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M. Arguin - One of the best experts on this subject based on the ideXlab platform.
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Semantic Proximity and Shape Feature Integration Effects in Visual Agnosia for Biological Kinds
Brain and Cognition, 1999Co-Authors: S. Lecours, M. Arguin, S. Caille, S. FontaineAbstract:Category specific Visual Agnosia (CSVA) for biological objects appears to be caused by a deficit in retrieving structural knowledge. We investigated the case of IL, a patient who suffers from CSVA, in order to examine the relationship between structural and semantic knowledge. Two experiments involving synthetic shapes, a Visual classification task and a picture‐word matching task, were conducted with IL and 5 neurologically intact subjects. Compared to normals, the patient’s results in the first task showed no perceptual categorization deficit, but in the second task they revealed interactive effects of Visual structure and of semantic category. The category specificity of CSVA is explained by the greater semantic proximity between Visually similar biological objects compared to artefacts. ≈ 1999 Academic Press
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the interaction of object form and object m eaning in the identification performance of a patient with category specific Visual Agnosia
Cognitive Neuropsychology, 1997Co-Authors: Mike J. Dixon, M. ArguinAbstract:Category-specific Visual Agnosia following bilateral inferior temporal lobe stroke was investigated in the patient ELM. Experiment 1 verified that computer-generated blobs could not be identified when members of a set varied along a single but not along multiple shape dimensions. Experiments 2 through 6 showed that for both ELM and, to a much lesser degree, healthy participants, this dimensionality effect was modulated by semantics. By pairing the exact same shapes with semantically close vs. disparate sounds or labels, the role of an object's semantics in category-specific Agnosia was assessed independently from object form. For single-dimension shape sets, the semantic proximity of the concepts associated with the shapes had no impact on ELM's identification performance. For multidimensional shape sets, ELM's error rates showed a strong positive correlation with semantic proximity (r= .84, P < .01). These results were interpreted using an exemplar model of categorisation in w hich a deficit in exemplar ...
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shape integration for Visual object recognition and its implication in category specific Visual Agnosia
Visual Cognition, 1996Co-Authors: M. ArguinAbstract:A series of experiments was conducted on a patient (ELM) with bilateral inferior temporal lobe damage and category-specific Visual Agnosia in order to specify the nature of his functional impairment. In Experiment 1, ELM performed a task of picture/word matching that used line drawings of fruits and vegetables as stimuli. The pattern of confusions exhibited by the patient suggested a failure in processing the full range of shape features necessary for the unique specification of the target relative to other structurally related items. This hypothesis of a shape integration impairment was tested and verified by subsequent Visual recognition experiments (Experiments 2-4), which used synthetic stimuli with shapes precisely defined on the dimensions of elongation, curvature, and tapering. Furthermore, it was determined (Experiment 5) that the integration deficit is specific to the retrieval of shape knowledge from memory and does not affect the encoding of the properties of Visual stimuli. It is argued that t...
Ria De Bleser - One of the best experts on this subject based on the ideXlab platform.
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Visual Agnosia a case of reduced attentional spotlight
Cortex, 1992Co-Authors: Josephine Semmes, Ria De BleserAbstract:Abstract A case study is presented of a patient with presenile dementia, for whom the dominant clinical feature from onset was a Visual Agnosia. The characteristics of the patient’s Visual Agnosia were investigated in light of her apparent use of a “feature-by-feature” strategy to identify objects. Results from various tasks showed that the patient was unable to use global shape information or other grossly defined property cues characteristic of a “wide angle” attentional processing stage (Treisman, 1988) in object recognition. The patient appeared instead to rely on ‘parts’ or identifying features of the objects for object recognition. The patient showed significant improvement when the size of the drawing was reduced in size, thus suggesting that the disorder may be functionally localized to a reduction of the patient’s attentional “spotlight”.
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Visual Agnosia: a case of reduced attentional "spotlight"?
Cortex, 1992Co-Authors: Josephine Semmes, Ria De BleserAbstract:Abstract A case study is presented of a patient with presenile dementia, for whom the dominant clinical feature from onset was a Visual Agnosia. The characteristics of the patient’s Visual Agnosia were investigated in light of her apparent use of a “feature-by-feature” strategy to identify objects. Results from various tasks showed that the patient was unable to use global shape information or other grossly defined property cues characteristic of a “wide angle” attentional processing stage (Treisman, 1988) in object recognition. The patient appeared instead to rely on ‘parts’ or identifying features of the objects for object recognition. The patient showed significant improvement when the size of the drawing was reduced in size, thus suggesting that the disorder may be functionally localized to a reduction of the patient’s attentional “spotlight”.
