Dissertations / Theses: 'Retinotopic'

1

Seidel, Dirk. "Retinotopic and spatiotopic accommodation responses in emmetropia and myopia." Thesis, Glasgow Caledonian University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289522.

Full text

Abstract:

The incidence of myopia has been rising steadily over the last century. Today the prevalence of the condition ranges from under 1% in remote parts of the world to over 90% in some highly industrialised urban areas. The associated pathological risk factors in connection with the continuous increase in the number of myopic individuals have put increasing pressure on the health and social systems worldwide. The aetiology and course of the condition has therefore always been of interest to patients, ophthalmic practitioners and researchers alike. Reduced accommodation responses as a precursor to or even a cause of myopia have been proposed for a long time. Increased lags of accommodation found in myopes, causing a reduction in the quality of the retinal image, seem to support animal models, which have suggested that retinal defocus if present over longer periods of time can lead to the elongation of the globe. In this work different aspects of the accommodation response have been studied in emmetropes (EMM), early-onset (EOM) and late-onset myopes (LOM) under a variety of viewing conditions. The steady state accommodation response, the microfluctuations of accommodation and accommodation step responses of different magnitudes (1-dioptre and 2-dioptre steps) were examined for retinotopic (eye referenced) and spatiotopic (body-referenced) viewing conditions. Retinotopic conditions involved viewing targets in Badal systems. Spatiotopic viewing involved real targets presented in free space thus providing size and proximity cues to the accommodation controller. The free space targets were viewed monocularly and binocularly, which examined the importance of vergence accommodation for the different refractive groups. Steady state accommodation responses were found to be similar across the refractive groups for all viewing conditions. LOM subjects however, showed higher variability of their steady-state response in Badal systems but not in free space viewing. LOMs also demonstrated significantly greater microfluctuations of accommodation in the retinotopic condition, while the fluctuations were of similar magnitude for all groups for free space viewing. While EMMs and EOMs responded promptly and quickly to step changes in target vergence in both retinotopic and spatiotopic conditions, LOMs showed slower reaction and response times in the blur-only environment. Analysis of the response rate (percentage of step changes made for a given number of stimulus changes) revealed that some LOMs hesitated to adjust their accommodation to small step changes in target distance when only retinotopic cues were present. Real targets alleviated these differences between the groups and increased the LOMs response rate considerably. The minimum blur threshold of the accommodation controller was examined presenting sinusoidal stimuli of very small dioptric magnitude in a Badal system. Fourier analysis revealed that EMMs and EOMs responded to stimuli < 0.15 D while LOMs required stimuli > 0.3 D. Cross-correlating the findings of the different experiments showed that LOMs with inaccurate and more variable accommodation responses in retinotopic conditions improve substantially with the introduction of real world targets, whereas EMMs and EOMs with sufficient blur accommodation show no significant improvement. The findings indicate a deficient blur processing in LOMs but demonstrate that there are no significant differences in accommodation performance between emmetropes and myopes in real world conditions. The implications of the findings on the development and progression of myopia are discussed at the end of the thesis.

APA, Harvard, Vancouver, ISO, and other styles

2

Choi, Yu Wing. "Neuromorphic implementation of retinotopic arrays of orientation selective hypercolumns /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202003%20CHOIY.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Cutts, Catherine Sarah. "The role of correlated activity in the developing retinotopic map." Thesis, University of Cambridge, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709507.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Silson, Edward H. "Functional specialization & parallel processing within retinotopic subdivisions of lateral occipital cortex." Thesis, University of York, 2013. http://etheses.whiterose.ac.uk/4966/.

Full text

Abstract:

This thesis aimed to probe the functional specializations present within several retinotopic divisions of human lateral occipital cortex (LO). The divisions of interest were LO1 and LO2, two neighbouring visual field maps that are found within object-selective LO; the posterior portion of a larger area referred to as the lateral occipital complex (LOC), and V5/MT, the well-known visual complex that is highly selective to visual motion. In order to seek out the causal roles played by these divisions in human visual perception, I used transcranial magnetic stimulation to temporarily disrupt neural processing within these areas, while observers performed visual tasks. The visual tasks I employed examined both spatial vision, through orientation and shape discriminations, and motion processing, through speed discrimination. The data revealed a number of double dissociations. A double dissociation was present between LO1 and V5/MT in the perceptions of orientation and speed. A similar pattern of results was present during orientation and speed discrimination of the same moving stimuli, although this effect was markedly weaker. Additionally, a double dissociation was present between LO1 and LO2 in the perceptions of static orientation and shape, respectively. These double dissociations suggest that LO1, LO2 and V5/MT exhibit functional specializations for orientation, shape and speed, respectively and moreover, perform these specialized roles largely independently of one another. It is unsurprising that I found evidence for parallel processing of motion and aspects of spatial processing because: (1) V5/MT has been shown to be a cluster of multiple visual field maps with a common foveal representation – a feature that has led to the idea that the maps within clusters perform related aspects of processing, but are independent of the processing undertaken in adjacent visual field map clusters like LO; (2) neuropsychological evidence, from studies of akinetopsia and visual form agnosia, points to a double dissociation in processing of motion and form and (3) there is evidence of parallel processing pathways from early visual areas and even subcortical structures to V5/MT. The parallel processing of orientation and shape in LO1 and LO2 is a novel and more surprising finding for the following reasons: (1) These visual field maps are adjacent maps within a single cluster and therefore, might be expected to perform a series of related and dependent roles and (2) shape, as defined here by curvature, could be seen as a property that is dependent on orientation processing. These findings therefore, point to an architecture whereby the extrastriate visual maps in LO sample visual information from antecedent visual areas in parallel, to extract higher order spatial statistics. Mutual retinotopic information and parallel processing not only reduces replicated information across maps but also, provides a common mechanism for communication between maps which exhibit different specializations. Importantly, the well-known category-selectivity of extrastriate regions, like LO, may simply emerge from patterns of unique and low-level visual computations, which encode category specific image statistics, performed by the individual visual field maps that subdivide these areas.

