scholarly journals Assessing functional reorganization in visual cortex with simulated retinal lesions

2021 ◽  
Author(s):  
Holly D. H. Brown ◽  
André D. Gouws ◽  
Richard J. W. Vernon ◽  
Samuel J. D. Lawrence ◽  
Gemma Donnelly ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Visual Processing ◽  
Vision Loss ◽  
Visual Stimulation ◽  
Retinal Lesions ◽  
Central Vision Loss ◽  
Central Disk ◽  
Mean Luminance ◽  
Cortical Regions ◽  
The Impact

AbstractMacular degeneration (MD) causes central vision loss, removing input to corresponding representations in the primary visual cortex. There is disagreement concerning whether the cortical regions deprived of input can remain responsive, and the source of reported cortical responses is still debated. To simulate MD in controls, normally sighted participants viewed a bright central disk to adapt the retina, creating a transient ‘retinal lesion’ during a functional MRI experiment. Participants viewed blocks of faces, scrambled faces and uniform grey stimuli, either passively or whilst performing a one-back task. To assess the impact of the simulated lesion, participants repeated the paradigm using a more conventional mean luminance simulated scotoma without adaptation. Our results suggest our attempt to create a more realistic simulation of a lesion did not impact on responses in the representation of the simulated lesion. While most participants showed no evidence of stimulus-driven activation within the lesion representation, a few individuals (22%) exhibited responses similar to a participant with juvenile MD who completed the same paradigm (without adaptation). Reliability analysis showed that responses in the representation of the lesion were generally consistent irrespective of whether positive or negative. We provide some evidence that peripheral visual stimulation can also produce responses in central representations in controls while performing a task. This suggests that the ‘signature of reorganization of visual processing’, is not found solely in patients with retinal lesions, consistent with the idea that activity may be driven by unmasked top–down feedback.

scholarly journals Assessing functional reorganization in visual cortex with simulated retinal lesions

2021 ◽  
Author(s):  
Holly D. H. Brown ◽  
André D. Gouws ◽  
Richard J. W. Vernon ◽  
Samuel J. D. Lawrence ◽  
Gemma Donnelly ◽  
...  
Keyword(s):  
Visual Cortex ◽  
Visual Processing ◽  
Vision Loss ◽  
Visual Stimulation ◽  
Retinal Lesions ◽  
Central Vision Loss ◽  
Central Disk ◽  
Mean Luminance ◽  
Cortical Regions ◽  
The Impact

Abstract Macular degeneration (MD) causes central vision loss, removing input to corresponding representations in the primary visual cortex. There is disagreement concerning whether the cortical regions deprived of input can remain responsive, and the source of reported cortical responses is still debated. To simulate MD in controls, normally sighted participants viewed a bright central disk to adapt the retina, creating a transient ‘retinal lesion’ during a functional MRI experiment. Participants viewed blocks of faces, scrambled faces and uniform gray stimuli, either passively or whilst performing a one-back task. To assess the impact of the simulated lesion, participants repeated the paradigm using a more conventional mean luminance simulated scotoma without adaptation. Our results suggest our attempt to create a more realistic simulation of a lesion did not impact on responses in the representation of the simulated lesion. While most participants showed no evidence of stimulus-driven activation within the lesion representation, a few individuals (22%) exhibited responses similar to a participant with juvenile MD who completed the same paradigm (without adaptation). Reliability analysis showed that responses in the representation of the lesion were generally consistent irrespective of whether positive or negative. We provide some evidence that peripheral visual stimulation can also produce responses in central representations in controls while performing a task. This suggests that the ‘signature of reorganization of visual processing’, is not found solely in patients with retinal lesions, consistent with the idea that activity may be driven by unmasked top-down feedback.

scholarly journals Reduction of collinear inhibition in observers with central vision loss using anodal transcranial direct current stimulation: A case series

