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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
181

MRI Integrated Systems for Multimodal Imaging

Ranajay Mandal (9750932) 10 December 2021 (has links)
In recent years, development of various imaging, recording and stimulation tools are rapidly advancing our knowledge of the human anatomy and its underlying interconnections. As a truly non-invasive tool, Magnetic Resonance Imaging (MRI), is creating new opportunities to understand large scale biological processes with a fine detail. Furthermore, novel materials and microfabrication techniques are allowing researchers to develop tools that record bio-signal or modulate complex physiology with high temporal precision. However, these tools, when used individually can elucidate only a partial view of the human body and the brain. There is a growing need in both the research and clinical community to find ways to perform these modalities together and visualize biological systems across a vast range of spatiotemporal scale. However, severe methodological challenges act as bottlenecks for any such multimodal integration.<br><div><br></div><div>To address this critical need, I have designed an MRI-safe platform for high-fidelity bio-signal recording and electrical stimulation during concurrent MRI imaging. Central to this system are novel miniaturized microelectronic devices, that operate wirelessly in synchrony with MRI scans. The system leverages surplus functionalities of a conventional scanner to integrate with the imaging system and provide a simple and inexpensive solution towards multimodal imaging. This work also describes a systematic approach for development and evaluation of this plug-and-play system through in-vivo experiments in animal models. The clinical relevance of the multimodal imaging platform was further showcased through a study on the mechanism of SUDEP (Sudden death in epilepsy), a terminal complication associated with epilepsy. With future refinements, I expect this platform will provide affordable, accessible, and reliable solutions for multimodal imaging in animals and humans, creating unique opportunities for basic scientific research and clinical diagnosis.<br></div>
182

Enterprise architectonics as a conceptual device to support a fundamental understanding of enterprise architecture

Mentz, Jan Carel 10 1900 (has links)
Evidence of the interest in enterprise architecture (EA) is seen in the number of enterprise architecture frameworks (EAF) in existence. An EAF is responsible for the realisation of an EA, and therefore acts as a container for the terminology of EA. The lack of acceptance of terms and definitions, coupled with the phenomenon of the large number of EAFs, indicate a silo type understanding of what EA is, which leads to a lack of clarity in the conceptual foundations of EA. By following a design science research (DSR) approach, a conceptual artefact (an enterprise architectonic (EAt)) is created to address the lack of clarity in the conceptual foundations of EA thinking and practice. The EAt serves as a conceptual device to represent the fundamental understanding of EA in terms of concepts and their relationships. The content of the EAt is derived from applying a structured interpretation method (SIM) to three prominent EAFs (The Open Group Architecture Framework, the Department of Defense Architecture Framework and the Zachman Framework for Enterprise Architecture). The SIM’s results are an EA understanding that consists of an EA claim: EA is similar in intent to the enterprise as a worldview is to the world. It is supported by six EA propositions:  Proposition 1: EA’s underlying theoretical knowledge is in a pre-suppositional state.  Proposition 2: EA is a description of the structure of the systems of an enterprise.  Proposition 3: EA represents the enterprise in time-oriented architectures such as an as-is, to-be and has-been architecture.  Proposition 4: EA translates the values/strategy of the enterprise into operational systems appropriate to the information society.  Proposition 5: EA provides a means to manage decisions about the IT/IS management and implementation in the enterprise.  Proposition 6: EA captures a representation of the enterprise in the form of a model or set of models. The six EA propositions are analysed through the lens of Heidegger's equipment analysis, to produce a set of architectonic elements. These elements are arranged in the EAt to create a conceptual device to support the fundamental understanding of EA. / Centre for Applied Information and Communication / Ph.D. (Information Systems)
183

Building Cloud-Based Information Systems Lab Architecture: Deriving Design Principles that Facilitate the Effective Construction and Evaluation of a Cloud-Based Lab Environment

