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This book explores the complex realm of hallucinations, and explains how they happen not only to people who are ill, but also to those who are completely healthy. Drawing on various studies, patient cases and the author’s own experiences, it describes the different causes and types of hallucinations, and shows that they're actually a common phenomenon that manifest in a variety of ways.

  • Anyone interested in psychology
  • Anyone who's ever seen, heard, smelt or felt something that wasn't there
  • Anyone who wants to understand the science and neurology behind hallucinations

Oliver Sacks is a world-renowned neurologist, writer and professor at the New York University School of Medicine. He's written several successful books, including Musicophilia: Tales of Music and the Brain and The Man Who Mistook His Wife for a Hat. His book Awakenings was adopted into an Academy Award-nominated film.

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Hallucinations

By Oliver Sacks
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Hallucinations by Oliver Sacks
Synopsis

This book explores the complex realm of hallucinations, and explains how they happen not only to people who are ill, but also to those who are completely healthy. Drawing on various studies, patient cases and the author’s own experiences, it describes the different causes and types of hallucinations, and shows that they're actually a common phenomenon that manifest in a variety of ways.

Key idea 1 of 9

Visual hallucinations can be caused by blindness, impaired sight or sensory deprivation.

Have you ever seen, smelled, heard, or felt something, only to realize it was your imagination? Hallucinations are perceptions that occur without a corresponding external reality. In other words, you hallucinate when you involuntarily sense something that's not really there.

People who become blind, or whose sight is otherwise impaired, often experience visual hallucinations. In fact, one study showed that out of nearly 600 elderly people with visual problems, about 90 percent experienced some form of hallucinations. Fifteen percent experienced complex hallucinations, where they “saw” things like people, animals or entire scenes. Eighty percent had simple hallucinations, meaning they saw shapes, colors and sometimes patterns.

When a person with partial or severe blindness experiences visual hallucinations, it's called the Charles Bonnet Syndrome (CBS). Charles Bonnet, a Genevan naturalist, first described it in 1760. He observed it in his grandfather, and later, in himself.

Oliver Sacks once had a blind patient named Rosalie who had complex CBS hallucinations that played before her like a movie. She saw highly realistic people wearing colorful Eastern dress, and they walked in and out of the scene before her without addressing her in any way.

One reason blind or partially blind people experience hallucinations like this is that the hallucinations spring from the same areas of the brain as visual perception. That means they're physiologically distinct from the images we create when we deliberately imagine something.

Sensory deprivation can also cause visual hallucinations. For example, people hallucinate when they're exposed to the same monotonous scene, like darkness, for a prolonged period of time. This is often called the prisoner's cinema.

The prisoner's cinema is so powerful that all people seem to experience it eventually after some period of isolation. Visions can range from simple geometric patterns to complex scenes, because of the increasing excitability of the visual cortex.

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