffers from the ‘bottleneck’ problem and results in a high network transmission load. Load-balancing spatial analysis between server side and browser side can be used to solve the above problems. This article focuses on one of the key building blocks of load-balancing spatial analysis, that is, SVG-based spatial analysis which enables spatial querying and analysis directly on SVG (on the browser side). After analyzing the workflow of spatial analysis, we identify and focus on two key issues in providing spatial analysis on SVG: SVG-based spatial information representation and SVG-based spatial extended structured query language (SSESQL). For the first issue, a theoretical foundation is set up to develop an SVG-based spatial information representation model. Some spatial operators are designed and integrated into an SSESQL to support spatial querying on SVG. Finally, we design and implement two case studies. The results of these case studies show that the proposed method is feasible and operable in supporting spatial analysis directly on SVG on the browser side. The proposed method can be easily incorporated with some existing methods (e.g., GML-based spatial analysis on the server side) to provide load-balancing spatial analysis (load balancing between server side and browser side) in XML/GML/SVG-based WebGIS. As a result, users can access high-performance spatial analysis simply via a web browser (such as Internet Explorer and Firefox).

Mental Representation of Spatial Information in Children with Non-Verbal and Reading Disabilities: Two Case Studies

Non-verbal learning disability (NLD) is a specific difficulty related to the processing of visuo-spatial material. The aim of the present study is to elucidate the profile of NLD as regards ability to process and comprehend spatial descriptions, through the analysis of individual cases. Our study examined one child with NLD (M.N.), plus a second child (G.B.) with reading disability (RD) for comparison. The two children had similar reading comprehension ability. They listened to two spatial descriptions, in both survey (i.e., bird's-eye view) and route (i.e., person's point of view) perspective, plus one non-spatial description. They then answered questions about the descriptions and relocated landmarks from the spatial descriptions on a map. Performance of the child with NLD was poor in spatial descriptions but good in the non-spatial description. In particular, task performance was poorer after survey description learning. Instead, G.B. performed well in both non-spatial and spatial (i.e., survey and route) descriptions. The NLD child was shown to be specifically impaired in ability to mentally represent spatial information in survey perspective.

Investigating presentation of rail-specific spatial information on handheld computer screens

Spatial information is one of the most commonly used items of information for rail maintenance workers and providing this information to track workers while mobile offers potential advantages in terms of efficiency and communication accuracy. However, displaying track diagrams and other rail-specific spatial information on the small screen of a handheld computer presents several human computer interaction challenges that need to be considered. Three experiments were conducted to investigate different aspects of presenting spatial information on handheld computers. These experiments were conducted with current job holders at their place of work. The first experiment aimed at investigating the differences between presenting rail-specific information on handheld computers compared with paper-based documents. Using a combination of qualitative and quantitative methods, the findings of this experiment demonstrate the potential for handheld computers to provide a more efficient and effective means of displaying rail spatial information. The second experiment aimed to discover the optimum amount of information that can be presented on the screen of a handheld computer device. The results of this experiment demonstrate that although different combinations of length of track and amount of information affect user's performance, the structure of spatial information displayed on the screen is also very important. The third experiment identified that although the type of information presented to the track workers did not have an effect on their performance, postexperiment interviews revealed the importance of the type of information for track workers depending on the type of task they perform. These findings have implications for the design of small screen representations of spatial information in future mobile devices.

Joint segmentation and reconstruction of hyperspectral data with compressed measurements

This work describes numerical methods for the joint reconstruction and segmentation of spectral images taken by compressive sensing coded aperture snapshot spectral imagers (CASSI). In a snapshot, a CASSI captures a two-dimensional (2D) array of measurements that is an encoded representation of both spectral information and 2D spatial information of a scene, resulting in significant savings in acquisition time and data storage. The reconstruction process decodes the 2D measurements to render a three-dimensional spatio-spectral estimate of the scene and is therefore an indispensable component of the spectral imager. In this study, we seek a particular form of the compressed sensing solution that assumes spectrally homogeneous segments in the two spatial dimensions, and greatly reduces the number of unknowns, often turning the underdetermined reconstruction problem into one that is overdetermined. Numerical tests are reported on both simulated and real data representing compressed measurements.