APA, Harvard, Vancouver, ISO, and other styles

5

Creutzfeldt, Claire. "The role of EphrinA for the retinotopic map formation in mouse visual cortex." Diss., lmu, 2003. http://nbn-resolving.de/urn:nbn:de:bvb:19-16896.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Strang, Niall C. "Modulation of foveal image quality in myopia : investigation of spatiotopic and retinotopic factors." Thesis, Glasgow Caledonian University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261581.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Gebhardt, Christoph [Verfasser], and M. [Akademischer Betreuer] Bastmeyer. "Development & Experimental Validation of a Novel Computational Model of Retinotopic Mapping = (Entwicklung und experimentelle Überprüfung eines neuen Computermodells der Entstehung retinotoper Karten) / Christoph Gebhardt. Betreuer: M. Bastmeyer." Karlsruhe : KIT-Bibliothek, 2011. http://d-nb.info/1014817838/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Voyatzis, Sylvie. "Neural activity controls retinotopic projections in the superior collicul us by modulating axon retraction and cell survival." Paris 6, 2009. http://www.theses.fr/2009PA066311.

Full text

Abstract:

L’activité spontanée joue un rôle important dans le développement des cartes retinotopiques. Nous avons utilisé un model de co-culture qui récapitule la mise en place de la carte retino-colliculaire afin de déterminer où l’activité agit. Nous avons démontré que l’activité neuronale est requise pour la rétraction des axones rétiniens induite par les éphrine-As. Elle nécessite l’entrée de calcium par des canaux calciques de type-L et des stocks internes de calcium. Nous avons déterminé que des fluctuations d’AMPc et de la PKA sont aussi essentielles. Nous avons cherché à montrer l’existence d’oscillations d’AMPc grâce à une technique d’imagerie basée sur le principe du FRET. Nous avons analysé la maturation des types cellulaires rétiniens au cours de la co-culture, afin de déterminer les circuits neuronaux sous-tendant l’émergence de l’activité spontanée. Nous avons analysé la mort cellulaire d’une population de CGR. Nous avons montré que la diminution du nombre de CGR avait lieu entre DIV4 et DIV7, correspondant à la période P0 à P3 : le pic de mort cellulaire développementale in vivo. Cette mort cellulaire dépend de la cible et de l’activité neuronale.

APA, Harvard, Vancouver, ISO, and other styles

9

Sayres, Rory. "Decoding fmri response patterns in visual cortex : effects of object category, identity, retinotopic position, and short-term experience /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

Full text

APA, Harvard, Vancouver, ISO, and other styles

10

Berman, Daniel. "From Photons to Photos: Mapping Functional and Organizational Properties of Human Visual Cortex with fMRI." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1422972281.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Godfrey, Keith B. "From synaptogenesis to map formation - modeling visual system development exploring the contribution of cellular mechanisms to the emergence of retinotopic projections and eye-specific segregation." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/5754.

Full text

Abstract:

The brain is composed of many anatomically distinct areas that control different functions. A common feature of these areas is that information is represented in a spatially organized manner. In the visual system, retinal representation is spatially mapped onto visual areas such that neighboring neurons respond to adjacent retinal locations, forming a retinotopic map. When axons from two retinas project to the same target structure, both produce similar retinotopic projections on the large scale but these segregate into eye-specific domains locally. How these spatial representations are formed is not well understood. Experimental studies have shown that many mechanisms are involved. Several modeling studies have addressed how such organization arises, with most representing different varying subsets of the mechanisms known to be present and showing how the particular representation of mechanisms can produce the emergent properties of organization. This results in models producing similar outputs yet coming to different conclusions that often cannot be reconciled. By omitting behaviors that are present and likely to be involved in organization, such as spiking neurons and the dynamics of axon and synapse growth and retraction, the models are poorly constrained. This limits their explanatory and predictive scope regarding how organization develops, and further limits their ability to examine how the different mechanisms interact. To more accurately analyze both how such organization develops and the interactions between underlying mechanisms, a model of the developing retinocollicular pathway was produced that represented a wide range of cellular and subcellular phenomena, including spike-timing dependent plasticity (STDP), chemoaffinity, spontaneous retinal activity, trophic factors, and growth and retraction of synapses and axons. The model demonstrated retinotopic refinement and eye-specific segregation across a wide range of parameters and variations in implementation. Results indicated that the mechanisms necessary for organization were chemoaffinity, retinal waves, trophic factors and homeostatic controls. Analysis of the relative roles of activity and chemoaffinity suggested that these mechanisms play distinct and complementary roles. Among the predictions of the model are that smaller synapses produce more refined projections and, surprisingly, that STDP does not play a significant role in organization.

APA, Harvard, Vancouver, ISO, and other styles

12

McKeefry, Declan J., Mark P. Burton, Chara Vakrou, Brendan T. Barrett, and A. B. Morland. "Induced deficits in speed perception by transcranial magnetic stimulation of human cortical areas V5/MT+ and V3A." Society for Neuroscience, 2008. http://hdl.handle.net/10454/4732.

Full text

Abstract:

no
In this report, we evaluate the role of visual areas responsive to motion in the human brain in the perception of stimulus speed. We first identified and localized V1, V3A, and V5/MT+ in individual participants on the basis of blood oxygenation level-dependent responses obtained in retinotopic mapping experiments and responses to moving gratings. Repetitive transcranial magnetic stimulation (rTMS) was then used to disrupt the normal functioning of the previously localized visual areas in each participant. During the rTMS application, participants were required to perform delayed discrimination of the speed of drifting or spatial frequency of static gratings. The application of rTMS to areas V5/MT and V3A induced a subjective slowing of visual stimuli and ( often) caused increases in speed discrimination thresholds. Deficits in spatial frequency discrimination were not observed for applications of rTMS to V3A or V5/MT+. The induced deficits in speed perception were also specific to the cortical site of TMS delivery. The application of TMS to regions of the cortex adjacent to V5/MT and V3A, as well as to area V1, produced no deficits in speed perception. These results suggest that, in addition to area V5/MT+, V3A plays an important role in a cortical network that underpins the perception of stimulus speed in the human brain.
BBSRC

APA, Harvard, Vancouver, ISO, and other styles

13

Ardin, Paul Björn. "How is an ant navigation algorithm affected by visual parameters and ego-motion?" Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/25500.

