Or seeing a person's form or shape in a chair or a coat-rack. Or seeing water shimmering on in the desert. Visual illusions are mirages. Visual illusion are fleeting or transitory. Visual hallucinations usually persist longer.
Visual illusions are more likely to occur in conditions of dim or poor lighting.
Visual illusions may, under circumstances of dim or poor light be normal. Or Visual illusion may be abnormal-a forerunner of visual hallucinations. Hallucinations of sound, auditory hallucinations, can be unformed or formed. Auditory hallucinations can be frightening, or pleasant. Unformed auditory hallucinations consist of hearing distorted noises, music, sounds, or voices.