Heterogeneous Representations in the Superior Parietal Lobule Are Common across Reaches to Visual and Proprioceptive Targets

The planning and control of sensory-guided movements requires the integration of multiple sensory streams. Although the information conveyed by different sensory modalities is often overlapping, the shared information is represented differently across modalities during the early stages of cortical processing. We ask how these diverse sensory signals are represented in multimodal sensorimotor areas of cortex in macaque monkeys. Although a common modality-independent representation might facilitate downstream readout, previous studies have found that modality-specific representations in multimodal cortex reflect upstream spatial representations. For example, visual signals have a more eye-centered representation. We recorded neural activity from two parietal areas involved in reach planning, area 5 and the medial intraparietal area (MIP), as animals reached to visual, combined visual and proprioceptive, and proprioceptive targets while fixing their gaze on another location. In contrast to other multimodal cortical areas, the same spatial representations are used to represent visual and proprioceptive signals in both area 5 and MIP. However, these representations are heterogeneous. Although we observed a posterior-to-anterior gradient in population responses in parietal cortex, from more eye-centered to more hand- or body-centered representations, we do not observe the simple and discrete reference frame representations suggested by studies that focused on identifying the "best-match" reference frame for a given cortical area. In summary, we find modality-independent representations of spatial information in parietal cortex, although these representations are complex and heterogeneous.

Stimulus Selectivity in Dorsal and Ventral Prefrontal Cortex after Training in Working Memory Tasks

The prefrontal cortex is known to represent different types of information in working memory. Contrasting theories propose that the dorsal and ventral regions of the lateral prefrontal cortex are innately specialized for the representation of spatial and nonspatial information, respectively (Goldman-Rakic, 1996), or that the two regions are shaped by the demands of cognitive tasks imposed on them (Miller, 2000). To resolve this issue, we recorded from neurons in the two regions, before and at multiple stages of training monkeys on visual working memory tasks. Before training, substantial functional differences were present between the two regions. Dorsal prefrontal cortex exhibited higher overall responsiveness to visual stimuli and higher selectivity for spatial information. After training, stimulus selectivity generally decreased, although dorsal prefrontal cortex retained higher spatial selectivity regardless of task performed. Ventral prefrontal cortex appeared to be affected to a greater extent by the nature of the task. Our results indicate that regional specialization for stimulus selectivity is present in the primate prefrontal cortex regardless of training. Dorsal areas of the prefrontal cortex are inherently organized to represent spatial information, and training has little influence on this spatial bias. Ventral areas are biased toward nonspatial information, although they are more influenced by training both in terms of activation and changes in stimulus selectivity.

Fine Spatial Information Represented in a Population of Retinal Ganglion Cells

Detailed measurement of ganglion cell receptive fields often reveals significant deviations from a smooth, Gaussian profile. We studied the effect of these irregularities on the representation of fine spatial information in the retina. We recorded from nearby clusters of ganglion cells, testing their ability to determine the location of small flashed spots, and we compared the results to the prediction of a Gaussian receptive field model derived from reverse correlation. Despite considerable receptive field overlap, almost all ganglion cell pairs signaled nearly independently. For groups of five cells with highly overlapping receptive fields, the measured light-evoked currents encoded ∼33% more information than predicted by the Gaussian receptive field model. Including measured local irregularities in the receptive field model increased performance to the level observed experimentally. These results suggest that instead of being an unavoidable defect, irregularities may be a positive design feature of population neural codes.

Sentence memorability reveals the mental representations involved in processing spatial descriptions

Enhanced memorability for first-sentence information was used as a probe to examine the mental representations underpinning the processing of spatial descriptions, with a focus on analogue, mental model representations versus propositional representations. In Experiment 1 rotating the visual layout of a spatial description slowed its recognition, a result that is strongly indicative of an analogue representation. In contrast, the surface details of spatial descriptions were recalled after 2 weeks, with advantages for information that was repeated or mentioned in first sentences. Although suggestive of propositional representations, these latter findings are not decisive. In Experiment 2, however, the determinacy of spatial relations influenced the recognition of their descriptions (indicative of analogue representations), but first-sentence information aided only the recall of the original text and not the spatial layout (indicative of propositional representations). Overall, these results are consistent with the existence of separate and non-integrated analogue and propositional representations of spatial information that trade computational efficiency for task appropriateness.

