The 6 types of visual agnosia and their symptoms

These are the different forms that this neurologically rooted perceptual disturbance can take.

Visual agnosia is an acquired neurological condition characterized by a difficulty in visually recognizing and processing objects. visually recognize and process objects. It has been described since the late 19th century and different types and manifestations are currently recognized.

In this article we will see what are the types of visual agnosiaWhat were its first definitions and what are its main manifestations.

What is visual agnosia?

Visual agnosia is an acquired difficulty in identifying objects through vision. It occurs without damage to the ocular system, without visual disturbances and without significant intellectual modifications. It mainly affects the ability to perceive and process elements such as colors, shapes and movements.

In other words, it is a condition in which the ocular ability to perceive objects persists, but the ability to recognize their characteristics, and therefore to integrate them, is lacking. the ability to recognize their characteristics and, therefore, to integrate them as an operative mental representation. as an operational mental representation.

Visual agnosia occurs when visual processing is carried out irregularly. Such processes involve the retinal receptors, which is an extension of the central nervous system, with circuits and nerve cells, as well as photoreceptor cells called rods and cones. The latter react to light and transmit the message to other cells that carry it to the brain.

After a complex process involving different types of cells and microsystems, the message reaches specifically the primary visual cortex of the brain, located in the occipital lobe, near the calcarine fissure. The specific region associated with the visual system, and therefore with agnosia, is the bilateral occipito-temporal junction.

In the latter, neurons are distributed in different areas according to the stimuli they process, and are responsible for analyzing the attributes of visual images. All of the above helps to initial representation of objects and their characteristics, which translates into a perception of the object.This is translated into a specific perception of the observer, and then into a stage of recognition centered on the object and its semantic information (the nomination is made).

It is in these latter stages that some difficulties leading to visual agnosia have been identified.

Background and first definitions

In 1890, the German neurologist Heinrich Lissauer defined this difficulty in visual recognition as "blindness of the mind" or "blindness of the soul", and divided it into two main types: apperceptive and associative. In his theory, strongly based on the recognition systems, agnosia is a consequence of the disorganization of the processes necessary to perform visual analysis and to attribute meaning to them..

It was in 1891 when Sigmund Freud, who in addition to being a psychoanalyst was a neurologist, baptized this condition as "agnosia". The word agnosia comes from the Greek "gnosis" which means knowledge, and the prefix "a" which means "absence of", so it refers to a condition characterized by an "absence or lack of knowledge".

6 types of visual agnosia

Several types of visual agnosia have been identified since its earliest definitions. For example, we speak of a pure visual agnosia when it manifests only through the sensory channel of vision, however, in many occasions it is also linked to the tactile or auditory channels (tactile agnosia, and auditory agnosia).

In any case, some of the main subtypes of visual agnosia are apperceptive agnosia, associative agnosia, prosopagnosia, achromatopsia, alexia and acinetopsia.

Visual apperceptive agnosia

Visual apperceptive agnosia is characterized by a difficulty in connecting the parts of an image into a comprehensible whole. This translates into a difficulty in understanding the relationships that exist between objects.

In other words, there is no structuring of the visual stimuli received, so it is a condition that affects the discriminative stage of visual identification, which ultimately has repercussions for the inability to represent such stimuli. For example, the person may have serious difficulties in representing or matching objects through drawings and images.

It is usually caused by lesions in the temporal lobe or parietal lobe, in both cerebral hemispheres.

2. Associative visual agnosia

Associative visual agnosia is characterized by a difficulty in evoking information associated with the names, uses, origins or specific characteristics of objects.

Both apperceptive agnosia and associative agnosia are usually assessed, for example, on the basis of the person's ability to copy pictures. In this case, the person can perform tasks such as drawing or picture matching, but has difficulty naming them. Similarly, the person can use objects that are shown to him or her, but has difficulty telling which object is being has difficulty saying what the object is..

3. Prosopagnosia

Prosopagnosia consists in the difficulty to recognize faces. It is caused by the specific functioning of the fusiform area, which is a region of the brain associated precisely with facial recognition. Prosopagnosia may occur, for example, in people with Alzheimer's disease and other neurodegenerative conditions.

4. Achromatopsia

Achromatopsia is characterized by difficulties in recognizing the colors of objects. In some cases there is recognition of colors but there is no possibility of naming them.. It is associated with lesions in the V4 region of the brain, and is related to the regions in charge of regulating linguistic activity.

5. Alexia

Alexia is the difficulty to visually recognize words. Sometimes people can speak and write without major difficulty, but they maintain problems telling what the word is once they see it written down.

6. Acinetopsia

Acinetopsia is characterized by a difficulty in recognizing motor activity. This means that the person presents some problems to perceive the movement of objects as a whole. In other words, movements are perceived as sequences of instantaneous actions without continuity.. The latter can occur in varying degrees. When the condition is severe, the person may lose the ability to recognize any type of movement.

Literature references:

• Healthline (2018). What causes agnosia?. Retrieved June 22, 2018. Available at https://www.healthline.com/symptom/agnosia.
• Maritza, J. (2010). Visual agnosia. Science and Technology for Eye and Vision Health. 8(1): 115-128.