Agnosia is the loss of the ability to recognize objects, faces, voices, or places. It’s a rare disorder involving one (or more) of the senses.
Agnosia usually affects only a single information pathway in the brain. If you have this condition you can still think, speak, and interact with the world.
There are several different types of agnosia. Visual agnosia, for example, is an inability to name or describe the use for an object placed in front of you when just looking at it. You’ll still be able to reach for it and pick it up. You can also use your sense of touch to identify what it is or its use once you’re holding it.
Agnosia occurs when the brain experiences damage along certain pathways. These pathways involve sensory processing areas. These parts of the brain store knowledge and information regarding perception and identification of things.
Agnosia is usually caused by lesions on the parietal, temporal, or occipital lobes of the brain. These lobes store semantic information and language. Strokes, head trauma, or encephalitis can cause lesions.
Other conditions that damage or impair the brain can also cause agnosia. These conditions include:
- brain cancer
- states of anoxia (loss of oxygen supply to the brain) including carbon monoxide poisoning
There are 3 main types of agnosia: visual, auditory, and tactile.
Visual agnosia occurs when there’s brain damage along the pathways that connect the occipital lobe of the brain with the parietal or temporal lobe.
The occipital lobe assembles incoming visual information. The parietal and temporal lobes allow you to understand the meaning of this information.
Apperceptive visual agnosia
Apperceptive visual agnosia causes difficulty in perceiving shapes or forms of an object that you see. This condition may cause you to have difficulty in perceiving the difference from one object to another upon visual inspection.
You may not be able to copy or draw a picture of an object. Instead, you may 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, and knowledge of what the object is used for remains intact.
Apperceptive visual agnosia is usually caused by lesions to the occipito-parietal cortex.
Associative visual agnosia
Associative visual agnosia is the inability to recall information associated with an object. This includes an object’s name and knowledge of its use.
This form of agnosia doesn’t prevent you from being able to draw a picture of an object.
Although you’re unable to name the object on visual inspection, you may be able to recognize and use an object shown to you when it’s accompanied by verbal or tactile cues.
Associative visual agnosia is usually due to lesions of the bilateral occipito-temporal cortex.
Prosopagnosia (face blindness)
Prosopagnosia is the inability to recognize familiar 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 can damage this region.
Autism may also cause difficulty recognizing faces. 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 (color blindness)
Achromatopsia, which is acquired color blindness with an inability to identify colors that you see. This is usually caused by a lesion in the left occipito-temporal region.
Agnosic alexia (pure alexia)
Pure alexia is the inability to recognize words visually. It’s not possible to read with pure alexia. You can usually still speak and write without difficulty though.
Akinetopsia (motion blindness)
Akinetopsia is the inability to perceive motion of visualized objects. This rare 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 verbal agnosia
Auditory verbal agnosia is also known as pure word deafness. It’s the inability to recognize and understand spoken words, despite intact hearing. It’s usually related to a lesion in the right temporal region.
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. There’s usually association with a lesion in the right half of the brain.
You can still understand words spoken by others if you have this condition. You may also still be able to 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 be unable to understand the significance or the use of the object. Lesions in the parietal lobe of the brain are commonly the cause of tactile agnosia.
You can still name objects by sight. You’re also able to draw pictures of objects, as well as reach for them.
Autotopagnosia is when you lose the ability to visually orient or recognize the parts of your own body.
Damage to the left parietal lobe of the brain can cause this condition. You are aware of where your limbs are in space at all times, even with closed eyes.
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.