Página 1 dos resultados de 4565 itens digitais encontrados em 0.009 segundos

Criação de mapas de disparidades empregando análise multi-resolução e agrupamento perceptual; Disparity maps generation employing multi-resolution analysis and Gestalt Grouping

Laureano, Gustavo Teodoro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 06/03/2008 Português
Relevância na Pesquisa
36.8%
O trabalho apresentado por essa dissertação busca contribuir com a atenuação do problema da correspondência em visão estéreo a partir de uma abordagem local de soluções. São usadas duas estratégias como solução às ambigüidades e às oclusões da cena: a análise multi-resolução das imagens empregando a estrutura piramidal, e a força de agrupamento perceptual, conhecida como Gestalt theory na psicologia. Inspirado no sistema visual humano, a visão estéreo é uma área de grande interesse em visão computacional, e está relacionada à recuperação de informações tridimensionais de uma cena a partir de imagens da mesma. Para isso, as imagens são capturadas em posições diferentes para o futuro relacionamento das várias projeções de um mesmo ponto 3D. Apesar de ser estudada há quase quatro décadas, ela ainda apresenta problemas de difícil solução devido às dificuldades relacionadas às distorções produzidas pela mudança da perspectiva de visualização. Dentre esses problemas destacam-se os relacionados à oclusão de pontos e também à ambigüidade gerada pela repetição ou ausência de textura nas imagens. Esses por sua vez compõem a base do problema estéreo, chamado de problema da correspondência. Os resultados obtidos são equivalentes aos obtidos por técnicas globais...

Effects of environmental conditions, human activity, reproduction, antler cycle and grouping on fecal glucocorticoids of free-ranging Pampas deer stags (Ozotoceros bezoarticus bezoarticus)

Pereira, RJG; Duarte, JMB; Negrao, J. A.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 114-122
Português
Relevância na Pesquisa
36.68%
In this study, a commercial enzyme immunoassay (EIA) was validated in detecting glucocorticoids in Pampas deer feces, in order to investigate the influence of several factors on the adrenocortical function. Fecal samples, behavioral data and information concerning male grouping and antlers status were collected at a monthly basis during a 1 year period from free-ranging stags living at Emas National Park, Brazil (18 degrees S/52 degrees W). The results revealed that concentrations of fecal glucocorticoids in winter were significantly higher than those corresponding to spring and summer. In addition, dry season data presented higher levels than during the wet season. Significant difference was found between fecal levels of breeding stags in summer and nonbreeding stags, whereas no difference was observed between breeding stags in winter and nonbreeding stags. on the other hand, males from areas with frequent human disturbance exhibited higher glucocorticoid concentrations and flight distances than individuals from areas of lower human activity. Males with antlers in velvet had elevated levels compared with animals in hard antler or antler casting. Also, we found that glucocorticoid levels were higher in groups with three or more males than in groups with only one male. The flight distances showed positive correlation with fecal glucocorticoid. These data indicate that fecal glucocorticoid provides a useful approach in the evaluation of physiological effects of environment...

A methodological approach for the study of export grouping schemes

Brito, Carlos; Silva, Susana Costa e
Fonte: Faculdade de Economia da Universidade do Porto Publicador: Faculdade de Economia da Universidade do Porto
Tipo: Artigo de Revista Científica
Publicado em //2005 Português
Relevância na Pesquisa
36.68%
Export grouping schemes have assumed an increasing role in the process of internationalization, especially for small- and medium-sized companies. Its network character has received the attention of a number of researchers who have focused both on their creation and development. Although cooperation has been recognized as a central feature, its collective action nature has been neglected. This paper aims at developing a methodological approach which takes into account that most export schemes involve a variety of actors who share common interests and are concerned with the promotion or defense of their collective interests.

Understanding export grouping schemes as issue-based nets

Brito, Carlos; Silva, Susana Costa e
Fonte: EIBA - European International Business Academy Publicador: EIBA - European International Business Academy
Tipo: Artigo de Revista Científica
Publicado em //2008 Português
Relevância na Pesquisa
36.89%
Many Portuguese SMEs firms used export networks as an internationalization strategy. In the process of internationalization of those firms export grouping schemes have assumed an increasing role. Export grouping schemes creation and development has been widely studied. The study of collective action within export grouping schemes has been neglected. This paper aims at developing a methodological approach which takes into account that most export schemes involve a variety of actors who share common interests and are concerned with the promotion or defense of their collective interests.

