A single case study of a brain damaged patient with a category-specific visual agnosia for living things is described. The patient's deficit is manifested as a profound inability to identify, label or classify biological visual objects at the basic level. Most similar cases in the literature have been described as due to damage to a pre-categorical structural description system. However, all these cases also displayed content-specific impairments in activating knowledge from words. ELM's ability to activate basic-level knowledge from pictures and words is investigated using accuracy-based and chronometric measures. The pattern of ELM's category-specific visual agnosia is concomitant with his failure to show priming and typicality effects for words. This suggests that ELM's deficit resides within the semantic memory system. Tests of the integrity of structural descriptions reveal that this patient retains implicit access to pre-categorical structural knowledge.

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Although the visual system is perhaps the most well understood system in the human brain, the precise organization of the neural system whose activity gives rise to higher order functions like visual recognition remains unknown. Furthermore, the manner in which damage involving this system relates to deficit, or the extent to which other factors modulate this relationship is unknown. Building on prior research in this laboratory and elsewhere, which has related focal brain damage to deficits in visual recognition pertaining to particular categories of stimuli, the present study examined both the specificity of lesion-deficit associations, and the relation between damage to the neural systems subserving visual recognition and the severity of a patient's impairment. In the first part, I employed a novel method to address the specificity of visual recognition impairments in relation to the categories of faces, animals, fruits/vegetables and tools/utensils. By using voxelwise logistic regression to parse out variance that could be attributed to deficits across multiple categories, I was able to identify areas that were uniquely predicted by impairment in a single category. In the second part, I examined the relation between the extent of damage in these "category-specific" regions and the severity of the recognition impairment in the same four categories, as well as potential modulating effects from various demographic (e.g., sex, handedness), neuropsychological (e.g., premorbid intellectual functioning, visual-spatial and visuoperceptual ability), and lesion (e.g., age at onset, time elapsed since onset, extent of damage in other ROIs, lesion size) variables. The findings indicated that the largest factor accounting for performance in the recognition of these entities was the extent of damage in the respective category-specific regions. However, within each of the categories, there were additional factors that were also associated with performance, which helped explain some of the additional variance in recognition performance that could not be explained by extent of damage alone. With regard to the latter, I found that damage in certain category-specific regions was related to the severity of deficit across multiple categories, thereby reinforcing the notion of relative specialization within the visual system.

Thesis (Ph.D.)--York University, 2008. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 228-251). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR39024

Thesis (Ph. D.)--University of Rhode Island, 2004. / Typescript. Includes bibliographical references (leaves 65-80).

The dramatic effects of brain damage can provide some of the most interesting insights into the nature of normal cognitive performance. In recent years a number of neuropsychological studies have reported a particular form of cognitive impairment where patients have problems recognising objects from one category but remain able to recognise those from others. The most frequent ‘category-specific’ pattern is an impairment identifying living things, compared to nonliving things. The reverse pattern of dissociation, i.e., an impairment recognising and naming nonliving things relative to living things, has been reported albeit much less frequently. The objective of the work carried out in this thesis was to investigate the organising principles and anatomical correlates of stored knowledge for categories of living and nonliving things. Three complementary cognitive neuropsychological research techniques were employed to assess how, and where, this knowledge is represented in the brain: (i) studies of normal (neurologically intact) subjects, (ii) case-studies of neurologically impaired patients with selective deficits in object recognition, and (iii) studies of the anatomical correlates of stored knowledge for living and nonliving things on the brain using magnetoencephalography (MEG). The main empirical findings showed that semantic knowledge about living and nonliving things is principally encoded in terms of sensory and functional features, respectively. In two case-study chapters evidence was found supporting the view that category-specific impairments can arise from damage to a pre-semantic system, rather than the assumption often made that the system involved must be semantic. In the MEG study, rather than finding evidence for the involvement of specific brain areas for different object categories, it appeared that, when subjects named and categorised living and nonliving things, a non-differentiated neural system was involved.

Thesis (M. Occ. Ther.(Faculty of Health Sciences))--University of Pretoria, 2009. / Summary in English. Includes bibliographical references.