In this study we sought to determine whether infants, like adults, utilize previous experience to guide figure/ground processing. After familiarization to a shape, 5-month-olds preferentially attended to the side of an ambiguous figure/ground test stimulus corresponding to that shape, suggesting that they were viewing that portion as the figure. Infants’ failure to exhibit this preference in a control condition in which both sides of the test stimulus were displayed as figures indicated that the results in the experimental condition were not due to a preference between two figure shapes. These findings demonstrate for the first time that figure/ground processing in infancy is sensitive to top-down influence. Thus, a critical aspect of figure/ground processing is functional early in life.

Listening comprehension has been the forgotten skill in second language acquisition. However, in recent years, more and more studies have focused on listening comprehension and now acknowledge its importance in language acquisition. Empirical studies have explored how listeners use the two main listening processes (top-down processing and bottom-up processing). In this study, 31 low-proficiency level Mandarin Chinese as a foreign language (CFL) learners from Brigham Young University took the Chinese Computer Adaptive Language Test (CCALT) and listened to four listening passages, measured by idea unit analysis and local and global question types. The data from these measurements suggest that low-proficiency level CFL participants in this study used both top-down and bottom-up processing while they listened to short listening passages. The results suggest listening comprehension at various proficiency levels needs to be studied further in Chinese and with different types of listening passages.

L2 listening research has moved toward a focus on understanding the process of listening. However, there are still few detailed studies of L2 listening that reveal learners’ comprehension processes when listening to scripted and unscripted listening texts. Studies in which such processing has been discussed have lacked detailed diagnoses of how bottom-up and top-down processing interactively affect listeners’ comprehension. This study was designed to show how listeners’ process and comprehend texts, with a focus on how their bottom-up and top-down processing either assist or impede their comprehension. In this study, a group of 30 L1 Japanese university English language learners’ listening abilities were diagnosed. The 30 participants were at three listening proficiency levels—high, mid, and low—based on TOEIC listening proficiency scores. The diagnostic procedure involved participants listening to two scripted and two unscripted listening texts and then reporting what they comprehended through three tasks—L1 oral recalls, L2 repetitions, and verbal reports. Other data was also collected in the study to relate the comprehension of listening texts to other important listening-related variables including listening proficiency, lexical knowledge, listening anxiety, study abroad experience, short-term phonological memory, and working memory. The main finding of the study was that miscomprehension of listening texts was invariably multi-causal, with a combination of both bottom-up and top-down factors leading to comprehension difficulty. Although not a new finding, the study offered more detail than current research about how bottom-up and top-down processing occur interactively. Regarding the overall difficulty of the listening texts, unscripted texts were more difficult to comprehend than scripted texts, and high-proficiency participants had fewer listening difficulties overall than mid- and low-proficiency participants. Quantitative and qualitative results revealed common processing difficulties among all participants due to L1-related phonological decoding issues (e.g., /l/ vs. /r/), connected speech, unknown lexis, and a lack of familiarity with unscripted speech hesitation phenomena (e.g., um, like). Qualitative transcript examples showed how top-down knowledge influenced misinterpretations of words and phrases interactively with bottom-up information, making inaccurate understandings of listening difficult to overcome. In addition to revealing participants’ difficulties and the severity of their comprehension difficulties, the diagnostic procedure showed common strengths—key words and phrases understood well by participants. High-frequency vocabulary and shorter utterances were both shown to be comprehended well. Finally, quantitative results in the study revealed relationships of participants’ listening comprehension with other important listening related variables. Listening proficiency and listening anxiety had strong relationships with listening comprehension of