Trevethan, Thomas J. 01 January 2015 (has links)
The problem explored in this dissertation report was that at the time of this study, there were no design principles or methodologies based on design science research (DSR) available to use for artifact construction, implementation, and effective evaluation of cloud-based networking lab environments that can be used to foster hands-on technology skills in students. Primarily based on Hevner’s 7 guidelines of DSR, Peffer’s design science research methodology (DSRM), and Gregor’s IS design theory, this study forms the groundwork for the development of procedures and specifications derived from DSR literature to facilitate the construction, implementation, and evaluation of a comprehensive cloud-based computer and information systems (CIS) laboratory artifact that is globally accessible 24 hours a day and 7 days a week. Secondarily, this study guided the construction and implementation of a prototype cloud-based lab environment using the procedures and specifications derived from DSR. The cloud-based lab environment was then evaluated based on the skill level attained by students enrolled in courses that leveraged the proposed system. Results of this study showed that the overwhelming majority of the students who participated in the experiment using the cloud-based lab environment showed statistically significant gains in pretest and posttest scores compared to the students who participated in the experiment using the classroom-based physical equipment. These results fully supported the first hypothesis for this study, that participation in the cloud-based lab environment would promote positive student outcomes. The second hypothesis also was supported. The majority of the experimental group students completed most of the labs and significantly spent more time on the system compared to the control group students using the traditional classroom-based physical lab equipment, which indicated the specifications derived from DSR positively influenced the use of the cloud-based system. An argument was made that the proposed study advances IS and education research through artifact construction and evaluation by correlating Hevner’s 7 steps of effective DSR theory, Peffer’s DSRM, and Gregor’s IS design theory to the problem statement, research questions, and hypothesis in order to develop guiding principles and specifications for building and assessing a cloud-based lab environment.
184

Anatomo-functional magnetic resonance imaging of the spinal cord and its application to the characterization of spinal lesions in cats

Cohen-Adad, Julien 11 1900 (has links)
Les lésions de la moelle épinière ont un impact significatif sur la qualité de la vie car elles peuvent induire des déficits moteurs (paralysie) et sensoriels. Ces déficits évoluent dans le temps à mesure que le système nerveux central se réorganise, en impliquant des mécanismes physiologiques et neurochimiques encore mal connus. L'ampleur de ces déficits ainsi que le processus de réhabilitation dépendent fortement des voies anatomiques qui ont été altérées dans la moelle épinière. Il est donc crucial de pouvoir attester l'intégrité de la matière blanche après une lésion spinale et évaluer quantitativement l'état fonctionnel des neurones spinaux. Un grand intérêt de l'imagerie par résonance magnétique (IRM) est qu'elle permet d'imager de façon non invasive les propriétés fonctionnelles et anatomiques du système nerveux central. Le premier objectif de ce projet de thèse a été de développer l'IRM de diffusion afin d'évaluer l'intégrité des axones de la matière blanche après une lésion médullaire. Le deuxième objectif a été d'évaluer dans quelle mesure l'IRM fonctionnelle permet de mesurer l'activité des neurones de la moelle épinière. Bien que largement appliquées au cerveau, l'IRM de diffusion et l'IRM fonctionnelle de la moelle épinière sont plus problématiques. Les difficultés associées à l'IRM de la moelle épinière relèvent de sa fine géométrie (environ 1 cm de diamètre chez l'humain), de la présence de mouvements d'origine physiologique (cardiaques et respiratoires) et de la présence d'artefacts de susceptibilité magnétique induits par les inhomogénéités de champ, notamment au niveau des disques intervertébraux et des poumons. L'objectif