The collective nature of export grouping schemes

Brito, Carlos; Silva, Susana Costa e
Fonte: Universidade Católica Portuguesa Publicador: Universidade Católica Portuguesa
Tipo: Artigo de Revista Científica
Publicado em //2011 Português
Relevância na Pesquisa
36.68%
Export grouping schemes have assumed an increasing role in the process of internationalization, especially for small- and medium-sized companies. Its network character has received the attention of a number of researchers who have focused both on their creation and development. Although cooperation has been recognized as a central feature, its collective action nature has been neglected. This paper aims at developing a methodological approach which takes into account that most export schemes involve a variety of actors who share common interests and are concerned with the promotion or defense of their collective interests.

Response bias in grouping

Masin,Sergio Cesare
Fonte: Universidade de São Paulo, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto Publicador: Universidade de São Paulo, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2004 Português
Relevância na Pesquisa
36.96%
Surface color similarity may cause the perceptual grouping of uniform achromatic surfaces on an achromatic background both when the background is homogeneous and when the background contains achromatic context surfaces. Empirical results reported here show that the grouping response due to the similarity in color of test surfaces is also affected by context surfaces. It is proposed that this response bias results from interference of the grouping response caused by the similarity in color of test surfaces with an implicit grouping response caused by the similarity in color between context surfaces and test surfaces.

Grouping in object recognition: The role of a Gestalt law in letter identification

Pelli, Denis G.; Majaj, Najib J.; Raizman, Noah; Christian, Christopher J.; Kim, Edward; Palomares, Melanie C.
Fonte: Psychology Press Publicador: Psychology Press
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27%
The Gestalt psychologists reported a set of laws describing how vision groups elements to recognize objects. The Gestalt laws “prescribe for us what we are to recognize ‘as one thing’” (Köhler, 1920). Were they right? Does object recognition involve grouping? Tests of the laws of grouping have been favourable, but mostly assessed only detection, not identification, of the compound object. The grouping of elements seen in the detection experiments with lattices and “snakes in the grass” is compelling, but falls far short of the vivid everyday experience of recognizing a familiar, meaningful, named thing, which mediates the ordinary identification of an object. Thus, after nearly a century, there is hardly any evidence that grouping plays a role in ordinary object recognition. To assess grouping in object recognition, we made letters out of grating patches and measured threshold contrast for identifying these letters in visual noise as a function of perturbation of grating orientation, phase, and offset. We define a new measure, “wiggle”, to characterize the degree to which these various perturbations violate the Gestalt law of good continuation. We find that efficiency for letter identification is inversely proportional to wiggle and is wholly determined by wiggle...

What is Grouping during Binocular Rivalry?

Stuit, Sjoerd M.; Paffen, Chris L. E.; van der Smagt, Maarten J.; Verstraten, Frans A. J.
Fonte: Frontiers Research Foundation Publicador: Frontiers Research Foundation
Tipo: Artigo de Revista Científica
Publicado em 18/10/2011 Português
Relevância na Pesquisa
27.07%
During binocular rivalry, perception alternates between dissimilar images presented dichoptically. Although perception during rivalry is believed to originate from competition at a local level, different rivalry zones are not independent: rival targets that are spaced apart but have similar features tend to be dominant at the same time. We investigated grouping of spatially separated rival targets presented to the same or to different eyes and presented in the same or in different hemifields. We found eye-of-origin to be the strongest cue for grouping during binocular rivalry. Grouping was additionally affected by orientation: identical orientations were grouped longer than dissimilar orientations, even when presented to different eyes. Our results suggest that eye-based and orientation-based grouping is independent and additive in nature. Grouping effects were further modulated by the distribution of the targets across the visual field. That is, grouping within the same hemifield can be stronger or weaker than between hemifields, depending on the eye-of-origin of the grouped targets. We also quantified the contribution of the previous cues to grouping of two images during binocular rivalry. These quantifications can be successfully used to predict the dominance durations of different studies. Incorporating the relative contribution of different cues to grouping...

