From the best-selling author of Musicophilia and The Man Who Mistook His Wife for a Hat, a provocative investigation into hallucinations--auditory, visual, tactile, olfactory--their many guises, their physiological sources, and their personal and cultural resonances.Hallucinations, for most people, imply madness. But there are many different types of non-psychotic hallucination caused by various illnesses or injuries, by intoxication--even, for many people, by falling sleep. From the elementary geometrical shapes that we see when we rub our eyes to the complex swirls and blind spots and zigzags of a visual migraine, hallucination takes many forms. At a higher level, hallucinations associated with the altered states of consciousness that may come with sensory deprivation or certain brain disorders can lead to religious epiphanies or conversions. Drawing on a wealth of clinical examples from his own patients as well as historical and literary...