The Japanese journal of neuropsychology

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ArticleTitle	Visual agnosia
Language	J
AuthorList	Katsuhiko Takeda¹⁾, Yuko Miyazaki²⁾
Affiliation	1) Department of Neurology, Mita Hospital, International University of Health and Welfare 2) Department of Neurology, Kawasaki Medical University
Publication	Japanese Journal of Neuropsychology: 22 (2), 95-104, 2006
Received
Accepted
Abstract	I explained several single case-studies of patients with visual agnosia. The neuropsychological literature on recognition disorders has traditionally adopted a dichotomous approach, which originates in the pioneering work of Lissauer (1890). HJA's case demonstrated, however, that a patient shows relatively good basic coding of shape and even though stored knowledge of objects is largely preserved. The deficit appears to affect a stage of visual processing intermediate between basic shape coding and visual access to memory representations, concerned with parallel perceptual grouping and the integration of perceptual parts into wholes. DF had a profound visual form agnosia. The anoxic episode affected her vision for perception but left her vision for action largely unscathed. Signals from the eyes first arrive at the primary visual cortex. Ungerleider and Mishikin argued that the signals were then routed forwards along two quite separate pathways. One of these routes, which they called the dorsal visual pathways, ended up in the posterior parietal lobe. The other (the so-called ventral pathways) ended up in the inferior temporal regions. DF's brain cannot put the elements (for example, lines and edges) together to form perceived 'wholes' due to damages in the ventral stream. DF's brain showed activation in the area of parietal lobe, the part of the human dorsal stream, which is known to be intimately associated with visual control of grasping. Visual mental imagery refers to the perception of a perceptual experience in the absence of visual input. Results of numerous studies demonstrate the functional equivalence between perception and imagery. There are, however, cases in whom imagery and perception are dissociable. The problem is how to reconcile these opposing views, each of which has a strong empirical foundation. Feinberg et al. (1986) studied a patient who had combined visual-tactile agnosia after a left hemisphere infarct. The authors thought complex tasks of tactile identification may share systems with those involved in visual recognition. On the contrary, a notion has been proposed that in order to percept visual form of objects tactile representations of objects are needed. I discuss that further study of patients with multiple agnosia are needed to clarify how the representation of visual modality and that of tactile modality are identified. Finally I introduced the paper which analyzed the visual functions of two patients with bilateral lesion of the primary visual cortex, which occurred at very early onset.
Keywords	integrative agnosia, ventral stream, dorsal stream, multimodal agnosia, visual agnosia after early onset lesions