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Artykuły w czasopismach na temat "Primate V1"
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Przybyszewski, Andrzej W., Igor Kagan i D. Max Snodderly. "Primate area V1". NeuroReport 25, nr 14 (październik 2014): 1109–15. http://dx.doi.org/10.1097/wnr.0000000000000235.
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Xu, Xiangmin, William H. Bosking, Leonard E. White, David Fitzpatrick i Vivien A. Casagrande. "Functional Organization of Visual Cortex in the Prosimian Bush Baby Revealed by Optical Imaging of Intrinsic Signals". Journal of Neurophysiology 94, nr 4 (październik 2005): 2748–62. http://dx.doi.org/10.1152/jn.00354.2005.
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Cells in primary visual cortex (V1) of primates and carnivores respond most strongly to a visual stimulus presented to one eye, in a particular visual field location, and at a particular orientation. Each of these stimulus attributes is mapped across the cortical surface, and, in macaque monkeys and cats, strong geometrical relationships exist between these feature maps. In macaque V1 and V2, correlations between feature maps and cytochrome oxidase (CO)-rich modules have also been observed. To see if such relationships reflect a conserved principle of V1 functional architecture among primate species, we examined these maps in the prosimian bush baby, a species that has been proposed to represent the ancestral primate organization. We found that the layout of individual feature maps in bush baby V1 is similar to that of other primates, but we found an entirely different organization of orientation preference in bush baby V2 compared with that reported in simian primates. Another striking distinction between bush baby and simian species is that we observed no strong relationships among maps of orientation, ocular dominance, and CO blobs in V1. Thus our findings suggest that precise relationships between feature maps are not a common element of the functional organization in all primates and that such relationships are not necessary for achieving basic coverage of stimulus feature combinations. In addition, our results suggest that specific relationships between feature maps in V1, and the subdivision of V2 into functional compartments, may have arisen comparatively late in the evolution of primates.
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Kaas, Jon H., i Mary K. L. Baldwin. "The Evolution of the Pulvinar Complex in Primates and Its Role in the Dorsal and Ventral Streams of Cortical Processing". Vision 4, nr 1 (30.12.2019): 3. http://dx.doi.org/10.3390/vision4010003.
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Current evidence supports the view that the visual pulvinar of primates consists of at least five nuclei, with two large nuclei, lateral pulvinar ventrolateral (PLvl) and central lateral nucleus of the inferior pulvinar (PIcl), contributing mainly to the ventral stream of cortical processing for perception, and three smaller nuclei, posterior nucleus of the inferior pulvinar (PIp), medial nucleus of the inferior pulvinar (PIm), and central medial nucleus of the inferior pulvinar (PIcm), projecting to dorsal stream visual areas for visually directed actions. In primates, both cortical streams are highly dependent on visual information distributed from primary visual cortex (V1). This area is so vital to vision that patients with V1 lesions are considered “cortically blind”. When the V1 inputs to dorsal stream area middle temporal visual area (MT) are absent, other dorsal stream areas receive visual information relayed from the superior colliculus via PIp and PIcm, thereby preserving some dorsal stream functions, a phenomenon called “blind sight”. Non-primate mammals do not have a dorsal stream area MT with V1 inputs, but superior colliculus inputs to temporal cortex can be more significant and more visual functions are preserved when V1 input is disrupted. The current review will discuss how the different visual streams, especially the dorsal stream, have changed during primate evolution and we propose which features are retained from the common ancestor of primates and their close relatives.
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Jones, H. E., K. L. Grieve, W. Wang i A. M. Sillito. "Surround Suppression in Primate V1". Journal of Neurophysiology 86, nr 4 (1.10.2001): 2011–28. http://dx.doi.org/10.1152/jn.2001.86.4.2011.
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We investigated the spatial organization of surround suppression in primate primary visual cortex (V1). We utilized drifting stimuli, configured to extend either from within the classical receptive field (CRF) to surrounding visual space, or from surrounding visual space into the CRF or subdivided to generate direction contrast, to make a detailed examination of the strength, spatial organization, direction dependence, mechanisms, and laminar distribution of surround suppression. Most cells (99/105, 94%) through all cortical layers, exhibited suppression (mean reduction 67%) to uniform stimuli exceeding the CRF, and 43% exhibited a more than 70% reduction. Testing with an annulus revealed two different patterns of surround influence. Some cells (37% of cells), classical surround suppression (CSS) cells exhibited responses to an annulus encroaching on the CRF that were less than the plateau in the spatial summation curve. The majority (63%), center-gated surround suppression (CGSS) cells, showed responses to annuli that equaled or exceeded the plateau in the spatial summation curve. Analysis suggested the CSS mechanism was implemented in all cells while the CGSS mechanism was implemented in varying strength across the sample with the extreme reflected in cells that gave larger responses to annuli than to a center stimulus. Reversing the direction of motion of the portion of the stimulus surrounding the CRF revealed four different patterns of effect: no reduction in the degree of suppression (22% of cells), a reduction in surround suppression (41%), a facilitation of the response above the level to the inner stimulus alone (37%), and a facilitation of the response above that to the inner stimulus alone that also exceeded the values associated with an optimal inner stimulus. The facilitatory effects were only seen for reverse direction interfaces between the central and surrounding stimulus at diameters equal to or more than the CRF size. The zones driving the suppressive influences and the direction contrast facilitation were often spatially heterogeneous and for a number of cells bore strong comparison with the class of behavior reported for surround mechanisms in MT. This suggests a potential role, for example, in extracting information about motion contrast in the representation of the three dimensional structure of moving objects.
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Song, Byeongwoon, Bert Gold, Colm O'hUigin, Hassan Javanbakht, Xing Li, Matthew Stremlau, Cheryl Winkler, Michael Dean i Joseph Sodroski. "The B30.2(SPRY) Domain of the Retroviral Restriction Factor TRIM5α Exhibits Lineage-Specific Length and Sequence Variation in Primates". Journal of Virology 79, nr 10 (15.05.2005): 6111–21. http://dx.doi.org/10.1128/jvi.79.10.6111-6121.2005.
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ABSTRACT Tripartite motif (TRIM) proteins are composed of RING, B-box 2, and coiled coil domains. Some TRIM proteins, such as TRIM5α, also possess a carboxy-terminal B30.2(SPRY) domain and localize to cytoplasmic bodies. TRIM5α has recently been shown to mediate innate intracellular resistance to retroviruses, an activity dependent on the integrity of the B30.2 domain, in particular primate species. An examination of the sequences of several TRIM proteins related to TRIM5 revealed the existence of four variable regions (v1, v2, v3, and v4) in the B30.2 domain. Species-specific variation in TRIM5α was analyzed by amplifying, cloning, and sequencing nonhuman primate TRIM5 orthologs. Lineage-specific expansion and sequential duplication occurred in the TRIM5α B30.2 v1 region in Old World primates and in v3 in New World monkeys. We observed substitution patterns indicative of selection bordering these particular B30.2 domain variable elements. These results suggest that occasional, complex changes were incorporated into the TRIM5α B30.2 domain at discrete time points during the evolution of primates. Some of these time points correspond to periods during which primates were exposed to retroviral infections, based on the appearance of particular endogenous retroviruses in primate genomes. The results are consistent with a role for TRIM5α in innate immunity against retroviruses.