the listening texts. Working memory and short-term phonological memory had no relationship with listening text comprehension. Finally, study abroad experience showed a relationship with comprehension, but with many caveats, and listening vocabulary knowledge was not related with comprehension, but again, with numerous caveats to consider. Based on the results, theoretical and pedagogical implications were posed. Theoretical implications from the study relate to the understanding of four concerns in L2 listening research. Mainly, data in the study will aid researchers’ understanding of how L2 English listeners process speech interactively (i.e., with bottom-up and top-down information) for comprehension, how L2 English listeners experience connected speech, how L2 listeners deal with unknown lexis, and how L2 listeners experience difficulties with features of unscripted speech. Pedagogical implications of the study include the need for increased teacher and learner awareness of the complexity of L2 listening, the need to have learners to track their own listening development, and the need for teachers to expose learners to unscripted listening texts and make them familiar with features of unscripted speech. Finally, suggestions for further research are posed, including conducting diagnostics assessments of L2 listening with listeners of different L1s and with more varied proficiency levels, using different diagnostic procedures to examine L2 listening comprehension, and using more instruments to understand listening-related variables’ relationships with L2 listening comprehension. / Teaching & Learning

Wahrnehmung ist kein vollständig durch sensorische Reize determinierter bottom-up Prozeß, sondern wird stark beeinflußt durch von diesen Reizen unabhängige top-down Prozesse wie etwa Aufmerksamkeit oder Erwartungen. Welche neuronalen Mechanismen liegen der Integration von bottom-up und top-down gerichteter Verarbeitung sensorischer Information zu Grunde? Im ersten Teil dieser Arbeit wurde diese Frage an Hand von Simulationen eines neuronales Netzwerks zweier vereinfachter kortikaler Areale untersucht. Dieses Netzwerk berücksichtigt hierbei jüngste zellphysiologische Befunde über die stark asymmetrischen funktionellen Eigenschaften kortikaler Neurone. Das simulierte Netzwerk repliziert zentrale neurophysiologische Befunde: 1) Top-down Signale erhöhen die Feuerraten der Neurone sowohl in einem hierarchisch hohen als auch tiefen kortikalen Areal. 2) Durch selektive top-down Signale wird die Verarbeitung simultaner Reize zu Gunsten eines faszilitierten Reizes moduliert. 3) Durch die reziproke Netzwerkarchitektur kommt es zu einem bidirektionalen Informationsfluß zwischen Arealen. Diese kooperative Verarbeitung bedingt gemeinsam mit einer nichtlinearen somato-dendritischen Interaktion neuronale Salvenentladungen, die ein hohes Signal-Rausch-Verhältnis aufweisen. Das simulierte Netzwerk demonstriert, welche zentrale Rolle die komplexen nichtlinearen Eigenschaften kortikaler Neurone bei der Integration bottom-up und top-down gerichteter Verarbeitung sensorischer Information spielen. Im Mittelpunkt der im zweiten Abschnitt vorgestellten experimentellen Studie steht die hochfrequente Synchronisation neuronaler Aktivität. Das große neurowissenschaftliche Interesse an der zeitlichen Struktur neuronaler Aktivität liegt insbesondere in der kontrovers diskutierten Hypothese eines „Synchronisationscodes“ begründet, gemäß welcher Information nicht nur durch die Feuerraten kortikaler Neurone, sondern auch durch die Synchronisation der Aktionspotentiale einer Neuronenpopulation codiert wird. Finden sich solche Synchronisationsphänomene in wachen, sich unter möglichst natürlichen Bedingungen verhaltenden Tieren wieder? Sind diese Synchronisationen selektiv für Eigenschaften des Reizes? Gelingt es, an Hand eines objektiven Kriteriums ein funktionelles Frequenzband neuronaler Synchronisation zu definieren? Diese Fragestellungen wurden mittels chronischer extrazellulärer Ableitungen im primären visuellen Kortex wacher, sich verhaltender Katzen untersucht: 1) Visuelle Stimulation induziert einen breitbandigen hochfrequenten Anstieg neuronaler Synchronisation. 2) Diese Synchronisation ist selektiv für die Orientierung visueller Reize. 