Full text

Abstract:

Ants typically use path integration and vision for navigation when the environment precludes the use of pheromones for trails. Recent simulations have been able to accurately mimic the retinotopic navigation behaviour of these ants using simple models of movement and memory of unprocessed visual images. Naturally it is interesting to test these navigation algorithms in more realistic circumstances, particularly with actual route data from the ant, in an accurate facsimile of the ant world and with visual input that draws on the characteristics of the animal. While increasing the complexity of the visual processing to include skyline extraction, inhomogeneous sampling and motion processing was conjectured to improve the performance of the simulations, the reverse appears to be the case. Examining closely the assumptions about motion, analysis of ants in the field shows that they experience considerable displacement of the head which when applied to the simulation leads to significant degradation in performance. The family of simulations rely upon continuous visual monitoring of the scene to determine heading and it was decided to test whether the animals were similarly dependent on this input. A field study demonstrated that ants with only visual navigation cues can return the nest when largely facing away from the direction of travel (moving backwards) and so it appears that ant visual navigation is not a process of continuous retinotopic image matching. We conclude ants may use vision to determine an initial heading by image matching and then continue to follow this direction using their celestial compass, or they may use a rotationally invariant form of the visual world for continuous course correction.

APA, Harvard, Vancouver, ISO, and other styles

14

Diomedi, Stefano. "Ricostruzione di mappe retinotopiche mediante filtri di Gabor." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15798/.

Full text

Abstract:

L'obiettivo della presente tesi è quello di ricostruire mappe retinotopiche o corticali della corteccia visiva umana a partire dall'attività neurale sviluppata in presenza di uno stimolo visivo e misurata mediante fMRI. Il modello si ottiene rappresentando ciascuna immagine mediante filtri di Gabor, che costituiscono una frame per lo spazio delle immagini. L'ipotesi di lavoro è che ci sia una relazione fra l'energia di un'immagine espressa in termini dei filtri, e l'attivazione fMRI. Un modello di encoding permette di esprimere formalmente questa relazione attraverso una matrice di pesi. Di conseguenza è possibile stimare le aree del campo visivo codificate da ogni area corticale e successivamente visualizzare le mappe retinotopiche, mediante il software FreeSurfer.

APA, Harvard, Vancouver, ISO, and other styles

15

Jennings, Michael. "Effect of Attentional Capture and Cross-Modal Interference in Multisensory Cognitive Processing." ScholarWorks, 2018. https://scholarworks.waldenu.edu/dissertations/4793.

Full text

Abstract:

Despite considerable research, the effects of common types of noise on verbal and spatial information processing are still relatively unknown. Three experiments, using convenience sampling were conducted to investigate the effect of auditory interference on the cognitive performance of 24 adult men and women during the Stroop test, perception of object recognition and spatial location tasks, and the perception of object size, shape, and spatial location tasks. The data were analyzed using univariate analysis of variance and 1-way multivariate analysis of variance. The Experiment 1 findings indicated reaction time performance for gender and age group was affected by auditory interference between experimental conditions, and recognition accuracy was affected only by experimental condition. The Experiment 2a results showed reaction time performance for recognizing object features was affected by auditory interference between age groups, and recognition accuracy by experimental condition. The Experiment 2b results demonstrated reaction time performance for detecting the spatial location of objects was affected by auditory interference between age groups. In addition, reaction time was affected by the type of interference and spatial location. Further, recognition accuracy was affected by interference condition and spatial location. The Experiment 3 findings suggested reaction time performance for assessing part-whole relationships was affected by auditory interference between age groups. Further, recognition accuracy was affected by interference condition between experimental groups. This study may create social change by affecting the design of learning and workplace environments, the neurological correlates of auditory and visual stimuli, and the pathologies of adults such as attention deficit hyperactivity disorder.

APA, Harvard, Vancouver, ISO, and other styles

16

Santos, Olavo Miguel Florêncio Sousa. "Análise da espessura cortical no cortex visual de pacientes com a doença neuro-degenerativa de Leber." Master's thesis, Faculdade de Ciências e Tecnologia, 2010. http://hdl.handle.net/10362/5660.

Full text

Abstract:

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Ciências de Engenharia Biomédica
A doença hereditária de Leber (Leber’s Hereditary Optic Neuropaty - LHON) é uma doença caracterizada pela degeneração das células ganglionares da retina (Retinal Ganglion Cells - RGCs) e seus axónios que leva a uma perda aguda ou semi-aguda da visão central. Com o objectivo de estudar a influência da LHON no cortex visual, foi realizada análise de espessura cortical (EC) em 16 pacientes com LHON. O software Brainvoyager Qx v2.0 foi usado para realizar análise anatómica e volumétrica (Volumetric Magnetic Resonance - VMR)de dados provenientes de ressonâncias magnéticas dos 16 pacientes com LHON. Os VMRs foram posteriormente usados para criar mapas retinotópicos, através de análise funcional dos dados, representando cinco áreas visuais distintas (V1, V2d, V2v, V3 e VP) do cortex visual. O objectivo foi verificar como estas áreas visuais se correlacionam nas suas alterações estruturais, descobrir pistas e formular hipóteses a serem exploradas em como a LHON afecta a EC no cortex visual. Para atingir este fim, a medição dos mapas retinotópicos permite a extracção de valores de EC de cada área visual. Os resultados dos 16 pacientes com LHON foram divididos em dois sub-grupos: menores de 21 anos, com 7 sujeitos; e maiores de 21 anos, com 9 sujeitos. Estes dois sub-grupos foram também definidos de acordo com as características da LHON em relação à sua progressão com o envelhecimento. Apesar da não existência de um grupo de controlo a pergunta vigente deste trabalho é: “Haverá atrofia cortical devido a perda de RGCs?” Resultados preliminares sugerem padrões de diferença entre hemisférios e correlações entre áreas visuais em pacientes com LHON. A investigação em curso vai esclarecer se estes padrões são específicos da doença e como dissociar as correlações de estrutura/função em sujeitos normais.

