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1
Nicholas, Julian Jesuratnam. "Information processing in #parallel' visual pathways." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386633.
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Gillett-Cooper, Anita M. "Development and degeneration in visual pathways." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670398.
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Maeda, Satomi. "Attentional Limitations and the Visual Pathways." Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1244773263.
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LaBonte, Christopher Edward. "Visual pathways and specific reading disabilities /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
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Cardin, V. Maria de la Paz. "The form pathways in the visual brain." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1444134/.
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The perception of visual forms is crucial for humans for successful interactions with the environment. This process occurs automatically, and its outcome is reflected in the inferences and decisions we constantly make. The focus of this thesis is on how the brain handles different aspects of the perception of forms. To study this in normal human individuals, experiments were performed using functional magnetic resonance imaging (fMRI), magnetoencephalography (MEG) and psychophysical methods. This thesis first discusses experiments designed to unravel the mechanisms of form construction, i.e. those from which all the component parts of a single form are assembled. Results suggest that the construction of very simple forms occurs in intermediate visual areas in a parallel and recursive process, with an increase in brain activity with increments in form complexity. A further experiment was performed to study how regularities or known characteristics of images, and the brain responses they elicit, will contribute to explain current percepts. Results from this experiment are consistent with a model where images with learnt attributes activate more strongly anterior visual areas and images with random patterns cause higher activations in earlier visual areas, probably due to top-down signals that reduce activity when it is possible to explain the causes of the sensory stimulation. Finally, it shows differences in the evoked neural activity when forms are either detected or classified, relating these processes to the activity generated in early visual areas. Based on the results of these experiments, a mechanism of top-down and bottom-up interactions between visual areas in the human brain is discussed in the context of the perception of forms.
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Mahajan, Supriya M. "Do visual pathways for action and perception respond differently to the Ebbinghaus Illusion? /." Connect to online version, 2006. http://ada.mtholyoke.edu/setr/websrc/pdfs/mhc/2006/182.pdf.
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Cecere, Roberto <1981>. "Residual visual processing following real or virtual lesions to primary visual pathways." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5896/1/Cecere_Roberto_tesi.pdf.
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Lesions to the primary geniculo-striate visual pathway cause blindness in the contralesional visual field. Nevertheless, previous studies have suggested that patients with visual field defects may still be able to implicitly process the affective valence of unseen emotional stimuli (affective blindsight) through alternative visual pathways bypassing the striate cortex. These alternative pathways may also allow exploitation of multisensory (audio-visual) integration mechanisms, such that auditory stimulation can enhance visual detection of stimuli which would otherwise be undetected when presented alone (crossmodal blindsight).
The present dissertation investigated implicit emotional processing and multisensory integration when conscious visual processing is prevented by real or virtual lesions to the geniculo-striate pathway, in order to further clarify both the nature of these residual processes and the functional aspects of the underlying neural pathways.
The present experimental evidence demonstrates that alternative subcortical visual pathways allow implicit processing of the emotional content of facial expressions in the absence of cortical processing. However, this residual ability is limited to fearful expressions. This finding suggests the existence of a subcortical system specialised in detecting danger signals based on coarse visual cues, therefore allowing the early recruitment of flight-or-fight behavioural responses even before conscious and detailed recognition of potential threats can take place.
Moreover, the present dissertation extends the knowledge about crossmodal blindsight phenomena by showing that, unlike with visual detection, sound cannot crossmodally enhance visual orientation discrimination in the absence of functional striate cortex. This finding demonstrates, on the one hand, that the striate cortex plays a causative role in crossmodally enhancing visual orientation sensitivity and, on the other hand, that subcortical visual pathways bypassing the striate cortex, despite affording audio-visual integration processes leading to the improvement of simple visual abilities such as detection, cannot mediate multisensory enhancement of more complex visual functions, such as orientation discrimination.<br>Una lesione alla via visiva primaria (genicolo-striata) causa cecità nel campo visivo controlesionale. Ciononostante, studi precedenti suggeriscono che, mediante vie visive alternative che non coinvolgono la corteccia striata, i pazienti con deficit di campo visivo potrebbero ancora riuscire ad elaborare implicitamente la valenza affettiva degli stimoli emotivi non visti (affective blindsight) e di sfruttare meccanismi multisensoriali (audio-visivi), cosicchè la stimolazione uditiva migliori la detezione visiva di stimoli non percepiti quando presentati da soli (crossmodal blindsight).
Nella presente tesi si sono indagate l’elaborazione emotiva implicita e l’integrazione multisensoriale osservabili quando l’elaborazione visiva cosciente è impedita da lesioni reali o virtuali della via genicolo-striata, in modo da chiarire sia la natura di tali processi sia gli aspetti funzionali dei circuiti neurali sottostanti.
Le evidenze sperimentali qui presentate dimostrano che, in assenza di elaborazione corticale, le vie visive alternative sottocorticali consentono l’elaborazione implicita del contenuto emotivo delle espressioni facciali, ma che tale abilità è limitata alle espressioni di paura. Questo suggerisce l’esistenza di un sistema sottocorticale specializzato nella detezione di segnali di pericolo a partire da segnali visivi grezzi, permettendo dunque il rapido reclutamento di risposte comportamentali di lotta o fuga già prima che possa avvenire un riconoscimento conscio e dettagliato delle potenziali minacce.
Inoltre, la presente tesi estende le conoscenze riguardo ai fenomeni di “crossmodal blindsight”, dimostrando che, a differenza della detezione visiva, la discriminazione di orientamento di linee non può essere migliorata dalla presentazione di suoni quando la corteccia striata non è funzionante. Questo dato suggerisce da un lato che la corteccia striata ha un ruolo causativo nel miglioramento “cross-modale” della sensibilità visiva all’orientamento e, dall’altro, che le vie visive sottocorticali che non coinvolgono la corteccia striata, anche se permettono l’integrazione di segnali audio-visivi e il miglioramento della semplice detezione, non possono potenziare abilità visive complesse, come la discriminazione di orientamento
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Cecere, Roberto <1981>. "Residual visual processing following real or virtual lesions to primary visual pathways." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5896/.
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Lesions to the primary geniculo-striate visual pathway cause blindness in the contralesional visual field. Nevertheless, previous studies have suggested that patients with visual field defects may still be able to implicitly process the affective valence of unseen emotional stimuli (affective blindsight) through alternative visual pathways bypassing the striate cortex. These alternative pathways may also allow exploitation of multisensory (audio-visual) integration mechanisms, such that auditory stimulation can enhance visual detection of stimuli which would otherwise be undetected when presented alone (crossmodal blindsight).
