The world of neuropsychology is full of different disorders that some people could never imagine. And if you ever wondered if there are people who can see, hear and feel objects for multiple times, but never can understand and recognize them, yes, there are. So, which term refers to the failure to recognize familiar objects perceived by the senses? The answer is ‘agnosia’.
Agnosia is the inability to recognize objects, sounds, places, faces, etc. Inability to recognize anything means that a person with a certain type of agnosia cannot identify certain objects that they have seen before. For example, people with prosopagnosia (inability to recognize faces) are not able to remember familiar faces when they see them. The main reason behind this disorder is is damage of the brain, and types and forms of agnosia refer to impairments of different brain parts. It usually affects only one pathway of the brain and does not affect other functions like thinking, memory, or speech. Coming back to the example with prosopagnosia, these people can recognize their friends and acquittances by recognizing their gait, clothing style, voice, etc.
Agnosia has two forms which are apperceptive agnosia and associative agnosia. All types of agnosia (visual, auditory, tactile and olfactory) can occur in apperceptive and associative forms.
Apperceptive Agnosia
Apperceptive Agnosia Definition
Apperceptive agnosia is inability to recognize visual, auditory, tactile or olfactory information due to disruption in the early stages of perception. This form of agnosia affects brain pathways that are in charge of perception itself which is why recognition of different objects, sounds, tactile feelings etc. fails. For example, people with apperceptive visual agnosia cannot recognize and copy or draw certain objects, because of the difficulty in perceiving forms and shapes of objects. It should be mentioned, that apperceptive visual agnosia is more common than apperceptive auditory, tactile and olfactory types.
Apperceptive Agnosia: Parts of Brain Damaged
It is hard to define exact part of the brain damaged that caused apperceptive agnosia, because each agnosic patient has unique disease patterns. However, it was noticed that impairments in the parietal, temporal, or occipital lobe is highly associated with apperceptive agnosia. Their functions are:
- parietal lobe – integration of sensory information from most regions of the body;
- temporal lobe – processing auditory information and encoding of memory.
- occipital lobe – processing of visual information.
Associative Agnosia
Associative Agnosia Definition
Knowing what apperceptive agnosia is, it is easier to define associative agnosia which is not inability to recognize objects due to perception damage, but difficulty connecting perceived objects with information about them. This means that associative agnosics are able to perceive objects accurately, but still cannot recognize them. For example, patients with apperceptive visual agnosia cannot copy and draw objects, while those with associative visual agnosia can copy and draw perceived objects, but still cannot name them or tell their main functions. This feature is usually used in order to distinct apperceptive and associative agnosics in the process of diagnostics.
Associative Agnosia: Parts of Brain Damaged
Due to its subjective nature, it is even harder to understand what damaged brain parts cause associative agnosia than in case of apperceptive agnosia. Lesions in different brain pathways can cause associative agnosia. However, one common neurological feature lies in all types of associative agnosia: damage to the inferior occipitotemporal regions. This part of the brain has many function, main of them are:
- lexical processing,
- memory,
- processing of visual information.
Apperceptive Agnosia vs Associative Agnosia
The short table to distinguish main differences between apperceptive and associative agnosia:
Apperceptive agnosia | Associative agnosia |
Failure in perceiving objects. | Failure in connecting objects with existing information about them. |
Inability to copy objects. | Ability to copy objects. |
Inability to perceive forms and other features of objects. | Ability to perceive forms and other features of objects. |
Three Types of Agnosia
Agnosia is classified into three types:
- visual,
- auditory,
- and sensorimotor.
Visual agnosia is the inability to recognize objects by their look. This includes:
- prosopagnosia as inability to recognize familiar faces;
- agnostic alexia as inability to recognize words visually and, as a result, inability to read;
- color agnosia as inability to recognize and identify colors despite not having any defection in perceiving visual information;
- other forms of visual agnosia.
Auditory agnosia, defined as the inability to recognize audial information, includes:
- phonagnosia – inability to recall familiar voices,
- amusia which is inability to recognize music and melodies,
- verbal auditory agnosia as inability to understand spoken words,
- nonverbal auditory agnosia as inability to recall familiar sounds.
Sensorimotor agnosia, or the inability to recognize objects by touch, includes:
- anosognosia as inability to recall weight and texture of objects,
- amorphognosia as difficulty in recognizing shapes and forms of objects by touch,
- autotopagnosia as inability to recognize different parts of one’s own body.
Diagnostics, Treatment and Management of Agnosia
Studies of agnosia are deeply multidisciplinary and mostly include knowledge from psychology, neurology, and neurobiology. It is also important that sometimes this disorder can be mistreated as neuropathy, cataracts, dyspraxia, dysphasia or other diseases. Which is why in order to diagnose agnosia of any form and type patients would go through different tests like CT and brain MR, psychological examination, tests for brain functioning etc.
There is no direct way to treat agnosia with surgical intervention or use of medicine. It is only possible to treat other disorders that come along with agnosia. However, there is practice of neuropsychological rehabilitation for agnosics. This includes proposing a patient a way to compensate what prevents them from living fully. For example:
- patients with prosopagnosia can be taught to recognize people by hairstyles, gait, scars, voice and so on,
- patients with verbal auditory agnosia can learn how to lipread,
- patients with different types of visual agnosia can be taught how to recognize objects by touch.
There is another type of rehabilitation which is restoration. This way of help is focused on training damaged brain pathway and restoration it functions with a program of certain exercises. Types of exercises depend on the damaged part of the brain.
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