Incremental grouping of image elements in vision

Roelfsema, Pieter R.; Houtkamp, Roos
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.07%
One important task for the visual system is to group image elements that belong to an object and to segregate them from other objects and the background. We here present an incremental grouping theory (IGT) that addresses the role of object-based attention in perceptual grouping at a psychological level and, at the same time, outlines the mechanisms for grouping at the neurophysiological level. The IGT proposes that there are two processes for perceptual grouping. The first process is base grouping and relies on neurons that are tuned to feature conjunctions. Base grouping is fast and occurs in parallel across the visual scene, but not all possible feature conjunctions can be coded as base groupings. If there are no neurons tuned to the relevant feature conjunctions, a second process called incremental grouping comes into play. Incremental grouping is a time-consuming and capacity-limited process that requires the gradual spread of enhanced neuronal activity across the representation of an object in the visual cortex. The spread of enhanced neuronal activity corresponds to the labeling of image elements with object-based attention.

Patients with Schizophrenia Do Not Preserve Automatic Grouping When Mentally Re-Grouping Figures: Shedding Light on an Ignored Difficulty

Giersch, Anne; van Assche, Mitsouko; Capa, Rémi L.; Marrer, Corinne; Gounot, Daniel
Fonte: Frontiers Research Foundation Publicador: Frontiers Research Foundation
Tipo: Artigo de Revista Científica
Publicado em 17/08/2012 Português
Relevância na Pesquisa
27.15%
Looking at a pair of objects is easy when automatic grouping mechanisms bind these objects together, but visual exploration can also be more flexible. It is possible to mentally “re-group” two objects that are not only separate but belong to different pairs of objects. “Re-grouping” is in conflict with automatic grouping, since it entails a separation of each item from the set it belongs to. This ability appears to be impaired in patients with schizophrenia. Here we check if this impairment is selective, which would suggest a dissociation between grouping and “re-grouping,” or if it impacts on usual, automatic grouping, which would call for a better understanding of the interactions between automatic grouping and “re-grouping.” Sixteen outpatients with schizophrenia and healthy controls had to identify two identical and contiguous target figures within a display of circles and squares alternating around a fixation point. Eye-tracking was used to check central fixation. The target pair could be located in the same or separate hemifields. Identical figures were grouped by a connector (grouped automatically) or not (to be re-grouped). Attention modulation of automatic grouping was tested by manipulating the proportion of connected and unconnected targets...

Functional specialization and generalization for grouping of stimuli based on colour and motion

Zeki, Semir; Stutters, Jonathan
Fonte: Academic Press Publicador: Academic Press
Tipo: Artigo de Revista Científica
Publicado em /06/2013 Português
Relevância na Pesquisa
27.04%
This study was undertaken to learn whether the principle of functional specialization that is evident at the level of the prestriate visual cortex extends to areas that are involved in grouping visual stimuli according to attribute, and specifically according to colour and motion. Subjects viewed, in an fMRI scanner, visual stimuli composed of moving dots, which could be either coloured or achromatic; in some stimuli the moving coloured dots were randomly distributed or moved in random directions; in others, some of the moving dots were grouped together according to colour or to direction of motion, with the number of groupings varying from 1 to 3. Increased activation was observed in area V4 in response to colour grouping and in V5 in response to motion grouping while both groupings led to activity in separate though contiguous compartments within the intraparietal cortex. The activity in all the above areas was parametrically related to the number of groupings, as was the prominent activity in Crus I of the cerebellum where the activity resulting from the two types of grouping overlapped. This suggests (a) that, the specialized visual areas of the prestriate cortex have functions beyond the processing of visual signals according to attribute...

Distinct Perceptual Grouping Pathways Revealed By Temporal Carriers and Envelopes

Rainville, Stéphane; Clarke, Aaron
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 21/11/2008 Português
Relevância na Pesquisa
27.07%
Guttman et al. [2005, Vis. Res., 45(8), 1021-1030] investigated whether observers could perform temporal grouping in multi-element displays where each local element was stochastically modulated over time along one of several potential dimensions – or “messenger types” – such as contrast, position, orientation, or spatial scale. Guttman et al.’s data revealed that grouping discards messenger type and therefore support a single-pathway model that groups elements with similar temporal waveforms. In the current study, we carried out three experiments in which temporal-grouping information resided either in the carrier, the envelope, or the combined carrier and envelope of each messenger’s timecourse. Results revealed that grouping is highly specific for messenger type if carrier envelopes lack grouping information but largely messenger nonspecific if carrier envelopes contain grouping information. The imply that temporal grouping is mediated by several messenger-specific carrier pathways as well as by a messenger-nonspecific envelope pathways. Findings also challenge simple temporal-filtering accounts of perceptual grouping [Adelson & Farid, 1999, Science, 286, 2231a].