3) Durch Analyse dieser Stimulusselektivität kann ein funktionelles Band neuronaler Synchronisation von etwa 45 Hz bis 120 Hz definiert werden. Diese Untersuchungen an wachen, sich unter vergleichsweise natürlichen Bedingungen verhaltenden Tieren demonstrieren eine überraschend breite Frequenzverteilung neuronaler Synchronisation, die im hochfrequenten Bereich weit über die üblicherweise untersuchten Frequenzbänder hinausreicht. Diese Befunde sprechen gegen die Hypothese hochfrequenter kortikaler Synchronisation als einem schmalbandigen statischen Phänomen. / Sensory perception is not purely a bottom-up process determined only by sensory stimuli, but is strongly dependent on top-down factors such as attention or expectations.Which neuronal mechanisms underlie the integration of bottom-up and top-down directed processing of sensory information? In the first part of this study this question was addressed by numerical simulations of a neural network model of two simplified cortical areas. The simulated network takes into account recent findings concerning the pronounced functional asymmetry of cortical neurons.The network replicates several important neurophysiological findings: 1) Top-down signals enhance firing rates in hierarchically high and low cortical areas. 2) The processing of two competing stimuli is biased towards one stimulus by selective top-down signals. 3) The reciprocal network architecture results in a bidirectional flow of information. Together with the implemented non-linear somato-dendritic interaction this leads to neuronal bursting behaviour with a high signal to noise ratio. The simulated network demonstrates the critical role of the complex non-linear properties of cortical neurons for the integration of bottom-up and top-down directed sensory processing. The central question of the second part of this study is the functional role of high-frequency synchronization of neuronal activity. The strong interest in the temporal dynamics of neuronal activity is particularly due to the hypothesis of a “synchronization-code” according to which information is not solely encoded by firing rates but also by the synchronization of neuronal ensembles. Is such synchronization observed in awake animals behaving under natural conditions? Are these synchronizations stimulus selective? Is it possible to define a functional frequency band of synchronization based on an objective criterion? These questions were addressed by chronic extracellular recordings of neuronal activity in primary visual cortex of awake behaving cats: 1) Visual stimulation induces neuronal synchronization in a broad and high frequency range. 2) This synchronization is selective for the orientation of a visual stimulus. 3) By analyzing the stimulus selectivity of synchronization a functional band of neuronal synchronization can be defined from about 45 to 120 Hz. These results from animals behaving under natural conditions show a surprisingly broad spectral distribution of synchronization that extends well beyond typically investigated frequency ranges. These results cast doubt on the hypothesis of cortical high-frequency synchronizations as a spectrally sharp and static phenomenon.

Perceptual rivalry refers to visual phenomena that are characterised by alternations between different percepts, despite an unchanging sensory input. Two common types of perceptual rivalry are (i) reversible figures — two-dimensional stable images that when viewed, are perceived to switch between different interpretations, and (ii) binocular rivalry — the alternations in image dominance resulting from the presentation of conflicting stimuli, one to each eye. Several investigators have suggested that these rivalling phenomena are mediated by similar neural mechanisms. Such a view, however, has not only been inadequately substantiated, but has also yet to be assessed in the context of a directly testable neurophysiological model. Miller and Pettigrew have proposed a novel, high-level interhemispheric switch (IHS) explanatory model of binocular rivalry. This model conceptualises the perceptual alternations as being mediated by alternations between one hemisphere’s selected image and the other hemisphere’s selected (rival) image. To assess their hypothesis, caloric vestibular stimulation (CVS) was used. CVS is a simple, inexpensive, and non-invasive brain stimulation technique that unilaterally activates high-level attentional areas. In accordance with the IHS model, CVS was found to significantly affect predominance (the duration that one image is perceived relative to the other, within a given viewing period) during conventional binocular rivalry with horizontal/vertical gratings and with orthogonal oblique gratings. The present thesis therefore aims, through the use of CVS, to extend this IHS model of binocular rivalry to reversible-figure alternations and propose a general IHS model of perceptual rivalry. Chapter 1 provides a detailed literature review of the field within the context of comparing both perceptual rivalries. In Chapter 2, investigations are presented on two different reversible figures — the perspective-reversing Necker cube and the figure–ground reversing Rubin’s vase–faces illusion. In these experiments, CVS was found to significantly change observers’ predominance compared to their baseline predominance. These