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Serge O Dumoulin - One of the best experts on this subject based on the ideXlab platform.
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role of population Receptive Field Size in complex visual dysfunctions a posterior cortical atrophy model
JAMA Neurology, 2019Co-Authors: Pieter B De Best, Serge O Dumoulin, Noa Raz, Nitzan Guy, Tamir Benhur, Yoni Pertzov, Netta LevinAbstract:Importance The neuronal mechanism of visual agnosia and foveal crowding that underlies the behavioral symptoms of several classic neurodegenerative diseases, including impaired holistic perception, navigation, and reading, is still unclear. A better understanding of this mechanism is expected to lead to better treatment and rehabilitation. Objective To use state-of-the-art neuroimaging protocols to assess a hypothesis that abnormal population Receptive Fields (pRF) in the visual cortex underlie high-order visual impairments. Design, Setting, and Participants Between April 26 and November 21, 2016, patients and controls were recruited from the Hadassah-Hebrew University medical center in a cross-sectional manner. Six patients with posterior cortical atrophy (PCA) were approached and 1 was excluded because of an inability to perform the task. Participants underwent functional magnetic resonance imaging–based cortical visual Field mapping and pRF evaluation and performed a masked repetition priming task to evaluate visuospatial perception along the eccentricity axis. The association between pRF Sizes and behavioral impairments was assessed to evaluate the role of abnormal pRF Sizes in impaired visual perception. Posterior cortical atrophy is a visual variant of Alzheimer disease that is characterized by progressive visual agnosia despite almost 20/20 visual acuity. Patients with PCA are rare but invaluable for studying visual processing abnormalities following neurodegeneration, as atrophy begins in visual cortices but initially spares other brain regions involved in memory and verbal communication. Exposures Participants underwent a magnetic resonance imaging scan. Main Outcomes and Measures Population Receptive Field Sizes and their association with visual processing along the fovea-to-periphery gradient. Results Five patients with PCA (4 men [80%]; mean [SEM] age, 62.9 [3.5] years) were compared with 8 age-matched controls (1 man [25%]; mean [SEM] age, 63.7 [3.7] years) and demonstrated an atypical pRF mapping that varied along the eccentricity axis, which presented as abnormally small peripheral and large foveal pRFs Sizes. Abnormality was seen in V1 (peripheral, 4.4° and 5.5°; foveal, 5.5° and 4.5° in patients and controls, respectively;P Conclusions and Relevance High-order visuocognitive functions may depend on abnormalities in basic cortical characteristics. These results may fundamentally change approaches to rehabilitation in such conditions, emphasizing the potential of low-level visual interventions.
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radial asymmetries in population Receptive Field Size and cortical magnification factor in early visual cortex
NeuroImage, 2018Co-Authors: Maria De Fátima C. Silva, Jan W Brascamp, Miguel Castelobranco, Ben M Harvey, Sónia Ferreira, Serge O DumoulinAbstract:Abstract Human visual cortex does not represent the whole visual Field with the same detail. Changes in Receptive Field Size, population Receptive Field (pRF) Size and cortical magnification factor (CMF) with eccentricity are well established, and associated with changes in visual acuity with eccentricity. Visual acuity also changes across polar angle. However, it remains unclear how RF Size, pRF Size and CMF change across polar angle. Here, we examine differences in pRF Size and CMF across polar angle in V1, V2 and V3 using pRF modeling of human fMRI data. In these visual Field maps, we find smaller pRFs and larger CMFs in horizontal (left and right) than vertical (upper and lower) visual Field quadrants. Differences increase with eccentricity, approximately in proportion to average pRF Size and CMF. Similarly, we find larger CMFs in the lower than upper quadrant, and again differences increase with eccentricity. However, pRF Size differences between lower and upper quadrants change direction with eccentricity. Finally, we find slightly smaller pRFs in the left than right quadrants of V2 and V3, though this difference is very small, and we find no differences in V1 and no differences in CMF. Moreover, differences in pRF Size and CMF vary gradually with polar angle and are not limited to the meridians or visual Field map discontinuities. PRF Size and CMF differences do not consistently follow patterns of cortical curvature, despite the link between cortical curvature and polar angle in V1. Thus, the early human visual cortex has a radially asymmetric representation of the visual Field. These asymmetries may underlie consistent reports of asymmetries in perceptual abilities.
