main disorders: visual agnosia; optic aphasia; and category-specific anomia. Patients having specific problems with face recognition are discussed later in the chapter.

Visual agnosia is the term used to describe patients who have severely impaired object recognition, in spite of the fact that visual information reaches the cortex. In addition, patients with visual agnosia are able to recognise objects by using other sense modalities (e.g., touch; hearing). We can distinguish between two forms of visual agnosia:

1. Apperceptive agnosia: in this condition, object recognition is impaired because of severe deficits in perceptual processing.

2. Associative agnosia: in this condition, perceptual processes are intact, and object recognition is poor because of impaired visual memories of objects or impaired access to semantic knowledge about objects from these memories.

Optic aphasia refers to a condition in which there are particular problems in naming visually presented objects even though the same objects can be named when handled. A distinction has been drawn between optic aphasia and visual agnosia, because optic aphasics have the ability to mime the appropriate use of visually presented objects that they cannot name. This has sometimes been interpreted as meaning that optic aphasics have normal access to semantic information about visually presented objects. However, the evidence suggests that such patients have some problems in accessing semantic information about objects (see Ellis & Humphreys, 1999). Schinder, Benson, and Scharre (1994, p. 455) argued that there were only minor differences between optic aphasia and visual agnosia, with the two conditions "differing primarily in the degree of callosal disconnection." More specifically, there is more damage to the corpus callosum (which connects the two hemispheres) in optic aphasics than in visual agnosics.

Category-specific anomia is a condition in which there is a selective impairment in naming certain categories of objects. The typical pattern in cases of category-specific anomia is that object naming is considerably worse for living things than for non-living things (e.g., Farah & Wallace, 1992).

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