APA, Harvard, Vancouver, ISO, and other styles

17

Koelle, Markus [Verfasser]. "Die Bedeutung retinotoper Kortexareale für die Verarbeitung von Orientierungskontrast / Markus Koelle." Ulm : Universität Ulm. Medizinische Fakultät, 2014. http://d-nb.info/104689000X/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Cotton, Philippa. "Retinotopy of rat visual cortex : an optical imaging and neuroanatomical study." Thesis, University of Manchester, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538491.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Cordier-Picouet, Marie-Jeanne. "Organisation du systeme visuel et mise en place de la retinotopie tectale chez les amphibiens anoures." Paris 7, 1987. http://www.theses.fr/1987PA077104.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Main, Keith Leonard. "Plasticity and Macular Degeneration: the Reorganization of Adult Cortical Topography." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14601.

Full text

Abstract:

This study evaluated whether cortical reorganization occurs in response to macular degeneration (MD), a progressive disorder of the retina that results in central vision loss. Past research has observed the ability of V1 to adapt to retinal damage, demonstrating that deafferented cortex is activated by the stimulation of intact retinal areas. It is still unclear, however, if and to what degree cortical reorganization is associated with specific forms of macular degeneration. This study evaluated the retinal health of MD participants (both age-related and juvenile) as well age-matched controls with computerized microperimetry. Contrast-reversing stimuli were then presented to different parts of the visual field while participants were scanned with functional magnetic resonance imaging (fMRI). For MD participants, stimulation of peripheral retinal areas elicited activation in deafferented cortex. This activation occurred for retinal areas adapted for eccentric viewing (preferred retinal locations), but not in preserved retina at the same eccentricity. These findings add to the scientific knowledge of plasticity in sensory systems by supporting an experience driven understanding of cortical reorganization. They could also have a meaningful impact on how macular degeneration is treated by informing the design of therapeutic training regimes.

APA, Harvard, Vancouver, ISO, and other styles

21

Efler, Daniela Margarete. "Wiedererkennung ungefilterter und Fourier-gefilterter Schwarzweissmuster duch Honigbienen (Apis mellifera L.) Evidenz für Parameterextraktion ohne retinotopes Template-Matching /." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972544100.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Di, Domenico Chiara. "A mathematical model for migraine aura." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/12350/.

Full text

Abstract:

Nella tesi è descritto un modello matematico per l'aura emicranica e, più precisamente, per lo scotoma scintillante (schema di fortificazione) e per la Cortical Spreading Depression, il fenomeno neuropatofisiologico alla base dell'aura. In particolare è spiegato un modello cinematico per l'evoluzione della CSD nella corteccia visiva primaria, considerata un mezzo debolmente eccitabile, la mappa retino-corticale e il modello, tramite fibrato, dei Pinwheels di V1.

APA, Harvard, Vancouver, ISO, and other styles

23

Seghier, Mohamed Lamine. "IRM fonctionnelle de la vision : arguments en faveur du traitement des contours illusoires dans les aires corticales de bas niveau." Grenoble 1, 2000. http://www.theses.fr/2000GRE10046.

Full text

Abstract:

Dans ce travail, nous nous sommes intéressés au traitement des contours illusoires au sein du système visuel. Nous avons, en particulier, cherché à vérifier si les aires visuelles de bas niveau sont impliquées lors de la perception de contours illusoires. A cet effet, nous avons développé des paradigmes irmf originaux utilisant des contours illusoires de type kanizsa. Dans un premier paradigme, de type bloc, nous avons exploité le mouvement de contours illusoires. Des premières expériences nous ont montré une implication des aires v1/v2, non-différenciées. Dans une seconde série d'expériences, en utilisant également des techniques irmf de délinéation des aires v1 et v2, nous avons pu clairement identifier une activation significative de l'aire v1. Parallèlement, des activations ont été obtenues dans les aires mt+ et los/ko. Les activations dans l'aire v1 ont été nettement plus significatives en présence qu'en absence de mouvement, suggérant une possible contribution d'effets de contre-réaction (mt+$$v1). Nous avons voulu vérifier, en une seconde étape, si des contours illusoires présentés à excentricité variable induisent des réponses le long de la scissure calcarine selon la représentation retinotopique de v1. A cette fin, nous avons mis au point un second paradigme, de type fourier. Les propriétés de phase des réponses fonctionnelles obtenues le long de la scissure calcarine semblent bien en accord avec les propriétés retinotopiques de v1. Ces expériences nous ont donc fourni des arguments cohérents en faveur de l'implication de v1 dans la perception de contours illusoires.

APA, Harvard, Vancouver, ISO, and other styles

24

Lam, Michael. "Retinotopic Preservation in Deep Belief Network Visual Learning." Thesis, 2011. http://hdl.handle.net/10012/5894.

Full text

Abstract:

One of the foremost characteristics of the mammalian visual system is the retinotopic mapping observed in the low-level visual processing centres; the spatial pattern of activation in the lateral geniculate nucleus and primary visual cortex corresponds topologically to the pattern of light falling on the retina. Various vision systems have been developed that take advantage of structured input such as retinotopy, however these systems are often not biologically plausible. Using a parsimonious approach for implementing retinotopy, one that is based on the biology of our visual pathway, we run simulations of visual learning using a deep belief network (DBN). Experiments show that we can successfully produce receptive fields and activation maps typical of the LGN and visual cortex respectively. These results may indicate a possible avenue of exploration into discovering the workings of the early visual system (and possibly more) on a neuronal level.

APA, Harvard, Vancouver, ISO, and other styles

25

Côté, Madeleine. "Retinotopic and spatiotopic factors in metacontrast : the role of apparent spatial separation." Thesis, 1985. http://spectrum.library.concordia.ca/4121/1/ML30707.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

"Characterizing Retinotopic Mapping Using Conformal Geometry and Beltrami Coefficient: a Preliminary Study." Master's thesis, 2013. http://hdl.handle.net/2286/R.I.21000.

