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
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
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.
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
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.