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Seidemann, Eyal, i Wilson S. Geisler. "Linking V1 Activity to Behavior". Annual Review of Vision Science 4, nr 1 (15.09.2018): 287–310. http://dx.doi.org/10.1146/annurev-vision-102016-061324.
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A long-term goal of visual neuroscience is to develop and test quantitative models that account for the moment-by-moment relationship between neural responses in early visual cortex and human performance in natural visual tasks. This review focuses on efforts to address this goal by measuring and perturbing the activity of primary visual cortex (V1) neurons while nonhuman primates perform demanding, well-controlled visual tasks. We start by describing a conceptual approach—the decoder linking model (DLM) framework—in which candidate decoding models take neural responses as input and generate predicted behavior as output. The ultimate goal in this framework is to find the actual decoder—the model that best predicts behavior from neural responses. We discuss key relevant properties of primate V1 and review current literature from the DLM perspective. We conclude by discussing major technological and theoretical advances that are likely to accelerate our understanding of the link between V1 activity and behavior.
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Rosa, Marcello G. P., Vivien A. Casagrande, Todd Preuss i Jon H. Kaas. "Visual Field Representation in Striate and Prestriate Cortices of a Prosimian Primate (Galago garnetti)". Journal of Neurophysiology 77, nr 6 (1.06.1997): 3193–217. http://dx.doi.org/10.1152/jn.1997.77.6.3193.
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Rosa, Marcello G. P., Vivien A. Casagrande, Todd Preuss, and Jon H. Kaas. Visual field representation in striate and prestriate cortices of a prosimian primate ( Galago garnetti). J. Neurophysiol. 77: 3193–3217, 1997. Microelectrode mapping techniques were used to study the visuotopic organization of the first and second visual areas (V1 and V2, respectively) in anesthetized Galago garnetti, a lorisiform prosimian primate. 1) V1 occupies ∼200 mm2 of cortex, and is pear shaped, rather than elliptical as in simian primates. Neurons in V1 form a continuous (1st-order) representation of the visual field, with the vertical meridian forming most of its perimeter. The representation of the horizontal meridian divides V1 into nearly equal sectors representing the upper quadrant ventrally, and the lower quadrant dorsally. 2) The emphasis on representation of central vision is less marked in Galago than in simian primates, both diurnal and nocturnal. The decay of cortical magnification factor with increasing eccentricity is almost exactly counterbalanced by an increase in average receptive field size, such that a point anywhere in the visual field is represented by a compartment of similar diameter in V1. 3) Although most of the cortex surrounding V1 corresponds to V2, one-quarter of the perimeter of V1 is formed by agranular cortex within the rostral calcarine sulcus, including area prostriata. Although under our recording conditions virtually every recording site in V2 yielded visually responsive cells, only a minority of those in area prostriata revealed such responses. 4) V2 forms a cortical belt of variable width, being narrowest (∼1 mm) in the representation of the area centralis and widest (2.5–3 mm) in the representation of the midperiphery (>20° eccentricity) of the visual field. V2 forms a second-order representation of the visual field, with the area centralis being represented laterally and the visual field periphery medially, near the calcarine sulcus. Unlike in simians, the line of field discontinuity in Galago V2 does not exactly coincide with the horizontal meridian: a portion of the lower quadrant immediately adjacent to the horizontal meridian is represented at the rostral border of ventral V2, instead of in dorsal V2. Despite the absence of cytochrome oxidase stripes, the visual field map in Galago V2 resembles the ones described in simians in that the magnification factor is anisotropic. 5) Receptive field progressions in cortex rostral to dorsal V2 suggest the presence of a homologue of the dorsomedial area, including representations of both quadrants of the visual field. These results indicate that many aspects of organization of V1 and V2 in simian primates are shared with lorisiform prosimians, and are therefore likely to have been present in the last common ancestor of living primates. However, some aspects of organization of the caudal visual areas in Galago are intermediate between nonprimates and simian primates, reflecting either an intermediate stage of differentiation or adaptations to a nocturnal niche. These include the shape and the small size of V1 and V2, the modest degree of emphasis on central visual field representation, and the relatively large area prostriata.
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Scholl, Benjamin, Johnathan Rylee, Jeffrey J. Luci, Nicholas J. Priebe i Jeffrey Padberg. "Orientation selectivity in the visual cortex of the nine-banded armadillo". Journal of Neurophysiology 117, nr 3 (1.03.2017): 1395–406. http://dx.doi.org/10.1152/jn.00851.2016.
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Orientation selectivity in primary visual cortex (V1) has been proposed to reflect a canonical computation performed by the neocortical circuitry. Although orientation selectivity has been reported in all mammals examined to date, the degree of selectivity and the functional organization of selectivity vary across mammalian clades. The differences in degree of orientation selectivity are large, from reports in marsupials that only a small subset of neurons are selective to studies in carnivores, in which it is rare to find a neuron lacking selectivity. Furthermore, the functional organization in cortex varies in that the primate and carnivore V1 is characterized by an organization in which nearby neurons share orientation preference while other mammals such as rodents and lagomorphs either lack or have only extremely weak clustering. To gain insight into the evolutionary emergence of orientation selectivity, we examined the nine-banded armadillo, a species within the early placental clade Xenarthra. Here we use a combination of neuroimaging, histological, and electrophysiological methods to identify the retinofugal pathways, locate V1, and for the first time examine the functional properties of V1 neurons in the armadillo ( Dasypus novemcinctus) V1. Individual neurons were strongly sensitive to the orientation and often the direction of drifting gratings. We uncovered a wide range of orientation preferences but found a bias for horizontal gratings. The presence of strong orientation selectivity in armadillos suggests that the circuitry responsible for this computation is common to all placental mammals.NEW & NOTEWORTHY The current study shows that armadillo primary visual cortex (V1) neurons share the signature properties of V1 neurons of primates, carnivorans, and rodents. Furthermore, these neurons exhibit a degree of selectivity for stimulus orientation and motion direction similar to that found in primate V1. Our findings in armadillo visual cortex suggest that the functional properties of V1 neurons emerged early in the mammalian lineage, near the time of the divergence of marsupials.