Marlene Behrmann - One of the best experts on this subject based on the ideXlab platform.
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altered large scale organization of shape processing in Visual Agnosia
Cortex, 2020Co-Authors: Erez Freud, Marlene BehrmannAbstract:Abstract Recent findings suggest that both dorsal and ventral Visual pathways process shape information. Nevertheless, a lesion to the ventral pathway alone can result in Visual Agnosia, an impairment in shape perception. Here, we explored the neural basis of shape processing in a patient with Visual Agnosia following a circumscribed right hemisphere ventral lesion and evaluated longitudinal changes in the neural profile of shape representations. The results revealed a reduction of shape sensitivity slopes along the patient's right ventral pathway and a similar reduction in the contralesional left ventral pathway. Remarkably, posterior parts of the dorsal pathway bilaterally also evinced a reduction in shape sensitivity. These findings were similar over a two-year interval, revealing that a focal cortical lesion can lead to persistent large-scale alterations of the two Visual pathways. These alterations are consistent with the view that a distributed network of regions contributes to shape perception.
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real world size coding of solid objects but not 2 d or 3 d images in Visual Agnosia patients with bilateral ventral lesions
Cortex, 2019Co-Authors: Desiree E Holler, Marlene Behrmann, Jacqueline C SnowAbstract:Abstract Patients with Visual Agnosia show severe deficits in recognizing two-dimensional (2-D) images of objects, despite the fact that early Visual processes such as figure-ground segmentation, and stereopsis, are largely intact. Strikingly, however, these patients can nevertheless show a preservation in their ability to recognize real-world objects –a phenomenon known as the ‘real-object advantage’ (ROA) in Agnosia. To uncover the mechanisms that support the ROA, patients were asked to identify objects whose size was congruent or incongruent with typical real-world size, presented in different display formats (real objects, 2-D and 3-D images). While recognition of images was extremely poor, real object recognition was surprisingly preserved, but only when physical size matched real-world size. Analogous display format and size manipulations did not influence the recognition of common geometric shapes that lacked real-world size associations. These neuropsychological data provide evidence for a surprising preservation of size-coding of real-world-sized tangible objects in patients for whom ventral contributions to image processing are severely disrupted. We propose that object size information is largely mediated by dorsal Visual cortex and that this information, together with detailed representation of object shape which is also subserved by dorsal cortex, serve as the basis of the ROA.
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differentiation of types of Visual Agnosia using eeg
Vision (Basel Switzerland), 2018Co-Authors: Sarah M Haigh, Amanda K Robinson, Pulkit Grover, Marlene BehrmannAbstract:Visual recognition deficits are the hallmark symptom of Visual Agnosia, a neuropsychological disorder typically associated with damage to the Visual system. Most research into Visual Agnosia focuses on characterizing the deficits through detailed behavioral testing, and structural and functional brain scans are used to determine the spatial extent of any cortical damage. Although the hierarchical nature of the Visual system leads to clear predictions about the temporal dynamics of cortical deficits, there has been little research on the use of neuroimaging methods with high temporal resolution to characterize the temporal profile of Agnosia deficits. Here, we employed high-density electroencephalography (EEG) to investigate alterations in the temporal dynamics of the Visual system in two individuals with Visual Agnosia. In the context of a steady state Visual evoked potential paradigm (SSVEP), individuals viewed pattern-reversing checkerboards of differing spatial frequency, and we assessed the responses of the Visual system in the frequency and temporal domain. JW, a patient with early Visual cortex damage, showed impaired SSVEP response relative to a control group and to the second patient (SM) who had right temporal lobe damage. JW also showed lower decoding accuracy for early Visual responses (around 100 ms). SM, whose lesion is more anterior in the Visual system, showed good decoding accuracy initially but low decoding after 500 ms. Overall, EEG and multivariate decoding methods can yield important insights into the temporal dynamics of Visual responses in individuals with Visual Agnosia.
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Behavioral Change and Its Neural Correlates in Visual Agnosia After Expertise Training
Journal of Cognitive Neuroscience, 2005Co-Authors: Marlene Behrmann, Jonathan Marotta, Isabel Gauthier, Michael J. Tarr, Thomas J. McKeeffAbstract:Agnosia, the impairment in object and face recognition despite intact vision and intelligence, is one of the most intriguing and debilitating neuropsychological deficits. The goal of this study was to determine whether S.M., an individual with longstanding Visual Agnosia and concomitant prosopAgnosia, can be retrained to perform Visual object recognition and, if so, what neural substrates mediate this reacquisition. Additionally, of interest is the extent to which training on one type of Visual stimulus generalizes to other Visual stimuli, as this informs our understanding of the organization of ventral Visual cortex. Greebles were chosen as the stimuli for retraining given that, in neurologically normal individuals, these stimuli can engage the fusiform face area. Posttraining, S.M. showed significant improvement in recognizing Greebles, although he did not attain normal levels of performance. He was also able to recognize untrained Greebles and showed improvement in recognizing common objects. Surprisingly, his performance on face recognition, albeit poor initially, was even more impaired following training. A comparison of preand postintervention functional neuroimaging data mirrored the behavioral findings: Face-selective voxels in the fusiform gyrus prior to training were no longer so and were, in fact, more Greeble-selective. The findings indicate potential for experience-dependent dynamic reorganization in Agnosia with the possibility that residual neural tissue, with limited capacity, will compete for representations.