Representation of Non-Spatial and Spatial Information in the Lateral Entorhinal Cortex

Some theories of memory propose that the hippocampus integrates the individual items and events of experience within a contextual or spatial framework. The hippocampus receives cortical input from two major pathways: the medial entorhinal cortex (MEC) and the lateral entorhinal cortex (LEC). During exploration in an open field, the firing fields of MEC grid cells form a periodically repeating, triangular array. In contrast, LEC neurons show little spatial selectivity, and it has been proposed that the LEC may provide non-spatial input to the hippocampus. Here, we recorded MEC and LEC neurons while rats explored an open field that contained discrete objects. LEC cells fired selectively at locations relative to the objects, whereas MEC cells were weakly influenced by the objects. These results provide the first direct demonstration of a double dissociation between LEC and MEC inputs to the hippocampus under conditions of exploration typically used to study hippocampal place cells.

What is 'anti' about anti-reaches? Reference frames selectively affect reaction times and endpoint variability.

Reach movement planning involves the representation of spatial target information in different reference frames. Neurons at parietal and premotor stages of the cortical sensorimotor system represent target information in eye- or hand-centered reference frames, respectively. How the different neuronal representations affect behavioral parameters of motor planning and control, i.e. which stage of neural representation is relevant for which aspect of behavior, is not obvious from the physiology. Here, we test with a behavioral experiment if different kinematic movement parameters are affected to a different degree by either an eye- or hand-reference frame. We used a generalized anti-reach task to test the influence of stimulus-response compatibility (SRC) in eye- and hand-reference frames on reach reaction times, movement times, and endpoint variability. While in a standard anti-reach task, the SRC is identical in the eye- and hand-reference frames, we could separate SRC for the two reference frames. We found that reaction times were influenced by the SRC in eye- and hand-reference frame. In contrast, movement times were only influenced by the SRC in hand-reference frame, and endpoint variability was only influenced by the SRC in eye-reference frame. Since movement time and endpoint variability are the result of planning and control processes, while reaction times are consequences of only the planning process, we suggest that SRC effects on reaction times are highly suited to investigate reference frames of movement planning, and that eye- and hand-reference frames have distinct effects on different phases of motor action and different kinematic movement parameters.

Qualitative modelling and analysis of regulations in multi-cellular systems using Petri nets and topological collections

In this paper, we aim at modelling and analyzing the regulation processes in multi-cellular biological systems, in particular tissues. The modelling framework is based on interconnected logical regulatory networks a la Rene Thomas equipped with information about their spatial relationships. The semantics of such models is expressed through colored Petri nets to implement regulation rules, combined with topological collections to implement the spatial information. Some constraints are put on the the representation of spatial information in order to preserve the possibility of an enumerative and exhaustive state space exploration. This paper presents the modelling framework, its semantics, as well as a prototype implementation that allowed preliminary experimentation on some applications.

Multivoxel fMRI analysis reveals the representation of spatial frequency information in human primary visual cortex

Multivoxel fMRI analysis reveals the representation of spatial frequency information in human primary visual cortex

Spatial Representation of a Virtual Room Space: Perspective and Vertical Movement

Evidence from prior research has demonstrated that exocentric views of the environment can facilitate the acquisition of survey knowledge in a virtual environment. The present study examined the effect of different exocentric views on judging the relative direction of objects. During the participants' vertical movement in a virtual room, participants learned the spatial layout in one of three conditions: two-perspective, attentive-elevation, and normal-elevation conditions, where the number of the exocentric perspectives from which the spatial layout was observed was different. After spatial learning, they made the judgment of the relative direction of objects. The analysis of spatial judgment showed that as the number of exocentric perspectives increased, the accuracy improved in the mental representation of spatial vertical information and spatial information in novel directions. Results indicated that the increased number of exocentric perspectives during the vertical movement facilitated the flexible acquisition of survey knowledge. Applications of this study included the design of effective navigation aids in virtual multilevel buildings.

Mental space travel: Damage to posterior parietal cortex prevents egocentric navigation and reexperiencing of remote spatial memories.