The present dissertation investigated implicit emotional processing and multisensory integration when conscious visual processing is prevented by real or virtual lesions to the geniculo-striate pathway, in order to further clarify both the nature of these residual processes and the functional aspects of the underlying neural pathways.
The present experimental evidence demonstrates that alternative subcortical visual pathways allow implicit processing of the emotional content of facial expressions in the absence of cortical processing. However, this residual ability is limited to fearful expressions. This finding suggests the existence of a subcortical system specialised in detecting danger signals based on coarse visual cues, therefore allowing the early recruitment of flight-or-fight behavioural responses even before conscious and detailed recognition of potential threats can take place.
Moreover, the present dissertation extends the knowledge about crossmodal blindsight phenomena by showing that, unlike with visual detection, sound cannot crossmodally enhance visual orientation discrimination in the absence of functional striate cortex. This finding demonstrates, on the one hand, that the striate cortex plays a causative role in crossmodally enhancing visual orientation sensitivity and, on the other hand, that subcortical visual pathways bypassing the striate cortex, despite affording audio-visual integration processes leading to the improvement of simple visual abilities such as detection, cannot mediate multisensory enhancement of more complex visual functions, such as orientation discrimination.<br>Una lesione alla via visiva primaria (genicolo-striata) causa cecità nel campo visivo controlesionale. Ciononostante, studi precedenti suggeriscono che, mediante vie visive alternative che non coinvolgono la corteccia striata, i pazienti con deficit di campo visivo potrebbero ancora riuscire ad elaborare implicitamente la valenza affettiva degli stimoli emotivi non visti (affective blindsight) e di sfruttare meccanismi multisensoriali (audio-visivi), cosicchè la stimolazione uditiva migliori la detezione visiva di stimoli non percepiti quando presentati da soli (crossmodal blindsight).
Nella presente tesi si sono indagate l’elaborazione emotiva implicita e l’integrazione multisensoriale osservabili quando l’elaborazione visiva cosciente è impedita da lesioni reali o virtuali della via genicolo-striata, in modo da chiarire sia la natura di tali processi sia gli aspetti funzionali dei circuiti neurali sottostanti.
Le evidenze sperimentali qui presentate dimostrano che, in assenza di elaborazione corticale, le vie visive alternative sottocorticali consentono l’elaborazione implicita del contenuto emotivo delle espressioni facciali, ma che tale abilità è limitata alle espressioni di paura. Questo suggerisce l’esistenza di un sistema sottocorticale specializzato nella detezione di segnali di pericolo a partire da segnali visivi grezzi, permettendo dunque il rapido reclutamento di risposte comportamentali di lotta o fuga già prima che possa avvenire un riconoscimento conscio e dettagliato delle potenziali minacce.
Inoltre, la presente tesi estende le conoscenze riguardo ai fenomeni di “crossmodal blindsight”, dimostrando che, a differenza della detezione visiva, la discriminazione di orientamento di linee non può essere migliorata dalla presentazione di suoni quando la corteccia striata non è funzionante. Questo dato suggerisce da un lato che la corteccia striata ha un ruolo causativo nel miglioramento “cross-modale” della sensibilità visiva all’orientamento e, dall’altro, che le vie visive sottocorticali che non coinvolgono la corteccia striata, anche se permettono l’integrazione di segnali audio-visivi e il miglioramento della semplice detezione, non possono potenziare abilità visive complesse, come la discriminazione di orientamento
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Beaudet, Luc. "Adaptation mechanisms in the salmonid visual system." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0002/NQ32704.pdf.
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Vierck, Esther, and n/a. "Direct selection by colour for visual encoding." University of Otago. Department of Psychology, 2005. http://adt.otago.ac.nz./public/adt-NZDU20070427.145655.
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The goal of this thesis was to investigate the role of colour in visual selective attention. Previous experiments exploring this topic in tasks where location varied led to mixed results. Some studies only found evidence of colour as a guide to a specific location where selection then takes place (e.g., Nissen, 1985). Others reported an effect, but could not decide clearly if the benefit was due to direct selection of colour in perception (e.g., Humphreys, 1981). One major contributor to the inconsistencies of findings seems to be the confounding of colour and location in these tasks. For that reason the initial paradigm used here was a rapid serial visual presentation (RSVP) task. Previous studies using similar paradigms have found no evidence for direct selection by colour (Poder, 2001; Shih & Sperling, 1996), but in these studies advance colour information was of limited usefulness because it only reduced the set of candidate stimuli by half. To assess an effect of colour in selection similar to the one associated with location, in all experiments reported here valid colour information led to only one item, as is typical in location cuing tasks.
The first RSVP experiment explored whether colour certainty improved performance over a colour uncertainty condition. Colour was the defining feature of the target participants had to discriminate. In one condition the target colour was certain; in the other it could be one of two colours. Performance was improved when participants could focus on one colour. Further experiments used colour not as a defining feature of the target but as additional information presented in the form of cues, similar to the typical use of location cues. The participants� task was to discriminate whether a target letter within the RSVP sequence appeared in its upper or lower case version, and an advance cue indicated the colour in which the target letter was most likely to occur. An accuracy benefit of valid colour information was found, supporting the hypothesis that colour cuing allows the direct selection of objects for further perceptual processing. In addition, an effect of invalid colour cues was also observed. Subsequent experiments investigated possible factors influencing the colour cuing effect. Together, task requirements and properties of the stimulus set were shown to have an influence on the effect size, whereas an increase in perceptual load had no impact. Furthermore, the colour cuing effect seems to be due partially to both automatic and strategic processes. In all these experimental variations, benefits of colour cuing remained, indicating that the effect is very robust. Colour cuing effects were also found in a design where location could vary, extending the previous findings from selection in the time domain to selection in space. The two last experiments investigated whether advance colour knowledge would also lead to a performance benefit in single item tasks. No effect of colour cuing was found, indicating that colour information is only helpful in multiple item displays when a selection of one target stimulus among distractor items is necessary.
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Zhang, Wenjian, and 張文劍. "Magnetic resonance imaging investigation of the auditory and visual functions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/208023.
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Functional magnetic resonance imaging (fMRI) is a noninvasive technique that can measure blood oxygenation level dependent (BOLD) signal changes in a large field of view with high spatial resolution. The objective of this dissertation is to explore and integrate novel and noninvasive fMRI methods at 7 Tesla to investigate the auditory and visual functions.