principal de cette thèse a donc été de développer des méthodes permettant de contourner ces difficultés. Ce développement a notamment reposé sur l'optimisation des paramètres d'acquisition d'images anatomiques, d'images pondérées en diffusion et de données fonctionnelles chez le chat et chez l'humain sur un IRM à 3 Tesla. En outre, diverses stratégies ont été étudiées afin de corriger les distorsions d'images induites par les artefacts de susceptibilité magnétique, et une étude a été menée sur la sensibilité et la spécificité de l'IRM fonctionnelle de la moelle épinière. Les résultats de ces études démontrent la faisabilité d'acquérir des images pondérées en diffusion de haute qualité, et d'évaluer l'intégrité de voies spinales spécifiques après lésion complète et partielle. De plus, l'activité des neurones spinaux a pu être détectée par IRM fonctionnelle chez des chats anesthésiés. Bien qu'encourageants, ces résultats mettent en lumière la nécessité de développer davantage ces nouvelles techniques. L'existence d'un outil de neuroimagerie fiable et robuste, capable de confirmer les paramètres cliniques, permettrait d'améliorer le diagnostic et le pronostic chez les patients atteints de lésions médullaires. Un des enjeux majeurs serait de suivre et de valider l'effet de diverses stratégies thérapeutiques. De telles outils représentent un espoir immense pour nombre de personnes souffrant de traumatismes et de maladies neurodégénératives telles que les lésions de la moelle épinière, les tumeurs spinales, la sclérose en plaques et la sclérose latérale amyotrophique. / Spinal cord injury has a significant impact on quality of life since it can lead to motor (paralysis) and sensory deficits. These deficits evolve in time as reorganisation of the central nervous system occurs, involving physiological and neurochemical mechanisms that are still not fully understood. Given that both the severity of the deficit and the successful rehabilitation process depend on the anatomical pathways that have been altered in the spinal cord, it may be of great interest to assess white matter integrity after a spinal lesion and to evaluate quantitatively the functional state of spinal neurons. The great potential of magnetic resonance imaging (MRI) lies in its ability to investigate both anatomical and functional properties of the central nervous system non invasively. To address the problem of spinal cord injury, this project aimed to evaluate the benefits of diffusion-weighted MRI to assess the integrity of white matter axons that remain after spinal cord injury. The second objective was to evaluate to what extent functional MRI can measure the activity of neurons in the spinal cord. Although widely applied to the brain, diffusion-weighted MRI and functional MRI of the spinal cord are not straightforward. Various issues arise from the small cross-section width of the cord, the presence of cardiac and respiratory motions, and from magnetic field inhomogeneities in the spinal region. The main purpose of the present thesis was therefore to develop methodologies to circumvent these issues. This development notably focused on the optimization of acquisition parameters to image anatomical, diffusion-weighted and functional data in cats and humans at 3T using standard coils and pulse sequences. Moreover, various strategies to correct for susceptibility-induced distortions were investigated and the sensitivity and specificity in spinal cord functional MRI was studied. As a result, acquisition of high spatial and angular diffusion-weighted images and evaluation of the integrity of specific spinal pathways following spinal cord injury was achieved. Moreover, functional activations in the spinal cord of anaesthetized cats was detected. Although encouraging, these results highlight the need for further technical and methodological development in the near-future. Being able to develop a reliable neuroimaging tool for confirming clinical parameters would improve diagnostic and prognosis. It would also enable to monitor the effect of various therapeutic strategies. This would certainly bring hope to a large number of people suffering from trauma and neurodegenerative diseases such as spinal cord injury, tumours, multiple sclerosis and amyotrophic lateral sclerosis.
185

