Visual agnosia

Mental blindness, and visual agnosia or visual agnosia is an error in the processing of visual stimuli by the brain, caused by damage to the visual cortex in the occipital lobe and causes that individuals are unable to recognize objects or faces, though they see them. The individual symptoms may vary depending on the exact cause and location of the damage. Some sufferers can, for example, emerge no pictures, but otherwise circumvent quite adept with objects. Typically, patients objects can indeed describe in great detail (eg by color, shape and texture of the surface ), but are not able to recognize them and name. The description of known objects from memory often poses no problem With special face blindness is called prosopagnosia. The counterpart while listening is the soul of deafness.

Origin of the term

The term mental blindness comes from Hermann Munk, who has the visual cortex surgically removed in dogs. They acted as though superficial blind, ie they could not visually recognize things, but they still responded to visual stimuli. Heinrich Lissauer transferred this concept to a disorder of the visual system in humans, after the patient Gottlieb L. studied:

" In fact, there was once that of the otherwise over all sensible information -giving man was except able to recognize a large portion of the most common sensory objects by means of the sense of sight. But well recognized and he described everything correctly, what he feel with your hands or could perceive by the ear. This involves the patient can see ... "

Lissauer proposed two different types of mental blindness before: the apperceptive mental blindness and the associative mental blindness:

• Apperceptive mental blindness occurs because of damage to the early visual areas and prevents object recognition by the inability of the various elements of visual perception into a coherent whole ( Lissauer called this a " performance" ) put together.

• Associative mindblindness contrast, occurs when the " idea " can not be brought together with the information and perceptions of other modalities to create a vorlinguistische representation of the object.

The term " agnostic " or " agnosia ", which today is mostly used instead of mental blindness comes from Sigmund Freud, including but more neuropsychological disorders of the visual system in a broader sense understood as only the soul blindness. In the Freudian sense, agnosia, in addition to the mental blindness also includes cortical blindness and optic aphasia. However, the term ( visual ) agnosia is used today for the soul blindness with the Lissauerschen subcategories.

Importance of mental blindness

As with many neurological disorders, as here, wearing the exact investigation of the disease not only for research into the disease itself, but also to a better understanding of the corresponding process in the healthy brain - in this case the visual process - at.

Studies of stroke patients and in monkeys have shown that the visual perceptual apparatus consists of two specialized systems. After the basic processing of visual stimuli in the primary visual cortex, the processing paths share ( centrally along the crest to front) in a parietal and a temporal ( to the temple directed towards ) processing power. These have different functions. And according to Mishkin Ungerleider processing flow for temporal especially object recognition (hence called What stream) is directed out of the running along the apex of the processing power of movement and distance determination (hence called also WO - current). This view has been challenged by Milner and Goodale. Due to a double dissociation of patients with visual apraxia, on the one hand recognize objects, but can not access targeted, and on the other hand, patients with visual Formagnosie ( a particularly severe form of apperceptive agnosia ) that take objects, but may not realize have Milner and Goodale proposed a now generally accepted reinterpretation of processing streams. The oriented to the temporal power is even still considered to be responsible for object recognition, but the apex oriented stream is no longer seen as for the processing of spatial information, but as necessary for the Visuomotor (ie the action- current).