First, different fMRI methods and stimulation paradigms were employed to explore some basic auditory functions such as sound pressure level (SPL) dependence in different brain structures, and periodotopy and tonotopy in the inferior colliculus (IC). BOLD signal changes increased significantly with SPL and the dependence was monotonic in the IC and lateral lemniscus (LL). The external cortex of IC (ECIC) had higher BOLD signal change than the central nucleus of IC and LL at high SPLs. This study indicates that sparse temporal sampling that is used to reduce the adverse effects of scanner noise may not be a prerequisite in auditory fMRI studies of the IC. Periodotopy and tonotopy in the IC was investigated using continuous imaging with passband balanced steady state free precession (bSSFP) sequence instead of sparse temporal sampling and echo planner imaging (EPI). The spatial gradients of best amplitude modulation frequency (referred to as periodotopy) and characteristic frequency (referred to as tonotopy) varied across the IC, but were approximately perpendicular at different locations. These findings enhance our understanding of how auditory information is preserved in the midbrain.
Second, higher order function of behaviorally relevant sounds response selectivity in subcortical structures was investigated. The IC was found to exhibit a stronger response to forward vocalization than to the temporally inverted one. Moreover, blocking cholinergic projections to the IC by atropine injection was observed to significantly reduce the IC response selectivity to the 22 kHz vocalizations. These findings demonstrate the IC response selectivity to vocalizations and suggest that the cholinergic projection contributes to IC responses selectivity to the 22 kHz vocalization. This study provides further understanding about the higher order auditory processing and may have implications for the neural mechanisms underlying human speech perception
Third, BOLD fMRI was applied to measure the brain response to stationary and apparent motion visual stimulation. The response of superior colliculus (SC) was weaker under dim light and saturates at higher intensities. Further, the BOLD signal changes and number of activated voxels were both significantly lower during 164 ˚/s apparent motion stimulation compared to stimuli at slower speeds. The results suggest that the SC was more sensitive to slow moving visual stimuli. This is the first fMRI study to investigate motion responsiveness and stimulus speed dependence in the rat SC.
Results from these studies complement current knowledge and demonstrate the sophisticated role of subcortical structures such as IC and SC, which may have strong clinical significance to the field of auditory and visual research. Findings from the animal studies should open up new avenues of research and lay the ground work for future human studies.<br>published_or_final_version<br>Electrical and Electronic Engineering<br>Doctoral<br>Doctor of Philosophy
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Parkyn, Daryl Charles. "Visual biology of salmonids with special reference to polarised light sensitivity." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ34280.pdf.
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Hayduk, Steven J. "Evidence against a transient system deficit in specific reading disability." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69559.
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This study was designed to test the claim that a deficit in low-level visual processing is a major factor in the etiology of developmental dyslexia. The transient and sustained pathways are neuro-anatomical pathways which underlie low level visual processing. Dyslexics are hypothesized to suffer from a transient pathway deficit which manifests itself in reading difficulties. Normal and disabled adult readers were compared on two visual processing tasks. One task measured the contrast threshold of subjects for flickering sinewave gratings; normal and disabled readers did not differ in contrast sensitivity. On the second task--a visual search task--disabled readers were consistently slower than normal readers, rather than showing the pattern of performance predicted by the transient deficit model; the results provide little evidence for a transient pathway deficit. The results of this and related studies are discussed; it is concluded that empirical evidence for a transient pathway deficit in dyslexia is equivocal.
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Ritchie, Kay Laird. "Visual attention and awareness : lessons from the damaged and intact brain." Thesis, University of Aberdeen, 2012. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=192179.
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The studies presented in this thesis address current issues in visual attention and awareness research. The first three experimental chapters investigate saccadic remapping of location and orientation information, with a particular focus on saccadic remapping in hemianopia. The results suggest that residual visual abilities in the blind field are necessary in order for a stimulus to be remapped from the blind to the sighted visual field. The results also suggest that remapping underpins our ability to maintain attention at specific spatiotopic locations across a series of saccades. Further evidence from both hemianopic and neurologically intact participants suggest that some orientation information is remapped across saccades. The second three experimental chapters investigate binocular rivalry in previously unstudied paradigms. The results show that the established face dominance and emotion dominance effects in binocular rivalry persist when the stimuli are viewed in peripheral vision. The results also suggest that a stable image presented in the opposite hemifield from the rival pair does not affect the perceived dominance of the separate images within the rival pair, but that the percepts in the rival pair tend to synchronise with those of a second rival pair presented in the opposite hemifield. Using Diaz-Caneja stimuli (half of each image presented to each eye) the results of the final experiments suggest a combination of eye- and object-dominance mechanisms in binocular rivalry in both the intact and the split-brain.
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Rebotier, Thomas P. "Vision and imagery : the role of cortical attractor dynamics /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p9908500.
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Gonzalez, Alvaro J. "Alpha stable human visual system models for digital halftoning." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 58 p, 2007. http://proquest.umi.com/pqdweb?did=1251904881&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Perens, Gregory S. "NMDA Receptor-mediated Synaptic Plasticity in Developing Mammalian Visual Pathways." VCU Scholars Compass, 1995. https://scholarscompass.vcu.edu/etd/5246.
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Precise connections in many mammalian nervous systems require a great deal of remodeling during development. In the visual system, many excess synapses are originally formed in the lateral geniculate nucleus and striate cortex. Only the correct set of axon terminals are retained during normal development, while imprecise ones withdraw. The mechanism by which only correct axons are retained requires neural activity, and may be regulated by specific receptors at synapses.
The transmission of neural signals at these synapses is carried out in part by the glutamate-activated NMDA receptor. It is hypothesized that NMDA receptor activation plays a crucial role in enhancing only those connections in the immature system which will form a retinotopically correct map in the LGN and cortex. NMDA receptor activation requires depolarization of the neuron membrane. Possibly, only neurons transmitting information from nearby areas in the retina summate to produce NMDA receptor- mediated currents. The result is an influx of Ca++ ions that has been shown to cause trophic effects within the cell that could enhance the synaptic connection. Thus, NMDA receptors may act to detect coincident neural activity in immature animals, thereby allowing only visuo-topically related axon terminals to undergo enhancement of synaptic transmission and structure. As development proceeds, NMDA receptor function decreases, possibly reducing these intracellular effects.