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Parra, Andres, Christopher A. Baker i M. McLean Bolton. "Regional Specialization of Pyramidal Neuron Morphology and Physiology in the Tree Shrew Neocortex". Cerebral Cortex 29, nr 11 (31.01.2019): 4488–505. http://dx.doi.org/10.1093/cercor/bhy326.
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Abstract The mammalian cerebral cortex is divided into different areas according to their function and pattern of connections. Studies comparing primary visual (V1) and prefrontal cortex (PFC) of primates have demonstrated striking pyramidal neuron (PN) specialization not present in comparable areas of the mouse neocortex. To better understand PFC evolution and regional PN specialization, we studied the tree shrew, a species with a close phylogenetic relationship to primates. We defined the tree shrew PFC based on cytoarchitectonic borders, thalamic connectivity and characterized the morphology and electrophysiology of layer II/III PNs in V1 and PFC. Similar to primates, the PFC PNs in the tree shrew fire with a regular spiking pattern and have larger dendritic tree and spines than those in V1. However, V1 PNs showed strikingly large basal dendritic arbors with high spine density, firing at higher rates and in a more varied pattern than PFC PNs. Yet, unlike in the mouse and unreported in the primate, medial prefrontal PN are more easily recruited than either the dorsolateral or V1 neurons. This specialization of PN morphology and physiology is likely to be a significant factor in the evolution of cortex, contributing to differences in the computational capacities of individual cortical areas.
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Srinivasan, Shyam, C. Nikoosh Carlo i Charles F. Stevens. "Predicting visual acuity from the structure of visual cortex". Proceedings of the National Academy of Sciences 112, nr 25 (8.06.2015): 7815–20. http://dx.doi.org/10.1073/pnas.1509282112.
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Three decades ago, Rockel et al. proposed that neuronal surface densities (number of neurons under a square millimeter of surface) of primary visual cortices (V1s) in primates is 2.5 times higher than the neuronal density of V1s in nonprimates or many other cortical regions in primates and nonprimates. This claim has remained controversial and much debated. We replicated the study of Rockel et al. with attention to modern stereological precepts and show that indeed primate V1 is 2.5 times denser (number of neurons per square millimeter) than many other cortical regions and nonprimate V1s; we also show that V2 is 1.7 times as dense. As primate V1s are denser, they have more neurons and thus more pinwheels than similar-sized nonprimate V1s, which explains why primates have better visual acuity.
Rozprawy doktorskie na temat "Primate V1"
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Stevens, Jean-Luc Richard. "Spatiotemporal properties of evoked neural response in the primary visual cortex". Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31330.
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Understanding how neurons in the primary visual cortex (V1) of primates respond to visual patterns has been a major focus of research in neuroscience for many decades. Numerous different experimental techniques have been used to provide data about how the spatiotemporal patterns of light projected from the visual environment onto the retina relate to the spatiotemporal patterns of neural activity evoked in the visual cortex, across disparate spatial and temporal scales. However, despite the variety of data sources available (or perhaps because of it), there is still no unified explanation for how the circuitry in the eye, the subcortical visual pathways, and the visual cortex responds to these patterns. This thesis outlines a research project to build computational models of V1 that incorporate observations and constraints from an unprecedented range of experimental data sources, reconciling each data source with the others into a consistent proposal for the underlying circuitry and computational mechanisms. The final mechanistic model is the first one shown to be compatible with measurements of: (1) temporal firing-rate patterns in single neurons over tens of milliseconds obtained using single-unit electrophysiology, (2) spatiotemporal patterns in membrane voltages in cortical tissues spanning several square millimeters over similar time scales, obtained using voltage-sensitive-dye imaging, and (3) spatial patterns in neural activity over several square millimeters of cortex, measured over the course of weeks of early development using optical imaging of intrinsic signals. Reconciling this data was not trivial, in part because single-unit studies suggested short, transient neural responses, while population measurements suggested gradual, sustained responses. The fundamental principles of the resulting models are (a) that the spatial and temporal patterns of neural responses are determined not only by the particular properties of a visual stimulus and the internal response properties of individual neurons, but by the collective dynamics of an entire network of interconnected neurons, (b) that these dynamics account both for the fast time course of neural responses to individual stimuli, and the gradual emergence of structure in this network via activity-dependent Hebbian modifications of synaptic connections over days, and (c) the differences between single-unit and population measurements are primarily due to extensive and wide-ranging forms of diversity in neural responses, which become crucial when trying to estimate population responses out of a series of individual measurements. The final model is the first to include all the types of diversity necessary to show how realistic single-unit responses can add up to the very different population-level evoked responses measured using voltage-sensitive-dye imaging over large cortical areas. Additional contributions from this thesis include (1) a comprehensive solution for doing exploratory yet reproducible computational research, implemented as a set of open-source tools, (2) a general-purpose metric for evaluating the biological realism of model orientation maps, and (3) a demonstration that the previous developmental model that formed the basis of the models in this thesis is the only developmental model so far that produces realistic orientation maps. These analytical results, computational models, and research tools together provide a systematic approach for understanding neural responses to visual stimuli across time scales from milliseconds to weeks and spatial scales from microns to centimeters.
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Thulin, Nilsson Linnea. "The Role of Primary Visual Cortex in Visual Awareness". Thesis, Högskolan i Skövde, Institutionen för biovetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:his:diva-11623.
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Despite its great complexity, a great deal is known about the organization and information-processing properties of the visual system. However, the neural correlates of visual awareness are not yet understood. By studying patients with blindsight, the primary visual cortex (V1) has attracted a lot of attention recently. Although this brain area appears to be important for visual awareness, its exact role is still a matter of debate. Interactive models propose a direct role for V1 in generating visual awareness through recurrent processing. Hierarchal models instead propose that awareness is generated in later visual areas and that the role of V1 is limited to transmitting the necessary information to these areas. Interactive and hierarchical models make different predictions and the aim of this thesis is to review the evidence from lesions, perceptual suppression, and transcranial magnetic stimulation (TMS), along with data from internally generated visual awareness in dreams, hallucinations and imagery, this in order to see whether current evidence favor one type of model over the other. A review of the evidence suggests that feedback projections to V1 appear to be important in most cases for visual awareness to arise but it can arise even when V1 is absent.
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Montardy, Quentin. "Lier l'activité de population de neurones du cortex visuel primaire avec le comportement oculomoteur : des saccades de fixation à V1, et de V1 à la réponse de suivi oculaire". Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM5069.
