Agnosia is a rare disorder in which a person cannot recognize or identify familiar objects, persons, or sounds, despite normally functioning senses. There are several different types of agnosia a person can experience after brain injury, depending on where the damage occurred.
In this article, you will learn more about the types and forms agnosia can take, plus some helpful ways to manage it.
What is Agnosia?
Agnosia causes problems with recognition. For example, a person with agnosia might see a pencil, but not recognize it as one. If you asked them what it was or what it was used for, they may not be able to tell you.
Many people often confuse agnosia with aphasia. However, while these conditions can present similarly, their underlying causes are different.
With certain types of aphasia, a person struggles with producing words. This means they can still understand what the object is, they just can’t find the word(s) to name or describe it. Therefore, if you showed them an apple, they would recognize it and know that it is a fruit, but may not be able to say the word “apple.”
On the other hand, a person with agnosia may not even recognize the apple. In some cases, this has to do with impairments in perceptual processing. However, there are other types of agnosia where the individual does not recognize the object despite not having impairments in perceptual processing.
Causes of Agnosia After Brain Injury
Agnosia is typically caused by lesions to the occipital, temporal, or parietal lobes. It occurs when the brain sustains damage along certain sensory pathways.
These pathways store knowledge about familiar objects, persons, and sounds. They are what allow you to instantly recognize what a cup, for example, is used for.
When these pathways become damaged, this knowledge can be lost. As a result, the brain cannot recognize/identify objects like it used to.
Categories of Agnosia After Brain Injury
Agnosia can manifest in several different ways, depending on where the brain damage occurred. Doctors typically separate agnosia into three basic categories:
- Visual agnosia
- Auditory agnosia
- Tactile agnosia
We’ll cover some examples of these types in the sections below.
Types of Visual Agnosia
Visual agnosia refers to the inability to recognize objects through vision, despite normal visual function.
Patients with visual agnosia can usually recognize an object by using their other senses, however. For instance, they could identify a cup by holding it and feeling its shape and texture.
Some common types of visual agnosia include the following:
Also known as face-blindness, this type of agnosia makes it difficult for a person to recognize familiar faces. For someone with prosopagnosia, staring at their best friend’s face can feel like staring at a stranger.
They can, however, usually still identify other aspects of a person such as their gender, hair, and clothing. They can also usually recognize their loved one by the sound of their voice.
Prosopagnosia is caused by lesions to the fusiform face area located on the inferior temporal cortex.
Some patients with prosopagnosia can still recognize facial expressions and cues, but some with more severe agnosia cannot. For example, they would not know that a smile means the person is happy, etc.
This type of agnosia refers to the inability to recognize objects when they appear together. They may be unable to grasp the overall meaning of a picture. For example, when looking at a house, a person with simultanagnosia may not perceive a house, but only doors or a window, depending on what they were looking at.
There are two main types of simultanagnosia that a person can experience after brain injury:
- Dorsal simultanagnosia. With this type, a patient cannot see more than one object at a time. When they focus on that one object, everything else disappears to them. They often bump into objects close together because they do not perceive them, and may have difficulty reading. This type is caused by bilateral damage to the occipital and temporal lobes.
- Ventral simultanagnosia. People with this type can see more than one object at once, but they cannot identify what the objects are unless they focus on one. Ventral simultanagnosia is caused by lesions in the left inferior occipital area.
Akinetopsia causes problems with perceiving motion.
Most people with this condition see moving objects as a series of stills, as if the objects are moving under a strobe light. In severe cases, a person would not see any motion at all.
Akinetopsia tends to occur after damage to the occipital lobe.
Color Agnosia and Pure Word Alexia
Color agnosia refers to the inability to identify or distinguish colors. This type of agnosia is hard to diagnose and is often confused with color blindness. But unlike color blindness, it is not caused by a defect in the eye but rather an injury to the occipital lobe.
Pure word alexia is another common type of agnosia. This type causes problems recognizing written words. As a result, the person with alexia may not be able to read. However, they can usually still write without difficulty.
Finally, this type of visual agnosia causes problems with navigating surroundings due to an inability to interpret spatial information. Therefore, the person may have trouble orienting themselves.
Even when a person has an excellent memory and can describe the layout of their home, they would still struggle to get to the kitchen from their bedroom.
This type of agnosia is caused by damage to the right posterior cingulate.
Types of Auditory and Tactile Agnosia
These types of agnosia affect a person’s senses of hearing and touch.
As with visual agnosia, the actual senses themselves are still intact, but the brain can no longer process the information they send.
Some types of auditory agnosia include:
- Verbal agnosia. Also known as pure word deafness, this makes a person unable to understand spoken words. However, these individuals can typically read, write, and speak properly, which is what distinguishes it from some types of aphasia.
- Phonagnosia. This causes an inability to recognize familiar voices. You can still understand words spoken by others, but you would not know who is speaking without looking.
- Non-verbal auditory agnosia. With this type, a person cannot identify or differentiate between non-verbal sounds. For example, when they hear a car motor start, they would not associate it with an engine or car.
- Amusia. This causes an inability to recognize music. For people with this condition, music is just another type of sound.
Damage to the temporal lobe causes these types of agnosia.
In addition, some types of tactile agnosia include:
- Amorphognosia. Difficulty identifying the shape and size of an object by touch. For example, you could not tell if an object is round or square just by feeling it.
- Anosognosia. Difficulty identifying other distinctive qualities of an object by touch, such as weight.
Tactile agnosia is caused by damage to the parietal lobe.
Managing Agnosia After Brain Injury
There is no direct cure for agnosia. Rather, occupational therapists will help their patients develop alternative cues and strategies. These strategies teach patients to compensate for their type of agnosia by relying on the other senses that have not been affected by the agnosia.
For example, a person with verbal agnosia might need to learn sign language or lip-reading. For patients with prosopagnosia, a therapist might teach the patient to recognize people by their hairstyles.
While these techniques will not reverse agnosia, they can make living with it a little easier.
Understanding the Types and Causes of Agnosia
Agnosia causes difficulty in recognizing familiar persons, objects, and sounds. While agnosia does not cause impairments to your senses directly, it will typically involve one of your senses of sight, sound, or touch, depending on where the damage occurred.
Agnosia sometimes resolves on its own as the brain heals. If it does not, you can learn different techniques to help you compensate for your deficits. Talk to an occupational or speech therapist for more suggestions about how to manage agnosia.
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