Simultanagnosia (or simultagnosia) is a rare neurological disorder characterized by the inability of an individual to perceive more than a single object at a time. This type of visual attention problem is one of three major components (the others being optic ataxia and optic apraxia) of Bálint's syndrome, an uncommon and incompletely understood variety of severe neuropsychological impairments involving space representation (visuospatial processing). The term "simultanagnosia" was first coined in 1924 by Wolpert to describe a condition where the affected individual could see individual details of a complex scene but failed to grasp the overall meaning of the image.

Simultanagnosia can be divided into two different categories: dorsal and ventral. Ventral occipito-temporal lesions cause a mild form of the disorder, while dorsal occipito-parietal lesions cause a more severe form of the disorder.

Patients with simultanagnosia, a component of Bálint's syndrome, have a restricted spatial window of visual attention and cannot see more than one object at a time in a scene that contains more than one object. For instance, if presented with an image of a table containing both food and various utensils, a patient will report seeing only one item, such as a spoon. If the patient's attention is redirected to another object in the scene, such as a glass, the patient will report that they see the glass but no longer see the spoon. As a result of this impairment, simultanagnosic patients often fail to comprehend the overall meaning of a scene.

In addition, patients note that one stationary object may spontaneously disappear from view as they become aware of another object in the scene.

Simultanagnosic patients often exhibit a phenomenon known as "local capture" where they only identify the local elements of stimuli containing local and global features. However, recent studies have demonstrated that implicit processing of the global structure can occur. With the appropriate stimulus conditions, explicit processing of the global form may occur. For example, a study performed with Navon hierarchical letters, which are large letters composed of smaller ones, revealed that the use of smaller and denser Navon letters biased the patient towards global processing.

Inconspicuous akinetopsia can be triggered by high doses of certain antidepressants with vision returning to normal once the dosage is reduced.

Inconspicuous akinetopsia can be selectively and temporarily induced using transcranial magnetic stimulation (TMS) of area V5 of the visual cortex in healthy subjects. It is performed on a 1 cm² surface of the head, corresponding in position to area V5. With an 800-microsecond TMS pulse and a 28 ms stimulus at 11 degrees per second, V5 is incapacitated for about 20–30 ms. It is effective between −20 ms and +10 ms before and after onset of a moving visual stimulus. Inactivating V1 with TMS could induce some degree of akinetopsia 60–70 ms after the onset of the visual stimulus. TMS of V1 is not nearly as effective in inducing akinetopsia as TMS of V5.

In terms of the specific rehabilitation of visuoperceptual disorders such as Bálint's syndrome, the literature is extremely sparse. According to one study, rehabilitation training should focus on the improvement of visual scanning, the development of visually guided manual movements, and the improvement of the integration of visual elements. Very few treatment strategies have been proposed, and some of those have been criticized as being poorly developed and evaluated.

Three approaches to rehabilitation of perceptual deficits, such as those seen in Bálint's syndrome, have been identified:

1. The adaptive (functional) approach, which involves functional tasks utilising the person's strengths and abilities, helping them to compensate for problems or altering the environment to lessen their disabilities. This is the most popular approach.

2. The remedial approach, which involves restoration of the damaged CNS by training in the perceptual skills, which may be generalised across all activities of daily living. This could be achieved by tabletop activities or sensorimotor exercises.

3. The multicontext approach, which is based on the fact that learning is not automatically transferred from one situation to another. This involves practicing of a targeted strategy in a multiple environment with varied tasks and movement demands, and it incorporates self-awareness tasks.

Bálint's syndrome is an uncommon and incompletely understood triad of severe neuropsychological impairments: inability to perceive the visual field as a whole (simultanagnosia), difficulty in fixating the eyes (oculomotor apraxia), and inability to move the hand to a specific object by using vision (optic ataxia). It was named in 1909 for the Austro-Hungarian neurologist and psychiatrist Rezső Bálint who first identified it.

Bálint's syndrome occurs most often with an acute onset as a consequence of two or more strokes at more or less the same place in each hemisphere. Therefore, it occurs rarely. The most frequent cause of complete Bálint's syndrome is said by some to be sudden and severe hypotension, resulting in bilateral borderzone infarction in the occipito-parietal region. More rarely, cases of progressive Bálint's syndrome have been found in degenerative disorders such as Alzheimer's disease or certain other traumatic brain injuries at the border of the parietal and the occipital lobes of the brain.

Lack of awareness of this syndrome may lead to a misdiagnosis and resulting inappropriate or inadequate treatment. Therefore, clinicians should be familiar with Bálint's syndrome and its various etiologies.

Memory disorders are the result of damage to neuroanatomical structures that hinders the storage, retention and recollection of memories. Memory disorders can be progressive, including Alzheimer's disease, or they can be immediate including disorders resulting from head injury.

Agnosia is the inability to recognize certain objects, persons or sounds. Agnosia is typically caused by damage to the brain (most commonly in the occipital or parietal lobes) or from a neurological disorder. Treatments vary depending on the location and cause of the damage. Recovery is possible depending on the severity of the disorder and the severity of the damage to the brain. Many more specific types of agnosia diagnoses exist, including: associative visual agnosia, astereognosis, auditory agnosia, auditory verbal agnosia, prosopagnosia, simultanagnosia, topographical disorientation, visual agnosia etc.