Blocking NMDA receptor activation experimentally does alter the normal set of connections in the visual system. Yet, is there a direct cause- and-effect relation between NMDA receptor activity and anatomical changes? Many cellular events probably result from NMDA-mediated currents. Intracellular changes in phosphorylation states and protein levels could eventually alter a synapse at the anatomical level. Study of the changing NMDA receptor subunit types making up the receptor within visual system structures could reveal, in part, the means by which plasticity is down-regulated. The experimental regulation of these subunits in vivo could reveal important information concerning their specific function if plasticity and development were to be altered as a result. A summary of previous studies, and proposals for further research concerning the role of the NMDA receptor and its various types in developing visual pathways are presented in this manuscript.
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Lee, Chak-pui Terence. "Unified percepts in three-dimensional space derived from motion in depth or rotation in depth." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B37943741.
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Lee, Chak-pui Terence, and 李澤沛. "Unified percepts in three-dimensional space derived from motion in depth or rotation in depth." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B37943741.
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Baldwin, David Hugh. "The role of visual subsystems in Drosophila phototaxis /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/5135.
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Szmajda, Brett A. "Subcortical pathways for colour vision /." Connect to thesis, 2006. http://eprints.unimelb.edu.au/archive/00003165.
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Thesis (Ph.D.)--University of Melbourne, The National Vision Research Institute of Australia and Dept. of Optometry & Vision Sciences, 2007.<br>Typescript. Includes bibliographical references (leaves 95-111).
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Zhou, Yi-Xiong. "Responses to envelope patterns in visual cortical neurons." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41806.
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Mammalian striate and circumstriate cortical neurons have long been understood as coding spatially localized retinal luminance variations, providing a basis for computing motion, stereopsis, and contours from the retinal image. However, such perceptual attributes do not always correspond to the retinal luminance variations in natural vision. Recordings from area 17 and 18 neurons revealed a specialized nonlinear processing stream that responded to stimulus attributes having no corresponding luminance variations. This nonlinear stream acts in parallel to the conventional luminance processing of single cortical neurons. The two streams were consistent in their preference for orientation and direction of motion, but distinct in processing spatial variations of the stimulus attributes. The ensemble of these neurons provides a combination of stimulus attributes with and without corresponding luminance variations.
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Sullivan, Thomas Joseph. "Computational models of feedforward and feedback pathways in the visual cortex /." Diss., Connect to a 24 p. preview or request complete full text in PDF formate. Access restricted to UC campuses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3236624.
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Daniels, Rebecca. "Electrophysiological studies of the visual pathways in Alzheimer's and Parkinson's disease." Thesis, Aston University, 1994. http://publications.aston.ac.uk/14612/.
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Dopamine (DA) and acetylcholine (ACH) are neurotransmitters that are present in the visual pathway. DA is present in the retina and is associated with the interplexiform cells and horizontal cells. ACH is also present in the retina and is associated with displaced amacrine cells; it is also present in the superior colliculus. DA is found to be significantly depleted in the brain of Parkinson's disease (PD) patients and ACH in Alzheimer's disease (AD) patients. For this reason these diseases were used to assess the function of DA and ACH in the electrophysiology of the visual pathway. Experiments were conducted on young normals to design stimuli that would preferentially activate the magnocellular or parvocellular pathway. These stimuli were then used to evoke visual evoked potentials (VEP) in patients with PD and AD, in order to assess the function of DA and ACH in the visual pathway. Electroretinograms (ERGs) were also measured in PD patients to assess the role of DA in the retina. In addition, peripheral ACH function was assessed by measuring VEPs, ERGs and contrast sensitivity (CS) in young normals following the topical instillation of hyoscine hydrobromide (an anticholinergic drug). The results indicate that the magnocellular pathway can be divided into two: a cholinergic tectal-association area pathway carrying luminance information, and a non-cholinergic geniculo-cortical pathway carrying spatial information. It was also found that depletion of DA had very little effect on the VEPs or ERGs, confirming a general regulatory function for this neurotransmitter.
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Hathibelagal, Amithavikram Rugvedi. "The role of noise on rod signaling in the visual pathways." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/122230/1/Amithavikram%20Rugvedi_Hathibelagal_Thesis.pdf.
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Rod and cone photoreceptors in the human eye operate simultaneously under dim (mesopic) illuminations, however, it's not clear how their signals interact to regulate our visual experience. These photoreceptor interactions were investigated using a new methodology designed to isolate rod-mediated vision by separating it from the effects of cone photoreceptor-specific noise. The outcomes revealed a mechanism requiring cone-directed transmission of rod signals through the primary visual pathways that optimizes human vision under twilight illumination.
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Fung, Chun Him. "A biomimetic active stereo head with torsional control /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?ECED%202006%20FUNG.
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Morgan, J. E. "The organization of the retinogenuculate pathways in normal and neonatally enucleated pigmented and albino ferrets." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371563.
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Peng, Xiaozhe, and 彭晓哲. "Visual path information on the active control of heading." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41633817.
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Peng, Xiaozhe. "Visual path information on the active control of heading." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B41633817.
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Roy, Sujata. "Segregation within afferent pathways in primate vision." Connect to thesis, 2009. http://repository.unimelb.edu.au/10187/4913.
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The current knowledge of the visual pathways in primates includes the patterns of projection from the retina through the dorsal lateral geniculate nucleus (dLGN) to the striate cortex (V1) and the extra-striate projections towards the dorsal and ventral streams. Cells with short wavelength sensitive cone (S-cone) inputs in the dLGN have been studied extensively in New World marmosets but not in Old World macaques. This thesis presents results from studies in the macaque monkey which are more relevant to humans since humans are closer in evolution to Old World than New World monkeys.<br>The spatial, temporal, chromatic and orientation preferences of neurons in the dLGN of the macaque were investigated by electrophysiological methods. The physiological findings of cells with S-cone inputs were compared to cells with opponent inputs from the long and medium wavelength sensitive cones (L-cones & M-cones, respectively). The cells receiving S-cone inputs (blue-yellow or B-Y cells) preferred lower spatial frequencies than the cells with opponent L-cone and M-cone inputs (red-green or R-G cells). Orthodromic latencies from optic chiasm stimulation were measured where possible to distinguish differences in conduction velocity between the cell groups. Although the B-Y cells usually had longer latencies than R-G cells, there wasconsiderable overlap between the cell groups.<br>The recorded cells were localised through histological reconstruction of dLGN sections stained for Nissl substance. The distribution of B-Y cells within the dLGN was compared to the distribution of R-G cells. The majority of B-Y cells were located within the intercalated koniocellular layers as well as the koniocellular bridges (extensions of the koniocellular layers into the adjacent parvocellular layers). The B-Y cells were also largely segregated within the middle dLGN layers (K3, P3, K4 & P4). The R-G cells were mainly concentrated within the parvocellular layers (P3, P4, P5 & P6) and were evenly distributed throughout the middle and outer layers of the dLGN.<br>The study also included recordings from the extra-striate middle temporal area (MT) to determine whether a fast S-cone input exists from the dLGN to area MT which bypasses V1. The pattern of cone inputs to area MT neurons was investigated before and during inactivation of V1. The inactivation was done through reversible cooling with a Peltier thermocouple device or focal inactivation with y-amino butyric acid (GABA) iontophoresis. Precise inactivation of V1 to the topographically matching visual fields of the recording sites in area MT revealed a preservation of all three coneinputs in many cells. The subcortical sources of these preserved inputs are discussed with their relevance to blindsight, which is the limited retention of visual perception after V1 damage. Analysis of the latencies of area MT cells revealed a rough segregation into latencies faster or slower than 70 ms. Cells both with and without a significant change in response during V1 inactivation were present in each group. The findings reported in this thesis indicate that some of the preserved inputs in area MT during V1 inactivation may be carried by a direct input from the dLGN which bypasses V1.
