Visual agnosia is characterized by the inability to recognize familiar objects. It is a rare condition in the visual centers of the brain making it unable to make sense of previously well-known visual stimuli. A more accurate visual agnosia definition would be the inability to recognize the import sensory impressions of familiar objects by sight, usually due to a lesion of one of the visual association areas. This condition may also be called object blindness or psychic blindness.
What causes visual agnosia?
It is believed that damage to the associated visual association cortex of the brain or parts of the central stream of vision due to a lesion on the parietal and temporal lobes are the primary cause of visual agnosia. These regions of the brain also store memories and are responsible for object association. Lesions to these parts of the brain may be caused by the following:
- Cerebrovascular accident (CVA): Otherwise known as a stroke, this condition can lead to the rapid loss of brain functionality. Stroke results in blood supply disturbance to the part of the brain it is located and can be the result of ischemia, thrombosis, arterial embolism, or a hemorrhage. Strokes typically result in motor function disability, with most affected individuals losing the ability to move particular limbs and/or muscles.
- Neurological disorders: Due to problems with the nervous system, either biochemical or electrical. They can originate in the brain, spinal cord, or nerves.
- Dementia: Commonly occurring in elderly individuals, but cases do exist before the age of 65. Dementia is the loss of cognitive functioning and memory impairment. It is not due to normal aging, with the most common cause of dementia being Alzheimer’s disease.
Other possible causes:
- Hereditary causes
- Brain infection
- Head injury
- Carbon monoxide poisoning
- Recovery from blindness
Symptoms and complications of visual agnosia
Most cases of visual agnosia are seen in older adults who have experienced brain damage to some degree. The following are symptoms they can experience:
- Common objects cannot be identified
- Inability to draw common objects
- Unable to copy drawings of common objects
- Impaired color recognition (achromatopsia)
- Inability to recognize familiar faces (prosopagnosia)
- Inability to recall familiar or learn new faces (prosopamnesia)
Types of visual agnosia
There exist many types and subtypes of visual agnosia. The most commonly recognized categories include:
- Apperceptive visual agnosia: The inability to recognize objects, even if they are in normal vision. For example, affected individuals would not be able to copy and draw a simple object
- Associative visual agnosia: Affected individuals can describe an object, how it affects various other senses, and its classification, but are unable to recognize them. However, they can still draw the object through copying.
- Prosopagnosia: Also known as face blindness, it is a cognitive disorder of facial perception—the inability to recognize faces, including one’s own face. Other aspects of visual processing and decision making generally remain intact. The specific part of the brain associated with prosopagnosia is the fusiform gyrus, known for activating in response to seeing faces.
- Topographagnosia: Characterized by the inability to orient oneself to their surroundings. It results from the inability to make sense of selective spatial information, such as landmarks. Affected individuals are also unable to form a mental representation of their environment or a “cognitive map,” which results in patients becoming disoriented.
- Pure alexia: Also known as pure world blindness and can result in individuals suffering from severe reading problems while other language skills such as naming, oral repetition, auditory comprehension, or writings typically remain intact.
Diagnosing and treating visual agnosia
Visual agnosia can be a difficult diagnosis to make, as people who have the condition are not aware there is a problem with their visual ability or feel that they can compensate without medical intervention. Therefore, suspicion of visual agnosia often arises when the patient is undergoing a routine doctor’s visit. This will often come in the form of the patient mentioning an issue with their vision they cannot easily describe, with accurate testing finding the diagnosis.
Diagnosis of visual agnosia will include looking for any previous events of brain damage such as a stroke. A previous medical history of any familial cases, health condition, or carbon monoxide poisoning will be ruled out. Additionally, general cognitive status tests will be done to see if symptoms of dementia or any other neurological deficits are present.
Other assessments may include visual fields, visual acuity, color perception, reading, drawing, facial recognition, and recognition of line drawings.
Specific visual agnosia diagnostic tests include:
- Boston naming test: Consists of 60-line drawings with the patient instructed to verbally name the picture within 20 seconds.
- Eye tracking: Measuring the point of gaze or motion of the eye relative to the head.
- Warrington recognition memory test: Consists of 50 printed words at the rate of one word every three seconds.
- Benton face recognition test: Testing the ability to recognize faces.
Treatment of visual agnosia will often take the form of treating the underlying condition. However, some cases may be deemed irreversible, as in the case of severe brain damage. Visual agnosia patients may find benefit from physical therapy and occupational therapy to improve their condition. Speech therapy may also be found useful.