What is Agnosia?
Agnosia is a neurological disorder that results in an inability to recognize objects (such as an apple or a key), persons, smells, or sounds despite normally functioning senses (such as visual or auditory). These deficits are not due to memory loss.
What causes Agnosia?
Agnosia results from brain damage in areas involved in spatial processing, integration of visual and motor information, and attention. Some of these areas include posterior parietal cortex and occipito-temporal areas. Agnosia can occur suddenly after a head injury or a stroke, or more gradually due to tumors or degeneration of brain tissue in certain areas of the brain.
How does Agnosia relate to Aphasia?
Agnosia is not a speech or language disorder per se. However, agnosia may affect a person’s ability to recognize speech or name objects and thus present with some similarities to Wernicke’s aphasia or anomia. Auditory agnosia, for example, is characterized with difficulty to distinguish speech from non-speech sounds even though hearing is normal. Persons with Wernicke’s aphasia also have troubles understanding speech but the underlying causes are different from those in agnosia and usually they recognize speech sounds as such (see Wernicke’s aphasia). In visual agnosia, patients cannot recognize objects. However, in anomia patients recognize the object but can’t recall its name. Neither anomia nor agnosia is a problem of memory.