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Nassi, Jonathan J. "Contributions of early parallel pathways to extrastriate visual cortex in macaque monkey." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3258528.
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Thesis (Ph. D.)--University of California, San Diego, 2007.<br>Title from first page of PDF file (viewed June 1, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Chatterjee, Soumya. "Early visual pathways in the Macaque monkey : cone contributions and cortical targets /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3144320.
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Colavincenzo, Justin. "Myelin debris clearance along the goldfish visual paths during Wallerian degeneration." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21529.
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This study aimed to better understand the clearance of myelin debris during Wallerian degeneration in the goldfish visual paths. Myelin debris was first examined immunohistochemically in the presence or absence of regenerating axons. From these preliminary experiments it was apparent that the clearance of myelin debris was not affected by regenerating axons and that the debris was removed in a differential pattern along the visual pathway. Specifically, in the distal stump of the nerve as well as in the optic tract, myelin debris had been effectively cleared by one-month postoperative, while in the cranial segment of the nerve debris persisted for at least 6 weeks after injury. The differential pattern of myelin debris in the optic nerve and tract was then analyzed qualitatively and quantitatively using thick and thin plastic sections at various time points during regeneration. The results suggested that highly activated peripheral macrophages were responsible for the effective clearance of myelin in the distal nerve stump. In the optic tract a number of cellular properties, including their unique population of astrocytes may have enhanced the rate of debris clearance. By contrast, in the cranial segment of the nerve persistent debris was found both intracellularly in phagosomes and extracellularly, suggesting that the resident phagocytes were deficient in effecting both phagocytosis and emigration. Deficient phagocytosis may be a result of the production of anti-inflammatory cytokines in this region, while the failure to emigrate is most likely due to the rigid network of astrocytes in the nerve.
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Oliveira, Elaine Aparecida de. "Desenvolvimento e avaliação de uma ferramenta para diagnostico da literacia visual, contextualizada no estudo de vias metabolicas." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/314741.
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Orientador: Eduardo Galembeck<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia<br>Made available in DSpace on 2018-08-15T17:08:58Z (GMT). No. of bitstreams: 1
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Previous issue date: 2010<br>Resumo: Representações externas são muito utilizadas no ensino de bioquímica. As vias metabólicas constituem um tipo de representação externa e envolvem habilidades visuais; estão, portanto, intimamente relacionados à literacia visual (capacidade de interpretar imagens). Há uma preocupação crescente em diagnosticar a dificuldade dos estudantes com a bioquímica. Este tipo de diagnóstico é importante para poder propor soluções pedagógicas que possam facilitar o aprendizado. O presente trabalho tem como objetivo descrever o desenvolvimento e a aplicação de um teste informatizado para diagnosticar a literacia visual, relacionada ao estudo de vias metabólicas, de estudantes de cursos das áreas biológica e da saúde. Inicialmente foram desenvolvidos testes piloto com itens (modelos e questões) que contemplavam habilidades visuais para a compreensão de vias metabólicas mais frequentemente representadas em livros didáticos de bioquímica. Os testes piloto foram aplicados em 2007 e 2008 com turmas de graduação de cursos da área biológica e da saúde. Os resultados obtidos serviram de subsídio para que alguns itens fossem reformulados e outros adicionados. Os resultados obtidos foram tratados com uso do modelo de Rasch, tanto no processo de equalização dos testes piloto (para definir os itens do teste final), como para o tratamento dos resultados obtidos com a calibração de itens-respondentes após as aplicações do teste final. Três grupos participaram da aplicação do teste final e compreenderam 79 estudantes distribuídos entre os cursos de educação física (UNICAMP), enfermagem (UNICAMP) e fisioterapia/nutrição (FAJ). A partir dos dados obtidos utilizou-se o processo de calibração de itens-respondentes, proposta pelo modelo de Rasch, obtendo-se a dificuldade dos itens e as habilidades visuais apresentadas pelos grupos. Os resultados observados sugerem que entre as dificuldades apresentadas pelos estudantes no aprendizado de metabolismo pode ser incluída a dificuldade em se compreender as representações externas de vias metabólicas. Essa dificuldade pode ser minimizada com explicações dos modelos antes de se entrar nos conteúdos específicos. O teste produzido permite o diagnóstico de estudantes ou de grupos. A necessidade de desenvolver práticas de visualização para melhorar a compreensão de conceitos bioquímicos pelos estudantes mostrou-se um aspecto importante no estudo de vias metabólicas<br>Abstract: External representations are used in teaching of biochemistry. The metabolic pathways are a type of external representation and involve visual skills, are therefore closely related to visual literacy (ability to interpret images). There is an increasing concern regarding the diagnosis of students with difficulty to the biochemistry, this type of diagnosis is important to be able to propose solutions that would facilitate learning. This paper aims to describe the development and implementation of a computerized test to diagnose the visual literacy, related to the study of metabolic pathways for undergraduate students enrolled in courses in the biological and health. Initially, pilot tests have been developed with (models and items) that looked visual skills for the understanding of metabolic pathways most often represented in textbooks of biochemistry. The pilot tests were applied in 2007 and 2008 on undergraduate classes of various courses in the biological and health. The results served as a subsidy for some items were reformulated and others added. The results are processed using the Rasch model, both in the process of equalizing the pilot tests (for set of the final test) and for the treatment of the results obtained with calibration of items-respondents the applications for the final test. Three groups participated in the implementation of the final test and included 79 students distributed among the courses of physical education (UNICAMP), nursing (UNICAMP) and physiotherapy/nutrition (FAJ). From the data we used the calibration of items-respondents proposed by Rasch model resulting in the difficulty of items and visual skills presented by the groups. The results suggest that among the difficulties presented by the students in the learning of metabolism may be included the difficulty in understanding the external representations of metabolic maps. This difficulty can be minimized with the explanations of the models before they enter the specific content. The test produced allows the diagnosis of students or groups. The need of developing imagery to improve the understanding of biochemical concepts by students were an important aspect in the study of metabolic pathways<br>Mestrado<br>Bioquimica<br>Mestre em Biologia Funcional e Molecular
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Bruce, Freyja Mairi. "Determining the roles of DSCAM and SDK proteins in vertebrate visual system development." Thesis, University of Aberdeen, 2012. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=185643.