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Nous avons analysé l'activité de population au sein du cortex visuel primaire en vue de comprendre (i) les mécanismes mis en jeu lors de l'intégration de l'information visuelle suite à un mouvement oculaire, et inversement (ii) de l'influence du traitement effectué au niveau de V1 sur la génération d'un mouvement oculaire.1. Nous avons enregistré des saccades de fixation, et mis en relation, essai par essai, ces mouvements avec la représentation de la position d'un stimulus local dans V1. Après une saccade de fixation, l'activité se déplace de façon cohérente dans V1. Le décours temporel des réponses au niveau des foyers pre- et post-saccadiques montre une dynamique biphasique. La taille du foyer d'activité augmente. Nous proposons que le comportement des populations de neurones s'explique par deux phénomènes principaux : (i) La réponse suppressive précoce attribuable à la décharge corollaire (ii) de connections latérales qui réactiveraient le foyer pre-saccadique.2. Nous avons enregistré l'OFR, et cherché à savoir si la réponse de V1 l'influençait. Les latences VSD précèdent les latences OFR. Il n'existe pas de corrélation à l'essai unique. Nous avons montré que la force et la dynamique des réponses de V1 n'étaient pas prédictives de l'OFR. La distance de la périphérie à un effet sur la réponse VSD, mais pas sur l'OFR. La dynamique de propagation de cette suppression, nous avons montré deux phases : une précoce sur l'ensemble de la carte, et une plus périphérique tardive. Nous proposons que la suppression précoce soit originaire de projections en retour de structures comme MT et MST, alors que la suppression plus lente s'explique par les connections horizontalesWe analyzed population activity in V1 to understand (i) the consequence of eye movements on integration of visual information, and (ii) the influence of the processing performed at the level of V1 on the generation of eye movements.1. We recorded fixational saccades, relating, trial-by-trial, these eye movements with the representation of the position of a local stimulus in V1. After a fixational saccade, activity moves consistently in V1. However, the time-course of responses display a biphasic dynamic. This results in a global increase of the extent of cortical activity representing the local stimulus. We propose that the behavior of populations of neurons studied is explained by the contribution of two main phenomena: (i) an early suppressive response that could be attributed to the corollary discharge and (ii) the lateral connections generating lateral interactions between pre and post-saccadic lci of activity.2. We recorded the ocular following response, determining whether the response of V1 influences the oculomotor response. We studied the contrast response function of the population V1 activity and the OFR. The dynamics of CRF for a local stimulus are similar and shifted in time. We found no correlations between the single trial latencies between V1 and the OFR. At the chosen scale, surround suppression was found to be distance-dependent only in V1. The dynamics of the surround suppression shows two phases: an early suppression present over a wide cortical area, and a later peripheral spread. We propose that the early surround suppression originates from feedback from MT and MST, while the later is explained by the horizontal connections
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Reynaud, Alexandre. "Rôle fonctionnel des interactions latérales dans l'intégration du mouvement visuel : étude en imagerie optique au niveau du cortex visuel primaire du singe éveillé". Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22129/document.
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La thématique principale de nos travaux est l'étude de l'intégration du mouvement au niveau de la population du cortex visuel primaire du singe éveillé : de l'identification des circuits corticaux impliqués dans le traitement du mouvement,jusqu'à l'identification et l'émergence d'un signal de mouvement. Nous avons ainsi principalement utilisé deux protocoles (mouvement réel ou apparent).La réponse neuronale de population à l'entrée du système (V1) a été comparée à une réponse comportementale en sortie, la réponse de suivi oculaire réflexe (OFR).L'activité de population dans le cortex visuel primaire est enregistrée par imagerie optique de composés sensible au potentiel.Nous avons alors montré que la réponse au contraste dans V1 est contrôlée par un bassin de normalisation dynamique qui évolue lentement via un recrutement progressif et polysynaptique des circuits récurrents locaux. Ce bassin reçoit des afférents horizontaux liés au contraste qui suppriment graduellement le gain au contraste et à la réponse neuronale.Ensuite, en comparant l'activité de population de V1 avec la réponse de suivi oculaire réflexe avec un stimulus dont l'échelle intermédiaire active à la fois l'entrée et la sortie du système, nous avons identifié deux mécanismes distincts, impliqués dans les interactions contextuelles étudiées : un mécanisme précoce et rapide agissant sur les entrées fortes provenant majoritairement de MT et un mécanisme lent et soutenu plus visible sur les entrées faibles provenant majoritairement de V1.Finalement, en étudiant l'intégration et la représentation du mouvement apparent à la surface de V1, nous avons observé que la dynamique de l'activité corticale générée par des stimuli de mouvement apparent induit une suppression non-linéaire à la surface du cortex qui permet à la population de V1 de ne représenter qu'un seul stimulus à la fois, et ferait donc émerger un signal de mouvement non-ambigu.Pour conclure, nos expériences montrent que les interactions non-linéaires entre et parmi les aires corticales entraînent la normalisation, la modulation et l'émergence de différents signaux de mouvementOur goal is to study motion integration at population level in V1 in the awake behaving onkey. We compare V1population recorded with optical imaging of voltage sensitive dyes with ocular following response.We have shown that contrast response function in V1 is controlled by a dynamic normalization pool. Then we identified two distinct mechanisms involved in contextual modulations: a fast transient one originating from MT and a show and sustained one, originating from V1. Finally, we have observed that cortical activity dynamics in presponse to apparent motion can induce a suppression wave at acortical surface
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Bohi, Amine. "Descripteurs de Fourier inspirés de la structure du cortex visuel primaire humain : Application à la reconnaissance de navires dans le cadre de la surveillance maritime". Thesis, Toulon, 2017. http://www.theses.fr/2017TOUL0002/document.
