Agnosias

The neuropsychological disorder, known as visual agnosia, refers to the impairment in deriving the meaning of a visually presented stimulus, in spite of the affected individual having intact sensory and low-level vision, and normal language and semantic function. This type of disorder is intriguing both clinically and scientifically, and vision scientists have studied visual agnosia as a means of shedding light on how the normal visual system functions. Considerable progress has been made in this domain, in parallel with detailed behavioral and neural investigations of the visual system of neurologically intact individuals and of nonhuman primates. Here, we focus specifically on the neuropsychological studies and provide a broad overview of the wide range of impairments that fall under the label 'visual agnosia', including those acquired following brain damage in premorbidly normal individuals, those that appear to have been present since birth, and those whose onset is late in life and is associated with neurodegeneration. We also outline the different subtypes of visual agnosia, including those that affect primarily the recognition of faces, words, or objects, and we lay out some of the key questions currently being addressed by researchers in this domain. Copyright © 2010 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.