2020 ◽  
Author(s):  
Rajkumar Nallour Raveendran ◽  
Amy Chow ◽  
Katelyn Tsang ◽  
Arijit Chakraborty ◽  
Benjamin Thompson
Keyword(s):  
Visual Cortex ◽  
Visual Processing ◽  
Vision Loss ◽  
Peripheral Vision ◽  
Case Series ◽  
Cortical Inhibition ◽  
Peripheral Retina ◽  
Central Vision ◽  
Direct Stimulation ◽  
Central Vision Loss

AbstractPeople with central vision loss (CVL) due to macular degeneration are forced to rely on their residual peripheral vision and often develop a preferred retinal locus (PRL), a region of intact peripheral retina that is used for fixation. At the PRL, visual processing is impaired due to crowding (cluttering of visual objects). The problem of crowding still persists when images are magnified to account for the lower resolution of peripheral vision. We assessed whether anodal transcranial direct stimulation (a-tDCS), a neuro-modulation technique that alters cortical inhibition, would reduce collinear inhibition (an early component of crowding) when applied to the visual cortex in patients with CVL. Our results showed that applying a-tDCS to the visual cortex for 20mins reduced crowding in three patients with CVL and that the effect was sustained for up to 30mins. Sham stimulation delivered in a separate session had no effect. These initial observations mandate further research into the use of a-tDCS to enhance cortical processing of residual retinal input in patients with CVL.

scholarly journals Autophagy: A new insight into pathogenesis and treatment possibilities in age-related macular degeneration

2020 ◽  
Vol 74 ◽  
pp. 213-223
Author(s):  
Agnieszka Kubicka-Trząska ◽  
Izabella Karska-Basta ◽  
Katarzyna Żuber-Łaskawiec
Keyword(s):  
Macular Degeneration ◽  
Vision Loss ◽  
Developed Countries ◽  
Age Related Macular Degeneration ◽  
Therapeutic Modalities ◽  
Central Vision Loss ◽  
Age Related ◽  
Genetic And Environmental Factors ◽  
The Impact ◽  
Insight Into

Age-related macular degeneration (AMD) is a significant problem in healthcare, because it is a leading cause of central vision loss in individuals over 50 years old in well-developed countries. Pathogenesis of AMD is multifactorial and still not completely understood. Proven risk factors include the following: natural senescence of retina, oxidative stress, complement activation, chronic subretinal inflammatory reaction, genetic and environmental factors. Data on links between autophagy and AMD development are being raised. Autophagy is a cellular process involving the degradation of long-lived proteins and damaged fragments and components of cells; it is responsible for the maintenance of dynamic intracellular homeostasis and it enables cell survival under stress conditions. Disturbances of autophagy mechanisms, i.e. its activation or inhibition, may lead to the development of many various pathologies. Thus, autophagy plays a dual role, as a mechanism responsible for protecting or killing cells. The paper describes autophagy mechanisms and their role in the natural process of retinal cells senescence and presents the autophagy impairment as a crucial cause of AMD development. We also describe the impact of intravitreal anti-VEGF therapy on retinal autophagy mechanisms and potential new therapeutic modalities for AMD based on autophagy modulation.

scholarly journals Spatial specificity and inheritance of adaptation in human visual cortex

2015 ◽  
Vol 114 (2) ◽  
pp. 1211-1226 ◽  
Author(s):  
Jonas Larsson ◽  
Sarah J. Harrison
Keyword(s):  
Visual Cortex ◽  
Visual Processing ◽  
Visual Motion ◽  
Downstream Processing ◽  
Selective Adaptation ◽  
Motion Direction ◽  
Visual Areas ◽  
Spatial Specificity ◽  
Fmri Adaptation ◽  
The Impact