results demonstrate that interhemispheric switching also mediates the alternations of these visual phenomena, in addition to binocular rivalry, thereby extending the IHS model to one of perceptual rivalry in general. Moreover, the findings are interpreted in a cognitive neuroscience context, including a novel proposal of a forebrain framework for the IHS model. Chapter 3 presents CVS experiments that address the issue of percept–to–hemisphere selection and the reproducibility of CVS effects, following Miller’s initial work on two types of conventional binocular rivalry. In planned analyses, significant predominance changes were not found in horizontal/vertical rivalry, oblique rivalry and Necker-cube rivalry. In post-hoc analyses that accounted for study-design differences between Miller’s original experiments and the present experiment, CVS was again not shown to induce significant predominance changes in any of the rivalry types. Assessment of directional predominance changes following CVS appeared to suggest an arbitrary selection of percept–to–hemisphere in all rivalry types, although no firm conclusions could be drawn from the obtained data on this issue. Nevertheless, the experiments further extend upon Miller’s earlier work by examining the inter- and intra-individual reproducibility of CVS-induced effects on predominance. Such reproducibility was found to be low and potential reasons for this are discussed. The experiments in Chapter 4 examine a type of binocular rivalry in which dichoptic presentation of Díaz-Caneja stimuli yields rivalry among four different stable images: half-field rivalry between the images presented to the eyes, and coherence rivalry in which aspects of each eye’s presented image are perceptually regrouped into rivalling coherent images. Each of these rivalries was found to occur for about half the given viewing time. Furthermore, CVS significantly shifted the predominance of perceived coherent images (coherence rivalry) but not half-field images (eye rivalry). This finding suggests that coherence rivalry (like conventional rivalry according to previous experiments) is mediated by interhemispheric switching at a high level, while eye rivalry is mediated by intrahemispheric mechanisms, most likely at a low level. In addition, it is proposed that Díaz-Caneja stimuli induce ‘meta-rivalry’ whereby these discrete high- and low-level competitive processes themselves rival for visual consciousness. The current thesis thus presents a novel meta-rivalry model of multistable binocular rivalry. It also presents the first direct evidence that interhemispheric switching mediates reversible-figure alternations, thereby supporting a generalised IHS model of perceptual rivalry. It is argued that both models provide a parsimonious exploratory framework within which specific predictions can be made and readily tested. Finally, the findings of all experiments in the current thesis are summarised.

Perceptual rivalry refers to visual phenomena that are characterised by alternations between different percepts, despite an unchanging sensory input. Two common types of perceptual rivalry are (i) reversible figures — two-dimensional stable images that when viewed, are perceived to switch between different interpretations, and (ii) binocular rivalry — the alternations in image dominance resulting from the presentation of conflicting stimuli, one to each eye. Several investigators have suggested that these rivalling phenomena are mediated by similar neural mechanisms. Such a view, however, has not only been inadequately substantiated, but has also yet to be assessed in the context of a directly testable neurophysiological model. Miller and Pettigrew have proposed a novel, high-level interhemispheric switch (IHS) explanatory model of binocular rivalry. This model conceptualises the perceptual alternations as being mediated by alternations between one hemisphere’s selected image and the other hemisphere’s selected (rival) image. To assess their hypothesis, caloric vestibular stimulation (CVS) was used. CVS is a simple, inexpensive, and non-invasive brain stimulation technique that unilaterally activates high-level attentional areas. In accordance with the IHS model, CVS was found to significantly affect predominance (the duration that one image is perceived relative to the other, within a given viewing period) during conventional binocular rivalry with horizontal/vertical gratings and with orthogonal oblique gratings. The present thesis therefore aims, through the use of CVS, to extend this IHS model of binocular rivalry to reversible-figure alternations and propose a general IHS model of perceptual rivalry. Chapter 1 provides a detailed literature review of the field within the context of comparing both perceptual rivalries. In Chapter 