Réduction des artéfacts de tuteur coronarien au moyen d’un algorithme de reconstruction avec renforcement des bords : étude prospective transversale en tomodensitométrie 256 coupes

Chartrand-Lefebvre, Carl 08 1900 (has links)
Les artéfacts métalliques entraînent un épaississement artéfactuel de la paroi des tuteurs en tomodensitométrie (TDM) avec réduction apparente de leur lumière. Cette étude transversale prospective, devis mesures répétées et observateurs avec méthode en aveugle, chez 24 patients consécutifs/71 tuteurs coronariens a pour objectif de comparer l’épaisseur de paroi des tuteurs en TDM après reconstruction par un algorithme avec renforcement des bords et un algorithme standard. Une angiographie coronarienne par TDM 256 coupes a été réalisée, avec reconstruction par algorithmes avec renforcement des bords et standard. L’épaisseur de paroi des tuteurs était mesurée par méthodes orthogonale (diamètres) et circonférentielle (circonférences). La qualité d’image des tuteurs était évaluée par échelle ordinale, et les données analysées par modèles linéaire mixte et régression logistique des cotes proportionnelles. L’épaisseur de paroi des tuteurs était inférieure avec l’algorithme avec renforcement des bords comparé à l’algorithme standard, avec les méthodes orthogonale (0,97±0,02 vs 1,09±0,03 mm, respectivement; p<0,001) et circonférentielle (1,13±0,02 vs 1,21±0,02 mm, respectivement; p<0,001). Le premier causait moins de surestimation par rapport à l’épaisseur nominale comparé au second, avec méthodes orthogonale (0,89±0,19 vs 1,00±0,26 mm, respectivement; p<0,001) et circonférentielle (1,06±0,26 vs 1,13±0,31 mm, respectivement; p=0,005) et diminuait de 6 % la surestimation. Les scores de qualité étaient meilleurs avec l’algorithme avec renforcement des bords (OR 3,71; IC 95% 2,33–5,92; p<0,001). En conclusion, la reconstruction des images avec l’algorithme avec renforcement des bords génère des parois de tuteurs plus minces, moins de surestimation, et de meilleurs scores de qualité d’image que l’algorithme standard. / Metallic artifacts can result in an artificial thickening of the coronary stent wall which can significantly impair computed tomography (CT) imaging in patients with coronary stents. The purpose of this study is to assess the in vivo visualization of coronary stent wall and lumen with an edge-enhancing CT reconstruction kernel, as compared to a standard kernel. This is a prospective cross-sectional study of 24 consecutive patients with 71 coronary stents, using a repeated measure design and blinded observers, approved by the Local Institutional Review Board. 256-slice CT angiography was used, as well as standard and edge-enhancing reconstruction kernels. Stent wall thickness was measured with orthogonal and circumference methods, averaging wall thickness from stent diameter and circumference measurements, respectively. Stent image quality was assessed on an ordinal scale. Statistical analysis used linear and proportional odds models. Stent wall thickness was inferior using the edge-enhancing kernel compared to the standard kernel, either with the orthogonal (0.97±0.02 versus 1.09±0.03 mm, respectively; p<0.001) or circumference method (1.13±0.02 versus 1.21±0.02 mm, respectively; p<0.001). The edge-enhancing kernel generated less overestimation from nominal thickness compared to the standard kernel, both with orthogonal (0.89±0.19 versus 1.00±0.26 mm, respectively; p<0.001) and circumference (1.06±0.26 versus 1.13±0.31 mm, respectively; p=0.005) methods. The average decrease in stent wall thickness overestimation with an edge-enhancing kernel was 6%. Image quality scores were higher with the edge-enhancing kernel (odds ratio 3.71, 95% CI 2.33–5.92; p<0.001). In conclusion, the edge-enhancing CT reconstruction kernel generated thinner stent walls, less overestimation from nominal thickness, and better image quality scores than the standard kernel.
186

Studie artefaktů v MR tomografických snímcích pro lékařské a technické aplikace / The Study of Artifacts in MR Tomographic Images for Medical and Technical Applications

Al Khaddour, Mouin Unknown Date (has links)
Tato disertační práce analyzuje artefakty v NMR obrazech. V lékařské praxi mohou artefakty zabránit diagnostice patologických tkání, a proto je třeba tyto nežádoucí jevy odstranit. Vzhledem k nutnosti vyloučit artefakty způsobené nehomogenitou statického magnetického pole jsou v dané souvislosti diskutovány také nové možnosti měření deformací. Práce popisuje metodu pro měření základního pole i RF pole a jejich nehomogenit na základě měření MR obrazů T2 a T2*. Metoda kombinuje akviziční postupy pro spinové a gradientní echo za účelem rozlišení relaxačních časů T2 a T2*. V této souvislosti také vyvstává potřeba provést exponenciální aproximaci relaxačního procesu. Experimentální výsledky pro plastové i měděné vzorky jsou prezentovány v příslušné části práce. Pokud jde o vlastní členení popisovaných jevů, je třeba uvést, že významný problém představují artefakty způsobené magnetickou susceptibilitou. Různé hodnoty magnetické vodivosti na rozhraní mezi dvěma materiály mohou způsobit deformaci magnetického pole, přičemž může dojít i k úplné ztrátě signálu.
187

Enterprise architectonics as a conceptual device to support a fundamental understanding of enterprise architecture

