9,117 research outputs found
Do eyes move as a tilt-pan like system? Physical plausibility of the coplanarity of the fixation planes
No full textGenetic differences in lithium-sodium exchange and regulation of the sodium-hydrogen exchanger in essential hypertension.
No full textActive fixation as an efficient coding strategy for neuromorphic vision
No full textAbstract Contrary to a photographer, who puts a great effort in keeping the lens still, eyes insistently move even during fixation. This benefits signal decorrelation, which underlies an efficient encoding of visual information. Yet, camera motion is not sufficient alone; it must be coupled with a sensor specifically selective to temporal changes. Indeed, motion induced on standard imagers only results in burring effects. Neuromorphic sensors represent a valuable solution. Here we characterize the response of an event-based camera equipped with fixational eye movements (FEMs) on both synthetic and natural images. Our analyses prove that the system starts an early stage of redundancy suppression, as a precursor of subsequent whitening processes on the amplitude spectrum. This does not come at the price of corrupting structural information contained in local spatial phase across oriented axes. Isotropy of FEMs ensures proper representations of image features without introducing biases towards specific contrast orientations
Geographic Information Systems (GIS) for land planning and surveying: the case of the city of Khouribga (Morocco)
No full textGeographic Information Systems, together with remote sensing, represent today a basic tool for land management and planning and for the monitoring of the environmental critical factors of human and natural origin. Their use has been increasing in the last years also thanks to software and hardware development; therefore the use of GIS has spread not only into the field of cartography or land management and planning but also into other particular sectors among which there are the environmental and civil protection, geomarketing, social and economical analyses, agriculture, water, the exploitation of underground and overground resources, etc. All this testifies the relevance that this technologies have acquired in the more advanced countries: they give the chance of a complete integration of the available information, guaranteeing the possibility of immediate and rational decisions by assisting the operator in the data organization and in the comprehension of their mutual spatial correlations.
In this paper, after a brief introduction to the geographic information systems through the definitions of their main basic concepts, we shall describe an information system created for the monitoring and the territorial planning of the city of Khouribga (Morocco), chosen as a model for the several environmental problems it presents. In fact the city and its surroundings are characterised by the presence of an intense mining activity for phosphate minerals and of extended areas in which phosphate waste materials are accumulated. These are a source of strong degradation, pollution and landscape alteration to which the competent local authorities want to find a solution
The Active Side of Stereopsis: Fixation Strategy and Adaptation to Natural Environments
No full textAbstractDepth perception in near viewing strongly relies on the interpretation of binocular retinal disparity to obtain stereopsis. Statistical regularities of retinal disparities have been claimed to greatly impact on the neural mechanisms that underlie binocular vision, both to facilitate perceptual decisions and to reduce computational load. In this paper, we designed a novel and unconventional approach in order to assess the role of fixation strategy in conditioning the statistics of retinal disparity. We integrated accurate realistic three-dimensional models of natural scenes with binocular eye movement recording, to obtain accurate ground-truth statistics of retinal disparity experienced by a subject in near viewing. Our results evidence how the organization of human binocular visual system is finely adapted to the disparity statistics characterizing actual fixations, thus revealing a novel role of the active fixation strategy over the binocular visual functionality. This suggests an ecological explanation for the intrinsic preference of stereopsis for a close central object surrounded by a far background, as an early binocular aspect of the figure-ground segregation process.</jats:p
Andrea Bacová
No full textAndrea Bacová focuses on research and teaching in the field of residential architecture. Her work includes systematic research on residential buildings and their urban context. She actively participates in promoting Slovak architecture and is the author of several publications and exhibitions
Vergence control learning through real V1 disparity tuning curves
No full textA neural network architecture able to autonomously learn effective disparity-vergence responses and drive the vergence eye movements of a simulated binocular active vision system is proposed. The proposed approach, instead of exploiting purposely designed resources, relies on the direct use of a set of real disparity tuning curves, measured in the primary visual cortex of two macaque monkeys and courteously made available by (Prince et al., 2002), that provides a distributed representation of binocular disparity. The network evolves following a differential Hebbian rule that exploits the overall population activity to measure the state of the system, i.e. The deviation from the desired vergence position, so as its modification as a consequence of the action performed. Accordingly, the signal provides an effective intrinsic reward to develop a stable and accurate vergence behaviour. Emerging from a direct interaction of the sensing system with the environment, the resulting control provides a precise and accurate control for small disparities, as well as a raw control on a broader working range when large disparities are experienced. The developed control converges to a stable state that intrinsically and continuously adapts to the characteristics of the ongoing stimulation. The results proved how actually naturally distributed resources allows for robust and flexible learning capabilities in changeable situations
A study on contestable regions in Europe through the use of a new rail cost function: An application to the Hinterland of the new container terminal of Leghorn Port
No full textIn this paper, the potential hinterland of the newcontainer terminal of the port of Leghorn (Livorno in Italian) is studied.The study actually analyses the competitiveness ofmajor European portswith respect to some of themost contestable regions in Europe. Travel time and monetary costs of railway paths, connecting ports to their hinterland, have been determined.The rail network of a large part of Europe wasmodelled using a graph. To each link, which represents a portion of the rail line, a cost function is associated.The travel time on the link is determined from the average speed, which has been determined from the maximum speed via formulae obtained through linear regression.The few cost functions that exist in current literature for the computation of the cost of a rail link are not detailed enough.Therefore, a new cost function has been developed. All cost components were determined in detail: the staff cost, the amortisation, maintenance, and insurance costs of locomotives and wagons, the cost of the usage of rail track, the traction cost.The traction cost was calculated in detail from all resistances to motion. Moreover, for each rail link, the number of locomotives needed to operate the train and themaximum towable weight were determined. Themonetary value of time in freight transport registers a high variability; therefore, three different optimisations of the paths-by travel times, monetary costs, and generalised costs-between each origin-destination pair were carried out. The rates of competitiveness of the ports with respect to the examined European contestable regions were analysed
Learning a Compositional Hierarchy of Disparity Descriptors for 3D Orientation Estimation in an Active Fixation Setting
No full textInteraction with everyday objects requires by the active visual system a fast and invariant reconstruction of their local shape layout, through a series of fast binocular fixation movements that change the gaze direction on the 3-dimensional surface of the object. Active binocular viewing results in complex disparity fields that, although informative about the orientation in depth (e.g., the slant and tilt), highly depend on the relative position of the eyes. Assuming to learn the statistical relationships between the differential properties of the disparity vector fields and the gaze directions, we expect to obtain more convenient, gaze-invariant visual descriptors. In this work, local approximations of disparity vector field differentials are combined in a hierarchical neural network that is trained to represent the slant and tilt from the disparity vector fields. Each gaze-related cell’s activation in the intermediate representation is recurrently merged with the other cells’ activations to gain the desired gaze-invariant selectivity. Although the representation has been tested on a limited set of combinations of slant and tilt, the resulting high classification rate validates the generalization capability of the approach
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