2, investigations are presented on two different reversible figures — the perspective-reversing Necker cube and the figure–ground reversing Rubin’s vase–faces illusion. In these experiments, CVS was found to significantly change observers’ predominance compared to their baseline predominance. These results demonstrate that interhemispheric switching also mediates the alternations of these visual phenomena, in addition to binocular rivalry, thereby extending the IHS model to one of perceptual rivalry in general. Moreover, the findings are interpreted in a cognitive neuroscience context, including a novel proposal of a forebrain framework for the IHS model. Chapter 3 presents CVS experiments that address the issue of percept–to–hemisphere selection and the reproducibility of CVS effects, following Miller’s initial work on two types of conventional binocular rivalry. In planned analyses, significant predominance changes were not found in horizontal/vertical rivalry, oblique rivalry and Necker-cube rivalry. In post-hoc analyses that accounted for study-design differences between Miller’s original experiments and the present experiment, CVS was again not shown to induce significant predominance changes in any of the rivalry types. Assessment of directional predominance changes following CVS appeared to suggest an arbitrary selection of percept–to–hemisphere in all rivalry types, although no firm conclusions could be drawn from the obtained data on this issue. Nevertheless, the experiments further extend upon Miller’s earlier work by examining the inter- and intra-individual reproducibility of CVS-induced effects on predominance. Such reproducibility was found to be low and potential reasons for this are discussed. The experiments in Chapter 4 examine a type of binocular rivalry in which dichoptic presentation of Díaz-Caneja stimuli yields rivalry among four different stable images: half-field rivalry between the images presented to the eyes, and coherence rivalry in which aspects of each eye’s presented image are perceptually regrouped into rivalling coherent images. Each of these rivalries was found to occur for about half the given viewing time. Furthermore, CVS significantly shifted the predominance of perceived coherent images (coherence rivalry) but not half-field images (eye rivalry). This finding suggests that coherence rivalry (like conventional rivalry according to previous experiments) is mediated by interhemispheric switching at a high level, while eye rivalry is mediated by intrahemispheric mechanisms, most likely at a low level. In addition, it is proposed that Díaz-Caneja stimuli induce ‘meta-rivalry’ whereby these discrete high- and low-level competitive processes themselves rival for visual consciousness. The current thesis thus presents a novel meta-rivalry model of multistable binocular rivalry. It also presents the first direct evidence that interhemispheric switching mediates reversible-figure alternations, thereby supporting a generalised IHS model of perceptual rivalry. It is argued that both models provide a parsimonious exploratory framework within which specific predictions can be made and readily tested. Finally, the findings of all experiments in the current thesis are summarised.

In this paper, top-down and bottom-up processing were studied regarding their effect on speech-in-noise. Three cognitive functions were also studied (divided attention, executive functioning, and semantic comprehension), and the effect they have on the speech processing and on each other. The research questions asked were if a difference in speech-in noise perception can be observed regarding the different levels of top-down and bottom-up support, if speech-in-noise is related to any of the researched cognitive abilities, and if there exists any correlation between these abilities. The method is a within-subject experimental design, consisting of four different tests: PASAT, to measure attention, LIT, to measure semantic comprehension, TMT, to measure executive functioning and SIN, to measure speech-in noise. The results showed a significant difference between top-down and bottom-up processing, a significant difference between top-down processing in decreasing and increasing conditions could also be seen. A negative correlation between the benefit of top-down support and the semantic comprehension task was found. Regarding the cognitive abilities a few correlations were found; the semantic comprehension task had a positive correlation to both the central executive task and the attentional task, the attentional task had a negative correlation to the central executive task, and both of the central executive subtasks had a positive correlation to each other. Most of the findings were expected, built on earlier cognitive hearing theories and studies.