Mentz, Jan Carel 10 1900 (has links)
Evidence of the interest in enterprise architecture (EA) is seen in the number of enterprise architecture frameworks (EAF) in existence. An EAF is responsible for the realisation of an EA, and therefore acts as a container for the terminology of EA. The lack of acceptance of terms and definitions, coupled with the phenomenon of the large number of EAFs, indicate a silo type understanding of what EA is, which leads to a lack of clarity in the conceptual foundations of EA. By following a design science research (DSR) approach, a conceptual artefact (an enterprise architectonic (EAt)) is created to address the lack of clarity in the conceptual foundations of EA thinking and practice. The EAt serves as a conceptual device to represent the fundamental understanding of EA in terms of concepts and their relationships. The content of the EAt is derived from applying a structured interpretation method (SIM) to three prominent EAFs (The Open Group Architecture Framework, the Department of Defense Architecture Framework and the Zachman Framework for Enterprise Architecture). The SIM’s results are an EA understanding that consists of an EA claim: EA is similar in intent to the enterprise as a worldview is to the world. It is supported by six EA propositions:  Proposition 1: EA’s underlying theoretical knowledge is in a pre-suppositional state.  Proposition 2: EA is a description of the structure of the systems of an enterprise.  Proposition 3: EA represents the enterprise in time-oriented architectures such as an as-is, to-be and has-been architecture.  Proposition 4: EA translates the values/strategy of the enterprise into operational systems appropriate to the information society.  Proposition 5: EA provides a means to manage decisions about the IT/IS management and implementation in the enterprise.  Proposition 6: EA captures a representation of the enterprise in the form of a model or set of models. The six EA propositions are analysed through the lens of Heidegger's equipment analysis, to produce a set of architectonic elements. These elements are arranged in the EAt to create a conceptual device to support the fundamental understanding of EA. / Centre for Applied Information and Communication / Ph. D. (Information Systems)
188

A tradução do planejamento em resultados: uma proposta de um artefato operacional de execução da estratégia para uma cooperativa agrícola

Bocolli, Aércio Fernando 06 January 2017 (has links)
Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2017-04-24T16:08:24Z No. of bitstreams: 1 Aércio Fernando Bocolli_.pdf: 3950029 bytes, checksum: 572dcc59505140bdf663d11a66928adc (MD5) / Made available in DSpace on 2017-04-24T16:08:24Z (GMT). No. of bitstreams: 1 Aércio Fernando Bocolli_.pdf: 3950029 bytes, checksum: 572dcc59505140bdf663d11a66928adc (MD5) Previous issue date: 2017-01-06 / Nenhuma / A execução da estratégia torna-se um fator desafiador e que se configura como um elemento fundamental para a sustentabilidade e o crescimento das organizações. Nesse sentido, o presente trabalho teve por objetivo elaborar e propor um artefato operacional de execução da estratégia para uma cooperativa agrícola do Rio Grande do Sul (RS). Para isso, partiu-se da seguinte questão: Quais as práticas necessárias para a tradução da estratégia em ações e resultados em uma cooperativa agrícola? A fim de se atingir o objetivo proposto, o estudo está ancorado nos fundamentos teóricos de DeLisi (2000), Neilson; Martin e Powers (2008), Spence (2009), Kaplan; Norton (2008), Higgins (2005), Zagotta e Robinson (2002), Bialoskorski Neto (2012), Oliveira (2015), entre outros. As unidades da cooperativa agrícola fizeram parte do estudo por meio de entrevista com gerentes e colaboradores de diferentes níveis setoriais. Como resultado da análise permitiu a identificação de barreiras à execução da estratégia, com também a consolidação dos aspectos considerados essenciais à execução. E a partir disso, foi elaborado e proposto um artefato operacional para execução do plano estratégico, constando todas as etapas fundamentais para a melhor performance na execução. Partindo-se da constatação de Oliveira (2015), de que as principiais dificuldades das cooperativas não são físicas e ambientais, mas sim gerenciais. / The execution of the strategy becomes a challenging factor and it is configured as a fundamental element for the sustainability and growth of organizations. In this sense, the present study had the objective of elaborating and proposing an operational artifact of execution of the strategy for an agricultural cooperative of Rio Grande do Sul (RS). For this, the following question arises: What are the practices necessary fot the translation of the strategy into actions and results in an agricultural cooperative? In order to achieve the proposed objective, the study is anchored in the theoretical foundations of DeLisi (2000), Neilson; Martin and Powers (2008), Spence (2009), Kaplan; Norton (2008), Higgins (2005), Zagotta and Robinson (2002), Bialoskorski Neto (1997), Oliveira (2015), among others. The agricultural cooperative units were part of the study through an interview with managers and employees from different sectoral levels. As a result of the analysis, it was possible to identify barriers to the execution of the strategy, as well as to consolidate the aspects considered essential to execution. And from that, an operational artifact was developed and proposed to execute the strategic plan, with all the key steps for the best execution performance. Based on Oliveira's (2015) observation, that the main difficulties of cooperatives are not physical and environmental, but rather managerial.
189

