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\"Visual agnosia is a rare but fascinating disorder of visual object recognition that can occur after a brain lesion. This book documents the case of John, who worked intensively with the authors for 26 years after acquiring visual agnosia following a stroke. It revisits John's case over twenty years after it was originally described in the book To See But Not To See, in 1987. As in the previous book, the condition is illuminated by John and his wife, Iris, in their own words. A Case Study in Visual Agnosia Revisited discusses John's case in the context of research into the cognitive neuroscience of vision over the past twenty years. It shows how John's problems in recognition can provide important insights into the way that object recognition happens in the brain, with the results obtained in studies of John's perception being compared to emerging work from brain imaging in normal observers. This book presents a much fuller analysis of the variety of perceptual problems that John experienced, detailing not only his impaired object recognition but also his face processing, his processing of different visual features (colour, motion, depth), his ability to act on and negotiate his environment, and his reading and writing. A Case Study in Visual Agnosia Revisited will be a key reference for those concerned with understanding how vision is implemented in the brain. It will be suitable for both undergraduate students taking courses in cognitive psychology and neuropsychology, and also researchers in the cognitive neuroscience of vision. The presentation of John's case, and the human aspects of the disorder, will also be of great interest to a general audience of lay people interested in perception\"-- Provided by publisher.

Examining post-acute care for vision rehabilitation following brain injury, this multidisciplinary book combines theory and practice, presenting clinical information and scientific literature to support the diagnostic and therapeutic strategies discussed.

The inferior longitudinal fasciculus (ILF) is a long-range, associative white matter pathway that connects the occipital and temporal-occipital areas of the brain to the anterior temporal areas. In view of the ILF's anatomic connections, it has been suggested that this pathway has a major role in a relatively large array of brain functions. Until recently, however, the literature data on these potential functions were scarce. Here, we review the key findings of recent anatomic, neuromodulation, and neuropsychological studies. We also summarize reports on how this tract is disrupted in a wide range of brain disorders, including psychopathologic, neurodevelopmental, and neurologic diseases. Our review reveals that the ILF is a multilayered, bidirectional tract involved in processing and modulating visual cues and thus in visually guided decisions and behaviors. Accordingly, sudden disruption of the ILF by neurologic insult is mainly associated with neuropsychological impairments of visual cognition (e.g., visual agnosia, prosopagnosia, and alexia). Furthermore, disruption of the ILF may constitute the pathophysiologic basis for visual hallucinations and socio-emotional impairments in schizophrenia, as well as emotional difficulties in autism spectrum disorder. Degeneration of the ILF in neurodegenerative diseases affecting the temporal lobe may explain (at least in part) the gradual onset of semantic and lexical access difficulties. Although some of the functions mediated by the ILF appear to be relatively lateralized, observations from neurosurgery suggest that disruption of the tract's anterior portion can be dynamically compensated for by the contralateral portion. This might explain why bilateral disruption of the ILF in either acute or progressive disease is highly detrimental in neuropsychological terms.

The Visual Brain and Peripheral Reading and Writing Disorders: A Guide to Visual System Dysfunction for Speech-Language Pathologists familiarizes the reader with the complex workings of the human visual system, the motor and sensory components of normal vision as they relate to the recognition of letters and words.

Optic Aphasia (OA) and Associative Visual Agnosia (AVA) are neuropsychological disorders characterized by impaired naming on visual presentation. From a cognitive point of view, while stimulus identification is largely unimpaired in OA (where access to semantic knowledge is still possible), in AVA it is not. OA has been linked with right hemianopia and disconnection of the occipital right-hemisphere (RH) visual processing from the left hemisphere (LH) language areas. In this paper, we describe the case of AA, an 81-year-old housewife suffering from a deficit in naming visually presented stimuli after left occipital lesion and damage to the interhemispheric splenial pathway. AA has been tested through a set of tasks assessing different levels of visual object processing. We discuss behavioral performance as well as the pattern of lesion and disconnection in relation to a neurocognitive model adapted from Luzzatti and colleagues ( 1998 ). Despite the complexity of the neuropsychological picture, behavioral data suggest that semantic access from visual input is possible, while a lesion-based structural disconnectome investigation demonstrated the splenial involvement. Altogether, neuropsychological and neuroanatomical findings support the assumption of visuo-verbal callosal disconnection compatible with a diagnosis of OA.

Visual anosognosia, associated with confabulations and cortical blindness in the context of occipital lobe injury, is known as Anton syndrome. Patients with this syndrome strongly deny their vision loss and confabulate to compensate for both visual loss and memory impairments. In this article, we present a case of a patient with some similarities to Anton syndrome, however, with several differences in clinical presentation. Bifrontal brain injury, bilateral enucleation, affective indifference (anosodiaphoria), generalized anosognosia, and the conviction that vision will resume mark clear clinical differences with Anton syndrome. Differentiating these findings from Anton syndrome will help occupational therapists, neuropsychologists, speech-language pathologists, physical therapists, and physicians when assessing frontal lobe brain injury with total and partial visual loss. This case demonstrates that visual anosognosia and confabulations can occur without occipital lobe dysfunction or cortical blindness.