Full text

Abstract:

abstract: Functional magnetic resonance imaging (fMRI) has been widely used to measure the retinotopic organization of early visual cortex in the human brain. Previous studies have identified multiple visual field maps (VFMs) based on statistical analysis of fMRI signals, but the resulting geometry has not been fully characterized with mathematical models. This thesis explores using concepts from computational conformal geometry to create a custom software framework for examining and generating quantitative mathematical models for characterizing the geometry of early visual areas in the human brain. The software framework includes a graphical user interface built on top of a selected core conformal flattening algorithm and various software tools compiled specifically for processing and examining retinotopic data. Three conformal flattening algorithms were implemented and evaluated for speed and how well they preserve the conformal metric. All three algorithms performed well in preserving the conformal metric but the speed and stability of the algorithms varied. The software framework performed correctly on actual retinotopic data collected using the standard travelling-wave experiment. Preliminary analysis of the Beltrami coefficient for the early data set shows that selected regions of V1 that contain reasonably smooth eccentricity and polar angle gradients do show significant local conformality, warranting further investigation of this approach for analysis of early and higher visual cortex.
Dissertation/Thesis
M.S. Computer Science 2013

APA, Harvard, Vancouver, ISO, and other styles

27

Rogers, Claude Joseph. "Discovery of New Roles for Chondroitin Sulfate in Neurotrophin Signaling and Retinotopic Development." Thesis, 2013. https://thesis.library.caltech.edu/7444/2/cjr_thesis.pdf.

Full text

Abstract:

Chondroitin sulfate (CS), a member of the glycosaminoglycan family of linear polysaccharides, is involved in the formation and maintenance of neuronal networks. CS has dual roles in regulating neuronal morphology: promoting or inhibiting neuronal outgrowth, depending on the context. A single sulfated epitope, CS-E, is capable of inducing both types of activity.

Members of the neurotrophin (NT) family of growth factors are required for CS- E-induced neurite outgrowth in hippocampal neurons. Here, we demonstrate that CS is capable of forming ternary complexes with NTs and their receptors. These complexes were discovered using a novel, carbohydrate microarray-based approach that allows for the rapid screening of such interactions. To support these findings, we computationally determined the CS-E-binding site of the complexes, suggesting a structural basis for the interaction. In addition, we showed that CS-E is capable of attenuating NT signaling in cells, consistent with our computational and microarray data. This is the first demonstration that CS-E is involved in NT signaling and that CS is capable of supporting multimeric signaling complexes.

In addition to stimulating growth factor signaling, CS has been known to repulsively guide retinal ganglion cell (RGC) axons for over twenty years. However, its function in vivo is unknown. RGCs are the only neuron type that transmits visual information to the brain, and their guidance, which maps a topographic projection of the retina to the superior colliculus (SC), is tightly regulated. Here, we show that CS-E is required for the proper formation of this topographic order. CS-E, but not the other major sulfation patterns, is a repellent guidance cue for RGC axons, with a graded activity profile from low to high along the dorsal-ventral axis of the retina, congruent with EphB3 expression. EphB3 binds specifically to CS-E with physiologically relevant affinity, and is required for CS-E-mediated guidance. CS-E-null mice have defects in topographic mapping in which ventral axons form ectopic termina- tions medial to their correct location in the SC. These results indicate that CS is a repulsive guidance cue required to map the dorsal-ventral axis of the retina along the lateral-medial axis of the SC. This is the first report of a non-protein topographical guidance cue.

APA, Harvard, Vancouver, ISO, and other styles

28

Chang, Yen-Ching, and 張晏菁. "The Role of Wrapping Glia in Formation of the Retinotopic Projection in Drosophila Visual System." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/4y4en8.

Full text

Abstract:

博士
國立陽明大學
生命科學系暨基因體科學研究所
106
Photoreceptor (PR) axons project from the retina to the optic lobe in brain and form a precise retinotopic map in the Drosophila visual system. Yet the role of retinal basal glia in the retinotopic map formation is not previously known. We examined the formation of the retinotopic map by marking single PR pairs and following their axonal projections. In addition to confirming previous studies that the spatial information is preserved from the retina to the optic stalk and then to the optic lamina, we found that the young PR R3/4 axons transiently overshoot and then retract to their final destination, the lamina plexus. We then examined the process of wrapping glia (WG) membrane extension in the eye disc and showed that the WG membrane extensions also follow the retinotopic map. We show that the WG is important for the proper spatial distribution of PR axons in the optic stalk and lamina, suggesting an active role of wrapping glia in the retinotopic map formation.

APA, Harvard, Vancouver, ISO, and other styles

29

Chang, Yao-wen, and 張耀文. "Retinotopic Mapping Using Multi-Focal Functional MRI: Visual Image Reconstruction of Brain Activities and its Optimization method." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/80867299933012723434.

Full text

Abstract:

碩士
國立臺灣科技大學
電機工程系
100
This thesis describes a study exploiting multi-focal functional MRI(fMRI) for retinotopic mapping, or retinotopy, in the primary visual cortex. We tried to reconstruct visual image according the retinotopy and brain activities obtained by fMRI. Multi-focal method divides the visual field into several blocks and each block has its own paradigm for the visual experiment. Using this method, researchers show that they are able to distinguish the brain areas corresponding to each block simultaneously. Despite visual fMRI, this method is also applied electrophysiological analysis of visual system. In this study, we performed a visual fMRI experiment using a specific pattern after multi-focal retinotopy. We then attempt to reconstruct the visual image by combining the results of visual fMRI and retinotopy. The study applied general linear model to analyze the fMRI signal and produced a t value to justify the existence of stimuli-related brain activities. However, judging the “existence” required selecting a threshold of the t value. We empirically found that the accuracy of the reconstructed visual image largely depended on the threshold selection. Therefore, this study proposed an approach to find the optimal t threshold according to a receiver operating characteristic analysis. The results obtained with 5 volunteers using the optimized t thresholds demonstrated an average accuracy of 80%. In conclusion, we successfully reconstructed the visual image by the fMRI technique. Compared to previous investigations, we regard the contributions of this thesis are the optimization method for visual image reconstruction. This method leads to a completely automatic reconstruction procedure and takes visual reconstruction a step forward.

