Chapter 21 Visual agnosia

Abstract

Publisher Summary This chapter provides an overview of the clinical types of visual agnosia and related syndromes, the anatomic systems underlying normal and abnormal visual processing, and information regarding clinical assessment of these conditions. Visual agnosia is divided into two types: apperceptive agnosia and associative agnosia. Apperceptive agnosia is a disorder of complex visual perceptual processing. Individuals with this condition are not blind since they can describe their visual experience, yet they do not have sufficient higher-level visual perception to accurately recognize objects. An individual with visual associative agnosia experiences a normal percept stripped of its meaning. The problem is in the process of associating a perception with more general knowledge-based representations. The most common cause of associative visual agnosia is bilateral infarction of the posterior cerebral arteries. Bilateral lesions involving the inferior temporo-occipital junction and subjacent white matter are the most common anatomic lesions associated with this associative visual agnosia. A patient with visual agnosia will have normal or near-normal visual capacity. More detailed tests of visual and perceptual processing are often needed to make distinctions among the various types of visual agnosia. A battery of tests of higher-order visual perceptual processing (Visual Object and Space Perception Battery—VOSP) are developed. This test is useful for demonstrating deficits in object and space perception. A similar test, focusing on object recognition (Birmingham Object Recognition Battery—BORB), is also available.