A Perceptual Grouping Hierarchy for Appearance-Based 3D Object Recognition

Nelson, Randal C. ; Selinger, Andrea
Fonte: University of Rochester. Computer Science Department. Publicador: University of Rochester. Computer Science Department.
Tipo: Relatório
Português
Relevância na Pesquisa
37%
In this report we consider the problem of 3D object recognition, and the role that perceptual grouping processes must play. In particular, we argue that a single level of perceptual grouping is inadequate, and that reliance on a single level of grouping is responsible for the specific weaknesses of several well-known recognition techniques. Instead, we argue that recognition must utilize a hierarchy of perceptual grouping processes, and describe an appearance-based system that uses four distinct levels of perceptual grouping, the upper two novel, to represent 3D objects in a form that not only allows recognition, but reasoning about 3D manipulation of a sort that has been supported in the past only by 3D geometric models.

Flaws on RFID grouping-proofs. Guidelines for future sound protocols

Peris-López, Pedro; Orfila, Agustín; Hernández-Castro, Julio C.; Van der Lubbe, Jan C.A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica Formato: application/octet-stream; application/octet-stream; application/pdf
Publicado em //2010 Português
Relevância na Pesquisa
36.68%
During the last years many RFID authentication protocols have been proposed with major or minor success (van Deursen and Radomirović, 2008). Juels (2004) introduced a different and novel problem that aims to evidence that two tags have been simultaneously scanned. He called this kind of evidence a yoking-proof that is supposed to be verifiable offline. Then, some authors suggested the generalization of the proof for a larger number of tags. In this paper, we review the literature published in this research topic and show the security flaws of the proposed protocols, named RFID grouping-proofs generally. More precisely, we cryptanalyze five of the most recent schemes and we also show how our techniques can be applied to older proposals. We provide some guidelines that should be followed to design secure protocols and preclude past errors. Finally, we present a yoking-proof for low-cost RFID tags, named Kazahaya, that conforms to the proposed guidelines.

Grouping pursuit through a regularization solution surface *

Shen, Xiaotong; Huang, Hsin-Cheng
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/06/2010 Português
Relevância na Pesquisa
27.04%
Extracting grouping structure or identifying homogenous subgroups of predictors in regression is crucial for high-dimensional data analysis. A low-dimensional structure in particular–grouping, when captured in a regression model, enables to enhance predictive performance and to facilitate a model's interpretability Grouping pursuit extracts homogenous subgroups of predictors most responsible for outcomes of a response. This is the case in gene network analysis, where grouping reveals gene functionalities with regard to progression of a disease. To address challenges in grouping pursuit, we introduce a novel homotopy method for computing an entire solution surface through regularization involving a piecewise linear penalty. This nonconvex and overcomplete penalty permits adaptive grouping and nearly unbiased estimation, which is treated with a novel concept of grouped subdifferentials and difference convex programming for efficient computation. Finally, the proposed method not only achieves high performance as suggested by numerical analysis, but also has the desired optimality with regard to grouping pursuit and prediction as showed by our theoretical results.

Truncated power laws reveal a link between low-level behavioral processes and grouping patterns in a colonial bird

Jovani, Roger; Serrano, David; Ursúa, Esperanza; Tella, José Luis
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artículo Formato: 260303 bytes; application/pdf
Português
Relevância na Pesquisa
36.8%
7 pages, 5 figures.-- PMID: 18431479 [PubMed].-- PMCID: PMC2292258.; [Background] Departures from power law group size frequency distributions have been proposed as a useful tool to link individual behavior with population patterns and dynamics, although examples are scarce for wild animal populations.; [Methodology/Principal Findings] We studied a population of Lesser kestrels (Falco naumanni) breeding in groups (colonies) from one to ca. 40 breeding pairs in 10,000 km2 in NE Spain. A 3.5 fold steady population increase occurred during the eight-year study period, accompanied by a geographical expansion from an initial subpopulation which in turn remained stable in numbers. This population instability was mainly driven by first-breeders, which are less competitive at breeding sites, being relegated to breed solitarily or in small colony sizes, and disperse farther than adults. Colony size frequency distributions shifted from an initial power law to a truncated power law mirroring population increase. Thus, we hypothesized that population instability was behind the truncation of the power law. Accordingly, we found a power law distribution through years in the initial subpopulation, and a match between the power law breakpoint (at ca. ten pairs) and those colony sizes from which the despotic behavior of colony owners started to impair the settlement of newcomers. Moreover...

