Visual Agnosia Definition
What is visual agnosia?
Visual agnosia is a neurological disorder characterized by the inability to recognized familiar objects. The brain is unable to make sense and use of normal visual stimulus. Individual with this disorder cannot perceive nor organize sensory input in long-term manner as the brain is unable to connect between sensory information and past experience.
Visual agnosia is categorized in to two major types and these are:
- Apperceptive visual agnosia – this type of visual agnnosia is unable to recognize object in high-level even if it is in normal vision. A simple task such as copying and drawing a simple object cannot be achieved.
- Associative visual agnosia – people with this type of visual agnosia can describe visually an object and scenes and its classification but still fail in recognizing them although they can still reproduce a certain object through copying.
Visual Agnosia Symptoms
The following may be considered as symptoms manifesting visual agnosia to an individual. Some of these symptoms are also subtypes of visual agnosia:
- Common objects cannot be identified
- Drawing a common object cannot be achieved
- Unable to copy drawings of common objects
- Impaired color recognition or achromatopsia
- Inability to recognize familiar faces or prosopagnosia
- Inability to recall familiar or any other human faces referred as prosopamnesia
Visual Agnosia Causes
Visual has been said to be caused by lesion on parietal and temporal lobes of the brain where memories and object association are stored. Lesion to the parietal and temporal lobes of the brain may have been caused by the following:
- Cerebrovascular Accident (CVA) – commonly known as stroke is rapid loss of brain functionality due to blood supply disturbance in the brain. The common causes for strokes are ischemia, thrombosis, arterial embolism, and hemorrhage. This results to inability to move one or more limbs on one side of the body, inability to understand and even formulate a speech and inability to perceive on one side of the visual field.
- Neurological disorders – a disorder of the nervous system characterized by abnormalities, whether biochemical or electrical, in the brain, spinal cord and other nerves.
- Dementia – commonly occur in geriatric group and may occur before the age of 65. However, dementia is a serious loss of global cognitive ability and is also expected in normal aging process.
Other causes of visual agnosia may include the following:
- Head injury
- Carbon monoxide poisoning
- Brain infection
- Recovery from blindness
Visual Agnosia Diagnosis
Diagnosing agnosia is a bit difficult as some individuals lack awareness that they already have it. Suspicion of clinical condition only arises when there is complain of visual problem even if they normal visual function.
Potential cause of patient’s agnosia should be excluded to isolate the condition. Careful testing of mental and general cognitive status must be done to isolate dementia or aphasia and other assessment should also be made such as:
- Visual fields
- Visual acuity
- Color perception
- Facial recognition
- Recognition of line drawings
- Recognition of real objects
Below are some of diagnostic test done to identify visual agnosia:
- Boston Naming Test – a commonly used neuropsychological assessment tool that contains 60 line drawings where the patient is instructed to name the picture verbally to the examiner in 20 seconds response time for each trial.
- Eye Tracking – measures the point of gaze or motion of an eye relative to the head.
- Warrington Recognition Memory Test – consists of 50 printed words at the rate of one word every 3 seconds count
- Benton Face Recognition Test – this test is done to measure the ability of an individual to faces and it is commonly utilized by neurologist and neuropsychologist for assessment purposes
Medical health professional also have to take or document medical history such as:
- Familial history of visual agnosia
- Health condition of the patient like if patient suffered stroke, dementia, head trauma and brain trauma
- If patient survived carbon monoxide poisoning
Visual Agnosia Treatment
Cure for visual has been unknown and treatment should start with treating the underlying condition of the patient. Some damages are irreversible while others are not. It is however, beneficial for patient with visual agnosia to undergo physical therapy and occupational therapy to improve the condition of the patient to some degree. Occupational therapy and speech therapy are two of the most recommended therapy for patient of visual agnosia.