Cultura organizacional, corpo artefato e embodiment : etnografia em uma livraria de shopping center

Flores-Pereira, Maria Tereza January 2007 (has links)
O tema da cultura organizacional tem sido visivelmente aprofundado a partir de mudanças na sua base epistemológica (de um paradigma funcionalista para um interpretativista) e na utilização de diferentes perspectivas conceituais (de uma abordagem gerencial para uma simbólica) e metodológicas (de pesquisas quantitativas para qualitativas). Todavia, a despeito de todos esses avanços, o tema não tem acompanhado o desenvolvimento alcançado pelos estudos antropológicos que enfocam o corpo como modo de repensar a problemática cultural. É meu objetivo nesta tese, portanto, desvelar de que modo um enfoque no corpo humano propicia um melhor entendimento da noção de cultura organizacional, a partir de dois eixos teóricos que trabalham com a relação corpo-cultura: o ‘corpo artefato’ (corpo sócio-histórico-cultural) e o ‘embodiment’ (experiência cultural incorporada). Para realizar ambas as análises, parto de observações oriundas de uma etnografia organizacional junto a uma grande livraria de shopping center, a Livraria Cultura de Porto Alegre. O grupo de informantes privilegiado nessas análises foi a equipe de vendedores. Com base nesse material empírico e, primeiramente, com base em estudos da Antropologia do Corpo (capítulo 2), na primeira parte deste trabalho, analisei o corpo do trabalhador como um artefato organizacional que se singulariza por seu caráter dinâmico, sua hierarquização e sua dimensão política. A partir dessas análises, foi possível repensar o caráter de objeto inanimado e a pouca atenção que é oferecida para questões como classificação, hierarquização e dimensão política dos artefatos organizacionais. Na segunda parte (capítulo 3), aponto para a relação cultural pré-objetiva (pré-reflexiva) que trabalhadores estabelecem com as organizações e com os produtos que comercializam, ou seja, como a cultura organizacional é experienciada e incorporada. Para isso, parto de estudos da Filosofia e de Ciências Sociais e Humanas para buscar compreender como os estudos de embodiment possibilitam um novo modo de se conduzir metodologicamente as pesquisas de cultura organizacional e como incrementam sua conceituação. Levantei que o foco no embodiment desvela o papel ativo que o corpo tem na vida organizacional e permite uma melhor compreensão da dinâmica do conceito de cultura. / The theme of organizational culture has been visibly deepened – changing its epistemological base (from a Functionalist paradigm to an interpretative one) generating different conceptual (from a managerial to a symbolic approach) and methodological perspectives (from quantitative to qualitative researches). However, in spite of all these advances, the theme has not been following the development reached by anthropological studies, which focus the body as a form of representing the culture. Therefore, it is my aim in this thesis to unveil in what way the focus on the human body propitiates a better understanding of the notion of organizational culture, starting from two theoretical orientations which work with the relation body-culture: the ‘body artifact’ (socio-historiccultural body) and the ‘embodiment’. In order to perform both analyses, I begin with observations resulting from an organizational ethnography in a great bookstore of shopping center, Livraria Cultura de Porto Alegre. The group of informers who have been privileged to participate in these analyses was the team of shop assistants. Based on this empirical material and, firstly, on studies of The Anthropology of Body (chapter two), I analyzed the body of the worker as an organizational artifact which is singularized by their dynamic feature, hierarchization, and political dimension. Based on these analyses, it was possible to reconsider the feature of inanimate object and the little attention that is offered to questions like classification, hierarchization, and political dimension of organizational artifacts. In the second part (chapter three), I indicate the pre-objective cultural relation (pre-reflexive) that the workers establish with the organizations and the products they commercialize, that is, the embodiment of organizational culture. Hence, I start from studies of Philosophy, Social, and Human Sciences to understand how studies of embodiment enable a new form of conducting methodologically researches about organizational culture and how they develop their conceptualization. I indicate that the focus on embodiment unveil the active role the body has in the organizational life and allows a better understanding of the dynamics of cultural concept.
190

