conceptual agnosia

http://crystaldream-panoramic-panoramic.blogspot.com/2007/10/asymptomatic-perception.html

Asymptomatic Perception

In The Aesthetic Ideology, Paul de Man reads a description of the sublime in Kant's Third Critique as a vision without synthesis--the sea as a floor, the sky as a ceiling, affectless, mere lines of the world as indifferent as those of a hotel room. The way de Man reads this passage sharply contrasts with the characteristic reading of Kant's sublime as a Romantic vision of imposing ravines, ravishing Nature, that conjures up an innate human desire for more knowledge. In his study of attention in modernity, Jonathan Crary writes, "Alongside the discovery of the linguistic disorders grouped under the category of aphasia, a set of related visual disruptions was described [by reseachers into linguistic and perceptual pathologies in the 1870s and 1880s] by the resonant term agnosia. Agnosia was one of the primary asymbolias, or impairments , of a hypothetical symbolic function. Essentially, it described a purely visual awareness to an object . . . an inability to make any conceptual or symbolic identification of an object, a failure of recognition, a condition in which visual information was experienced as a kind of primal strangeness" (56). Crary connects this research into agnosia with the increasing construction of perception in the latter half of the nineteenth-century as the work of the perceiving subject rather than the passive reception of the classical subject. Along with such perceptual agency, according to Crary, comes the idea of a reality socially contracted, of what Pierre Janet calls "the reality function" (56). If what de Man sees in Kant is a form of agnosia, could this be construed as a kind of "modernist sublime," a vision as yet unmoored from a social body which would place it? How might such a sublime connect back to the awareness and representation of the body as locus of perception? How might it connect to cinematic vision, which is purely synthesis of a lost referent?

Encephale. 2004 Nov-Dec;30(6):570-7. Links
[Awareness of deficits and anosognosia in Alzheimer's disease.][Article in French]


Antoine C, Antoine P, Guermonprez P, Frigard B.
Centre Hospitalier Intercommunal de Wasquehal, Le Molinel, 59290 Wasquehal.

This article reviews studies concerning unawareness of deficits in Alzheimer's disease. Unawareness of the deficits associated with dementia has frequently been reported in clinical descriptions of the later stages of the disease. Consistent with the literature, we shall use the expressions impaired awareness, unawareness of deficits, anosognosia, and lack of insight interchangeably. Anosognosia can be defined as an impaired ability to recognize the presence or appreciate the severity of deficits in sensory, perceptual, motor, affective, or cognitive functioning. Unawareness has been operationally defined in a variety of ways. Unawareness can be measured as the discrepancy between the patient's self-report and the report of a natural caregiver or the clinical rating of a health care professional. The reports generally concern with several domains, most often memory domain. Discrepancy between subjective ratings and neuropsychological performance during clinical assessment has also been used to measure anosognosia. Advantages, limits and equivalence of these different methods are discussed. The impact of family burden has to be considered as a systematic methodological bias if the natural caregiver is implicated in the assessment. The psychometric properties of the clinical assessment have also to be discussed. The psychological nature of the discrepancy between patient's self-report and cognitive performances has to be analyzed and the necessity of ecological protocols, longitudinal assessment is discussed. The major results concerning prevalence, nature of anosognosia and the associated disorders are analyzed. In particular, the notion of heterogeneity of anosognosia and the correlates with depression, severity of dementia and executive dysfunction are developed. Prevalence is largely function of methodological choices and conceptual definition of anosognosia. Three major researches are compared and the contrast between their results (prevalence from 23% to 75% in AD) is analyzed. Particularly, the hypotheses about anosognosia play a great role in the findings. At first time of research, anosognosia was considered as a general symptom and so, studies were centered on the unawareness related to only one cognitive function. But the 90's findings suggest that patients with AD have impaired awareness for some types of deficits (affective or cognitive functions) but can more accurately appraise other deficits. Currently anosognosia cannot be considered as a unitary entity. It may be that patients with AD are unaware of some types of deficits, but are aware of others, and that nature and intensity of their anosognosia may change during the course of the dementia. It has been proposed that depression is more common when disease is mild and awareness of deficits is retained, and that depression becomes less common when disease increases and awareness declines. Depression is conceived as a psychological reaction. However, the correlations between anosognosia level and depression scores reveal either weak relationships or no relationships. Alternative hypothesis is that anosognosia is related to overall dementia severity and to memory impairment. However, correlations of unawareness of deficits, i.e. the difference between self-report and relative's -rating, with a measure of dementia and with patient's performance on objective memory tasks did not reveal strong, consistent relationships between degree of anosognosia and severity of dementia or of memory impairment. On the other hand, the best neuropsychological predictors of impaired insight are Trail Making Test or Wisconsin Card Sorting Test, i.e. tests that have been shown to be sensitive to a frontal lobe dysfunction. SPECT measures of regional cerebral blood flow have been used in the study of anosognosia. The main findings are that unawareness in AD is associated with hypoperfusion of the right dorsolateral frontal lobe. Anosognosia may result from the disruption of broader cognitive process that is subsumed by the frontal lobes. The mechanisms of unawareness are not well known and studies are essentially descriptive works and try to give information about pre-valence or clinical associated disorders of anosognosia. Several authors have proposed that unawareness is part of a defensive mechanism that would protect demented patients from depressive feelings. Other authors have proposed that anosognosia may result from dysfunction in specific brain areas. It is suggested that anosognosia in AD may result from greater impairment of a central executive system, which is a metacognitive structure that is involved in planning, cognitive resource allocation, and set shifting. The main problem with those both major hypotheses is their incapacity to explain the heterogeneous impairment of awareness. Other authors speculate that the impaired insight of Alzheimer's disease has several components, psychological and neuropsychological. This view doesn't seem convincing and new components have to be taken in account in order to propose a theoretical framework about anosognosia in AD. Environmental and dispositional components and an interactional view could be interesting. Those possible directions for future research and solutions concerning methodological and conceptual problems are outlined. In particular, a neuro-psycho-social view of unawareness is introduced.