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the role of color in object recognition evidence from Visual Agnosia
Neurocase, 1997Co-Authors: Daniela Mapelli, Marlene BehrmannAbstract:Abstract The extent to which the presence of color in a Visual display (perceptual or surface color) assists object recognition has been much debated. Whereas edge-based theories argue that perceptual color is not helpful, surface-based theories claim that color is a valuable and salient clue. Consistent with the edge-based account, we showed that surface color plays a minimal role in aiding object recognition in a brain-damaged patient with an object recognition deficit (Visual Agnosia) but normal color processing. We found, however, that under certain conditions, such as when shape is ambiguous, stored knowledge of color can help disambiguate the object. Based on these results, we argue that the contribution of perceptual color is small but that long-term color knowledge plays an important top-down role in object recognition.
Rose Bruffaerts - One of the best experts on this subject based on the ideXlab platform.
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pearls oy sters Visual Agnosia an overlooked cortical sign
Neurology, 2016Co-Authors: Bruno Bergmans, Olivier Deryck, Rose BruffaertsAbstract:We report a 77-year-old patient with Visual Agnosia as a cortical sign of neurodegenerative disease. The authors thank Patrick Santens for comments on this case and Jan Casselman and Frank De Geeter for providing the MRI and DaTscan images.
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Pearls & Oy-sters: Visual Agnosia: An overlooked cortical sign.
Neurology, 2016Co-Authors: Bruno Bergmans, Olivier Deryck, Rose BruffaertsAbstract:We report a 77-year-old patient with Visual Agnosia as a cortical sign of neurodegenerative disease. The authors thank Patrick Santens for comments on this case and Jan Casselman and Frank De Geeter for providing the MRI and DaTscan images.
Charles A Heywood - One of the best experts on this subject based on the ideXlab platform.
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A spurious category-specific Visual Agnosia for living things in normal human and nonhuman primates
J Cogn Neurosci, 1993Co-Authors: David Gaffan, Charles A HeywoodAbstract:Patients with Visual associative Agnosia have a particular difficulty in identifying Visually presented living things (LTs) as opposed to nonliving things (NLTs). It has been claimed that this effect cannot be explained by differences in the inherent Visual discriminability of LTs and NLTs. Two experiments with normal Ss tested this claim. In Exp 1, 5 observers (aged 23-45 yrs) identified objects in tachistoscopically presented line drawings (LNDs). Ss made more errors with LTs than with NLTs. In Exp 2, 6 monkeys learned to discriminate among the same LNDs for food reward. They made many more errors in discriminating among LTs than NLTs. Agnosic patients' responses to the same LNDs were correlated with normal Ss' responses in Exps 1 and 2. It is concluded that a category-specific Visual Agnosia for LTs can arise as a consequence of a modality-specific impairment in Visual representation. ((c) 1997 APA/PsycINFO, all rights reserved)
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A Spurious Category-Specific Visual Agnosia for Living Things in Normal Human and Nonhuman Primates
Journal of Cognitive Neuroscience, 1993Co-Authors: David Gaffan, Charles A HeywoodAbstract:Patients with Visual associative Agnosia have a particular difficulty in identifying Visually presented living things (plants and animals) as opposed to nonliving things. It has been claimed that this effect cannot be explained by differences in the inherent Visual discriminability of living and nonliving things. To test this claim further, we performed two experiments with normal subjects. In Experiment 1 normal human observers were asked to identify objects in tachistoscopically presented line drawings. They made more errors with living things than with nonliving things. In Experiment 2 normal monkeys learned to discriminate among the same line drawings for food reward. They made many more errors in discriminating among living things than nonliving things. Agnosic patients' responses to the same line drawings were made available to us for correlative analysis with the subjects' responses to these drawings in Experiments 1 and 2. We conclude that a category-specific Visual Agnosia for living things can arise as a consequence of a modality-specific but not category-specific impairment in Visual representation, since living things are more similar to each other Visually than nonliving things are.
