perceptual defect, any of a broad group of disorders or dysfunctions of the central nervous system that interfere with the conscious mental recognition of sensory stimuli. Such conditions are caused by lesions at specific sites in the cerebral cortex that may result from any illness or trauma affecting the brain at any age or stage of development. Impairment of mental activity, cognitive processes, and emotional responses may be diffuse, as occurs in organic mental disorders, such as the psychoses, delirium, and dementia, and in attention deficit disorder, or they may be manifested focally, as in aphasia, apraxia, epilepsy, disorders of memory, cerebrovascular disorders, and various intercranial neoplasms.