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Axons are directed along stereotypic pathways to their targets by cues arrayed in the extracellular environment. Identifying the cellular and molecular nature of these signals is of high interest and the developing optic pathway is a useful model system for achieving this. Although previous studies have identified several molecules essential for optic pathway formation, in vivo only subsets of retinal axons rely on them. I focused on the Dscam (Down’s syndrome cell adhesion molecule) and Sidekick (Sdk) cell adhesion molecules for potentially playing crucial roles in this system. In situ hybridisation in the embryonic mouse visual system showed Dscam and Sdk-1 expression in the RGC layer of the retina, along the optic pathway and in the visual targets. Sdk-2 was detected in the glia of the optic nerve and optic chiasm, marking the pathway that RGC axons follow, but not in RGCs. No DscamL1 was detected in RGCs or the optic pathway at the stages investigated and it was discounted from future analysis. In vitro, DSCAM promoted RGC axon outgrowth, whereas SDK 1 was inhibitory. SDK 2 had no effect on RGC axon outgrowth, suggesting it does not play a direct role in their pathfinding. Repeating this assay using retinal explants from the Dscamdel17 mouse mutant, showed that DSCAM enhanced retinal axon outgrowth, at least in part, through homophilic interactions. Analysis of visual system development in Dscam mutants showed DSCAM involvement in RGC axon fasciculation and in enhancing their growth, particularly within the ipsilateral optic tract. Retinal cell counts revealed that DSCAM played diverse roles in controlling cell number. Pre- and postnatal retinas lacking DSCAM contained more RGCs and mitotic cells. Postnatally, Dscam-/- retinas also show decreased cell death. In many cases, defect severity was dose-dependent, with an intermediate phenotype in the heterozygous mice, implicating DSCAM in the neurological defects of Downs’ Syndrome patients.
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Ghinescu, Rodica. "A modeling-based approach for investigating multiple processing pathways in simple visual tasks /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p3164509.
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Schnell, Bettina. "Structure, Function and Input Pathways of Motion-sensitive Visual Interneurons in Drosophila melanogaster." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-125189.
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Davidson, Miriam. ""Catching time" : pathways to engagement in the elementary classroom through the visual arts." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0019/NQ54391.pdf.
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Farivar-Mohseni, Reza. "Object recognition by integration of information across the dorsal and ventral visual pathways." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21982.
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The brain decomposes visual information into its form and motion components and processes the two aspects largely independently by way of anatomically distinct pathways that originate early in the visual system and continue ventrally to the occipito-temporal visual areas and dorsally to the occipito-parietal visual areas, respectively. Certain cues of shape, such as 3-D structure-from-motion (SFM), appear to be computed exclusively by dorsal-stream mechanisms, yet these cues can describe complex objects whose recognition depends on mechanisms in the ventral stream. This dissertation discusses theoretical means by which dorsally-computed 3-D cues may provide input to ventral stream object recognition mechanisms. Psychophysical and neuropsychological data presented here suggest that 3-D SFM cues do indeed empower complex object recognition, and recognition of shapes defined by 3-D SFM likely require integration of information across the two pathways. Additionally, neuropsychological data are presented for a dissociation of 3-D SFM processing from 2-D form-from-motion processing. Finally, utilizing functional imaging (FMRI), data are presented to suggest that SFM-defined objects do not engage category-selective areas in the human brain in the same manner as photographs of those objects do. Together these results suggest that visual object recognition may be subserved by mechanisms distributed between the two pathways.<br>Le cerveau décompose l'informations visuelle en ses composants de forme et de mouvement, et les traite de manière indépendante par deux voies anatomiques distinctes‹l¹information ayant attrait au mouvement et à la relation spatiale par la voie dorsale qui se termine dans le lobe pariétal et l¹information ayant attrait à la forme par la voie ventrale qui se termine dans le cortex inférotemporal. Certaines informations de profondeur, tel que la structure-par-mouvement 3-D (SPM), sont presque entièrement analysées par la voie dorsale; toutefois, les objets décris par la SPM sont aussi reconnus par les voies ventrales. Cette thèse débute par une discussion théorique décrivant la manière dont l¹information de profondeur calculée par la voie dorsale peut contribuer aux machinismes de reconnaissance des objets (voie ventrale). Les résultats des expériences psychophysiques et neuropsychologiques indiquent que l¹information de SPM peut permettre la reconnaissance des objets complexes, même des visages peu familiers, et cela peut constituer un case d¹intégration entre les deux voies indépendantes. De plus, les résultats des expériences neuropsychologiques présentées suggèrent que la perception de forme-par-mouvement 2-D est dissociable de celle de structure par mouvement 3-D. Finalement, par le biais d'imagerie par résonance magnétique fonctionnelle, nous avons démontré que les objets décris par SPM n¹activent pas le même méchanisme cérébral que des photos de ces mêmes objets. Ensemble, les résultats présentés ci-après suggèrent que la reconnaissance des objets visuels peut être distribuée entre les deux voies visuelles.
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Kogan, Cary. "The expression of neurofilament protein and mRNA levels in the lateral geniculate nucleus and area V1 of the developing and adult vervet monkey (Ceorcopithicus aethiops) /." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0028/MQ50807.pdf.
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Xing, Kai, and 邢锴. "Functional magnetic resonance imaging (fMRI) of rodent visual and auditory system." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47849939.