APA, Harvard, Vancouver, ISO, and other styles

30

Chien-ShuChu and 朱謙恕. "Expertise effect in early visual cortex: the influence of its retinotopic response properties, and the task demand." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/cq7fnk.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Creutzfeldt, Claire [Verfasser]. "The role of ephrinA for retinotopic map formation in mouse visual cortex : an optical imaging study / vorgelegt von Claire Creutzfeldt." 2003. http://d-nb.info/970271832/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Rosen, Maya. "Functional MRI and behavioral investigations of long-term memory-guided visuospatial attention." Thesis, 2015. https://hdl.handle.net/2144/16356.

Full text

Abstract:

Real-world human visual perception is superb, despite pervasive attentional capacity limitations that can severely impact behavioral performance. Long-term memory (LTM) is suggested to play a key role in efficiently deploying attentional resources; however, the nature of LTM-attention interactions remains poorly understood. Here, I present a series of behavioral and functional magnetic resonance imaging (fMRI) investigations of the mechanisms of LTM-guided visual attention in 139 healthy participants (18-34 years). In Experiment 1, I hypothesized that humans can use memory to guide spatial attention to multiple discrete locations that have been previously studied. Participants were able to simultaneously attend to more than one spatial location using an LTM cue in a novel change-detection behavioral paradigm also used in fMRI Experiments 2 and 4. Cortical networks associated with LTM and attention often interact competitively. In Experiment 2, I hypothesized that the cognitive control network supports cooperation between LTM and attention. Three posterior regions involved with cognitive control were more strongly recruited for LTM-guided attention than stimulus-guided attention: the posterior precuneus, posterior callosal sulcus, and lateral intraparietal sulcus. In Experiment 3, I hypothesized that regions identified in Experiment 2 are specifically activated for LTM-guided attention, not for LTM retrieval or stimulus-guided attention alone. This hypothesis was supported. Taken together, the results of Experiments 2 and 3 identify a cognitive control subnetwork specifically recruited for LTM-guided attention. Experiment 4 tested how LTM-guided attention affected spatial responsivity of maps within intraparietal sulcus. I hypothesized that left parietal maps would change their spatial responsivity due to the left lateralized effects of memory retrieval. During stimulus-guided attention, contralateral visuotopic maps in the right but not left intraparietal sulcus responded to the full visual field. In contrast, during LTM-guided attention, maps in both the left and right intraparietal sulcus responded to the full visual field, providing evidence for complementary forms of dynamic recruitment under different attentional conditions. Together, these results demonstrate that LTM-guided attention is supported by a parietal subnetwork within the cognitive control network and that internal attentional states influence the spatial specificity of visuotopically mapped regions in parietal cortex.

APA, Harvard, Vancouver, ISO, and other styles

33

Boros, Marianna. "Reading specific brain regions beyond the ventral visual stream." Praca doktorska, 2019. https://ruj.uj.edu.pl/xmlui/handle/item/81949.

Full text

Abstract:

Umiejętność rozpoznawania słowa pisanego klasycznie przypisuje się rejonowi mózgowemu znajdującemu się w lewej brzusznej korze potyliczno-skroniowej, zwanemu również obszarem formy wzrokowej słowa (ang. Visual Word Form Area - VWFA). Obszar ten jest częścią kory pozaprążkowej, która specjalizuje się w rozpoznawaniu obiektów. Czytanie aktywuje jednak również wzrokowe obszary mózgowe znajdujące się poza korą potyliczno-skroniową, zwłaszcza w zadaniach, w których przetwarzanie językowe jest ograniczone. Efekty związane ze sprawnym czytaniem zaobserwowano we wczesnych obszarach kory wzrokowej na poziomie V1 do V4. W niniejszej pracy przedstawiono trzy badania eksperymentalne, których celem była funkcjonalna i strukturalna charakterystyka aktywowanych w trakcie czytania regionów mózgowych, które znajdują się poza brzusznym strumieniem wzrokowym. Przy użyciu metod neuroobrazowania mózgowego, przeprowadzono serię eksperymentów, w których porównano przetwarzanie liter i innych symboli w zadaniach, które nie wymagały czytania lub przetwarzania językowego. Eksperyment 1. miał na celu za pomocą funkcjonalnego rezonansu magnetycznego zidentyfikować obszary mózgowe niezbędne do wyksztalcenia się umiejętności sprawnego czytania, które uczestniczą w poprawnym rozpoznawaniu znaków pisanych. Uzyskane wyniki pokazują, że szybkie i równoległe rozpoznawanie liter poza VWFA rekrutuje również wczesne obszary retinotopowe oraz dolny zakręt czołowy (ang. inferior frontal gyrus - IFG) w celu skutecznego pośredniczenia między znakami pisanymi i ich fonologią. W Eksperymencie 2. badano obszary mózgu, które mogą odpowiadać za brak automatyzacji czytania u dzieci dyslektycznych. Wykazano, że u dzieci z dysleksją, w porównaniu do sprawnie czytających dzieci w tym samym wieku, aktywność mózgowa w VWFA jest mniejsza. Co ciekawe, deficyt stwierdzono również w środkowym zakręcie potylicznym (ang. middle occipital gyrus - MOG), obszarze odpowiedzialnym za przetwarzanie wzrokowo-przestrzenne. Chociaż istnieją sprzeczne relacje nt. roli MOG w czytaniu, wydaje się, że jest on zaangażowany w przetwarzanie ortograficzne - albo poprzez wspieranie kodowania pozycji litery w słowie, albo poprzez identyfikowanie liter. Celem Eksperymentu 3. w związku z tym było zbadanie roli MOG metodą przyczynowo-skutkową za pomocą przezczaszkowej stymulacji magnetycznej. Wyniki Eksperymentu 3. są niejednoznaczne z powodu niewystarczającej mocy statystycznej, wynikającej z trudnej dostępności miejsc do stymulacji i niezrównoważonych warunków eksperymentalnych. Niemniej jednak uzyskano efekt identyfikacji litery w korze ciemieniowej. Ogół wyników trzech eksperymentów opisanych w niniejszej rozprawie potwierdza pogląd, że we wzrokowym rozpoznawaniu słów pośredniczy rozproszona i interaktywna sieć obszarów mózgowych, które razem stanowią podstawę szybkiego i sprawnego czytania.
Expert written word recognition has long been associated with a region in the left ventral occipitotemporal cortex also called the Visual Word Form Area (VWFA), which is thought to be part of the extrastriate category-selective areas. However reading related activations are repeatedly reported in visual regions outside the occipitotemporal cortex, especially in tasks, where lexical processing is constricted. Notably, expertise effects in reading were observed in early cortical areas at the level of V1 to V4. The present thesis presents three studies, which aim is to characterize the functional and structural properties of brain regions activated in fast visual word recognition beyond the ventral visual stream. A series of neuroimaging experiments were used where the processing of letters and other symbols were compared in tasks that did not involve explicit reading or lexical processing. Study 1 aimed at identifying, with functional magnetic resonance imaging, the brain areas that participate in the correct recognition of written stimuli, which might form the basis of effortless, skilled reading. Its results demonstrate, that efficient recognition of letters in addition to the VWFA recruits early to intermediate retinotopic visual areas for fast and parallel recognition and inferior frontal areas for efficient mediation between written signs and their phonology. Study 2 investigated brain regions which might cause reading deficits in reading disabled children. In addition to the VWFA, the middle occipital gyrus (MOG) - an area responsible for visuospatial processing - was found to be underactivated in dyslexic children when compared to age matched controls. There have been conflicting accounts as to the role of the MOG in written word recognition, although it seems that it is implicated in orthographic processing by supporting either letter position encoding or letter identity processing. Therefore Study 3 was designed to test its role causally with the use of transcranial magnetic stimulation. Although the results of Study 3 are inconclusive due to insufficient power being a result of the difficult accessibility of the stimulation sites and unbalanced experimental conditions, it did point to an effect of letter identification in the parietal cortex. Taken together, the results of the three experiments described in the present doctoral thesis support the view that visual word recognition is mediated by a distributed and interactive network of brain areas that together form the basis of fast, effortless skilled reading.