THIS THESIS IS IN THE EXAMINATION PROCESS The ability to locate symbols on a visual display forms an integral part of the effective use of AAC systems. Characteristics of display design and perceptual features of symbols have been shown to influence rate and accuracy of symbol location (Thistle&Wilkinson, 2009; Wilkinson, Carlin,&Jagaroo, 2006). The current study endeavoured to compare the use of two colour-coded organisational strategies (alphabetical order and subcategorisation) for their effectiveness in symbol location and to investigate if some bottom-up features influenced the performance of the participants in these tasks. 114 learners in Grade 1 to 3 in a mainstream school were randomly divided into two groups. Both of the groups were exposed to two visual search tests in alternating order. The tests involved searching for 36 visual targets amongst 81 coloured Picture Communication Symbols on a computer screen in one of two colour-coded organizational methods, namely alphabetical order or subcategorisation. The data from the research task was collected through computer logging of all mouse selections. Findings showed that locating symbols on a computer screen with a subcategorisation strategy was significantly faster and more accurate than with an alphabetical strategy for the Grade 1 to 3 participants. The differences between the rates and accuracy of target symbol location using the two strategies decreased significantly as grade increased. It was also found that although the tests in this study placed heavy top-down processing demands on the participants, there was still evidence of bottom-up factors influencing their performance. Implications for display design in AAC clinical practice were discussed. / Thesis (PhD)--University of Pretoria, 2012. / Centre for Augmentative and Alternative Communication (CAAC) / Unrestricted

本研究旨在探討不同聽力教學法對台灣國小學童聽力表現之影響，並試圖了解國小學童處理聽力之過程。本研究將七十六位國小五年級學童，其中包括五十二位男性與二十四位女性，分為「自下而上教學(bottom-up)」與「相互作用教學(interactive)」兩組，進行十五週之聽力教學。學童於聽力教學前後，均以劍橋兒童英檢初級(Starter Level)之聽力測驗進行前測與後測；同時，學童於每週聽力教學後，均須完成一份聽力小考，共計十五份。受試學童之前測、後測與十五次聽力小考皆以統計計量法加以計算，作為探討兩種聽力教學法成效之依據。此外，後測結束後，「相互作用教學(interactive)」組之學童接受問卷調查，以了解國小學童處理聽力之過程。 本研究主要發現「自下而上教學(bottom-up)」與「相互作用教學(interactive)」兩組之聽力表現並無重大差異。但整體而言，「相互作用教學(interactive)」組之平均分數較優於「自下而上教學(bottom-up)」組。問卷結果顯示，受訪之國小學童較常使用「由上而下」之訊息處理方式(top-down processing)，但大多數之受訪者表示，了解每一個單字的意義是聽力理解之關鍵因素。本研究最後提出若干相關建議以供參考。 / The purposes of this study were to identify effective teaching activities that improve elementary EFL students’ listening comprehension and to investigate when learners rely on top-down processing, bottom-up processing, and interactive processing. Participants in this study were 76 fifth graders from two classes in an elementary private school in Taipei County, including 52 males and 24 females. One of the two classes was treated with bottom-up pre-listening activities, while the other class was treated with interactive pre-listening activities. A pre-test and a post-test, adopted from the Starter level in the Cambridge Young Learners’ English Test, were implemented before and after a 15-week listening instruction. During the 15-week listening teaching, participants were also required to take a listening quiz after each session of teaching. Scores of the pre-test, post-test and the 15 listening quizzes were calculated by employing statistical measures to investigate the effectiveness of the two types of pre-listening activities, namely interactive and bottom-up pre-listening activities. Further, a questionnaire was administered for the interactive group after the post-test to investigate when learners relied on top-down processing, bottom-up processing and interactive processing. The major findings of the study are: first, results from participants’ listening scores revealed that there was no significant improvement between pre-test and post-test of the two groups although the mean scores of the interactive group were higher than that of the bottom-up group; second, results from the questionnaire indicated that participants employed top-down processing more frequently than bottom-up processing in their listening, while they viewed the understanding of each word (bottom-up processing) as essential to listening comprehension. Suggestions and implications are made at the end of the study.

