visual hallucination
visual perception in the absence of any external stimulus. Visual hallucinations may be unformed (e.g., shapes, colors) or complex (e.g., figures, faces, scenes). In hallucination associated with psychoses (e.g., paranoid schizophrenia, alcohol- or hallucinogen-induced psychotic disorder), the individual is unaware of the unreality of the perception, whereas insight is retained in other conditions (e.g., pathological states of the visual system). Visual hallucinations may arise in association with lesions of the peripheral or central visual pathway or visual cortical areas; they are often present in temporal-lobe epilepsy and may appear during prolonged isolation. See also peduncular hallucinosis.