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Dans cette thèse, nous développons une approche supervisée de reconnaissance d’objets basée sur l’utilisation de nouveaux descripteurs d’images globaux inspirés du modèle du cortex visuel humain primaire V1 en tant que groupe de roto-translations semi-discrètes SE (2,N)=R² x ZN produit semi-direct entre R² et ZN. La méthode proposée est basée sur des descripteurs de Fourier généralisés et rotationnels définis sur le groupe SE (2,N), qui sont invariants aux transformations géométriques (translations, et rotations). De plus, nous montrons que ces descripteur de Fourier sont faiblement complets, dans le sens qu’ils permettent de discriminer sur un ensemble ouvert et dense L² (SE(2,N)) de fonctions à support compact, donc distinguer entre des images réelles. Ces descripteurs sont ensuite utilisés pour alimenter un classifieur de type SVM dans le cadre de la reconnaissance d’objets. Nous avons mené une séries d’expérimentations dans le but d’évaluer notre méthode sur les bases de visages RL, CVL et ORL et sur la base d’images d’objets variés COIL-100, et de comparer ses performances à celles des méthodes basées sur des descripteurs globaux et locaux. Les résultats obtenus ont montré que notre approche est en mesure de concurrencer de nombreuses techniques de reconnaissance d’objets existantes et de surpasser de nombreuse autres. Ces résultats ont également montré que notre méthode est robuste aux bruits. Enfin, nous avons employé la technique proposée pour reconnaître des navires dans un contexte de surveillance maritimeIn this thesis, we develop a supervised object recognition method using new global image descriptors inspired by the model of the human primary visual cortex V1. Mathematically speaking, the latter is modeled as the semi-discrete roto-translation group SE (2,N)=R² x ZN semi-direct product between R² and ZN. Therefore, our technique is based on generalized and rotational Fourier descriptors defined in SE (2,N) , and which are invariant to natural geometric transformations (translations, and rotations). Furthermore, we show that such Fourier descriptors are weakly complete, in the sense that they allow to distinguish over an open and dense set of compactly supported functions in L² (SE(2,N)) , hence between real-world images. These descriptors are later used in order to feed a Support Vector Machine (SVM) classifier for object recognition purposes. We have conducted a series of experiments aiming both at evaluating and comparing the performances of our method against existing both local - and global - descriptor based state of the art techniques, using the RL, the CVL, and the ORL face databases, and the COIL-100 image database (containing various types of objects). The obtained results have demonstrated that our approach was able to compete with many existing state of the art object recognition techniques, and to outperform many others. These results have also shown that our method is robust to noise. Finally, we have applied the proposed method on vessels recognition in the framework of maritime surveillance
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Capern, Simon. "Système visuel primaire et Modèles de perception du mouvement". Paris 6, 2008. http://www.theses.fr/2008PA066417.
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La reconnaissance de ces mécanismes préliminaires de perception du mouvement a fait l’objet de nombreux travaux, comme ceux, incontournables, d’Hubel et Wiesel en 1959, qui ont montré l’indiscutable importance de l’aire V1 dans la perception du mouvement. Dans le domaine connexe de la modélisation, des modèles simples, rendant néanmoins compte de beaucoup des aspects physiologiques, ont été proposés : le modèle simple de perception du mouvement par computation de gradients, le modèle de Reichardt, ou encore le modèle de « Motion Energy ». J’essayerai d’apporter un éclairage physiologique sur ces modèles et proposer des exemples d’applications. Mon travail a donc porté dans un premier temps sur la compréhension et la justification sur le plan physiologique de ces différents modèles. J’ai ensuite essayé d’expliquer certains enregistrements corticaux de V1 en imagerie optique portant sur l’activité des micro-colonnes d’orientation. Afin de rendre compte de l’activité de ces colonnes, j’ai utilisé un modèle de « Motion energy » basé sur des hypothèses simples de champs récepteur ou de distribution de fréquences et de phases préférées au sein de la population de la colonne
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Seriès, Peggy. "Étude théorique des modulations centre/pourtour des propriétés des champs récepteurs du cortex visuel primaire : circuits, dynamiques et corrélats perceptifs". Paris 6, 2002. http://www.theses.fr/2002PA066333.
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La réponse des neurones du cortex visuel primaire (V1) à un stimulus présenté dans le champ récepteur peut être modulée par la stimulation du pourtour du champ récepteur. L'origine et le rôle fonctionnel de ces modulations " centre/pourtour " restent peu compris. Par la modélisation, et en interaction avec des approches psychophysiques et physiologiques, nous cherchons à répondre à 2 questions : Quels sont les circuits responsables de la diversité de ces effets ? Nous fournissons des outils théoriques pour évaluer les modèles existants, les réconcilier au sein d'un même formalisme, et comprendre comment les diverses caractéristiques spatiales des modulations centre/ pourtour peuvent résulter des propriétés connues de V1. Quelles sont les conséquences des dynamiques de ces effets sur les réponses neuronales et sur la perception visuelle? Nos résultats suggèrent que les réponses de V1 et la perception des objets visuels dépendent non seulement du contexte spatial, mais aussi du contexte temporel dans lequel ces objets sont présentés. Nous discutons les implications fonctionnelles possibles de ce mécanisme pour l'analyse d'objets statiques ou en mouvementThe response of primary visual cortex (V1) neurons to a stimulus presented within the receptive field can be modulated by the stimulation of the surround of the receptive field. The origin and functional role of these " center/surround " modulations is yet poorly understood. Using computational methods in interaction with electrophysiological and psychophysical approaches, we try to answer 2 questions : What are the circuits responsible for the diversity of these phenomena ? We provide theoretical tools to evaluate current models, reconcile them in a common formalism and understand how the spatial characteristics of center/surround modulations can result from the known properties of V1 ; What are the consequences of the dynamics of these effects on cortical responses and visual perception ? Our results suggest that V1 responses and the perception of visual objects should depend not only on the spatial context, but also on the temporal context in which these objects are embedded. We discuss the functional implications of this mechanism for the analysis of static and moving objects
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Cavalcante, André Borges. "Campos receptivos similares às wavelets de Haar são gerados a partir da codificação eficiente de imagens urbanas;V1". Universidade Federal do Maranhão, 2008. http://tedebc.ufma.br:8080/jspui/handle/tede/314.
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Previous issue date: 2008-02-25Efficient coding of natural images yields filters similar to the Gabor-like receptive fields of simple cells of primary visual cortex. However, natural and man-made images have different statistical proprieties. Here we show that a simple theoretical analysis of power spectra in a sparse model suggests that natural and man-made images would need specific filters for each group. Indeed, when applying sparse coding to man-made scenes, we found both Gabor and Haar wavelet-like filters. Furthermore, we found that man-made images when projected on those filters yielded smaller mean squared error than when projected on Gabor-like filters only. Thus, as natural and man-made images require different filters to be efficiently represented, these results suggest that besides Gabor, the primary visual cortex should also have cells with Haar-like receptive fields.
A codificação eficiente de imagens naturais gera filtros similares às wavelets de Gabor que relembram os campos receptivos de células simples do córtex visual primário. No entanto, imagens naturais e urbanas tem características estatísticas diferentes. Será mostrado que uma simples análise do espectro de potência em um modelo eficiente sugere que imagens naturais e urbanas requerem filtros específicos para cada grupo. De fato, aplicando codificação eficiente à imagens urbanas, encontramos filtros similares às wavelets de Gabor e de Haar. Além disso, observou-se que imagens urbanas quando projetadas nesses filtros geraram um menor erro médio quadrático do que quando projetadas somente em filtros de similares a Gabor. Desta forma, como imagens naturais e urbanas requerem filtros diferentes para serem representadas de forma eficiente, estes resultados sugerem que além de Gabor, o córtex visual primário também deve possuir células com campos receptivos similares às wavelets de Haar.
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FONTENELE, NETO Antonio Jorge. "Implementação de um protocolo experimental para estudo de propriedades de resposta visual de neurônios do córtex visual primário (V1) em ratos utilizando matrizes de eletrodos". Universidade Federal de Pernambuco, 2015. https://repositorio.ufpe.br/handle/123456789/17698.