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Functional MRI or Functional Magnetic Resonance Imaging (fMRI) is a type of specialized MRI scan which measures the hemodynamic response related to neural activity in the brain or spinal cord of humans and animals. Due to its relatively low invasiveness, absence of radiation exposure, and relatively wide availability, functional MRI has come to dominate the brain mapping field since the early 1990s. The objective of this thesis work is to develop and apply functional MRI methods at 7 Tesla, for in vivo investigation of rodent visual and auditory system. Firstly, the development of the rat visual pathway was studied by blood oxygenation level–dependent (BOLD) contrast from the time of eyelid opening (P14) to adulthood (P60) in normal rat brain. By studying BOLD-fMRI measurements in the normal brain superior colliculus (SC), we determined that the regional BOLD response undergoes a systematic increase in amplitude especially over the third postnatal week.
Secondly, the potential for plasticity of the rodent superior colliculus (SC) was studied using BOLD fMRI. By studying BOLD-fMRI measurements in the SC of three groups of rats (normal, HI-injured with left SC partially damaged and HI-injured with left SC completely damaged), we can evaluate the extent of plastic changes, compensatory and transneuronal plasticity after varying degrees of SC injury. We also applied BOLD-fMRI using very short repetition time (TR) of 0.2s on rats to measure the difference in response temporal dynamics between the SC and LGN, which has not been measured conclusively or with high temporal resolution. The primary finding in this study is that there is an approximately 0.8s difference between the BOLD responses of the rat contralateral SC and LGN to the visual stimuli. In addition, the amplitude of the SC response is larger than that of the LGN. Thirdly, BOLD-fMRI is used to measure the SC hemodynamic responses, in normal adult Sprague-Dawley (SD) rats, during a dynamic visual stimulus similar to those used in long-range apparent motion studies. The stimulation paradigm mimic effective speeds of motion between 7 and 164?/s, the results suggest that the SC is sensitive to slow moving visual stimuli but the hemodynamic response is reduced at higher speeds.
Finally, BOLD-fMRI is used to study hemodynamic response temporal dynamics in the superior colliculus (SC) and inferior colliculus (IC) following visual and auditory associated stimulation. Our results show the baselines of SC BOLD signal (in two sides) increase during the ON period of auditory stimulation, which demonstrate that auditory stimulation can increase ROI activation signal intensity in superior colliculus (SC). The previous dominant theory is that individual senses each have separate areas of the brain dedicated to processing each sense, while the individual sense perceptions are integrated together to produce a multi-sensory experience. As a result of new research over the past several years, however, this view has been challenged by studies showing that processing in the visual area of the brain can be directly influenced by hearing and touch. All these discoveries represent a new view of how the brain is actually organized.<br>published_or_final_version<br>Electrical and Electronic Engineering<br>Master<br>Master of Philosophy
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Ghali, Rodney. "Non-neuronal cell response to axonal damage in the visual paths of goldfish." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=24005.
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Patterns of proliferation and changes in total cell number in the optic nerve, tract and tectum of goldfish have been examined following optic nerve crush or optic enucleation, using bromodeoxyuridine to label the proliferating cells. In general, an increase in proliferation and total cell number in all parts of the visual system was observed peaking between 7 and 14 days and resolving itself to normal or near normal levels by 32 days postoperative. Enucleation resulted in elevated proliferation values as compared to animals with an optic nerve crush, at least one early timepoint in each part of the visual system, but overall, there is little to suggest that axons are exerting a major effect on the cellular response. Finally, a seasonal effect on the proliferative response of non-neuronal cells and axonal regrowth has been demonstrated. Fish acclimatized under autumn-like conditions showed a faster initiation of the non-neuronal cell response and an enhanced rate of axonal regrowth when compared to fish acclimatized under spring-like conditions. It is believed that photoperiod plays a major role in the seasonal effects observed with temperature playing only a minor one.
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Lowenger, Elizabeth. "Studies of early neural regeneration in the visual system of the goldfish." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66031.
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Lytle, Grace E. "Effects of various nitric oxide synthase inhibitors on the choroidal and growth responses in emmetropization in chicks /." Adobe Acrobat Reader required to view document, 2008. http://www.neco.edu/library/theses/LytleThesisJune08.pdf.
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Durán, Gabriela. "Effects of concurrent task performance on object processing." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Svoboda, Hanno. "The role of protein synthesis in branching and synaptogenesis in the visual system." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610032.
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Medrado, Ramon Gomes. "Formalização de uma linguagem visual para descrição de sistemas biológicos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2009. http://hdl.handle.net/10183/27661.
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Vias biológicas representam interações entre entidades químicas complexas (proteínas, substratos, metabólitos etc.) que ocorrem no nível molecular das células. A representação e compreensão do comportamento destas vias é o principal alvo de estudos da Biologia Sistêmica. Esta área de estudos envolve a construção de modelos matemáticos que possam simular in silico (computacionalmente) o comportamento destes sistemas biológicos verificados in vivo (experimentalmente). Do ponto de vista computacional é evidente que tais sistemas são complexos para abordar e descrever de modo intuitivo. São necessários modelos com valor preditivo, isto é, que permitam descrever os comportamentos do sistema que são experimentalmente verificáveis. Algumas notações gráficas foram propostas para descrever vias biológicas. Entre elas, os diagramas de processos tem sido amplamente utilizados. Um diagrama de processos é essencialmente um grafo no qual vértices e arestas representam componentes biológicos, e há uma notação gráfica associada com cada elemento. Nesta dissertação propomos uma fundamentação formal para a linguagem dos diagramas de processos definindo a sintaxe usando gramática de grafos. Nós definimos primeiramente um grafo chamado BioProc, descrevendo o meta-modelo dos diagramas de processos. Instâncias do grafo BioProc são portanto diagramas de processos modelando vias biológicas. Para descrever a semântica foi proposta uma tradução algébrica dos grafos BioProc para redes de Petri estocásticas generalizadas (GSPNs) já amplamente utilizadas na modelagem de processos biológicos. O uso de gramática de grafos como formalismo intermediário na tradução habilita a verificação sintática da via com a checagem dos tipos válidos que podem ser definidos para cada reação antes da simulação na rede de Petri e usá-las posteriormente para explorar propriedades estruturais e estocásticas do modelo. Além disso serve como base para a evolução do modelo proposto. Isto é relevante já que modelos frequentemente são construídos incrementalmente para se adaptar a novos requisitos e/ou incluir novas características.<br>Biological pathways represent interactions between complex chemical entities (proteins, substrates, metabolites, etc.) that occur at the molecular level of cells. The representation and comprehension of biological pathways behavior is the main target of research in the field of Systems Biology. This area investigates the construction of mathematical models that can simulate in silico (computationally) the behavior of biological systems checked in vivo (experimentally). From a computational view point it is clear that such systems are too complex to analyze and describe in an intuitiveway. Models with predictive value are needed, describing the behaviors that are experimentally verifiable. There are some graphical notations to describe biological pathways. Among them, process diagrams have been widely used. A process diagram is essentially a graph in which vertices and edges represent biological components, and there is a graphical notation associated with each element. In this master thesis we give a formal foundation for biological process diagrams, by defining their (concrete and abstract) syntax and semantics using a formalism called graph grammars. We first build a graph called BioProc Graph, describing the meta-model of process diagrams. Instances of this BioProc graph are concrete process diagrams modeling biological pathways. To describe the semantics we proposed a translation of BioProc diagrams to generalized stochastic Petri networks (GSPNs) already widely used in modeling biological processes. The use of graph grammar formalism as a basis for translation enables the syntatic verification to check the valid types that can be defined for each reaction after the simulation of Petri net and before that to explore structural and stochastic properties of the model. In addition it serves as the basis for model evolution proposed. This is relevant because models are often built incrementally to adapt to new requirements and/or include new features.