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the relationship between cortical magnification factor and population Receptive Field Size in human visual cortex constancies in cortical architecture
The Journal of Neuroscience, 2011Co-Authors: Ben M Harvey, Serge O DumoulinAbstract:Receptive Field (RF) Sizes and cortical magnification factor (CMF) are fundamental organization properties of the visual cortex. At increasing visual eccentricity, RF Sizes increase and CMF decreases. A relationship between RF Size and CMF suggests constancies in cortical architecture, as their product, the cortical representation of an RF (point image), may be constant. Previous animal neurophysiology studies of this question yield conflicting results. Here, we use fMRI to determine the relationship between the population RF (pRF) and CMF in humans. In average and individual data, the product of CMF and pRF Size, the population point image, is near constant, decreasing slightly with eccentricity in V1. Interhemisphere and subject variations in CMF, pRF Size, and V1 surface area are correlated, and the population point image varies less than these properties. These results suggest a V1 cortical processing architecture of approximately constant Size between humans. Up the visual hierarchy, to V2, V3, hV4, and LO1, the population point image decreases with eccentricity, and both the absolute values and rate of change increase. PRF Sizes increase between visual areas and with eccentricity, but when expressed in V1 cortical surface area (i.e., corticocortical pRFs), they are constant across eccentricity in V2/V3. Thus, V2/V3, and to some degree hV4, sample from a constant extent of V1. This may explain population point image changes in later areas. Consequently, the constant factor determining pRF Size may not be the relationship to the local CMF, but rather pRF Sizes and CMFs in visual areas from which the pRF samples.
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population Receptive Field estimates in human visual cortex
NeuroImage, 2008Co-Authors: Serge O Dumoulin, Brian A WandellAbstract:We introduce functional MRI methods for estimating the neuronal population Receptive Field (pRF). These methods build on conventional visual Field mapping that measures responses to ring and wedge patterns shown at a series of visual Field locations and estimates the single position in the visual Field that produces the largest response. The new method computes a model of the population Receptive Field from responses to a wide range of stimuli and estimates the visual Field map as well as other neuronal population properties, such as Receptive Field Size and laterality. The visual Field maps obtained with the pRF method are more accurate than those obtained using conventional visual Field mapping, and we trace with high precision the visual Field maps to the center of the foveal representation. We report quantitative estimates of pRF Size in medial, lateral and ventral occipital regions of human visual cortex. Also, we quantify the amount of input from ipsi- and contralateral visual Fields. The human pRF Size estimates in V1–V3 agree well with electrophysiological Receptive Field measurements at a range of eccentricities in corresponding locations within monkey and human visual Field maps. The pRF method is non-invasive and can be applied to a wide range of conditions when it is useful to link fMRI signals in the visual pathways to neuronal Receptive Fields.
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The fidelity of the cortical retinotopic map in human amblyopia.
The European journal of neuroscience, 2007Co-Authors: Serge O Dumoulin, Behzad Mansouri, Robert F. HessAbstract:To delineate the fidelity of the functional cortical organization in humans with amblyopia, we undertook an investigation into how spatial information is mapped across the visual cortex in amblyopic observers. We assessed whether the boundaries of the visual areas controlled by the amblyopic and fellow fixing eye are in the same position, the fidelity of the retinotopic map within different cortical areas and the average Receptive Field Size in different visual areas. The functional organization of the visual cortex was reconstructed using a fMRI phase-encoded retinotopic mapping analysis. This method sequentially stimulates each point in the visual Field along the axes of a polar-coordinate system, thereby reconstructing the representation of the visual Field on the cortex. We found that the cortical areas were very similar in normals and amblyopes, with only small differences in boundary positions of different visual areas between fixing and fellow amblyopic eye activation. Within these corresponding visual areas, we did find anomalies in retinotopy in some but not all amblyopes that were not simply a consequence of the poorer functional responses and affected central and peripheral Field regions. Only a small increase in the average (or collective) Receptive Field Size was found for full-Field representation in amblyopes and none at all for central Field representation. The former may simply be a consequence of the poorer functional responses.