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Antonio Jorge Fontenele Neto.pdf: 9942923 bytes, checksum: 9de5bf466a9fc72acbc6a2a2d3a9c57c (MD5)Made available in DSpace on 2016-08-18T12:54:46Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Antonio Jorge Fontenele Neto.pdf: 9942923 bytes, checksum: 9de5bf466a9fc72acbc6a2a2d3a9c57c (MD5) Previous issue date: 2015-08-25
CAPEs
O córtex visual primário (V1) é a região do córtex cerebral responsável pela primeira etapa de processamento da informação visual capturada pela retina. Por ser uma das áreas corticais melhor compreendidas, V1 constitui um dos principais paradigmas de compreensão do processamento sensorial. Desde os anos 70 há uma extensa literatura que estuda propriedades de resposta de neurônios de V1, principalmente com eletrodos individuais e utilizando-se como modelo animal gatos e macacos. Tem-se conhecimento de onde partem seus principais inputs e quais estímulos fazem os neurônios dispararem (grades senoidais com determinadas frequências espaciais e temporais). Mais recentemente, com o uso de matrizes de eletrodos, se tornou possível a investigação de propriedades coletivas da atividade e codificação neurais, que não eram possíveis de serem desvendadas com eletrodos individuais. Além disso, no estado da arte tecnológico atual, o uso do rato como modelo animal permite o registro da atividade neural com os animais em comportamento livre (sem anestesia ou contenção). No entanto, pouco se sabe sobre especificidades das propriedades de resposta dos neurônios do córtex visual do rato. Este trabalho teve por objetivo desenvolver um aparato e um protocolo experimental no Laboratório de Neurociência de Sistemas e Computacional adequado para estudo das propriedades de resposta de neurônios de V1 de ratos usando matrizes de eletrodos. Finalmente, apresentamos resultados experimentais onde caracterizamos respostas de neurônios de V1 a diferentes estímulos visuais (Funções de Gabor ou Grades) seja em ruído denso ou rarefeito, variando as propriedades de frequências temporal e espacial de estimulação, densidades de estímulos, velocidade, etc. Concluímos que implementamos com sucesso a técnica experimental, que abre inúmeras perspectivas futuras de pesquisas nesta linha no Departamento de Física da Universidade Federal de Pernambuco.
The primary visual cortex (V1) is the cerebral cortex region responsible for the first processing step of the visual information captured by the retina. Being one of the most studied and well described cortical sensory areas, V1 is one of the main paradigms for the study of sensory processing. Since the 70s, there is a vast literature that studies properties of V1’s neurons, specially using single electrodes and using cats and monkeys as animal models. The anatomical conectivity of the visual pathway is known, from the retina to the lateral geniculate nucleus to V1, as well as the main visual stimulations that make V1 neurons fire (sinusoidal gratings with certain spatial and temporal frequencies). More recently, using multielectrode arrays, it became possible to study coletive properties of the activity and neural codification, that could not be unveiled with single electrodes. Furthermore with, the current state of the art in multielectrode recordings it is possible to record the neural activity in frelly behaving rats (without anesthesia or restraint). This represents an advantage in using the rat as animal model. However, little is known about specificities of the V1 neurons response properties in the rat. The aim of this work is to develop, in the Laboratório de Neurociência de Sistemas e Computacional, an apparatus and an experimental protocol suitable for the study of visual response properties of V1’s neurons in rats, using multielectrode array recordings. Finally, we present experimental results that characterize the response of V1’s neurons with different visual stimuli (Gabor or Grating Functions), either in dense os sparse noise modes, varying the spatial and temporal stimulation frequencies, stimulus density, speed, etc. We conclude that the experimental technique was implemented successfully. These results open important perspectives of future research on this field for the Departamento de Física at the Universidade Federal de Pernambuco.
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Durand, Jean-Baptiste. "Traitement cortical de l'espace visuel tridimentionnel dans l'aire visuelle primaire du singe vigile". Phd thesis, Université Paul Sabatier - Toulouse III, 2004. http://tel.archives-ouvertes.fr/tel-00125420.
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Dans la représentation centrale du champ visuel, la disparité rétinienne horizontale est impliquée directement dans la perception stéréoscopique. Son implication en vision périphérique est moins évidente tout comme celui de la disparité verticale dont le rôle fonctionnel reste controversé.Par des enregistrements extra-cellulaires réalisés chez le singe vigile, nous montrons que la disparité horizontale est codée de façon préférentielle dans la représentation fovéale du champ visuel du cortex visuel primaire (aire V1). En périphérie, les interactions fortes entre disparités horizontales et verticales et leur lien étroit avec la sélectivité à l'orientation (en accord avec le modèle d'énergie binoculaire) suggèrent leur implication dans la construction du percept stéréoscopique dans les zones excentrées du champ visuel. De plus les modulations de l'activité visuelle des neurones par la direction du regard que nous observons dans l'aire V1 également, nous permettent de conclure que le cortex visuel primaire participe aux mécanismes neuronaux de reconstruction de l'espace tridimensionnel.
Książki na temat "Primate V1"
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Buettner-Janusch, John. Evolutionary and Genetic Biology of Primates V1. Elsevier Science & Technology Books, 2012.
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Chirimuuta, Mazviita, i Ian Gold. The Embedded Neuron, the Enactive Field? Redaktor John Bickle. Oxford University Press, 2009. http://dx.doi.org/10.1093/oxfordhb/9780195304787.003.0010.
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This article examines the concept of the receptive field (RF) of visual neurons. It introduces the concept of visual RFs by discussing the classical picture of primary visual cortex (V1) physiology and discusses the psychophysics and computational vision of contrast discrimination to place the visual neurophysiology in context. It evaluates some recent data which questioned the classical conception of the RF and considers some options available for absorbing these data into visual theory.
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Gori, Simone. The Rotating Tilted Lines Illusion. Oxford University Press, 2017. http://dx.doi.org/10.1093/acprof:oso/9780199794607.003.0066.
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This chapter describes the Rotating-Tilted-Lines illusion , which is a new motion illusion that arises in a circular pattern composed by black, radial lines tilted to the right and presented on a white background. When one approaches the stimulus pattern, the radial lines appear to rotate in the counterclockwise direction, whereas when one recedes from it, they appear to rotate clockwise. It is the simplest pattern able to elicit illusory rotatory motion in presence of physical radial expansion. This surprising misperception of motion seems to be a result of the competition between two motion processing units in the primary visual cortex (V1, V5)
Części książek na temat "Primate V1"
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Angelucci, Alessandra, i Paul C. Bressloff. "Contribution of feedforward, lateral and feedback connections to the classical receptive field center and extra-classical receptive field surround of primate V1 neurons". W Visual Perception - Fundamentals of Vision: Low and Mid-Level Processes in Perception, 93–120. Elsevier, 2006. http://dx.doi.org/10.1016/s0079-6123(06)54005-1.
