The visual agnosia is a comprehensive review and updated list of disorders top view that relates these disorders with current conceptions of the top view of cognitive science, which illuminate both neuropsychological disorders and the nature of normal objects visual recognition.
Brain damage can lead to selective problems with visual perception , including visual agnosia, the inability to recognize objects even though elementary visual functions remain intact, such disorders are relatively rare, they provide a window on how the normal brain might perform the complex task of vision.
What is visual agnosia?
It is an impediment in the recognition of the objects presented visually, it is not due to a deficit of vision (acuity, visual field and exploration), language , memory or intellect. While cortical blindness results from injury to the primary visual cortex, visual agnosia results from damage to the anterior cortex, such as the posterior occipital and / or temporal lobe in the brain.
It is a rare condition in the visual centers of the brain that prevents it from making sense of previously known visual stimuli. A more precise definition of visual agnosia would be the inability to recognize imported sensory impressions of familiar objects by sight, usually due to injury to one of the visual association areas, this condition can also be called objective blindness or psychic blindness.
Types of visual agnosia
There are many types and subtypes of visual agnosia. The most commonly recognized categories include:
Agnosia visual aperceptiva
It is a visual impairment that results in the inability of the patient to name objects. While agnosics suffer severe deficits, patients’ visual acuity and other visual abilities such as perceiving parts and colors remain intact. The deficits appear to occur due to damage to early-level perceptual processing.
Although patients can effectively allocate attention to locate the object and perceive the parts, they cannot group the parts they see and name the object precisely, this is demonstrated by the fact that patients are more effective at naming two attributes of a single object than to name an attribute on each of the two overlapping objects. In addition, they are still able to describe objects in detail and recognize objects by touch.
Associative visual agnosia
It is an impairment in the recognition or assignment of meaning to a stimulus that is accurately perceived and is not associated with a generalized deficit in intelligence, memory , language, or attention .
The disorder appears to be very rare in a “pure” or uncomplicated form and is generally accompanied by other complex neuropsychological problems due to the nature of the etiology. Distressed people can accurately distinguish the object, as evidenced by the ability to accurately draw or categorize it, but they cannot identify the object, its characteristics, or its functions.
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 to activate in response to seeing faces.
Characterized by the inability to orient themselves to their environment. It is the result of the inability to make sense of selective spatial information, such as landmarks. Affected people are also unable to form a mental representation of their environment or a ‘cognitive map’, causing patients to become disoriented.
Also known as pure world blindness and it can cause people with severe reading problems, while other language skills such as nomenclature, oral repetition, listening comprehension or writing remain normally intact.
What Causes Visual Agnosia?
Damage to the associated visual association cortex of the brain or parts of the central stream of vision due to injury to the temporal and parietal lobes is believed to be the primary cause of visual agnosia. These brain regions also store memories and are responsible for the association of objects, lesions in these parts of the brain can be caused by the following:
- Stroke: This condition can lead to rapid loss of brain function, causing disturbances in the blood supply to the part of the brain where it is located and can be the result of ischemia, thrombosis, arterial embolism, or hemorrhage. Strokes often result in impaired motor function, and most affected people lose the ability to move certain limbs and / or muscles.
- Neurological disorders: Due to problems with the nervous system, whether biochemical or electrical, they can originate in the brain, spinal cord, or nerves.
- Dementia : It commonly occurs in the elderly, but cases exist before age 65. The Dementia is the loss of cognitive function and memory impairment. It is not due to normal aging, as the most common cause of dementia is 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 you may experience:
- Common objects cannot be identified.
- Inability to draw common objects.
- Impaired color recognition (achromatopsia).
- Inability to recognize familiar faces (prosopagnosia).
- Inability to remember new or familiar faces ( prosopamnesia ).
Diagnosis of visual agnosia
Visual agnosia can be a difficult diagnosis to make , as people with the condition are unaware that there is a problem with their visual ability or feel that they can compensate for it without medical intervention. Therefore, the suspicion of visual agnosia often arises when the patient undergoes a routine doctor visit, this will come in the form of the patient mentioning a problem with his vision that he cannot easily describe, with precise tests to find. the diagnosis.
The diagnosis will include the search for any previous event of brain damage, such as a stroke, a previous medical history of any family case, health condition or carbon monoxide poisoning will be excluded. In addition, general cognitive status tests will be performed to see if there are symptoms of dementia or any other neurological deficits.
Other assessments may include visual fields, visual acuity, color perception, reading, drawing, facial recognition, and picture recognition.
Diagnostic tests for specific visual agnosia include:
- Boston nomenclature test: Consists of 60-line drawings with the patient who is asked to verbally name the image in 20 seconds.
- Eye tracking: Measures the point of gaze or eye movement relative to the head.
- Warrington Recognition Memory Test: Consists of 50 words printed at the rate of one word every three seconds.
- Benton Facial Recognition Test : Test of the ability to recognize faces.
Treatment of visual agnosia
The cure for eyesight is unknown and treatment should begin with treating the patient’s underlying condition. Some damages are irreversible while others are not but it is beneficial for the visual agnosia patient to undergo physical therapy and occupational therapy to improve the patient’s condition to some extent.
Occupational therapy and speech therapy are two of the most recommended therapies for the visual agnosia patient.
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