Adaptation at early stages of sensory processing can be propagated to downstream areas. Such inherited adaptation is a potential confound for functional magnetic resonance imaging (fMRI) techniques that use selectivity of adaptation to infer neuronal selectivity. However, the relative contributions of inherited and intrinsic adaptation at higher cortical stages, and the impact of inherited adaptation on downstream processing, remain unclear. Using fMRI, we investigated how adaptation to visual motion direction and orientation influences visually evoked responses in human V1 and extrastriate visual areas. To dissociate inherited from intrinsic adaptation, we quantified the spatial specificity of adaptation for each visual area as a measure of the receptive field sizes of the area where adaptation originated, predicting that adaptation originating in V1 should be more spatially specific than adaptation intrinsic to extrastriate visual cortex. In most extrastriate visual areas, the spatial specificity of adaptation did not differ from that in V1, suggesting that adaptation originated in V1. Only in one extrastriate area—MT—was the spatial specificity of direction-selective adaptation significantly broader than in V1, consistent with a combination of inherited V1 adaptation and intrinsic MT adaptation. Moreover, inherited adaptation effects could be both facilitatory and suppressive. These results suggest that adaptation at early visual processing stages can have widespread and profound effects on responses in extrastriate visual areas, placing important constraints on the use of fMRI adaptation techniques, while also demonstrating a general experimental strategy for systematically dissociating inherited from intrinsic adaptation by fMRI.

scholarly journals Relearning to See in Cortical Blindness

2015 ◽  
Vol 22 (2) ◽  
pp. 199-212 ◽  
Author(s):  
Michael D. Melnick ◽  
Duje Tadin ◽  
Krystel R. Huxlin
Keyword(s):  
Quality Of Life ◽  
Visual Cortex ◽  
Vision Loss ◽  
Relative Effectiveness ◽  
Neural Substrates ◽  
Cortical Blindness ◽  
Future Research ◽  
Recent Developments ◽  
The Impact

The incidence of cortically induced blindness is increasing as our population ages. The major cause of cortically induced blindness is stroke affecting the primary visual cortex. While the impact of this form of vision loss is devastating to quality of life, the development of principled, effective rehabilitation strategies for this condition lags far behind those used to treat motor stroke victims. Here we summarize recent developments in the still emerging field of visual restitution therapy, and compare the relative effectiveness of different approaches. We also draw insights into the properties of recovered vision, its limitations and likely neural substrates. We hope that these insights will guide future research and bring us closer to the goal of providing much-needed rehabilitation solutions for this patient population.

scholarly journals Impact of living with a bilateral central vision loss due to geographic atrophy—qualitative study

BMJ Open ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. e047861
Author(s):  
Gopinath Madheswaran ◽  
S Ve Ramesh ◽  
Shahina Pardhan ◽  
Raju Sapkota ◽  
Rajiv Raman
Keyword(s):  
Qualitative Study ◽  
Thematic Analysis ◽  
Vision Loss ◽  
Negative Impact ◽  
Geographic Atrophy ◽  
Age Related Macular Degeneration ◽  
Central Vision ◽  
Central Vision Loss ◽  
Age Related ◽  
The Impact

ObjectiveGeographic atrophy (GA), a type of dry age-related macular degeneration, affects vision as central vision loss (CVL). The challenges faced due to bilateral CVL in activities of daily living and strategies taken to overcome those challenges are not very well understood in the Indian population. This qualitative study aims to understand the impact on everyday life activities and related adaptive and coping strategies in people with long-standing bilateral CVL due to GA in India.Design, participants, setting and methodsA qualitative study using a semistructured face-to-face interview was conducted on 10 people with bilateral CVL after obtaining written informed consent. The interviews were audio-recorded, and were transcribed verbatim. Thematic analysis was carried out to understand the challenges faced and adaptive methods due to the impact of CVL.ResultsTen participants (50% male) with a median age (IQR) of 72 (70, 74) years were interviewed. All the participants had best-corrected visual acuity of ≤6/60 in the better eye and reported an absolute central scotoma with the home Amsler chart. Qualitative thematic analysis identified four main themes: challenges in everyday living (difficulty in face identification, reading), challenges with lifestyle and socialisation (driving, cooking, reading for a longer duration, watching TV, socially inactive), psychological implications (depression, poor self-esteem, fear due to poor vision) and strategies to overcome the challenges (voice identification, technology support).ConclusionGA has a severe negative impact on the quality of life in people with CVL. Inability to recognise faces was the main reason for dependency on others and being socially disconnected. The findings will help clinicians in providing improved rehabilitative care.