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Afef, Ouelhazi, Rudy Lussiez i Molotchnikoff Stephane. "Cortical Plasticity under Ketamine: From Synapse to Map". W Sensory Nervous System - Computational Neuroimaging Investigations of Topographical Organization in Human Sensory Cortex [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.104787.
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Sensory systems need to process signals in a highly dynamic way to efficiently respond to variations in the animal’s environment. For instance, several studies showed that the visual system is subject to neuroplasticity since the neurons’ firing changes according to stimulus properties. This dynamic information processing might be supported by a network reorganization. Since antidepressants influence neurotransmission, they can be used to explore synaptic plasticity sustaining cortical map reorganization. To this goal, we investigated in the primary visual cortex (V1 of mouse and cat), the impact of ketamine on neuroplasticity through changes in neuronal orientation selectivity and the functional connectivity between V1 cells, using cross correlation analyses. We found that ketamine affects cortical orientation selectivity and alters the functional connectivity within an assembly. These data clearly highlight the role of the antidepressant drugs in inducing or modeling short-term plasticity in V1 which suggests that cortical processing is optimized and adapted to the properties of the stimulus.
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Rodman, Hillary R. "Behavioral and neural alterations following V1 damage in immature primates". W Reprogramming the Cerebral Cortex, 91–114. Oxford University Press, 2006. http://dx.doi.org/10.1093/acprof:oso/9780198528999.003.0005.
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Assis, Ana Beatriz Carneiro de, Maria das Dores Viana Pinheiro, Charles Nonato da Cunha Santos, Márcia Naildes da Costa Lima do Carmo, Paulo Giovanni Lima Santiago, Juliana de Sousa Oliveira Ximenes Cruz, Mauricio Pereira da Luz i in. "Phytotherapy In Primary Health Care: An Integrative Literature Review". W Collection of International Topics in Health Science- V1. Seven Editora, 2023. http://dx.doi.org/10.56238/colleinternhealthscienv1-092.
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Objective: The present study aimed to analyze the use of phytotherapy and medicinal plants in Primary Health Care. Methodology: This is an exploratory and descriptive qualitative research carried out through an integrative literature review. The study used three databases, from 2017 to 2022, using 21 publications. Results and Discourse: Older articles were used due to the wealth of information. The use of medicinal plants results from a vast knowledge that for centuries have been used by different ethnic groups resulting in what we now know as traditional medicine, which was recognized by the World Health Organization. Final Considerations: It was possible to identify in the study that there is a great shortage in terms of studies and publications regarding phytotherapy, even though our country is the largest plant biodiversity in the world. With training, information and research incentives, Primary Health Care has great potential to change this reality.
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Pathan, Reshma, Rizwan Pathan i Ayisha Afreen. "Evaluating the Results of Endoscopic Dacryocystorhinostomy as Primary Treatment for Acute Dacryocystitis". W Current Overview on Disease and Health Research Vol. 1, 70–76. Book Publisher International (a part of SCIENCEDOMAIN International), 2022. http://dx.doi.org/10.9734/bpi/codhr/v1/16549d.
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Manov, Andre, Amanpreet Kaur i Ashan Hatharasinghe. "Primary Aldosteronism Due to a Sub Centimeter Unilateral Adrenal Adenoma: A Case Report". W New Frontiers in Medicine and Medical Research Vol. 1, 166–72. Book Publisher International (a part of SCIENCEDOMAIN International), 2021. http://dx.doi.org/10.9734/bpi/nfmmr/v1/2823f.
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Kawabe, Kazumi, Seigo Sasaki, Yuichiro Azuma, Hideya Ono, Tadatoshi Suruda i Yoshiaki Minakata. "A Case of Primary Racemose Hemangioma: An Approach towards Disappearance of Endobronchial Lesion". W New Horizons in Medicine and Medical Research Vol. 1, 29–34. Book Publisher International (a part of SCIENCEDOMAIN International), 2022. http://dx.doi.org/10.9734/bpi/nhmmr/v1/1946a.
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Gupta, Anshu. "Primary Ewing Sarcoma of Fronto-parietal Bone with Major Soft Tissue Extension: A Rare Case Presentation". W Current Overview on Disease and Health Research Vol. 1, 86–89. Book Publisher International (a part of SCIENCEDOMAIN International), 2022. http://dx.doi.org/10.9734/bpi/codhr/v1/2466a.
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Barakat, Amin J. "Clinical Presentation of Renal Disease in Children: The Role of the Pediatrician and Primary Care Physician". W Current Innovations in Medicine and Medical Science Vol. 1, 1–15. Book Publisher International (a part of SCIENCEDOMAIN International), 2022. http://dx.doi.org/10.9734/bpi/cimms/v1/2731a.
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Esmael, Amanne Feisal, Hanaa Abdel-Sadek Oraby i Soheir Mohamed El Nahas. "Study on Cytochrome P450 Family 1 B1 Gene Mutations in Primary Congenital Glaucoma Affected Egyptian Patients". W Highlights on Medicine and Medical Research Vol. 1, 62–75. Book Publisher International (a part of SCIENCEDOMAIN International), 2021. http://dx.doi.org/10.9734/bpi/hmmr/v1/2199e.
Pełny tekst źródłaStreszczenia konferencji na temat "Primate V1"
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Carman, George J. "The function of topography in the visual pathway". W OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/oam.1992.fo6.
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Such basic functions of vision as stereopsis and kineopsis can be accomplished through the use of topographic mappings of the visual field, such as those seen in the primate visual pathway. In binocular or motion parallax viewing, parallax cues to depth are contained in pairs of images that differ locally by a combination of translations, rotations, and dilations. These generalized disparities can be represented by a pair of scaler harmonic potentials defined on the visual field. These potentials are used to determine a flow of visual information that nulls these disparities so as to fuse the pair of images. The values of these potentials at each point of the visual field are computed through use of a Green’s function, which contains an explicit specification of a composition of conformal mappings of the visual field. These mappings may be interpreted as a sequence of topographic transformations of the visual field and are qualitatively similar to those seen in the lateral geniculate nucleus (LGN) and the primary and secondary cortical areas (V1 and V2) of the primate visual pathway.
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Sereno, Margaret E. "Neural network model of visual motion processing". W OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1989. http://dx.doi.org/10.1364/oam.1989.wj5.
