Agnosia

Agnosia (a-gnosis, "non-knowledge") is a loss of ability to recognize objects, persons, sounds, shapes or smells while the specific sense is not defective nor is there any significant memory loss. It is usually associated with brain injury or neurological illness, particularly after damage to the temporal lobe.

Visual agnosia is associated with lesions of the left occipital lobe and temporal lobes. Many patients have a severe visual field defects.

Object Agnosia is inability to recognize objects. Subtypes: Form agnosia: Patients perceive only parts of details, not the whole object.

Simultagnosia: Patients recognize objects or details but only one at the time. They cannot make out the scene they belong to or make out a whole image out of the details. They literally cannot see the forest for the trees.

Associative Agnosia: Patients can describe visual scenes and classes of objects but still fail to recognize them. He may, for example, know that fork is something you eat with but may mistake it for a spoon.

face perception disorder

See prosopagnosia entry for more details.

Agnostic alexia: Inability to recognize text.

Color agnosia: There is a distinction between color perception versus color recognition. Central Achromatosia refers to deficiency in color perception

Auditory agnosia refers to similar symptoms with environmental, nonverbal auditory cues. This is separate from word deafness which is agnosia connected to auditory information. Receptive amusia is agnosia for music. Cortical deafness refers to people who do not respond to any auditory info but their hearing is intact.

Somatosensory Agnosia or Astereognosia is connected to tactile sense - that is, touch. Patient finds it difficult to recognize objects by touch based on its texture, size and weight. However, they may be able to describe it verbally or recognize same kind of objects from pictures or draw pictures of them. Thought to be connected to lesions or damage in somatosensory cortex.

Agnosia can result from strokes, dementia, or other neurological disorders. For all practical purposes, there is no direct cure. Patients may improve if information is presented in other modalities than the damaged one.

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See also

• aphasia
• apraxia
• prosopagnosia

This is hardly a comprehensive text...