scholarly journals A Comparative Analysis of Visual Encoding Models Based on Classification and Segmentation Task-Driven CNNs

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Ziya Yu ◽  
Chi Zhang ◽  
Linyuan Wang ◽  
Li Tong ◽  
Bin Yan
Keyword(s):  
Comparative Analysis ◽  
Visual Processing ◽  
Visual Stimulation ◽  
Matching Pursuit ◽  
Linear Mapping ◽  
Human Information Processing ◽  
Model Based ◽  
Visual Encoding ◽  
Segmentation Task ◽  
The Impact

Nowadays, visual encoding models use convolution neural networks (CNNs) with outstanding performance in computer vision to simulate the process of human information processing. However, the prediction performances of encoding models will have differences based on different networks driven by different tasks. Here, the impact of network tasks on encoding models is studied. Using functional magnetic resonance imaging (fMRI) data, the features of natural visual stimulation are extracted using a segmentation network (FCN32s) and a classification network (VGG16) with different visual tasks but similar network structure. Then, using three sets of features, i.e., segmentation, classification, and fused features, the regularized orthogonal matching pursuit (ROMP) method is used to establish the linear mapping from features to voxel responses. The analysis results indicate that encoding models based on networks performing different tasks can effectively but differently predict stimulus-induced responses measured by fMRI. The prediction accuracy of the encoding model based on VGG is found to be significantly better than that of the model based on FCN in most voxels but similar to that of fused features. The comparative analysis demonstrates that the CNN performing the classification task is more similar to human visual processing than that performing the segmentation task.

scholarly journals Influence of Retinal Microsecond Pulse Laser Treatment in Central Serous Chorioretinopathy: A Short-Term Optical Coherence Tomography Angiography Study

2021 ◽  
Vol 10 (11) ◽  
pp. 2418
Author(s):  
Michelle Prasuhn ◽  
Yoko Miura ◽  
Aysegül Tura ◽  
Felix Rommel ◽  
Vinodh Kakkassery ◽  
...  
Keyword(s):  
Optical Coherence Tomography ◽  
Central Serous Chorioretinopathy ◽  
Vision Loss ◽  
Subretinal Fluid ◽  
Spot Size ◽  
Optical Coherence ◽  
Non Invasive ◽  
Central Vision Loss ◽  
The Impact ◽  
Fellow Eyes

Background: Central serous chorioretinopathy (CSC) is a common macular condition characterized by detachment of the neuroretina and is a frequent cause of central vision loss in adults. Among the various therapeutic strategies, subthreshold microsecond pulsed laser (SML) treatment has become a useful option. Despite the suggested involvement of choroidal circulatory disturbances in CSC, the effects of this treatment on macular microperfusion have not been fully evaluated yet. Herein, we report the impact of SML on retinal and choroidal microvascular flow using non-invasive optical coherence tomography (OCT) angiography (OCTA). Methods: In this study, CSC patients with persistent subretinal fluid (SRF) with or without secondary choroidal neovascularization (CNV) were included (referred to as the pachychoroid neovasculopathy (PNV) group and the CSC group, respectively). SML was conducted using a yellow (577 nm) laser with a duty cycle of 10%, spot size of 200 µm and duration of 200 ms. Best corrected visual acuity (BCVA) as well as OCT and OCTA images were evaluated at baseline and 4 weeks after SML. OCTA parameters of interest included full retinal perfusion (FRP), choriocapillaris perfusion (CCP), Sattler’s layer perfusion (SLP), and Haller’s layer perfusion (HLP), which were evaluated longitudinally and compared to unaffected fellow eyes. Results: 27 affected eyes and 17 fellow eyes from 27 patients were included. Before treatment, central retinal thickness (CRT) and subfoveal choroidal thickness (SFCT) of affected eyes were significantly larger than in fellow eyes. Four weeks after SML, CRT decreased significantly, whereas perfusion parameters did not change. In subgroup analyses, the CSC group showed a significant decrease in SFCT, whereas the PNV group did not despite the decrease in CRT. Conclusion: Our results suggest that the SML may affect the SFCT of the CSC, but not the PNV patients at least within four weeks following treatment. This effect seems to be independent of the change in choroidal perfusion measured with OCTA.