Viés de resposta no agrupamento; Response bias in grouping

Masin, Sergio Cesare
Fonte: Universidade de São Paulo. Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto Publicador: Universidade de São Paulo. Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf
Publicado em 01/04/2004 Português
Relevância na Pesquisa
36.96%
A similaridade da cor da superfície pode causar um agrupamento perceptual de superfícies acromáticas uniformes sobre um fundo acromático tanto quando o fundo é homogêneo e quando o fundo contém superfícies de contexto acromáticas. Os resultados empíricos aqui relatados demonstram que a resposta de agrupamento devido à similaridade em cor da superfície de teste é afetada também pelas superfícies de contexto. Foi proposto que este viés da resposta resulta da interferência da resposta de agrupamento causada pela similaridade em cor da superfície de teste com uma resposta de agrupamento implícita causada pela similaridade em cor entre superfícies de contexto e as superfícies de teste.; Surface color similarity may cause the perceptual grouping of uniform achromatic surfaces on an achromatic background both when the background is homogeneous and when the background contains achromatic context surfaces. Empirical results reported here show that the grouping response due to the similarity in color of test surfaces is also affected by context surfaces. It is proposed that this response bias results from interference of the grouping response caused by the similarity in color of test surfaces with an implicit grouping response caused by the similarity in color between context surfaces and test surfaces.

Proposed Arabic grouping system and cross-map with the International Standard Organization ISO 9541 Grouping System

Tawil, Mohamad
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
37%
This project, will attempt to identify as many Arabic fonts as possible and develop a grouping system similar to the basic system used in ISO 9541-1 (International Standard Organization). Fonts will be classified according to their visual design in a three-level hierarchical structure. The highest level of this hierarchy is the class the most general level. Each class is divided into subclasses the second level of this grouping system. Subclasses are divided into groups the third level and the most specific level. The purpose is to cover as many design variations as possible within the same class. I will compare the elements in my grouping system with the ones in the ISO 9541-1, and establish a relationship between the two systems. The result of this comparison can be utilized in any multi-lingual printing and publishing job using Arabic and any of the scripts used in ISO 9541 grouping system.

Grouping related attributes

Dawara, Santosh
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado Formato: 13676 bytes; 625017 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
36.96%
Grouping objects that are described by attributes, or clustering is a central notion in data mining. On the other hand, similarity or relationships between attributes themselves is equally important but relatively unexplored. Such groups of attributes are also known as directories, concept hierarchies or topics depending on the underlying data domain. The similarities between the two problems of grouping objects and attributes might suggest that traditional clustering techniques are applicable. This thesis argues that traditional clustering techniques fail to adequately capture the solution we seek. It also explores domain-independent techniques for grouping attributes. The notion of similarity between attributes and therefore clustering in categorical datasets has not received adequate attention. This issue has seen renewed interest in the knowledge discovery community, spurred on by the requirements of personalization of information and online search technology. The problem is broken down into (a) quantification of this notion of similarity and (b) the subsequent formation of groups, retaining attributes similar enough in the same group based on metrics that we will attempt to derive. Both aspects of the problem are carefully studied. The thesis also analyzes existing domainindependent approaches to building distance measures...

Honeybee Memory: Navigation by associative grouping of visual stimuli

Zhang, Shao Wu; Lehrer, M; Srinivasan, Mandyam V
Fonte: Academic Press Publicador: Academic Press
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
36.68%
Studies of navigation in bees and ants are beginning to reveal that foraging insects traveling repeatedly to a food source navigate by using a series of visual images of the environment acquired en route (Collett, 1996; Collett et al., 1993; Judd and Collett, 1998; Wehner et al., 1990, 1996). By comparing the currently viewed scene with the appropriate stored image, the insect is able to ascertain whether or not it is on the correct path and make any necessary corrections. If a bee happens to forage at more than one site, then she needs not only to memorize a separate set of images for each route that she has learned but also to retrieve the set of images that is appropriate to each route. Here we examine the bee's capacity to learn and later retrieve from memory two different sets of visual stimuli. Bees were trained to fly through a compound Y-maze where they were presented alternately with two different sequences of visual stimuli on their route to a food reward. We find that bees can indeed store two different sequences of images simultaneously. Furthermore, the trained bees are able to classify the memorized images into two groups, one pertaining to each three-stimulus set. Exposure to any of the images pertaining to one set triggers recall of all of the other images associated with that set. Associative grouping and recall of visual stimuli...