Chapter 21 Visual apperception and agnosia

Abstract

Publisher Summary Cerebral lesions may interfere with object identification and recognition in patients with normal or near normal sensory abilities, a condition known as “visual agnosia” (Greek, “not knowing”), sometimes called “associative agnosia.” Visual agnosia in the modern sense of Teuber comprises a family of memory related (mnestic) defects that are not adequately explained by low-level sensory or perceptual loss. These patients have a pathological inability to recognize previously familiar objects by vision alone. This chapter discusses apperceptive and associative disturbances by examining differences among patients with visual associative agnosia and related defects of pattern identification and reading (alexia) and patients with visuoperceptual, visuospatial, attentional and visuomotor deficits, including Balint's syndrome and its subcomponents, and akinetopsia. It includes comments on the effects of the disturbances on key daily activities—especially automobile driving. It begins with a brief overview of key evidence and opinions underlying our understanding of the functional organization of the human visual system.