APA, Harvard, Vancouver, ISO, and other styles

34

Sampaio, Joana Machado. "Cerebral reorganization and neurosensory plasticity." Master's thesis, 2019. http://hdl.handle.net/10316/87873.

Full text

Abstract:

Trabalho de Projeto do Mestrado Integrado em Engenharia Biomédica apresentado à Faculdade de Ciências e Tecnologia
Plasticidade neuronal é um tópico muito contemporâneo mas ao mesmo tempo bastante controverso. O conceito de plasticidade reflete mudanças na estrutura e função por adaptação ao ambiente onde se está inserido ao longo da vida. O sistema visual é um dos modelos mais robustos para estudar fenómenos de plasticidade devido ao vasto conhecimento sobre a sua estrutura e propriedades. De facto, estudos em humanos investigando as alterações causadas pela falta de informação vinda da visão periférica escasseiam na literatura. Neste trabalho questionamos se populações de neurónios visuais se reorganizam em resposta a alterações percetuais numa doença em que a perda visual é geneticamente pré-determinada resultando em escotomas (regiões cegas) periféricos em adultos. A Doença Pigmentar (RP) é uma doença genética rara que leva à degeneração dos fotorrecetores e consequentemente à perda de campo visual periférico, afetando progressivamente a visão central também. Foram adquiridos dados anatómicos e funcionais de doze doentes em diferentes estágios da doença e vinte-e-cinco indivíduos controlo saudáveis de modo a investigar as propriedades de uma população de campos recetivos (pRF) de neurónios visuais, cujas alterações podem sugerir reorganização em resposta à ausência de informação sensorial. Aplicou-se uma técnica recente denominada mapeamento de population receptive fields (pRFs), uma alternativa mais sofisticada à Retinotopia tradicional, de modo a analisar o tamanho dos campos recetores para cada hemisfério de cada participante. Em geral, e como esperado, os tamanhos médios dos pRFs aumentaram dentro das áreas visuais e ao longo de 11 graus de excentricidade. No entanto, o padrão de variação foi diferente do dos controlos. Além disso, a análise dos declives das retas de ajuste para cada uma das áreas visuais e entre os grupos RP e Controlo revelou uma interação significativa. Na realidade, ao contrário dos controlos, o grau de mudança dos tamanhos médios dos pRFs ao longo da excentricidade é muito similar nas diferentes áreas visuais de RP, o que sugere uma perda de convergência de informação de V1 para V2, e mais tarde para V3. Em adição, o tamanho médio dos pRFs em V1 na zona de representações periféricas foi significativamente maior nos pacientes com RP, o que indica uma reorganização funcional para compensar a falta de informação recebida por parte da periferia. De forma a clarificar se este remapeamento tem como origem uma adaptação a curto-prazo ou se é devido a fenómenos de plasticidade a longo-prazo, foram adquiridos dados de controlos estimulados com escotomas artificiais (AS) que simulam o campo visual de cada um dos pacientes com RP. Foi verificada uma baixa variância explicada e uma diminuição do tamanho dos pRFs no grupo AS, ao contrário dos doentes, confirmando a existência de plasticidade a longo-prazo em vez de mecanismos de adaptação rápida. Resumindo, descobrimos evidências de mecanismos de reorganização a longo-prazo na população de campos recetores de neurónios em resposta à degeneração do campo visual periférico em pacientes adultos com RP. Deste modo, estes acontecimentos devem ser levados em consideração devido às suas implicações no desenvolvimento de estratégicas de terapêutica e reabilitação nestes pacientes.
The topic of neural plasticity is very contemporary but is still very controversial. Plasticity reflects changes on the structure and function following environmental demands throughout life. The visual system is one of the finest models to study plasticity phenomena due to the extensive knowledge of its structure and properties. Indeed, there is a lack of human studies investigating the alterations caused by a loss of input from peripheral vision. In this work we questioned if populations of visual neurons do reorganize in response to a genetically-determined perceptual alteration due to peripheral loss of vision (scotomas) in adults. Retinitis Pigmentosa (RP) is a rare disease that leads to the degeneration of photoreceptors causing a loss of the peripheral visual field that progresses towards the center.We acquired anatomical and functional data from twelve patients in different stages of the disease and twenty-five healthy controls in order to study population receptive field (pRF) properties of visual neurons, whose alterations can be indicative of reorganization in response to the loss of sensory input. We used a recent technique called population receptive field (pRF) mapping, an optimized alternative to traditional Retinotopy, to estimate the sizes of population receptive fields for each hemisphere of each participant. In general, mean pRF sizes showed the expected increase within the visual areas along 11 degrees of eccentricity. However, the pattern of the variation was different from controls. Moreover, the analysis of slopes of the fitting lines for each visual area and between RP and Control groups revealed a significant interaction. In fact, in contrast to controls, the degree of change of mean pRF sizes along eccentricity was similar across visual areas in RP, suggesting a loss of input convergence from V1 to V2, and later to V3. Furthermore, the mean pRF size of V1 in the peripheral representations was significantly higher in RP patients, which indicates a functional reorganization to compensate the lack of peripheral visual input. In order to understand if this remapping is a short-term adaptation or along-term plasticity phenomena, we acquired data from controls stimulated with artificial scotomas (AS) simulating the visual field of each RP patient. We found a lower explained variance and lower pRF sizes in the AS group, as compared to RP, confirming that there is long-term plasticity rather than rapid adaptation mechanisms in the latter.To sum up, we found evidence for long-term reorganization mechanisms of neural pRFs in response to peripheral visual field degeneration in adult RP patients. Therefore, these plasticity phenomena should be taken in consideration due to their strong implications for therapeutic and rehabilitation strategies in these patients.
FCT
FCT
FCT

