Beyond its literal sense concerning the visual system, the term<unk>  is also used metaphorically in several fields, including neurology, neuropsychology, psychology, philosophy, and politics. The common theme of all the figurative senses is of a gap not in visual function but in the mind's perception, cognition, or world view. Their concrete connection to the literal sense, however, is by the connection between the nervous system and the mind, via the chain of links from sensory input, to nerve conduction, to the brain, to perception (the processing and interpreting of that input) via the brain-mind correlation, to psychological function. Thus there is not only (or not necessarily) a visual inability to see an aspect of reality but also (or instead) a mental inability to conceive even the possibility of seeing that aspect, due to a cognitive schema that lacks any provision for it. At the most concrete level, there is neuropsychological<unk> . One example is the hemispatial neglect that is sometimes experienced by people who have had strokes. Another type is the phenomenon of reverse or negative phantom limb, in which nerve injuries to the limbs, such as trauma in which a limb's nerves are severed but the limb is spared from amputation, can affect the mind's body schema in such a way that an existing limb seems to its owner like it should not exist, and its presence thus seems uncanny. Neurologist Oliver Sacks, who experienced a reverse phantom leg that later resolved, considered it a form of spatial neglect in the body schema analogous to hemispatial neglect in that the mind could not conceive of the leg as self because it could not conceive that there was any space for the leg to exist in. Sacks and others agreed that the leg thus seemed like someone else's leg, including sometimes a cadaverous one, which was part of the reason for the dysphoria but not the sole explanation. Even for people who intellectually understood that the leg or hand was supposed to be theirs simply could not believe it emotionally and could not completely reconcile reality with schema, prompting great unease. Given how hard this is to comprehend for a person who has not experienced it, people recently experiencing it for the first time consider it both uncanny and ineffable (as Sacks self-reported and found in others). Sacks also explored the regular type of phantom limb (a positive phantom), which does not produce a neuropsychological<unk>  but shares with reverse phantoms the trait that the body schema resists revision despite a person's perfect intellectual awareness and acceptance of the current physical reality (that is, that the amputated limb is gone or that the spared limb is still present). This suggests that aspects of schema in the mind (body schema, world schema) have neurologic bases that cannot be revised by mere intellectual understanding—at least not quickly. Sacks does explore the topic of how people adapt to phantoms over the years and how positive phantom limbs often gradually foreshorten and sometimes disappear; but some remain for the rest of life. At a higher level of abstraction are what have been called , in which a person's self-perception of his or her own personality is judged by others to have a gap in perceptive ability. Thus, in psychology,<unk>  can refer to a person's inability to perceive personality traits in themselves that are obvious to others. And at the highest abstraction level are what have been called intellectual<unk> s, in which a person cannot perceive distortions in their world view that are obvious to others. Thus, in philosophy or politics, a person's thoughts or beliefs might be shaped by an inability to appreciate aspects of social interaction or institutional structure.
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