Cases reported "Agnosia"

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1/11. Musical instrument naming impairments: the crucial exception to the living/nonliving dichotomy in category-specific agnosia.

    In category-specific agnosia (CSA) patients typically have more trouble naming animals, fruits, and vegetables than tools, furniture, and articles of clothing. A crucial exception to this living vs nonliving rule involves the category of musical instruments. patients with problems naming living objects often repeatedly fail to name musical instruments. In CSA it is crucial to equate living and nonliving object lists on object name frequency, complexity, and familiarity. The present study shows, however, that even the most rigorously controlled object lists can lead to erroneous conclusions if nonliving stimuli contain an overrepresentation of musical instruments. Naming capabilities of a herpes encephalitis patient were assessed using matched lists of living and nonliving objects and showed no indication of category-specific deficits. When exemplars were separated into biological objects, musical instruments and man-made artifacts, strong category-specificity emerged: artifact naming was flawless whereas musical instrument and biological object naming were both severely impaired. It is concluded that CSA is a veridical phenomenon but that our understanding of CSA is limited by adhering to the spurious living/nonliving distinction.
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2/11. Neuronal representation of object orientation.

    The dissociation between object identity and object orientation observed in six patients with brain damage, has been taken as evidence for a view-invariant model of object recognition. However, there was also some indication that these patients were not generally agnosic for object orientation but were able to gain access to at least some information about objects' canonical upright. We studied a new case (KB) with spared knowledge of object identity and impaired perception of object orientation using a forced choice paradigm to contrast directly the patient's ability to perceive objects' canonical upright vs non-upright orientations. We presented 2D-pictures of objects with unambiguous canonical upright orientations in four different orientations (0 degrees, -90 degrees, 90 degrees, 180 degrees ). KB showed no impairment in identifying letters, objects, animals, or faces irrespective of their given orientation. Also, her knowledge of upright orientation of stimuli was perfectly preserved. In sharp contrast, KB was not able to judge the orientation when the stimuli were presented in a non-upright orientation. The findings give further support for a distributed view-based representation of objects in which neurons become tuned to the features present in certain views of an object. Since we see more upright than inverted animals and familiar objects, the statistics of these images leads to a larger number of neurons tuned for objects in an upright orientation. We suppose that probably for this reason KB's knowledge of upright orientation was found to be more robust against neuronal damage than knowledge of other orientations.
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3/11. Is autotopoagnosia real? EC says yes. A case study.

    We report a case of pure autotopagnosia (AT) following a left subcortical vascular accident. The absence of any language disorder, general mental deterioration or other cognitive impairments in this patient allowed an in-depth study of AT. Several tests of body representation and object and animal representation, as well as tests assessing semantic skills were administered to verify current interpretations of AT. Results showed a clear-cut dissociation between defective performances in body representation tests and normal performances on tests involving other kinds of stimuli.The patient's performances were particularly defective on tests relying on visuo-spatial body representation, but her semantic and linguistic knowledge seemed to be spared. This dissociation between different aspects of body representation supports Sirigu et al.'s hypothesis that multiple, partially independent systems are involved in body knowledge. In agreement with this hypothesis, in the present patient AT seems be due to a deficit in a system that processes the structural properties and relative position of single body parts.The present results, reporting the first observation of a subject not affected by any cognitive impairment other than AT, strongly support the existence of a system specifically devoted to body representation.
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4/11. Characteristics of auditory agnosia in a child with severe traumatic brain injury: a case report.

    We present a case that is unusual in many respects from other documented incidences of auditory agnosia, including the mechanism of injury, age of the individual, and location of neurological insult. The clinical presentation is one of disturbance in the perception of spoken language, music, pitch, emotional prosody, and temporal auditory processing in the absence of significant deficits in the comprehension of written language, expressive language production, or peripheral auditory function. Furthermore, the patient demonstrates relatively preserved function in other aspects of audition such as sound localization, voice recognition, and perception of animal noises and environmental sounds. This case study demonstrates that auditory agnosia is possible following traumatic brain injury in a child, and illustrates the necessity of assessment with a wide variety of auditory stimuli to fully characterize auditory agnosia in a single individual.
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5/11. Sensitivity to eye gaze in prosopagnosic patients and monkeys with superior temporal sulcus ablation.