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Carvajal, Carlos. "Dynamic interplay between standard and non-standard retinal pathways in the early thalamocortical visual system : A modeling study." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0209/document.
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Comprendre le comportement du système visuel rétino-thalamo-cortico-colliculaire (i.e. précoce) dans une situation d'images naturelles est d'une importance capitale pour comprendre ce qui se passe ensuite dans le cerveau. Pour comprendre ces comportements, les neurobiologistes ont étudié les voies standard, Parvocellulaires et Magnocellulaires, depuis des décennies. Cependant, il y a aussi la voie non-standard, ou Koniocellulaire, qui joue un rôle modulateur important dans les traitements local, global, et entremêlé, pour atteindre de tels comportements. Particulièrement, l'analyse standard du mouvement réalisée par la voie Magno est alternée avec des réactions rapides, comme la fuite ou l'approche à des mouvements spécifiques, qui sont pré-câblés dans la voie Konio. De plus, l'étude d'une tâche de fixation dans une situation réelle, par exemple quand un prédateur s'approche lentement de sa proie, implique non seulement un mécanisme de mouvement, mais nécessite également l'utilisation de la voie Parvo, qui analyse, au moins, le contraste de l'image. Ici, nous étudions dans un modèle neuronal de calcul bio-inspiré comment ces voies peuvent être modélisées avec un ensemble minimal de paramètres, afin de fournir des résultats numériques robustes lors d'une tâche réelle. Ce modèle repose sur une étude approfondie pour intégrer des éléments biologiques dans l'architecture des circuits, les constantes de temps et les caractéristiques de fonctionnement des neurones. Nos résultats montrent que notre modèle, bien que fonctionnant via des calculs locaux, montre globalement un bon comportement de réseau en termes d'espace et de temps, et permet d'analyser et de proposer des interprétations de l'interaction entre le thalamus et le cortex. À une échelle plus macroscopique, les comportements du modèle sont reproductibles et peuvent être qualitativement comparés à des mesures de fixation oculaire chez l'homme. Cela est également vrai lorsque l'on utilise des images naturelles, où quelques paramètres sont légèrement modifiés, en gardant des résultats qualitativement humains. Les résultats de robustesse montrent que les valeurs précises des paramètres ne sont pas critiques, mais leur ordre de grandeur l'est. Une instabilité numérique ne se produit qu'après une variation de 100% d'un paramètre. Nous pouvons donc conclure que cette approche systémique est capable de représenter les changements de l'attention en utilisant des images naturelles, tout en étant algorithmiquement robuste. Cette étude nous donne ainsi une interprétation possible sur le rôle de la voie Konio, tandis qu'en même temps elle nous permet de participer au débat sur les low et high-roads des flux attentionnel et émotionnel. Néanmoins, d'autres informations, comme la couleur, sont également présentes dans le système visuel précoce, et pourraient être prises en considération, ainsi que des mécanismes corticaux plus complexes, dans les perspectives de ce travail<br>Understanding the behavior of the retino-thalamo-cortico-collicular (i.e. early) visual system in a natural images situation is of utmost importance to understand what further happens in the brain. To understand these behaviors, neuroscientists have looked at the standard Parvocellular and Magnocellular pathways for decades. However, there is also the non-standard Koniocellular pathway, which plays an important modulating role in the local, global, and intermingled processing carried out to achieve such behaviors. Particularly, the standard motion analysis carried out by the Magno pathway is alternated with rapid reactions, like fleeing or approaching to specific motions, which are hard-wired in the Konio pathway. In addition, studying a fixation task in a real situation, e.g., when a predator slowly approaches its prey, not only involves a motion mechanism, but also requires the use of the Parvo pathway, analyzing, at least, the image contrast. Here, we study in a bio-inspired computational neural model how these pathways can be modeled with a minimal set of parameters, in order to provide robust numerical results when doing a real task. This model is based upon an important study to integrate biological elements about the architecture of the circuits, the time constants and the operating characteristics of the different neurons. Our results show that our model, despite operating via local computations, globally shows a good network behavior in terms of space and time, and allows to analyze and propose interpretations to the interplay between thalamus and cortex. At a more macroscopic scale, the behaviors emerging from the model are reproducible and can be qualitatively compared to human-made fixation measurements. This is also true when using natural images, where just a few parameters are slightly modified, keeping the qualitatively human-like results. Robustness results show that the precise values of the parameters are not critical, but their order of magnitude matters. Numerical instability occurs only after a 100% variation of a parameter. We thus can conclude that such a reduced systemic approach is able to represent attentional shifts using natural images, while also being algorithmically robust. This study gives us as well a possible interpretation about the role of the Konio pathway, while at the same time allowing us to participate in the debate between low and high-roads in the attentional and emotional streams. Nevertheless, other information, such as color, is also present in the early visual system, and should be addressed together with more complex cortical mechanisms in a sequel of this work
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The Best PhD Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,2009-2010<br>published_or_final_version<br>Electrical and Electronic Engineering<br>Doctoral<br>Doctor of Philosophy
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Darcy, Natasha [Verfasser]. "Effects of stimulus degradation on neural object processing in the two visual pathways / Natasha Darcy." Berlin : Medizinische Fakultät Charité - Universitätsmedizin Berlin, 2020. http://d-nb.info/1206180846/34.
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