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Annals of Indian Academy of Neurology Oct 2022Cerebral visual disorders include a range of common and rare deficits. They can be divided into effects on low-, intermediate-, and high-level forms of visual...
Cerebral visual disorders include a range of common and rare deficits. They can be divided into effects on low-, intermediate-, and high-level forms of visual processing. Low-level deficits are various forms of homonymous hemifield scotomata, which affect all types of vision within their borders. Intermediate-level deficits refer to impairments of colour or motion perception, which affect either one hemifield or the entire field when lesions are bilateral. High-level deficits are divided into those of the ventral (occipitotemporal) or dorsal (occipitoparietal) stream. Occipitotemporal lesions affect various aspects of object recognition, ranging from general visual agnosia to selective agnosias, such as prosopagnosia or topographagnosia from right or bilateral lesions, and pure alexia from left-sided lesions. Occipitoparietal lesions cause the various components of Bálint syndrome, namely, simultanagnosia, optic ataxia, and ocular motor apraxia. They can also cause other impairments of visuospatial or visuotemporal processing, such as astereopsis and sequence-agnosia. Because of anatomic proximity, certain deficits cluster together to form a number of cerebral visual syndromes. Treatment of these disorders remains challenging, with frequent reliance on strategic substitutions rather than restorative approaches.
PubMed: 36589033
DOI: 10.4103/aian.aian_136_22 -
Handbook of Clinical Neurology 2021This chapter starts by reviewing the various interpretations of Bálint syndrome over time. We then develop a novel integrative view in which we propose that the various...
This chapter starts by reviewing the various interpretations of Bálint syndrome over time. We then develop a novel integrative view in which we propose that the various symptoms, historically reported and labeled by various authors, result from a core mislocalization deficit. This idea is in accordance with our previous proposal that the core deficit of Bálint syndrome is attentional (Pisella et al., 2009, 2013, 2017) since covert attention improves spatial resolution in visual periphery (Yeshurun and Carrasco, 1998); a deficit of covert attention would thus increase spatial uncertainty and thereby impair both visual object identification and visuomotor accuracy. In peripheral vision, we perceive the intrinsic characteristics of the perceptual elements surrounding us, but not their precise localization (Rosenholtz et al., 2012a,b), such that without covert attention we cannot organize them to their respective and recognizable objects; this explains why perceptual symptoms (simultanagnosia, neglect) could result from visual mislocalization. The visuomotor symptoms (optic ataxia) can be accounted for by both visual and proprioceptive mislocalizations in an oculocentric reference frame, leading to field and hand effects, respectively. This new pathophysiological account is presented along with a model of posterior parietal cortex organization in which the superior part is devoted to covert attention, while the right inferior part is involved in visual remapping. When the right inferior parietal cortex is damaged, additional representational mislocalizations across saccades worsen the clinical picture of peripheral mislocalizations due to an impairment of covert attention.
Topics: Apraxias; Attention; Cogan Syndrome; Humans; Parietal Lobe; Perceptual Disorders; Space Perception; Visual Perception
PubMed: 33832679
DOI: 10.1016/B978-0-12-821377-3.00011-8 -
Brain Imaging and Behavior Jun 2022Simultanagnosia is a common symptom of posterior cortical atrophy, and its association with brain structural and functional changes remains unclear. In our study, 18...
Simultanagnosia is a common symptom of posterior cortical atrophy, and its association with brain structural and functional changes remains unclear. In our study, 18 posterior cortical atrophy patients with simultanagnosia, 29 patients with Alzheimer's disease and 20 cognitively normal controls were recruited and subjected to full neuropsychological evaluation, including simultanagnosia tests, and structural and resting-state functional MRI. The gray matter volume was assessed by voxel-based morphometry, while the intrinsic functional connectivity was evaluated using the reduced gray matter volume regions of interest as the seed. In contrast to the patients with Alzheimer's disease, those with posterior cortical atrophy showed the following: (1) markedly lower simultanagnosia test scores, (2) an altered regional gray matter volume of the left middle occipital gyrus and ventral occipital areas, and (3) lowered intrinsic functional connectivity with the left middle occipital gyrus, left lingual gyrus and right middle occipital gyrus separately. Additionally, the gray matter volume of the left middle occipital gyrus and left inferior occipital gyrus were each correlated with simultanagnosia in posterior cortical atrophy patients. The intrinsic functional connectivity of the left middle occipital gyrus with the right superior occipital gyrus and that of the right middle occipital gyrus with the left superior parietal gyrus were also correlated with simultanagnosia in posterior cortical atrophy patients. In summary, this study indicated that simultanagnosia is associated with gray matter reductions and decreased functional connectivity in the left middle occipital gyrus and the left inferior occipital gyrus in patients with posterior cortical atrophy.