The ability to navigate in a familiar environment depends on both an intact mental representation of allocentric spatial information and the integrity of systems supporting complementary egocentric representations. Although the hippocampus has been implicated in learning new allocentric spatial information, converging evidence suggests that the posterior parietal cortex (PPC) might support egocentric representations. To date, however, few studies have examined long-standing egocentric representations of environments learned long ago. Here we tested 7 patients with focal lesions in PPC and 12 normal controls in remote spatial memory tasks, including 2 tasks reportedly reliant on allocentric representations (distance and proximity judgments) and 2 tasks reportedly reliant on egocentric representations (landmark sequencing and route navigation; see Rosenbaum, Ziegler, Winocur, Grady, & Moscovitch, 2004). Patients were unimpaired in distance and proximity judgments. In contrast, they all failed in route navigation, and left-lesioned patients also showed marginally impaired performance in landmark sequencing. Patients' subjective experience associated with navigation was impoverished and disembodied compared with that of the controls. These results suggest that PPC is crucial for accessing remote spatial memories within an egocentric reference frame that enables both navigation and reexperiencing. Additionally, PPC was found to be necessary to implement specific aspects of allocentric navigation with high demands on spontaneous retrieval.

Highly redundant population coding explains the representation of spatial frequency information in primary visual cortex

Highly redundant population coding explains the representation of spatial frequency information in primary visual cortex

A labile representation of spatial information in the visual cortex

Classical ideas of space perception based on local sign (Lotze, 1884) have been challenged in recent years by phenomena in which the spatial location of moving, apparently moving or flashed lines associated with movement appears to be spatially displaced. Position on the retina or in a cortical topographic map does not determine apparent position. However, it is unlikely that representations in the brain are physically shifted within a cortical map. We have developed a neurally plausible mechanism, based on an encoding of the local differential structure of images, by which the representation of spatial information can be modified in place to mimic a physical spatial or temporal shift. We claim that this requirement of a labile representation places an essential constraint on the form of the neural representation of spatial pattern.

Visual stability based on remapping of attention pointers

When we move our eyes, we easily keep track of where relevant things are in the world. Recent proposals link this stability to the shifting of receptive fields of neurons in eye movement and attention control areas. Reports of 'spatiotopic' visual aftereffects have also been claimed to support this shifting connectivity even at an early level, but these results have been challenged. Here, the process of updating visual location is described as predictive shifts of location 'pointers' to attended targets, analogous to predictive activation seen cross-modally. We argue that these location pointers, the core operators of spatial attention, are linked to identity information and that such a link is necessary to establish a workable visual architecture and to explain frequently reported positive spatiotopic biases.

The New Cartographers: Crisis Map Mashups and the Emergence of Neogeographic Practice

Crisis situations are ripe for expansion of the neogeographer population and skill set. We qualitatively examine the design and creation of crisis map mashups to describe emergent neogeographic practices in this particular domain. We analyze the circumstances that led to their creation, data selection, and design choices vis-à-vis spatial and temporal information representation. We then discuss the implications of emergent neogeographic practice based on two case examples, which illustrate the merging of professional and participatory geotechnologies, and the opportunity a blending of the two provides for widespread cartographic literacy.

Monocular patching may induce ipsilateral “where” spatial bias

Spatial bias is an asymmetry of perception and/or representation of spatial information – “where” bias –, or of spatially directed actions – “aiming” bias. A monocular patch may induce contralateral “where” spatial bias (the Sprague effect [Sprague, J. M. (1966). Interaction of cortex and superior colliculus in mediation of visually guided behavior in cat. Science, 153(3743), 1544–1547]). However, an ipsilateral patch-induced spatial bias may be observed if visual occlusion results in top-down, compensatory re-allocation of spatial perceptual or representational resources toward the region of visual deprivation. Tactile distraction from a monocular patch may also contribute to an ipsilateral bias. To examine these hypotheses, neurologically normal adults bisected horizontal lines at baseline without a patch, while wearing a monocular patch, and while wearing tactile-only and visual-only monocular occlusion. We fractionated “where” and “aiming” spatial bias components using a video apparatus to reverse visual feedback for half of the test trials. The results support monocular patch-induced ipsilateral “where” spatial errors, which are not consistent with the Sprague effect. Further, the present findings suggested that the induced ipsilateral bias may be primarily induced by visual deprivation, consistent with compensatory “where” resource re-allocation.

The study for particle image velocimetry system based on binocular vision

In this paper, a new matching model is integrated into standard techniques of three-dimensional (3D) particle image velocimetry (PIV) based on the binocular vision. A 3D space is first segmented and aligned to 2D planes. Then the 2D PIV method or the particle tracking velocimetry (PTV) method is applied to match particles within different interrogation windows. Using the proposed algorithm, problems on spatial stereo matching and information representation can be solved. At last, the algorithm is applied to the real and synthetic particle images, and the results are analyzed. These experiments demonstrate that the proposed approach is effective and practical.