Disorder of Higher Cortical Function in the Visual System

Object Agnosia- This refers to failure in identifying the character or meaning and use of objects while the visual detail in the stimulus is normally perceived. For Lissauer (1890) these cases were characterized by "associative blindness'' in which the patient is unable to match percepts with memory traces of previous exposure to the visual scene or with traces in other modalities that contribute to meaning. This contrasts with ''apperceptive blindness" in which the basic visual percept is disordered. The latter cases merge by imperceptible steps with true blindness or amblyopia of the cortical type. The lesions producing object agnosia are variable and even diffuse. Most authors point to lesions, usually bilateral, involving the occipital convexity as typical, though there is great variability from one case report to another.