Topics: Alzheimer Disease; Atrophy; Brain; Brain Mapping; Gray Matter; Humans; Magnetic Resonance Imaging
PubMed: 34787788
DOI: 10.1007/s11682-021-00568-8 -
Handbook of Clinical Neurology 2021The term visual agnosia is used to refer to recognition disorders that are confined to the visual modality, that are not due to an impairment in sensory functions, and...
The term visual agnosia is used to refer to recognition disorders that are confined to the visual modality, that are not due to an impairment in sensory functions, and that cannot be explained by other cognitive deficits or by general reduction in intellectual ability. Here, we describe the different types of visual agnosia that have been reported (form agnosia, integrative agnosia, associative agnosia, transformational and orientation agnosia as well as category-specific impairments such as pure alexia and prosopagnosia) and how they relate to the current understanding of visual object recognition. Together with related disorders such as simultanagnosia, texture agnosia, aphantasia, and optic aphasia, these visual perceptual impairments can have severe consequences for those affected. We suggest how in-depth assessment can be carried out to determine the type and the extent of these impairments. In the context of clinical assessment, a step-by-step approach reflecting a posterior to anterior gradient in visual object recognition, from more perceptual to more memory-related processes, is suggested. Individually tailored interventions targeting the identified impairments can be initiated based on the results of the assessment.
Topics: Agnosia; Cognition Disorders; Humans; Neuropsychological Tests; Orientation; Visual Perception
PubMed: 33832675
DOI: 10.1016/B978-0-12-821377-3.00008-8 -
Archives of Clinical Neuropsychology :... May 2022Simultanagnosia is a rare neuropsychological symptom characterized by difficulty recognizing global structures while preserving perception of local detail. The condition...
OBJECTIVE
Simultanagnosia is a rare neuropsychological symptom characterized by difficulty recognizing global structures while preserving perception of local detail. The condition is classified into ventral and dorsal types. Clinical presentation of ventral simultanagnosia includes a reduced ability to recognize multiple visual stimuli rapidly, that is, part-by-part recognition. Here, we report a case of ventral simultanagnosia with a unique presentation; when short-duration visual stimuli were presented, the patient could perform global recognition by improving his part-by-part approach. To investigate the relationship between local and global perception bias and the duration of the present stimulus, we conducted a visual perception test using hierarchically organized Navon figures.
METHODS/RESULTS
The patient was a 62-year-old right-handed man who suffered from cerebral infarction in the right occipitotemporal lobe. He had no language dysfunction but exhibited left unilateral neglect, prosopagnosia, and ventral-type simultanagnosia. We conducted a visual perception test using the Navon figures and control figures as a visual stimulus. We randomly presented the figures for intervals of 0.2 or 20 s and let the patient report all the letters (global and/or local element) that he recognized. Global elements of the Navon letter were recognized a rate of 0% and 78.3% at intervals of 20 and 0.2 s, respectively, indicating that shorter presentation made the part-by-part approach less likely to manifest.
CONCLUSIONS
We assumed that the simultanagnosia in this case was caused by failure to maintain the initially perceived global information for a long period of time during visual presentation, due to right occipitotemporal damage.
Topics: Agnosia; Humans; Male; Middle Aged; Neuropsychological Tests; Recognition, Psychology
PubMed: 34664637
DOI: 10.1093/arclin/acab088 -
Proceedings (Baylor University. Medical... Jan 2020Simultanagnosia is a well-known neurologic symptom characterized by the inability to conceptualize the whole picture despite being able to see individual elements within...
Simultanagnosia is a well-known neurologic symptom characterized by the inability to conceptualize the whole picture despite being able to see individual elements within a visual scene. The pathophysiology involves a lesion to the bilateral parieto-occipital lobe. We report two unusual cases of simultanagnosia and juxtaposed homonymous visual field loss involving aqueductal stenosis-related obstructive hydrocephalus and cardiac arrest due to Brugada syndrome. Clinicians should be aware that simultanagnosia can be the presenting symptom of neuro-ophthalmic disease.
PubMed: 32063790
DOI: 10.1080/08998280.2019.1656013 -
NeuroImage Jul 2021Lesions to posterior temporo-parietal brain regions are associated with deficits in perception of global, hierarchical shapes, but also with impairments in the...
Lesions to posterior temporo-parietal brain regions are associated with deficits in perception of global, hierarchical shapes, but also with impairments in the processing of objects presented under demanding viewing conditions. Evidence from neuroimaging studies and lesion patterns observed in patients with simultanagnosia and agnosia for object orientation suggest similar brain regions to be involved in perception of global shapes and processing of objects in atypical ('non-canonical') orientation. In a localizer experiment, we identified individual temporo-parietal brain areas involved in global shape perception and found significantly higher BOLD signals during the processing of non-canonical compared to canonical objects. In a multivariate approach, we demonstrated that posterior temporo-parietal brain areas show distinct voxel patterns for non-canonical and canonical objects and that voxel patterns of global shapes are more similar to those of objects in non-canonical compared to canonical viewing conditions. These results suggest that temporo-parietal brain areas are not only involved in global shape perception but might serve a more general mechanism of complex object perception. Our results challenge a strict attribution of object processing to the ventral visual stream by suggesting specific dorsal contributions in more demanding viewing conditions.
