Agnosia- This is a violation of various types of perception that occurs when the cerebral cortex and the nearest subcortical structures are affected.
Agnosia is associated with a lesion of the secondary (projection-association) divisions of the cerebral cortex, which are part of the cortical level of the tester systems.
The defeat of the primary (projection) parts of the cortex causes only elementary sensitivity disorders (impaired visual function, pain and tactile sensitivity, hearing loss). With the defeat of the secondary sections of the cerebral cortex of the hemispheres, the elementary susceptibility of a person is saved, but he loses the ability to test and synthesize incoming information, which leads to a violation of various types of perception.
There are several main types of agnosia:
Visual Agnosiaappear with the defeat of the secondary occipital cortex. They are manifested in the fact that a person - with sufficiently safe visual acuity - cannot recognize objects and their images (subject agnosia),to distinguish between spatial features of objects, basic spatial coordinates (spatial agnosia); he disrupts the process of identifying persons with the safety of the perception of objects and their images (facial agnosia, or prozopagnosia), disrupts the ability to classify colors while preserving color vision (color agnosia), the ability to distinguish letters (alphabetic agnosia) is lost, the volume of simultaneously perceived objects is sharply reduced (simultaneous agnosia).
The nature of visual agnosia is determined by the side of the lesion and the localization of the lesion within the secondary cortical fields of the occipital parts of the large hemispheres and the adjacent parietal and temporal areas.
Tactile agnosiaappear when the secondary cortical fields of the parietal lobe of the left or right hemisphere are affected and manifest as a disorder in the identification of objects by touch (astereognosis) or in a violation of the recognition of parts of one’s own body, a violation of the body’s schema (somatoagnosis).
Auditory agnosiaappear with the defeat of the secondary cortical fields of the temporal lobe. With the defeat of the temporal cortex of the left hemisphere, auditory or hearing-speech agnosia manifests itself as a violation of phonemic hearing, i.e.violations of the likelihood of distinguishing speech sounds, which leads to speech disorders; with the defeat of the temporal cortex of the right hemisphere (in right-handed people), auditory agnosia itself occurs - the improbability of recognizing familiar non-musical sounds and noises (for example, barking dogs, creaking sounds, rain noise, etc.) or amusia - the improbability of recognizing familiar melodies, disorder of music hearing