Ben M Harvey - One of the best experts on this subject based on the ideXlab platform.
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radial asymmetries in population Receptive Field Size and cortical magnification factor in early visual cortex
NeuroImage, 2018Co-Authors: Maria De Fátima C. Silva, Jan W Brascamp, Miguel Castelobranco, Ben M Harvey, Sónia Ferreira, Serge O DumoulinAbstract:Abstract Human visual cortex does not represent the whole visual Field with the same detail. Changes in Receptive Field Size, population Receptive Field (pRF) Size and cortical magnification factor (CMF) with eccentricity are well established, and associated with changes in visual acuity with eccentricity. Visual acuity also changes across polar angle. However, it remains unclear how RF Size, pRF Size and CMF change across polar angle. Here, we examine differences in pRF Size and CMF across polar angle in V1, V2 and V3 using pRF modeling of human fMRI data. In these visual Field maps, we find smaller pRFs and larger CMFs in horizontal (left and right) than vertical (upper and lower) visual Field quadrants. Differences increase with eccentricity, approximately in proportion to average pRF Size and CMF. Similarly, we find larger CMFs in the lower than upper quadrant, and again differences increase with eccentricity. However, pRF Size differences between lower and upper quadrants change direction with eccentricity. Finally, we find slightly smaller pRFs in the left than right quadrants of V2 and V3, though this difference is very small, and we find no differences in V1 and no differences in CMF. Moreover, differences in pRF Size and CMF vary gradually with polar angle and are not limited to the meridians or visual Field map discontinuities. PRF Size and CMF differences do not consistently follow patterns of cortical curvature, despite the link between cortical curvature and polar angle in V1. Thus, the early human visual cortex has a radially asymmetric representation of the visual Field. These asymmetries may underlie consistent reports of asymmetries in perceptual abilities.
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the relationship between cortical magnification factor and population Receptive Field Size in human visual cortex constancies in cortical architecture
The Journal of Neuroscience, 2011Co-Authors: Ben M Harvey, Serge O DumoulinAbstract:Receptive Field (RF) Sizes and cortical magnification factor (CMF) are fundamental organization properties of the visual cortex. At increasing visual eccentricity, RF Sizes increase and CMF decreases. A relationship between RF Size and CMF suggests constancies in cortical architecture, as their product, the cortical representation of an RF (point image), may be constant. Previous animal neurophysiology studies of this question yield conflicting results. Here, we use fMRI to determine the relationship between the population RF (pRF) and CMF in humans. In average and individual data, the product of CMF and pRF Size, the population point image, is near constant, decreasing slightly with eccentricity in V1. Interhemisphere and subject variations in CMF, pRF Size, and V1 surface area are correlated, and the population point image varies less than these properties. These results suggest a V1 cortical processing architecture of approximately constant Size between humans. Up the visual hierarchy, to V2, V3, hV4, and LO1, the population point image decreases with eccentricity, and both the absolute values and rate of change increase. PRF Sizes increase between visual areas and with eccentricity, but when expressed in V1 cortical surface area (i.e., corticocortical pRFs), they are constant across eccentricity in V2/V3. Thus, V2/V3, and to some degree hV4, sample from a constant extent of V1. This may explain population point image changes in later areas. Consequently, the constant factor determining pRF Size may not be the relationship to the local CMF, but rather pRF Sizes and CMFs in visual areas from which the pRF samples.
Jose M Alonso - One of the best experts on this subject based on the ideXlab platform.
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population Receptive Fields of on and off thalamic inputs to an orientation column in visual cortex
Nature Neuroscience, 2011Co-Authors: Jianzhong Jin, Harvey A Swadlow, Yushi Wang, Jose M AlonsoAbstract:The primary visual cortex of primates and carnivores is organized into columns of neurons with similar preferences for stimulus orientation, but the developmental origin and function of this organization are still matters of debate. We found that the orientation preference of a cortical column is closely related to the population Receptive Field of its ON and OFF thalamic inputs. The Receptive Field scatter from the thalamic inputs was more limited than previously thought and matched the average Receptive Field Size of neurons at the input layers of cortex. Moreover, the thalamic population Receptive Field (calculated as ON - OFF average) had separate ON and OFF subregions, similar to cortical neurons in layer 4, and provided an accurate prediction of the preferred orientation of the column. These results support developmental models of orientation maps that are based on the Receptive Field arrangement of ON and OFF visual inputs to cortex.