Purpose of ReviewHistorical and contemporary treatments of visual agnosia and neglect regard these disorders as largely unrelated. It is thought that damage to different neural processes leads directly to one or the other condition, yet apperceptive variants of agnosia and object-centered variants of neglect share remarkably similar deficits in the quality of conscious experience. Here we argue for a closer association between “apperceptive” variants of visual agnosia and “object-centered” variants of visual neglect. We introduce a theoretical framework for understanding these conditions based on “scale attention”, which refers to selecting boundary and surface information at different levels of the structural hierarchy in the visual array.Recent FindingsWe review work on visual agnosia, the cortical structures and cortico-cortical pathways that underlie visual perception, visuospatial neglect and object-centered neglect, and attention to scale. We highlight direct and indirect pathways involved in these disorders and in attention to scale. The direct pathway involves the posterior vertical segments of the superior longitudinal fasciculus that are positioned to link the established dorsal and ventral attentional centers in the parietal cortex with structures in the inferior occipitotemporal cortex associated with visual apperceptive agnosia. The connections in the right hemisphere appear to be more important for visual conscious experience, whereas those in the left hemisphere appear to be more strongly associated with the planning and execution of visually guided grasps directed at multi-part objects such as tools. In the latter case, semantic and functional information must drive the selection of the appropriate hand posture and grasp points on the object. This view is supported by studies of grasping in patients with agnosia and in patients with neglect that show that the selection of grasp points when picking up a tool involves both scale attention and semantic contributions from inferotemporal cortex. The indirect pathways, which include the inferior fronto-occipital and horizontal components of the superior longitudinal fasciculi, involve the frontal lobe, working memory and the “multiple demands” network, which can shape the content of visual awareness through the maintenance of goal- and task-based abstractions and their influence on scale attention.SummaryRecent studies of human cortico-cortical pathways necessitate revisions to long-standing theoretical views on visual perception, visually guided action and their integrations. We highlight findings from a broad sample of seemingly disparate areas of research to support the proposal that attention to scale is necessary for typical conscious visual experience and for goal-directed actions that depend on functional and semantic information. Furthermore, we suggest that vertical pathways between the parietal and occipitotemporal cortex, along with indirect pathways that involve the premotor and prefrontal cortex, facilitate the operations of scale attention.

The concept of functional modularity in human visual processing was proposed 25 years ago with the distinction between a ventral pathway for object recognition and a dorsal pathway for action processing. Lesions along these pathways yield selective deficits. A 15-year-old patient (MW) presented with a seizure due to a lesion in the left occipitotemporal cortex. Surgical resection of the lesion was performed with sparing of the classic language areas and visual fields. Postoperatively MW had great difficulty reading and had a specific agnosia for more complex visual stimuli in the right hemifield. No deficit was seen for lower level visual discrimination tasks. Gradual improvement of hemi-agnosia was paralleled by slower reaction times reflecting a speed–accuracy trade-off. Absolute reading speed improved markedly over time, doubling at 6 weeks. MW fully recovered after 18 months. Postoperative functional Magnetic Resonance Imaging (fMRI) illustrated an overlap of the lesion with object and word processing areas. Diffusion Tensor Imaging showed damage to the white matter tracts [inferior fronto-occipital fasciculus and inferior longitudinal fasciculus (ILF)] interconnecting ventral temporal areas. A transient higher order deficit can result from a disruption of the neural network supporting visual word and object processing. Most visual system research has focused on cortical areas, while the underlying subcortical network received much less attention. We believe that white matter tracts, in particular the ILF, play a critical role in object perception by connecting visual areas along the ventral visual stream. Lesions of the ILF should be taken into consideration in agnosia.

Optic ataxia and visual agnosia have been proposed to constitute a double dissociation which provides the main argument for the assimilation of the anatomical distinction between a dorsal and a ventral visual stream to the functional distinction between perception and action. In the present review, we argue that insufficient evidence has been collected to argue for this double dissociation. Several criteria are reviewed: (1) exploration of the visuomotor behavior in central versus peripheral vision has not been matched for the two types of patients; (2) the temporal constraints of visual processes that are impaired in the two neurological conditions appear to play a crucial role in the apparent dissociation; (3) the necessary reductionism of experimental conditions used to study action has led to an overconsideration of optic ataxia as a global deficit for action. Altogether optic ataxia appears to result from a specific impairment of immediate visuomotor control rather than of visually guided action as a whole. These results are discussed in the light of recent research on optic ataxia and on motor control, and directions for future research are proposed.

Dual visuomotor channel theory proposes that reaching depends on two neural pathways that extend from visual cortex (V1) to motor cortex via the parietal lobe. The Reach pathway directs the hand to the target’s location and the Grasp pathway shapes the hand and digits for purchase. Sighted human participants integrate the Reach and the Grasp, but without vision they dissociate the movements to capitalize on tactile cues. They use a Reach with a relatively open hand to locate the target and then they use touch cues to shape the fingers to Grasp. After a V1 lesion, the rhesus monkey, Helen, learned to make near-normal visual discriminations based on size and brightness but displayed visual agnosia. She also learned to reach for food with her mouth and her hands. The present analysis of film of her reaching behavior shows that she dissociated the Reach and the Grasp, as do unsighted human participants reaching for a food target at a fixed location. Her rapid and direct Reach was made with an open hand and extended fingers to contact the food with the palm whereas her Grasp was initiated after she touched the food. She also visually fixated the target during the Reach and visually disengaged after target contact, as do sighted human participants. In contrast, Helen did integrate the Reach and the Grasp to take food from her mouth, demonstrating that she could integrate the movements using online tactile cues. The finding that extrastriate pathways can direct the hand toward extrinsic target properties (location) but not intrinsic target properties (size and shape) is discussed as a novel addition to dual visuomotor channel theory.