scholarly journals Effects of Transient Loss of Vision on Head and Eye Movements during Visual Search in a Virtual Environment

2020 ◽  
Vol 10 (11) ◽  
pp. 841
Author(s):  
Erwan David ◽  
Julia Beitner ◽  
Melissa Le-Hoa Võ
Keyword(s):  
Virtual Reality ◽  
Visual Search ◽  
Eye Movements ◽  
Vision Loss ◽  
Peripheral Vision ◽  
Visual Stimulation ◽  
Past Research ◽  
Head Movements ◽  
Field Of View ◽  
The Impact

Central and peripheral fields of view extract information of different quality and serve different roles during visual tasks. Past research has studied this dichotomy on-screen in conditions remote from natural situations where the scene would be omnidirectional and the entire field of view could be of use. In this study, we had participants looking for objects in simulated everyday rooms in virtual reality. By implementing a gaze-contingent protocol we masked central or peripheral vision (masks of 6 deg. of radius) during trials. We analyzed the impact of vision loss on visuo-motor variables related to fixation (duration) and saccades (amplitude and relative directions). An important novelty is that we segregated eye, head and the general gaze movements in our analyses. Additionally, we studied these measures after separating trials into two search phases (scanning and verification). Our results generally replicate past on-screen literature and teach about the role of eye and head movements. We showed that the scanning phase is dominated by short fixations and long saccades to explore, and the verification phase by long fixations and short saccades to analyze. One finding indicates that eye movements are strongly driven by visual stimulation, while head movements serve a higher behavioral goal of exploring omnidirectional scenes. Moreover, losing central vision has a smaller impact than reported on-screen, hinting at the importance of peripheral scene processing for visual search with an extended field of view. Our findings provide more information concerning how knowledge gathered on-screen may transfer to more natural conditions, and attest to the experimental usefulness of eye tracking in virtual reality.

scholarly journals Task context impacts visual object processing differentially across the cortex

2014 ◽  
Vol 111 (10) ◽  
pp. E962-E971 ◽  
Author(s):  
Assaf Harel ◽  
Dwight J. Kravitz ◽  
Chris I. Baker
Keyword(s):  
Visual Cortex ◽  
Visual Processing ◽  
Visual Representations ◽  
Visual Object ◽  
Object Identity ◽  
Top Down ◽  
Object Processing ◽  
Hierarchical Processing ◽  
Early Visual Cortex ◽  
The Impact

Perception reflects an integration of “bottom-up” (sensory-driven) and “top-down” (internally generated) signals. Although models of visual processing often emphasize the central role of feed-forward hierarchical processing, less is known about the impact of top-down signals on complex visual representations. Here, we investigated whether and how the observer’s goals modulate object processing across the cortex. We examined responses elicited by a diverse set of objects under six distinct tasks, focusing on either physical (e.g., color) or conceptual properties (e.g., man-made). Critically, the same stimuli were presented in all tasks, allowing us to investigate how task impacts the neural representations of identical visual input. We found that task has an extensive and differential impact on object processing across the cortex. First, we found task-dependent representations in the ventral temporal and prefrontal cortex. In particular, although object identity could be decoded from the multivoxel response within task, there was a significant reduction in decoding across tasks. In contrast, the early visual cortex evidenced equivalent decoding within and across tasks, indicating task-independent representations. Second, task information was pervasive and present from the earliest stages of object processing. However, although the responses of the ventral temporal, prefrontal, and parietal cortex enabled decoding of both the type of task (physical/conceptual) and the specific task (e.g., color), the early visual cortex was not sensitive to type of task and could only be used to decode individual physical tasks. Thus, object processing is highly influenced by the behavioral goal of the observer, highlighting how top-down signals constrain and inform the formation of visual representations.

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