Uma das tarefas básicas dos mecanismos atencionais é decidir qual a localização dentro do campo visual, em que devemos prestar atenção primeiro. Um objeto que contenha características distintas, tais como orientação, forma, cor, tamanho, brilho, textura, etc. diferentes, pode atrair a atenção de uma maneira \"bottom-up\". A informação \"top-down\" baseia-se no conhecimento prévio e tem uma grande influência nas localizações atendidas. Inspirado nos mecanismos da Atenção Visual Humana, embora sem a pretensão de simulá-la, este trabalho prevê o desenvolvimento de uma nova metodologia que integra os dois tipos de informações: \"bottom-up\" e \"top-down\". Características \"bottom-up\" são geradas a partir de Momentos e essas informações são utilizadas em mapas de saliência, enquanto que um conhecimento prévio é utilizado para gerar pistas \"top-down\". Neste trabalho, desenvolveu-se uma metodologia específica para a busca e o reconhecimento visual em cenas com múltiplos objetos, utilizando para isso uma rede \"fuzzy\" contendo três subsistemas \"fuzzy\". Dada uma imagem de entrada, o objetivo consiste em se detectar regiões que possam conter informações mais significativas, a fim de que se possa guiar e restringir processamentos mais complexos. A inclusão de mecanismos de atenção (seleção de uma região de interesse dentro da imagem) é de fundamental importância pois os resultados obtidos pelo método podem ser usados para controlar a aquisição da imagem de uma maneira dinâmica. O modelo proposto está estruturado em três estágios principais: O primeiro estágio consiste em se segmentar os objetos e extrair características globais dos mesmos baseadas principalmente na teoria dos momentos, tais como tamanho, orientação, formato e distância e também média de nível de cinza. Por intermédio da comparação de um objeto com os outros presentes na cena, características \"bottom-up\" de conspicuidade são usadas para guiar a atenção ao objeto mais diferente. Por intermédio do uso da lógica \"fuzzy\" é possível inferir com grande flexibilidade algumas regras de decisão baseadas nos princípios de percepção visual tais como as leis Gestalt. O segundo estágio consiste de um subsistema \"fuzzy top-down\" que combina diferentes características de acordo com a relevância das mesmas em diferentes tarefas. Finalmente, o terceiro estágio consiste de um subsistema \"fuzzy\" que integra as informações obtidas dos subsistemas anteriores e fornece um índice geral de saliência, e indica a provável localização do objeto a ser reconhecido. A nova abordagem foi testada com objetos geométricos levando-se em consideração as características que atraem a atenção dos serem humanos / One of the basic tasks assigned to the human attentional mechanisms is to decide which location in the visual field we must pay attention first. An object containing distinctive features (such as different orientation, shape, color, size, shine, texture, etc.) can attract attention in a bottom-up way. Top-down information is based on the previous knowledge and has a large influence on the attended locations. Inspired on human visual attention mechanisms, although it doesn\'t want simulate it, this work presents a new methodology to integrate two different kind of information: bottom-up and top-down. Bottom-up features are obtained from Moment Theory and this information is used in salience maps, while a previous knowledge is used to create top-down hints. In this work, an specific methodology to visual search and recognition was developed to be applied to scenes containing multiple objects by a fuzzy net with three fuzzy subsystems. The aim of this methodology is to detect regions that may contain the most significant information, in order to guide and to restrict most complex processing. The inclusion of attentional mechanisms (the selection of a region of interest in the image) is fundamental and can be used to control the image acquisition in a dynamic way. The proposed model is structured in three main stages. The first stage segments the objects and extracts global features of them, based on the Moment Theory such as size, orientation, shape and distance and gray level average. By comparing one object with the other ones present in the scene, bottom-up features of conspicuity are used to guide the attention to the most different object. The Fuzzy Logic allows us to infer with great flexibility some of decision rules based on the visual perception principles such as the Gestalt Laws. The second stage is a top-down fuzzy subsystem that combines different features according to the relevance of them in different tasks. Finally, the third stage is a fuzzy subsystem that integrates the information obtained from the previous sub-systems and gives us a general salience index. The new methodology was tested in geometrical objects considering the feature that attracts attention to human beings