PMID: 15738860 [PubMed - indexed for MEDLINE]

1: Hum Brain Mapp. 2001 Aug;13(4):199-212.Links
A role for left temporal pole in the retrieval of words for unique entities.Grabowski TJ, Damasio H, Tranel D, Ponto LL, Hichwa RD, Damasio AR.
Department of Neurology, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA. thomas-grabowski@uiowa.edu

Both lesion and functional imaging studies have implicated sectors of high-order association cortices of the left temporal lobe in the retrieval of words for objects belonging to varied conceptual categories. In particular, the cortices located in the left temporal pole have been associated with naming unique persons from faces. Because this neuroanatomical-behavioral association might be related to either the specificity of the task (retrieving a name at unique level) or to the possible preferential processing of faces by anterior temporal cortices, we performed a PET imaging experiment to test the hypothesis that the effect is related to the specificity of the word retrieval task. Normal subjects were asked to name at unique level entities from two conceptual categories: famous landmarks and famous faces. In support of the hypothesis, naming entities in both categories was associated with increases in activity in the left temporal pole. No main effect of category (faces vs. landmarks/buildings) or interaction of task and category was found in the left temporal pole. Retrieving names for unique persons and for names for unique landmarks activate the same brain region. These findings are consistent with the notion that activity in the left temporal pole is linked to the level of specificity of word retrieval rather than the conceptual class to which the stimulus belongs. Copyright 2001 Wiley-Liss, Inc.

PMID: 11410949 [PubMed - indexed for MEDLINE]
Copyright © 2007 Elsevier Ltd All rights reserved.
Implicit integration in a case of integrative visual agnosia





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Hillel Aviezera, Ayelet N. Landaub, c, Lynn C. Robertsonb, c, Mary A. Petersond, Nachum Sorokere, Yaron Sachere, Yoram Bonnehf and Shlomo Bentina, ,

aDepartment of Psychology, Hebrew University, 91905 Jerusalem, Israel

bUniversity of California, Berkeley, CA, United States

cVeterans Affairs Medical Research, Martinez, CA, United States

dUniversity of Arizona, AZ, United States

eLowenstein Rehabilitation Hospital, Raanana and Sackler Faculty of Medicine, Israel

fThe Weizmann Institute of Science, Rehovot, Israel


Received 24 August 2006; revised 29 January 2007; accepted 31 January 2007. Available online 9 February 2007.

Abstract
We present a case (SE) with integrative visual agnosia following ischemic stroke affecting the right dorsal and the left ventral pathways of the visual system. Despite his inability to identify global hierarchical letters [Navon, D. (1977). Forest before trees: The precedence of global features in visual perception. Cognitive Psychology, 9, 353–383], and his dense object agnosia, SE showed normal global-to-local interference when responding to local letters in Navon hierarchical stimuli and significant picture-word identity priming in a semantic decision task for words. Since priming was absent if these features were scrambled, it stands to reason that these effects were not due to priming by distinctive features. The contrast between priming effects induced by coherent and scrambled stimuli is consistent with implicit but not explicit integration of features into a unified whole. We went on to show that possible/impossible object decisions were facilitated by words in a word-picture priming task, suggesting that prompts could activate perceptually integrated images in a backward fashion. We conclude that the absence of SE's ability to identify visual objects except through tedious serial construction reflects a deficit in accessing an integrated visual representation through bottom-up visual processing alone. However, top-down generated images can help activate these visual representations through semantic links.

Keywords: Integrative agnosia; Visual agnosia; Local–global processing; TPJ; Grouping