Topics: Adult; Female; Humans; Magnetic Resonance Imaging; Male; Parietal Lobe; Photic Stimulation; Recognition, Psychology; Temporal Lobe; Visual Perception; Young Adult
PubMed: 33757908
DOI: 10.1016/j.neuroimage.2021.117982 -
Neuropsychologia Oct 2021Attentional resource and distribution are specifically impaired in simultanagnosia, and also in the visuo-attentional form of developmental dyslexia. Both clinical...
Attentional resource and distribution are specifically impaired in simultanagnosia, and also in the visuo-attentional form of developmental dyslexia. Both clinical conditions are conceived as a limitation of simultaneous visual processing after superior parietal lobule (SPL) dysfunction (review in Valdois et al., 2019). However, a reduced space-based attentional window (i.e. a limited visual eccentricity at which the target object can be identified, Khan et al. 2016) has been demonstrated in simultanagnosia versus a reduced object-based span (i.e. a limited number of objects processed at each fixation, Bosse et al., 2007) in developmental dyslexia. In healthy individuals, the cost in reaction times per item in serial search tasks suggests that a group of objects is processed simultaneously at a time, but this group is also undefined and depends on the visual complexity of the task. Healthy individuals and a patient with simultanagnosia performed serial search tasks involving either symbols (made of separable features) or objects made of non-separable features, and with distractors that were either all identical or all dissimilar. We used a moving window paradigm to determine whether the task was performed with a "working space" versus a "working span" limitation in control group and in patient with bilateral SPL damage. We found that healthy individuals performed search in a color task comprising non-separable feature objects and dissimilar distractors with a limited space-based attentional window; this attentional window, as well as the mean saccade amplitude used to displace it across the visual display, were independent of set size, thus inconsistent with an object-based attentional span. In the symbol task comprising a feature-absent search in which all feature-present distractors were dissimilar, we observed that mean saccade amplitude decreased with set size and that search performance could not be mimicked by a moving window of a single diameter; instead participants seemed to process a fixed number of symbols at a time (object-based span). Following bilateral SPL lesions, patient IG demonstrated a similar space-based search process in the color search task with a normal attentional window. In contrast, her cost-per-item in the symbol task increased dramatically, demonstrating a clear deficit of simultaneous object perception. These results confirmed the specific contribution of the SPL to the visual processing of multiple objects made of separable features (like letters), and more dramatically when they are all different, which explains the specific difficulty for a reading beginner in case of SPL dysfunction.
Topics: Cognition; Female; Humans; Parietal Lobe; Reaction Time; Saccades; Visual Perception
PubMed: 34474063
DOI: 10.1016/j.neuropsychologia.2021.108013 -
MedRxiv : the Preprint Server For... Nov 2023Posterior Cortical Atrophy (PCA) is a syndrome characterized by a progressive decline in higher-order visuospatial processing, leading to symptoms such as space...
INTRODUCTION
Posterior Cortical Atrophy (PCA) is a syndrome characterized by a progressive decline in higher-order visuospatial processing, leading to symptoms such as space perception deficit, simultanagnosia, and object perception impairment. While PCA is primarily known for its impact on visuospatial abilities, recent studies have documented language abnormalities in PCA patients. This study aims to delineate the nature and origin of language impairments in PCA, hypothesizing that language deficits reflect the visuospatial processing impairments of the disease.
METHODS
We compared the language samples of 25 patients with PCA with age-matched cognitively normal (CN) individuals across two distinct tasks: a visually-dependent picture description and a visually-independent job description task. We extracted word frequency, word utterance latency, and spatial relational words for this comparison. We then conducted an in-depth analysis of the language used in the picture description task to identify specific linguistic indicators that reflect the visuospatial processing deficits of PCA.
RESULTS
Patients with PCA showed significant language deficits in the visually-dependent task, characterized by higher word frequency, prolonged utterance latency, and fewer spatial relational words, but not in the visually-independent task. An in-depth analysis of the picture description task further showed that PCA patients struggled to identify certain visual elements as well as the overall theme of the picture. A predictive model based on these language features distinguished PCA patients from CN individuals with high classification accuracy.
DISCUSSION
The findings indicate that language is a sensitive behavioral construct to detect visuospatial processing abnormalities of PCA. These insights offer theoretical and clinical avenues for understanding and managing PCA, underscoring language as a crucial marker for the visuospatial deficits of this atypical variant of Alzheimer's disease.
PubMed: 38045263
DOI: 10.1101/2023.11.21.23298864