The 5 Types Of Agnosia (visual, Auditory, Tactile, Motor And Body)
Brain injuries frequently cause cognitive deficits that affect a specific sensory modality, such as vision or touch.
When these problems are due to the lack of recognition of stimuli, the diagnosis of “agnosia” is used. In this article we will describe the 5 types of agnosias: visual, auditory, tactile, bodily and motor
Agnosia is defined as inability to process certain kinds of sensory stimulation Depending on the cognitive systems that are affected, deficits may appear in different functions, for example in the recognition of visual information, in the execution of sensorimotor patterns or in language comprehension.
Generally, agnosias appear as a consequence of brain lesions; They are very common in those resulting from ischemic strokes, neurological disorders such as dementia or traumatic brain injuries, particularly when the regions where the occipital and temporal lobes join are involved.
In these disorders the perception of stimuli is not altered in itself but rather the problem is located at a higher stage of the perceptual process: it is associated with the memory (more specifically with the recovery) of specific cues that allow us to relate the information we perceive with the information we have stored in memory.
The term “agnosia” comes from classical Greek and It can be translated as “absence of knowledge” or “of recognition.” It was coined by Sigmund Freud, the father of psychoanalysis, in 1891, but pioneers of neuropsychology such as Carl Wernicke or Heinrich Lissauer had theorized about similar concepts in the previous decades.
The most common thing is that agnosias occur in a single sensory modality. Therefore it is useful to divide The main classes of agnosias and their corresponding subtypes depending on whether they fundamentally affect the perception of visual information, sounds, touch, motor schemes or the perception of our own body.
1. Visuals
Most visual agnosias consist of deficits in the recognition of objects through sight. without any involvement of the sensory organs The most famous case of visual agnosia is probably the one that gave the title to “The Man Who Mistook His Wife for a Hat,” the best-seller by neurologist Oliver Sacks.
This type of agnosia normally occurs due to lesions in the left occipital lobe or any of the temporal lobes. We can divide visual agnosias into two categories: the apperceptive, in which there are problems categorizing objects, and the associative characterized by the inability to name them.
Prosopagnosia, which consists of a deficit in face recognition (but is also associated with problems naming animals or car brands, for example), is the best-known type of associative visual agnosia. Regarding apperception, simultagnosia is worth highlighting, in which the elements are processed appropriately but not the whole.
2. Auditory
In auditory agnosias, recognition problems occur in relation to sound stimuli. Although when the brain lesions that cause agnosia are very important, the deficits can be general in nature, the most common thing is that they only affect the brain. a type of auditory stimulation, such as receptive language or music (amusia)
Verbal auditory agnosia, also known as “pure word deafness,” is one of the most relevant agnosias within this category. In these cases, the affected person has difficulties distinguishing speech sounds from the rest of the auditory stimuli that he perceives, or recovering the meaning of sets of phonemes.
3. Tactile or somatosensory (stereognosias)
Tactile or somatosensory agnosia can be defined as a inability to identify objects through touch, based on aspects such as its texture or size, despite the fact that there are no sensory alterations. Another name for this type of disorder is “stereognosia.”
A clinically significant subtype is digital agnosia, which specifically affects recognition through the fingers. It generally occurs together with agraphia, acalculia and left-right disorientation in the context of Gerstmann syndrome, caused by lesions in the lower part of the parietal lobe.
4. Motor (apraxias)
The term “motor apraxia” is used very infrequently due to the great popularity of one of its synonyms: “apraxia.” Apraxias consist of difficulties remembering and executing motor schemes intentionally learned; However, the same movements can appear spontaneously in their natural contexts.
Three main types of motor agnosia have been described: ideational apraxia, in which there are difficulties in carrying out sequences of movements, ideomotor, characterized by the inability to execute actions in response to a verbal request, and constructive, which consists in trouble constructing shapes or drawing figures.
5. Corporal
In bodily agnosias there is a inability to identify one’s own body We talk about somatognosia when the problems are related to the entire body, hemiasomatognosia if they appear only in one of its halves, and autotopagnosia in cases where the person is able to spatially locate the parts of his or her body.
