Agnosia : The Mechanism and Its Diagnosis

Abstract

  The agnosia is defined as ʻimpaired recognition of previously meaningful stimuli which is restricted to special sensory modalityʼ. Most of the reported literatures about agnosia is those of visual agnosia, followed by auditory agnosia. Patients complain ʻI cannot see.ʼ or ʻI cannot hear.ʼ, so they are easily misdiagnosed as the disturbance of visual or hearing acuity, dementia, and psychiatric disorders. The naming task is useful to know whether the patient can understand the object correctly. The name and the meaning or concept are the two sides of one coin, and, if one side is recalled, another is automatically recalled. The perception of the object, the recollection of the meaning and concept, the integration of both, and the retrieval of its name function regularly, if the patient can name it correctly. The agnosia is interpreted as the dysfunction of the integration between perceived image and the meaning and concept in special sensory modality. The nomenclature of the visual and auditory agnosia is confused. The dichotomy of the apperceptive and associative agnosia can be easily understood, but, in the real clinical situations, there are many cases which cannot be categorized to either. It is important to describe the symptom correctly and elaborately.