[Agnosia]

Abstract

The term agnosia defines an impairment of stimulus recognition, limited to one modality and not explainable in terms of sensory deficits or general mental deterioration. Visual object agnosia refers to the inability to recognize objects and prosopagnosia to the failure to recognize faces that are well familiar to the patient, when stimuli are visually perceived. Both deficits may appear in an apperceptive form, where it is the internal and external structure of the stimulus to be unrecognized and an associative form where the patient achieves a good percept, but cannot assign it a meaning. Apperceptive forms are preferentially associated with bilateral occipital damage, object associative agnosia with left occipital damage and associative prosopagnosia with right occipital damage.