APA, Harvard, Vancouver, ISO, and other styles

35

Bastien, Danielle. "Asymétries fonctionnelles du cortex visuel observées par spectroscopie proche de l’infrarouge fonctionnelle." Thèse, 2014. http://hdl.handle.net/1866/11588.

Full text

Abstract:

Les objectifs de ce mémoire sont d’étudier la rétinotopie et les asymétries fonctionnelles du cortex visuel chez l’humain avec la spectroscopie proche de l’infrarouge fonctionnelle (SPIRf), tout en confirmant la fiabilité de cette technique. Tel qu’attendu, les résultats montrent une activation plus forte dans l’hémisphère controlatéral et dans le cortex haut/bas inverse à l’hémichamp stimulé. Nous avons également mesuré une activation significativement plus forte dans le cortex visuel supérieur (lorsque le champ visuel inférieur était stimulé) que l’activation dans le cortex visuel inférieur (lorsque le champ visuel supérieur était stimulé), surtout lorsque ces stimuli étaient présentés dans le champ visuel droit. Il s’agit de la première étude en SPIRf à observer les asymétries horizontale et verticale du cortex visuel et à ainsi confirmer l’existence de ces asymétries. Cette étude témoigne également de la fiabilité de la SPIRf comme technique d’imagerie pour cartographier le cerveau humain.
The present study aimed to further investigate retinotopic mapping and functional asymmetries within the human visual cortex using functional near-infrared spectroscopy (fNIRS), as well as the reliability of this technique. As expected, results showed a stronger visual cortical activation in the controlateral hemisphere and in the inverse upper/lower quadrant to the stimulation. We also measured significant stronger activations in the upper visual cortex (when lower hemifield stimuli were presented) compared to activations in the lower visual cortex (when upper hemifield stimuli were showed), especially when the visual stimulation was presented in the right visual field. This is the first study to confirm the vertical and horizontal asymmetries of the visual cortex with fNIRS technique. The present work also settles the reliability of this technique for functional mapping of the human brain.

APA, Harvard, Vancouver, ISO, and other styles

36

Schnabel, Michael. "Eine Symmetrie der visuellen Welt in der Architektur des visuellen Kortex." Doctoral thesis, 2008. http://hdl.handle.net/11858/00-1735-0000-0006-B4A1-D.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Ceurremans, Per [Verfasser]. "Objektive retinotope Sinnesphysiologie mit Hilfe des Pupillenlichtreflexes / vorgelegt von Per Ceurremans." 2006. http://d-nb.info/979494478/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

Nassim, Marouane. "Organisation rétinotopique des structures visuelles révélée par imagerie optique cérébrale chez le rat normal." Thèse, 2008. http://hdl.handle.net/1866/8252.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

D'Souza, Dany Vijay. "An fMRI study of chromatic processing in humans." Doctoral thesis, 2009. http://hdl.handle.net/11858/00-1735-0000-000D-F250-7.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Efler, Daniela Margarete [Verfasser]. "Wiedererkennung ungefilterter und Fourier-gefilterter Schwarzweißmuster duch Honigbienen (Apis mellifera L.) : Evidenz für Parameterextraktion ohne retinotopes Template-Matching / von Daniela Margarete Efler." 2004. http://d-nb.info/972544100/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

41

Böhm, Katrin. "Makulatranslokation mit 360 Retinotomie zur Behandlung der altersbedingten Makuladegeneration: funktionelle Ergebnisse und Komplikationen : Ergebnisse einer prospektiven Studie an 150 Augen aus retinologischer Sicht /." 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014193460&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Jeans, Rhiannon. "Form perception and neural feedback: insights from V1 and V2." Thesis, 2014. http://hdl.handle.net/1885/12731.

Full text

Abstract:

In the brain, every cortical inter-area feedforward projection shares a reciprocal feedback connection. Despite its pervasive nature in the brain, our understanding of the functional role of neural feedback in form perception remains incomplete, particularly in behaving animals. This problem is addressed in humans with a novel form completion paradigm. Seven subjects (5 female) had their EEG waveforms analysed using three linear models showing non-significant differences between stimulus conditions designed to produce differences by manipulating neural feedback to V1. Two of these subjects (one female), in addition to EEG waveforms, had combined magnetic resonance imaging (MRI) and functional MRI (fMRI) cortical maps that allowed anatomically close areas such as V1 and V2 to have their signals decomposed and neural feedback inferred. Differences between stimulus conditions arose once signals had been divided into V1 and V2. Significant differences (p < .05) for one subject in V1 and V2 suggests cortical interactions at 100ms and 350ms. This suggests the form completion paradigm has utility at investigating the influence of the V2 far receptive field surround on V1, given future given signal to noise issues are resolved.

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Retinotopic'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles