Cases reported "Agnosia"

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1/6. 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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2/6. Varieties of functional deficits in prosopagnosia.

    prosopagnosia is a neurologically based deficit characterized by the inability to recognize faces of known individuals in the absence of severe intellectual, perceptual, and memory impairments. The nature of the underlying disturbance was investigated in three patients in an attempt to identify the structural and functional levels at which the processing of faces breaks down, the relation between prosopagnosia and associated deficits, and the specificity of the prosopagnosic disturbance. The breakdown of face processing resulted from unilateral damage in different cerebral structures of the right hemisphere in the three patients, and it involved different functional levels of face processing, but all three patients displayed perceptual impairments of unequal severity. In one patient (R.M.), the deficit encompassed all perceptual operations on faces, including matching identical views of the same faces, but it did not extend to all categories of objects characterized by a close similarity among their instances; the second patient (P.M.) exhibited a less severe perceptual impairment but was unable to derive the configurational properties from a facial representation and to extract its physiognomic invariants; the third patient (P.C.) had not lost the capacity to differentiate faces on the basis of their configurations but could not associate a facial representation with its pertinent memories. Associated deficits were present in each patient but differed depending on the anatomofunctional locus of the breakdown, although all patients were impaired at recognizing noncanonical views of objects that they readily recognized when shown from a conventional viewpoint. However, performance dissociation within patients and double dissociation between patients suggest that these associated deficits are not necessary concomitants of prosopagnosia.
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3/6. Can recognition of living things be selectively impaired?

    brain damage sometimes seems to impair recognition of living things, despite relatively preserved recognition of nonliving things. The most straightforward interpretation of this dissociation is that the recognition of living things depends on some specialized mechanisms that are not needed for the recognition of nonliving things. However, there are alternative interpretations of the dissociation in terms of the greater complexity or inter-item similarity of living things, or the more specific, within-category identifications that are usually required for living things. Surprisingly, the relevant tests to discriminate among these rival hypotheses have never been performed. We took the factors of visual complexity, inter-item similarity, specificity of identification, as well as others, into account in analyzing the visual recognition performance of two head-injured visual agnosic patients. In each case we found that recognition of living things was still disproportionately impaired when the effects of the other factors were accounted for.
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4/6. Category-specificity and modality-specificity in semantic memory.

    Studies of agnosia have revealed two apparently orthogonal dimensions along which knowledge may break down. In some cases, knowledge of specific categories (such as living things) seems lost, regardless of the modality being tested. In other cases, knowledge in specific modalities (such as vision) seems lost, regardless of the category of stimuli being tested. These different sets of phenomena suggest different organizations for knowledge in the brain, the first by category and the second by modality. Unfortunately, possible confoundings between category, modality, and difficulty level in the previous studies prevent us from drawing strong conclusions from these data. The present study was aimed at assessing the nature of the breakdown in the semantic memory of a prosopagnosic patient, by orthogonally varying category and modality, while assessing difficulty level. The findings do not implicate a simple categorical or modality-dependent organization of his knowledge, but rather an organization in which both category and modality play a role.
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ranking = 8
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5/6. Is there semantic specificity in overlapping-figures agnosia?

    A case of apperceptive visual agnosia, revealing difficulties only in the performance on a standard overlapping-figures test, has been studied. Unusually, the patient demonstrated difficulties only with two semantic categories of the overlapped figures (clothes and school accessories); preserving, however, the knowledge of the same figures when presented isolated. We propose that the underlying deficit is only of a pseudo-semantic nature and is actually due to certain similarities of the two overlapping combinations, creating difficulties still on the apperception level only.
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6/6. Category specificity in object agnosia: preservation of sensorimotor experiences related to objects.

    We report a case of semantic agnosia, characterized by category specificity. Object recognition, mainly involving visual representation, was severely impaired, whereas object recognition involving both visual and sensorimotor representations, was relatively well preserved. His ability to recognize gestures and produce appropriate gestural responses to objects was remarkable. These two factors lead the authors to form a hypothesis, in an attempt to explain the mechanisms involved in object recognition. It has been argued that manipulation of an object may give access to a certain amount of knowledge about it, and that preservation of sensorimotor experiences of objects might be important in recognizing some of them. This could account for the category specificity, described in object agnosia.
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ranking = 6
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