scholarly journals Retinotopic organization of primary visual cortex in glaucoma: Comparing fMRI measurements of cortical function with visual field loss

2007 ◽  
Vol 26 (1) ◽  
pp. 38-56 ◽  
Author(s):  
Robert O. Duncan ◽  
Pamela A. Sample ◽  
Robert N. Weinreb ◽  
Christopher Bowd ◽  
Linda M. Zangwill
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Primary Visual Cortex ◽  
Visual Field Loss ◽  
Cortical Function ◽  
Retinotopic Organization

Retinotopic Organization of Primary Visual Cortex in Glaucoma: A Method for Comparing Cortical Function with Damage to the Optic Disk

2007 ◽  
Vol 48 (2) ◽  
pp. 733 ◽  
Author(s):  
Robert O. Duncan ◽  
Pamela A. Sample ◽  
Robert N. Weinreb ◽  
Christopher Bowd ◽  
Linda M. Zangwill
Keyword(s):  
Visual Cortex ◽  
Primary Visual Cortex ◽  
Optic Disk ◽  
Cortical Function ◽  
Retinotopic Organization

scholarly journals Cortical reorganization of the visual system in post-stroke hemianopia studied with fMRI

Stroke ◽  
2001 ◽  
Vol 32 (suppl_1) ◽  
pp. 334-334
Author(s):  
Gereon Nelles ◽  
Guido Widmann ◽  
Joachim Esser ◽  
Anette Meistrowitz ◽  
Johannes Weber ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Visual System ◽  
Primary Visual Cortex ◽  
Visual Stimuli ◽  
Checkerboard Pattern ◽  
Partial Recovery ◽  
Area 18 ◽  
Area 19 ◽  
Stimulation Of

102 Introduction: Restitution of unilateral visual field defects following occipital cortex lesions occurs rarely. Partial recovery, however, can be observed in patients with incomplete lesion of the visual cortex. Our objective was to study the neuroplastic changes in the visual system that underlie such recovery. Methods and Results: Six patients with a left PCA-territory cortical stroke and 6 healthy control subjects were studied during rest and during visual stimulation using a 1.5 T fMRI with a 40 mT gradient. Visual stimuli were projected with a laptop computer onto a 154 x 115 cm screen, placed 90 cm in front of the gantry. Subjects were asked to fixate a red point in the center of the screen during both conditions. During stimulation, a black-and-white checkerboard pattern reversal was presented in each hemifield. For each side, 120 volumes of 48 contiguous axial fMRI images were obtained during rest and during hemifield stimulation in alternating order (60 volumes for each condition). Significant differences of rCBF between stimulation and rest were assessed as group analyses using statistical parametric mapping (SPM 99; p<0.01, corrected for multiple comparison). In controls, strong increases of rCBF (Z=7.6) occurred in the contralateral primary visual cortex V1 (area 17) and in V3a (area 18) and V5 (area 19). No differences were found between the right and left side in controls. During stimulation of the unaffected (left) visual field in hemianopic patients, activation occurred in contralateral V1, but the strongest increases of rCBF (Z>10) were seen in contralateral V3a (area 18) and V5 (area 19). During stimulation of the hemianopic (right) visual field, no activation was found in the primary visual cortex of either hemisphere. The most significant activation (Z=9.2) was seen in the ipsilateral V3a and V5 areas, and contralateral (left) V3a. Conclusions: Partial recovery from hemianopia is associated with strong ipsilateral activation of the visual system. Processing of visual stimuli in the hemianopic side spares the primary visual cortex and may involve recruitment of neurons in ipsilateral (contralesional) areas V3a and V5.

scholarly journals Near-optimal combination of disparity across a log-polar scaled visual field

2019 ◽  
Author(s):  
Guido Maiello ◽  
Manuela Chessa ◽  
Peter J. Bex ◽  
Fabio Solari
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Visual System ◽  
Primary Visual Cortex ◽  
Depth Perception ◽  
Binocular Disparity ◽  
Spatial Scales ◽  
Visual Input ◽  
Depth Information ◽  
Central Vision

AbstractThe human visual system is foveated: we can see fine spatial details in central vision, whereas resolution is poor in our peripheral visual field, and this loss of resolution follows an approximately logarithmic decrease. Additionally, our brain organizes visual input in polar coordinates. Therefore, the image projection occurring between retina and primary visual cortex can be mathematically described by the log-polar transform. Here, we test and model how this space-variant visual processing affects how we process binocular disparity, a key component of human depth perception. We observe that the fovea preferentially processes disparities at fine spatial scales, whereas the visual periphery is tuned for coarse spatial scales, in line with the naturally occurring distributions of depths and disparities in the real-world. We further show that the visual field integrates disparity information across the visual field, in a near-optimal fashion. We develop a foveated, log-polar model that mimics the processing of depth information in primary visual cortex and that can process disparity directly in the cortical domain representation. This model takes real images as input and recreates the observed topography of disparity sensitivity in man. Our findings support the notion that our foveated, binocular visual system has been moulded by the statistics of our visual environment.Author summaryWe investigate how humans perceive depth from binocular disparity at different spatial scales and across different regions of the visual field. We show that small changes in disparity-defined depth are detected best in central vision, whereas peripheral vision best captures the coarser structure of the environment. We also demonstrate that depth information extracted from different regions of the visual field is combined into a unified depth percept. We then construct an image-computable model of disparity processing that takes into account how our brain organizes the visual input at our retinae. The model operates directly in cortical image space, and neatly accounts for human depth perception across the visual field.

scholarly journals A machine-learning algorithm correctly classifies cortical evoked potentials from both natural retinal stimulation and electrical stimulation of the optic nerve

2021 ◽  
Author(s):  
Vivien Gaillet ◽  
Elodie Geneviève Zollinger ◽  
Diego Ghezzi
Keyword(s):  
Electrical Stimulation ◽  
Visual Cortex ◽  
Optic Nerve ◽  
Visual Field ◽  
Primary Visual Cortex ◽  
Nerve Stimulation ◽  
Visual Stimulation ◽  
Cortical Activity ◽  
Artificial Vision ◽  
Optic Nerve Stimulation

AbstractObjectiveOptic nerve’s intraneural stimulation is an emerging neuroprosthetic approach to provide artificial vision to totally blind patients. An open question is the possibility to evoke individual non-overlapping phosphenes via selective intraneural optic nerve stimulation. To begin answering this question, first, we aim at showing in preclinical experiments with animals that each intraneural electrode could evoke a distinguishable activity pattern in the primary visual cortex.ApproachWe performed both patterned visual stimulation and patterned electrical stimulation in healthy rabbits while recording evoked cortical activity with an electrocorticogram array in the primary visual cortex. Electrical stimulation was delivered to the optic nerve with the intraneural array OpticSELINE. We used a support vector machine algorithm paired to a linear regression model to classify cortical responses originating from visual stimuli located in different portions of the visual field and electrical stimuli from the different electrodes of the OpticSELINE.Main resultsCortical activity induced by visual and electrical stimulation could be classified with nearly 100% accuracy relative to the specific location in the visual field or electrode in the array from which it originated. For visual stimulation, the accuracy increased with the separation of the stimuli and reached 100% for separation higher than 7 degrees. For electrical stimulation, at low current amplitudes, the accuracy increased with the distance between electrodes, while at higher current amplitudes, the accuracy was nearly 100% already for the shortest separation.SignificanceOptic nerve’s intraneural stimulation with the OpticSELINE induced discernible cortical activity patterns. These results represent a leap forward for intraneural optic nerve stimulation towards artificial vision.

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