Көру арқылы заттарды тану қабілетінің бұзылуы

Impairment in recognition of visually presented objects
Visual agnosia is an impairment in recognition of visually presented objects. It is not due to a deficit in vision (acuity, visual field, and scanning), language, memory, or intellect. While cortical blindness results from lesions to primary visual cortex, visual agnosia is often due to damage to more anterior cortex such as the posterior occipital and/or temporal lobe(s) in the brain. [2] There are two types of visual agnosia: apperceptive agnosia and associative agnosia. Recognition of visual objects occurs at two primary levels. At an apperceptive level, the features of the visual information from the retina are put together to form a perceptual representation of an object. At an associative level, the meaning of an object is attached to the perceptual representation and the object is identified. If a person is unable to recognize objects because they cannot perceive correct forms of the objects, although their knowledge of the objects is intact (i. e. they do not have anomia), they have apperceptive agnosia. If a person correctly perceives the forms and has knowledge of the objects, but cannot identify the objects, they have associative agnosia.

While most cases of visual agnosia are seen in older adults who have experienced extensive brain damage, there are also cases of young children with less brain damage during developmental years acquiring the symptoms. Commonly, visual agnosia presents as an inability to recognize an object in the absence of other explanations, such as blindness or partial blindness, anomia, memory loss, etc. Other common manifestations of visual agnosia that are generally tested for include difficulty identifying objects that look similar in shape, difficulty with identifying line drawings of objects, and recognizing objects that are shown from less common views, such as a horse from a top down view. Although he can recognize facial features and emotions – indeed he sometimes uses a standout feature to recognize a face – face recognition is almost impossible purely from visual stimuli, even for faces of friends, family, and himself. The disorder also affects his memory of faces, both in storing new memories of faces and recalling stored memories. This occurs even when no damage has been done to the eyes or optic tract that leads visual information into the brain; in fact, visual agnosia occurs when symptoms cannot be explained by such damage. Damage to specific areas of the ventral stream impair the ability to recognize certain categories of visual information, such as the case of prospagnosia. For example, patient DF had lesions to the ventral surface that gave her apperceptive agnosia.

Broadly, visual agnosia is divided into apperceptive and associative visual agnosia. Apperceptive agnosia is failure of object recognition even when the basic visual functions (acuity, color, motion) and other mental processing, such as language and intelligence, are normal. The brain must correctly integrate features such as edges, light intensity, and color from sensory information to form a complete percept of an object. If a failure occurs during this process, a percept of an object is not fully formed and thus it cannot be recognized. Tasks requiring copying, matching, or drawing simple figures can distinguish the individuals with apperceptive agnosia because they cannot perform such tasks. Associative agnosia is an inability to identify objects even with apparent perception and knowledge of them. It involves a higher level of processing than apperceptive agnosia.

Patient C. K. was born in 1961 in England and emigrated to Canada in 1980. In January 1988, C. K. sustained a head injury from a motor vehicle accident while out for a jog. Following the accident, C. K. experienced many cognitive issues, mood swings, poor memory, and temper outbursts. C. K. also had motor weakness on the left side and a left homonymous hemianopia. He recovered well, retaining normal intelligence and normal visual acuity. He was able to complete a master's degree in history, later working as a manager at a large corporation. Although his recovery was successful in other areas of cognition, C. K. still struggles to make sense of the visual world.

Magnetic resonance imaging (MRI) showed bilateral thinning of C. K.'s occipital lobe which resulted in associative visual agnosia. C. K. makes many mistakes when trying to identify objects. For example, he called an abacus "skewers on a kebab" and a badminton racquet a "fencer's mask". A dart was a "feather duster" and a protractor was mistaken for a "cockpit". Despite this impairment in visual object recognition, C. K. retained many abilities such as drawing, visual imagery, and internal imagery. As a native of England, he was tasked with drawing England, marking London and where he was born. His accurate drawing of England is just one example of his excellent drawing abilities.

Patient C. K. provided evidence for a double dissociation between face processing and visual object processing. Patients with prosopagnosia have damage to the Fusiform Face Area (FFA) and are unable to recognize upright faces. C. K. has no difficulty with face processing and matches the performance of controls when tasked with identifying upright famous faces. When shown inverted faces of famous people, C. K. performs significantly worse than controls. This is because processing inverted faces involves a piecemeal strategy. C. K.'s performance is compared to patients with prosopagnosia who are impaired in face processing but perform well identifying inverted faces. This was the first evidence for a double dissociation between face and object processing suggesting a face specific processing system.

A famous report on this condition is the title essay of Oliver Sacks' book, The Man Who Mistook His Wife for a Hat. The murder suspect in the Picket Fences episode "Strangers" supposedly had agnosia. The patient in the House episode "Adverse Events" had agnosia. In the graphic novel Preacher, the character Lorie has an extreme version of agnosia resulting from being born with a single eye. For example, she perceives Arseface, a man with severe facial deformities, as resembling a young James Dean. Val Kilmer's character has visual agnosia in the film At First Sight. In "Folie à Deux", a fifth season episode of The X Files, Mulder succumbs to the same belief as telemarketer Gary Lambert, that his boss Greg Pincus is a monster who disguises his true appearance by means of hypnosis. Scully, although believing this notion preposterous, suggests that what Mulder describes is analogous to an induced visual agnosia. The short story "Liking What You See: A Documentary" by Ted Chiang examines the cultural effects of a noninvasive medical procedure that induces a visual agnosia toward physical beauty.