Simultanagnosia (or simultagnosia) is a rare neurological disorder characterized by the inability of an individual to visually 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).
[2] 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.
Patients take a clearly piecemeal approach to interpreting the scene by reporting isolated items from the image.
[1] Upon examination of higher nervous system functions, patients display no general intellectual impairments.
For example, one study found that four patients with progressive dementia eventually developed symptoms of simultanagnosia as well as components of Gerstmann's syndrome and transcortical sensory aphasia.
[11] In addition, patients with Huntington's disease have been found to exhibit visual impairments similar to those of simultanagnosia.
In contrast to Bálint's hypothesis, Thaiss and De Bleser studied a patient who had a physical restriction of her attentional window.
The patient's ability to perceive multiple objects and identify global structures significantly improved as the size of the presented image decreased.
People without simultanagnosia are able to perceive numerous objects at once because they can shift their attention rapidly enough between stimuli so that percepts are integrated before they decay from short-term memory.
Parietal lesions damage the master map of locations, and as a result, a variety of deficits can occur, including simultanagnosia.
Since only a single explicit binding could occur between spatial and shape information, the patient was incapable of perceiving more than one object at a time.
[9] Bilateral lesions to the parieto-occipital junction may cause the ventral circuit to slow down; as a result, patients with simultanagnosia have difficulty discriminating among visual features.
[17] The results suggest that impairments in parsing, such as the process by which important regions are extracted from the retinal image, or difficulty in discriminating elementary visual features led to simultanagnosia.
The indexed features, or anchor points, can serve as a "spotlight" that directs focal attention to certain objects, which can then channel visual information to specialized systems for space and shape analysis.
In addition, perception is slowed, and low-level visual processing is disrupted since the patient would not be able to extract and index salient features.
[7] However, a recent study demonstrated that recovery may be related to finding ways to expand the restricted attentional window—their global gestalt perception—that characterizes the disorder.