    Accuracy at perceiving frontal eye gaze was studied in monkeys and human subjects using a forced-choice detection task on paired photographs of a single human face. Monkeys learned the task readily, but after bilateral removal of the banks and floor of the superior temporal sulcus (STS) they failed to perform the task efficiently. This result is consistent with the conclusion, based on recordings from single cells in awake, behaving monkeys [Perret et al., Physiological Aspects of Clinical Neuro-ophthalmology, Chapman & Hall, london, 1988] that this region of the temporal lobe is important for coding information about eye-gaze of a confronting animal. Human subjects were given identical stimuli in a task where they were asked to detect "the face that is looking straight at you". Human performance is sensitive to the degree of angular deviation from the frontal gaze position, being poorest at small angular deviations from 0 degrees. This was also true of monkeys viewing these stimuli, pre- and post-operatively. Compared with normal controls, two humans prosopagnosics were impaired at this task. However the extent of impairment was different in the two patients. These findings are related to earlier reports (including those for patients with right-hemisphere damage without prosopagnosia), to normal performance with upright and inverted face photographs, and to notions of independent subsystems in face processing.
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6/11. A disorder of lightness discrimination in a case of visual form agnosia.

    Benson and Greenberg (1969) described an "agnosic" patient whose severe visual recognition disorder could be accounted for in terms of a deficit in the perception of shape. We report here on a recent case of this disorder (visual form agnosia), and have found that she performs very poorly on tasks of discriminating shades of grey, although she is able to discriminate between hues. This sensory deficit helps to explain some of her perceptual difficulties; it also provides further evidence for parallel feature-processing in the human brain complementary to and consistent with recent physiological data on the visual cortex in animals.
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7/11. Two visual systems in mental imagery: dissociation of "what" and "where" in imagery disorders due to bilateral posterior cerebral lesions.

    We studied two patients with impaired visual perception and imagery caused by bilateral posterior cerebral lesions. The first had prosopagnosia and achromatopsia, and the imagery disorder involved the description of objects from memory, especially faces and animals, and colors of objects. The second had visual disorientation; the imagery problem involved the description of spatial relations from memory. Impairments of visual imagery, like disorders of visual perception, can be dissociated. Object and color imagery may be dissociated from imagery for spatial relations. A given imagery deficit tends to be associated with the corresponding type of perceptual deficit.
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8/11. Autotopagnosia. Occurrence in a patient without nominal aphasia and with an intact ability to point to parts of animals and objects.

    A patient with a metastasis in the left parietal lobe demonstrated difficulty in pointing to body parts although he could name them when they were pointed to by someone else. As he had no nominal aphasia, could understand complex verbal instructions and could correctly describe the functions of named body parts, his autotopagnosia is unlikely to be a result of a category-specific comprehension deficit. As he is able to point to parts of objects, plants and animals on command, his disorder is also unlikely to be part of a general inability to analyse a whole into its details. Instead, his difficulty appears to be one of locating body parts in relation to the whole body. Such a disorder provides support for the existence of a discrete body image that can be disrupted by a lesion of the left parietal lobe.
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9/11. Thalamic neglect.

    Three patients with right thalamic hemorrhage showed contralateral neglect and limb akinesia. They also had anosognosia, visuospatial disorders, and emotional flattening. In animals, neglect can be induced by lesions along a cortico-limbic-reticular loop including the intralaminar thalamic nuclei. We propose that an activation defect is responsible not only for the neglect and akinesia, but also for the visuospatial and emotional defects usually associated with right-hemisphere cortical dysfunction.
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10/11. Partial recovery from visual object agnosia: a 10 year follow-up study.

    We describe a young woman, J.R., who sustained a very severe head injury in 1981 at the age of 17 years. She was assessed in 1982 and found to have visual agnosia. Since then J.R. has been assessed on several occasions over a period of ten years. Her agnosia for real objects has resolved and she has improved on the identification of other classes of stimuli. However, she still has some problems with the identification of line drawings, photographs and model animals. Her drawing from memory remains particularly poor and she has difficulty with visual imagery. We consider her residual deficits in the light of Farah's (1990) theoretical framework; this proposes that associative agnosia could be due to a disconnection syndrome, a loss of stored visual representations or to the loss of knowledge of how to perceive objects. J.R.'s residual impairments appear to be mainly due to a loss of access to visual representations in the absence of visual input.
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