Wenjie Luo - One of the best experts on this subject based on the ideXlab platform.
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understanding the effective Receptive Field in deep convolutional neural networks
Neural Information Processing Systems, 2016Co-Authors: Wenjie Luo, Raquel Urtasun, Richard S ZemelAbstract:We study characteristics of Receptive Fields of units in deep convolutional networks. The Receptive Field Size is a crucial issue in many visual tasks, as the output must respond to large enough areas in the image to capture information about large objects. We introduce the notion of an effective Receptive Field Size, and show that it both has a Gaussian distribution and only occupies a fraction of the full theoretical Receptive Field Size. We analyze the effective Receptive Field in several architecture designs, and the effect of sub-sampling, skip connections, dropout and nonlinear activations on it. This leads to suggestions for ways to address its tendency to be too small.
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Understanding the effective Receptive Field in deep convolutional neural networks
Advances in Neural Information Processing Systems, 2016Co-Authors: Wenjie Luo, Yujia Li, Raquel Urtasun, Richard ZemelAbstract:We study characteristics of Receptive Fields of units in deep convolutional networks. The Receptive Field Size is a crucial issue in many visual tasks, as the output must respond to large enough areas in the image to capture information about large objects. We introduce the notion of an effective Receptive Field, and show that it both has a Gaussian distribution and only occupies a fraction of the full theoretical Receptive Field. We analyze the effective Receptive Field in several architecture designs, and the effect of nonlinear activations, dropout, sub-sampling and skip connections on it. This leads to suggestions for ways to address its tendency to be too small.
Charles D Gilbert - One of the best experts on this subject based on the ideXlab platform.
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rapid axonal sprouting and pruning accompany functional reorganization in primary visual cortex
Neuron, 2009Co-Authors: Homare Yamahachi, Sally A Marik, Justin N J Mcmanus, Winfried Denk, Charles D GilbertAbstract:Summary The functional architecture of adult cerebral cortex retains a capacity for experience-dependent change. This is seen following focal binocular lesions, which induce rapid changes in Receptive Field Size and position. To follow the dynamics of the circuitry underlying these changes, we imaged the intrinsic long-range horizontal connections within the lesion projection zone (LPZ) in adult macaque primary visual cortex. To image the same axons over time, we combined viral vector-mediated EGFP transfer and two-photon microscopy. The lesion triggered, within the first week, an ∼2-fold outgrowth of axons toward the center of the LPZ. Over the subsequent month, axonal density declined due to a parallel process of pruning and sprouting but maintained a net increase relative to prelesion levels. The rate of turnover of axonal boutons also increased. The axonal restructuring recapitulates the pattern of exuberance and pruning seen in early development and correlates well with the functional changes following retinal lesions.
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Receptive Field dynamics in adult primary visual cortex
Nature, 1992Co-Authors: Charles D Gilbert, Torsten N WieselAbstract:THE adult brain has a remarkable ability to adjust to changes in sensory input. Removal of afferent input to the somatosensory, auditory, motor or visual cortex results in a marked change of cortical topography1–10. Changes in sensory activity can, over a period of months, alter Receptive Field Size and cortical topography11. Here we remove visual input by focal binocular retinal lesions and record from the same cortical sites before and within minutes after making the lesion and find immediate striking increases in Receptive Field Size for cortical cells with Receptive Fields near the edge of the retinal scotoma. After a few months even the cortical areas that were initially silenced by the lesion recover visual activity, representing retinotopic loci surrounding the lesion. At the level of the lateral geniculate nucleus, which provides the visual input to the striate cortex, a large silent region remains. Furthermore, anatomical studies show that the spread of geniculocortical afferents is insufficient to account for the cortical recovery. The results indicate that the topographic reorganization within the cortex was largely due to synaptic changes intrinsic to the cortex, perhaps through the plexus of long-range horizontal connections.
