What is agnosia?
Agnosia is the loss of the ability to recognize objects, faces, voices, or places. It is a rare disorder. If you have this condition you can still think, speak, and interact with the world. Agnosia usually affects only a single information pathway in the brain.
There are different types of agnosia. Visual agnosia, for example, causes you to be unable to name or describe the use of an object placed in front of you. You will still be able to reach for it and pick it up. You can also use your sense of touch to identify its use once you are holding it.
What causes agnosia?
Agnosia occurs when the brain suffers damage along certain pathways. These pathways connect the primary sensory processing areas. These parts of the brain store knowledge and information. Primary sensory processing areas include the visual and auditory cortices.
Agnosia is usually caused by lesions on the parietal and temporal lobes of the brain. These lobes store semantic information and language. Strokes, head traumas, or encephalitis can cause lesions. Other conditions that damage or impair the brain can also cause agnosia. These conditions include dementia, carbon monoxide poisoning, and anoxia.
Types of agnosia
There are three main types of agnosia: visual, auditory, and tactile.
Visual agnosia occurs when there is brain damage along the pathways that connect the occipital lobe of the brain with the parietal and temporal lobes. The occipital lobe assembles incoming visual information. The parietal and temporal lobes allow you to understand the meaning of this information.
Apperceptive visual agnosia
Visual apperceptive agnosia causes difficulty in assembling parts of an image into an understandable whole. This condition may cause you to have difficulty understanding the relationship between objects.
You may, for instance, try to copy a picture of a circle and end up drawing a series of concentric scribbles. You can still use vision to navigate your environment and pick up objects without trouble. Apperceptive visual agnosia is usually caused by lesions to the parietal or temporal lobes on both sides of the brain.
Associative visual agnosia
Associative visual agnosia is the inability to recall information associated with an object. This can include an object’s name, use, or origin. This form of agnosia does not prevent you from being able to draw a picture of an object.
You may be unable to name the object in the drawing. You could recognize and use an object shown to you but may be unable to say what the name of the object is.
Prosopagnosia (face blindness)
Prosopagnosia is the inability to recognize faces. It’s caused by issues with the fusiform face area (FFA), a specific region of the brain that recognizes faces. Difficulty with facial recognition can also occur in Alzheimer’s disease. It happens because brain deterioration damages this region.
Autism can also cause difficulty recognizing faces. A 2014 article discussed how children with autism spectrum disorders may learn to recognize faces in a different way. They may find it more difficult to understand another person’s identity or emotional state.
Achromatopsia is the loss of color vision due to lesions in the V4 region of the brain. It’s the inability to name colors despite being able to perceive them. Color anomia results when a lesion separates the V4 regions of the brain from the language areas.
Agnosic alexia (pure alexia)
Pure alexia is the inability to recognize words visually. It is not possible to read with pure alexia. You can usually still speak and write without difficulty.
Akinetopsia (motion blindness)
Akinetopsia is the inability to perceive motion. This condition can cause you to see moving objects as a series of stills, like an object moving under a strobe light. If the condition is severe, you may not be able to see any motion at all.
Auditory agnosia is also known as pure word deafness. It’s the inability to recognize or process sounds despite intact hearing. It develops when the A1 sound-processing region of the brain is disconnected from its language centers. You can still read, write, and speak with pure word deafness.
Phonagnosia is the inability to recognize and identify familiar voices. It develops when the brain suffers damage to a certain part of the sound association region. This region is located in the right half of the brain. You can still understand words spoken by others if you have this condition. You can also recognize environmental sounds or sounds made by objects.
Tactile agnosia is the inability to recognize objects by touch. You may be able to feel the weight of the object. Yet you may be unable to understand the significance or the use of the object. Lesions in the parietal lobe of the brain are the cause of tactile agnosia.
Astereognosis is the inability to identify objects by touch alone. This condition makes you unable to associate information about size, weight, and texture with the right words. You can still name objects by sight. You are also able to draw pictures of objects, as well as reach for them.
Autotopagnosia is when you lose the ability to orient the parts of your own body. Damage to the left parietal lobe of the brain causes this condition. You are aware of where your limbs are in space at all times, even with closed eyes. But this awareness gets distorted when the brain’s internal representation of the body is damaged.
Treating the underlying cause and caring for symptoms is the primary way to treat agnosia. The main goal is to enable you to function independently in your day-to-day life.