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Extensions of a neural network model for human motion perception are described [Sereno, J. Opt. Soc. Am. A 3(13), p 72 (1986)]. The task is to calculate the true pattern velocity of a group of elements in a moving image from ambiguous local motion measurements–that is, to solve the aperture problem for motion. A parallel network is used with two layers of units patterned after the primate visual cortical areas V1 and MT. Units in the first layer extract components of motion perpendicular to the orientation of a moving edge using V1-like tuning curves. A second layer contains units tuned to different pattern velocities. The network learns to estimate patterned object velocity from image data by example. The fundamental computation performed by the model is a rapid disambiguation given simultaneous input information from adjacent portions of the velocity field. To evaluate the performance of the model, a weighted average of activity produced by units in the output layer determines values of speed and direction for individual translating patterns. When the model is tested with a set of patterns translating with different velocities, it produces results comparable to human performance.
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Dehsorkh, Sajjad Abdi, i Reshad Hosseini. "Predicting the neural response of primary visual cortex (v1) using deep learning approach". W 2023 28th International Computer Conference, Computer Society of Iran (CSICC). IEEE, 2023. http://dx.doi.org/10.1109/csicc58665.2023.10105321.
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Chatelard, Patrick, Joe¨lle Fleurot, Olivier Marchand i Patrick Drai. "Assessment of ICARE/CATHARE V1 Severe Accident Code". W 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/icone14-89307.
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The ICARE/CATHARE code system has been developed by the French “Institut de Radioprotection et de Suˆrete´ Nucle´aire” (IRSN) in the last decade for the detailed evaluation of Severe Accident (SA) consequences in a primary system. It is composed of the coupling of the core degradation IRSN code ICARE2 and of the thermalhydraulics French code CATHARE2. It has been extensively used to support the level 2 Probabilistic Safety Assessment (PSA-2) of the 900 MWe PWR. This paper presents the synthesis of the ICARE/CATHARE V1 assessment which was conducted in the frame of the “International ICARE/CATHARE Users’ Club”, under the management of IRSN. The ICARE/CATHARE V1 validation matrix is composed of more than 60 experiments, distributed in few thermal-hydraulics non-regression tests (to handle the front end phase of a severe accident), numerous Separate-Effect Tests, about 30 Integral Tests covering both the early and the late degradation phases, as well as a “circuit” experiment including hydraulics loops. Finally, the simulation of the TMI-2 accident was also added to assess the code against real conditions. This validation task was aimed at assessing the ICARE/CATHARE V1 capabilities (including the standalone ICARE2 V3mod1 version) and also at proposing recommendations for an optimal use of this version (“Users’ Guidelines”). Thus, with a correct account for the recommended guidelines, it appeared that the last ICARE/CATHARE V1 version could be reasonably used to perform best-estimate reactor studies up to a large corium slumping into the lower head.
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Songnian, Zhao, Zou Qi, Jin Zhen, Xiong Xiaoyun, Yao Guozheng, Yao Li i Liu Yijun. "A Computational Model that Realizes a Sparse Representation of the Primary Visual Cortex V1". W 2009 WRI World Congress on Software Engineering. IEEE, 2009. http://dx.doi.org/10.1109/wcse.2009.40.
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Moore, Michael J., Richard Linderman, Morgan Bishop i Robinson Pino. "A columnar primary visual cortex (V1) model emulation using a PS3 Cell-BE array". W 2010 International Joint Conference on Neural Networks (IJCNN). IEEE, 2010. http://dx.doi.org/10.1109/ijcnn.2010.5596903.
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Petzova, Jana, Marek Adamech i David Slnek. "Application of Small Punch Testing Methods for Thermal Ageing Assessment at Steam-Generators Materials From Decommissioned V1 NPP to LTO Support on VVER Type Units in Slovakia". W ASME 2022 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/pvp2022-83875.
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Abstract The main degradation mechanism of NPP’s components is radiation damage, but these processes are situated only in the core region of the reactor pressure vessel (RPV). The main mechanical loading of all individual parts of NPP’s primary circuit are the influence of high pressure at elevated temperature till 300°C. These processes lead to the fatigue damage of structural materials, which is characterized as the thermal fatigue or thermal ageing. The decommissioning of two V1 units in Slovakia provides a great opportunity to preserve materials from equipment that was in conditions of real operation for decades (app. 28–29 campaigns). VUJE, in cooperation with other partners, prepared necessary steps to create a material archive and related database including all relevant information from the decommissioned units of WWER-440 reactors. The main goal is to evaluate the real influence of long-term operation (LTO) on the degradation of NPP parts, such as steam-generators (SGs). The Small Punch Test (SPT) methods are mainly used for evaluation of materials actual state. By the SPT technique it is possible to evaluate the basic tensile properties as the ultimate tensile strength and the yield stress of the tested materials from a very small amount of obtained material. The paper deals with description of special sampling from steam generators of operating units in Slovakia and subsequent testing of samples taken by the SPT method. All these results were compared with reference testing on materials taken from decommissioned V1 NPP.
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Ward, Monica. "Using Irish NLP resources in Primary School Education". W Proceedings of the First Celtic Language Technology Workshop. Stroudsburg, PA, USA: Association for Computational Linguistics and Dublin City University, 2014. http://dx.doi.org/10.3115/v1/w14-4602.
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Matin, Leonard, i Wenxun Li. "Linear summation of visual influences on perceived eye level". W OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1989. http://dx.doi.org/10.1364/oam.1989.wcc4.
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A stationary pitched visual field generates deviations of the elevation of visually perceived eye level (VPEL) ≅ 0.6 × the pitch angle; deviations are as large if the field consists of a single line pitched from vertical in darkness as if the field is complexly structured. Horizontal lines have minimal influence.1 In psychophysical measurements with fields pitched between −30° and +20° we obtain linear summation of influences on VPEL from two pitched from vertical lines; summation is identical whether the lines are adjacent or separated by 60°. The following model relates known cortical neurophysiology to observer centered spatial localization and accounts for the results: Employing a spherical approximation to the eye in primary viewing position, the influence on VPEL derives from the location of the intersection point (IP) of the great circle (GC) containing the image of a straight line with the central vertical retinal meridian (CVRM). Summation of influences on VPEL occurs in V1 among neural units whose orientations serve a single retinal GC and across members of GCs with a commom IP on the CVRM. Pitching an erect frontoparallel plane by θ° shifts the IPs of the GCs containing the images of a set of vertical lines from the upper and lower poles by θ° on the CVRM, and leads to outputs from different neural processors uniquely related to visual pitch.
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Laarmann-Quante, Ronja, Lukas Knichel, Stefanie Dipper i Carina Betken. "Annotating Spelling Errors in German Texts Produced by Primary School Children". W Proceedings of the 10th Linguistic Annotation Workshop held in conjunction with ACL 2016 (LAW-X 2016). Stroudsburg, PA, USA: Association for Computational Linguistics, 2016. http://dx.doi.org/10.18653/v1/w16-1705.
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