The temporal interplay of vision and eye movements

Kovalenko, Lyudmyla 19 May 2016 (has links)
Das visuelle System erreicht enorme Verarbeitungsmengen, wenn wir unsere Augen auf ein Objekt richten. Mehrere Prozesse sind aktiv bevor unser Blick das neue Objekt erreicht. Diese Arbeit erforscht die räumlichen und zeitlichen Eigenschaften drei solcher Prozesse: 1. aufmerksamkeitsbedingte Steigerung der neuronalen Aktivität und sakkadische Suppression; 2. aufmerksamkeitsbasierte Auswahl des Zielreizes bei einer visuellen Suchaufgabe; 3. zeitliche Entwicklung der Detektiongenauigkeit bei der Objekt-Substitutionsmaskierung. Wir untersuchten diese Prozesse mit einer Kombination aus humaner Elektroenzephalografie (EEG), eye tracking und psychophysischen Verhaltensmessungen. Zuerst untersuchten wir, wie die neuronale Repräsentation eines Reizes von seiner zeitlichen Nähe zur Sakkade geprägt wird. Wir zeigten, dass direkt vor der Sakkade erscheinende Reize am meisten durch Aufmerksamkeit und Suppression geprägt sind. In Studie 2 wurde die Sichtbarkeit des Reizes mit der Objekt-Substitutionsmaskierung verringert, und wir analysierten das Verhältnis zwischen sakkadischen Reaktionszeiten und ihrer Genauigkeit. Dazu erfassten wir neuronale Marker der Aufmerksamkeitslenkung zum Zielreiz und eine subjektive Bewertung seiner Wahrnehmbarkeit. Wir stellten fest, dass schnelle Sakkaden der Maskierung entgingen und Genauigkeit sowie subjektive Wahrnehmbarkeit erhöhten. Dies zeigt, dass bereits in frühen Verarbeitungsstadien eine bewusste und korrekte Wahrnehmung des Reizes entstehen kann. Wir replizierten diesen Befund für manuelle Antworten, um eine Verfälschung der Ergebnisse durch sakkadenspezifische Prozesse auszuschließen. Neben ihrer theoretischen Bedeutung liefern diese Studien einen methodischen Beitrag zum Forschungsgebiet der EEG-Augenbewegung: Entfernung sakkadischer Artefakte aus dem EEG bzw. Erstellung eines künstlichen Vergleichsdatensatzes. Die Arbeit stellt mehrere Ansätze zur Untersuchung der Dynamik visueller Wahrnehmung sowie Lösungen für zukünftige Studien dar. / The visual system achieves a tremendous amount of processing as soon as we set eyes on a new object. Numerous processes are active already before eyes reach the object. This thesis explores the spatio-temporal properties of three such processes: attentional enhancement and saccadic suppression that accompany saccades to target; attentional selection of target in a visual search task; the timecourse of target detection accuracy under object-substitution masking. We monitored these events using a combination of human electrophysiology (EEG), eye tracking and behavioral psychophysics. We first studied how the neural representation of a visual stimulus is affected by its temporal proximity to saccade onset. We show that stimuli immediately preceding a saccade show strongest effects of attentional enhancement and saccadic suppression. Second, using object-substitution masking to reduce visibility, we analyzed the relationship between saccadic reaction times and response accuracy. We also collected subjective visibility ratings and observed neural markers of attentional selection, such as the negative, posterior-contralateral deflection at 200 ms (N2pc). We found that fast saccades escaped the effects of masking, resulted in higher response accuracy and higher awareness ratings. This indicates that early visual processing can trigger awareness and correct behavior. Finally, we replicated this finding with manual responses. Discovering a similar accuracy timecourse in a different modality ruled out saccade-specific mechanisms, such as saccadic suppression and retinal shift, as a potential confound. Next to their theoretical impact, all studies make a methodological contribution to EEG-eye movement research, such as removal of large-scale saccadic artifacts from EEG data and composition of matched surrogate data. In sum, this work uses multiple approaches to describe the dynamics of visual perisaccadic perception and offers solutions for future studies in this field.

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