rachelmanija | Hallucinations, by Oliver Sacks

A book on hallucinations which are not caused by schizophrenia and other psychotic disorders. (It also doesn’t deal much with culturally normal hallucinations, which is too bad.) Hallucinations – sensory perceptions which occur during waking and are not based on consensus reality - are surprisingly common, and include many experiences which probably most people don’t think to define as hallucinatory.

While drifting off to sleep, with my eyes closed, I often see kaleidoscope-like geometric patterns, faces (often grotesque or witch-like), and occasionally swarming insects. They are not dreams, are not perceived as being part of reality or projected into the real visual field, and do not have emotional connotations. I always assumed they were caused by going from visual perception to blank darkness while drifting toward sleep: a sort of meditative optical illusion/visual imagination.

They are called hypnogogic hallucinations and are extremely common, and the particular things I see are commonly seen, along with other stereotyped visuals. (“Stereotyped” as in common to people who experience the phenomenon, as opposed to “unique.”) They are caused, in simple terms, by the visual centers of the brain “idling” before sleep.

Hypnopompic hallucinations are less common, and are more vivid, often briefly perceived as real, often frightening illusions which occur upon waking from sleep. I've had those too, thankfully only a few times; mine were quite unpleasant, full-sensory illusions of being entombed in stone. They were not nightmares, though; I could also see my real surroundings. Once someone in the room with me verified that I had my eyes wide open and could track movement and respond to voices.

I have also sometimes, while wide awake, heard my name being called, when no one is there or when nobody called it. This is also extremely common. People in dangerous situations often hear voices giving helpful commands or suggestions; grieving people often see or hear their loved ones. These phenomena are common and “normal.”

I wish Sacks had analyzed those situations more in neurological terms, because I find that fascinating. The main theory he suggests, regarding auditory hallucinations in general, is that they’re a glitch caused by the brain failing to recognize its own thoughts. Another possibility is that people become consciously aware of the non-verbal stream of consciousness beneath their articulated thoughts, and perceive it as coming from the outside.

Sacks covers a number of hallucinatory experiences caused by neurological conditions, such as Charles Bonnet Syndrome, in which blind people hallucinate certain types of sights. Also, in a fairly funny chapter, his own youthful drug use.

The non-psychotic hallucinations are typically either never experienced as “real,” or are easily believed to be unreal once someone explains that they aren’t real, or are understood to not be real once they’re over. This is quite different from psychotic disorder-type hallucinations, which are often believed to be real, even when they end. (A person with PTSD may hallucinate, but they typically either always know the hallucination isn’t real, or, as in the case with flashbacks, figure it out in retrospect.) Regarding culturally normal hallucinations like ghosts, people may believe that they did literally see a spirit, but they also regard it as a spirit – a visitor from another realm. That’s a different experience from literally believing that Abraham Lincoln is living in your guest bedroom. (To avoid wank, let’s assume that I am only discussing those perceptions of spirits, God, etc, when they really are hallucinated and not objectively real.)

Hallucinations without accompanying delusions don’t usually cause major life problems for people. They are not “crazy,” though they might worry that they are. Delusions seem to be what cause the life problems.

The book is well-written and intriguing, as one would expect from Sacks, but more descriptive than analytical. Some types of hallucinations, particularly visual ones with a clear-cut neurological basis such as migraine auras, are explained in neurological terms, but others are simply described. The descriptions are quite evocative and the material is fascinating, but I would have liked more neurological speculation, especially on why certain situations or conditions create certain types of hallucinations, like fever deliriums causing distorted perceptions of size, which are almost invariably perceived as unpleasant or threatening.

I also wish he’d covered auditory hallucinations in more depth. At times he speculated on historical figures who might have heard voices. The problem is, many people write about the simple perception of their own thoughts in voice-like terms, so it’s very hard to tell whether someone literally meant they heard a voice, or only that their thoughts were so vivid that they seemed voice-like. It seems entirely possible, too, that two different people might have a neurologically identical experience, but one might attribute it to an outside voice and one to distinctive inner thoughts.

Please discuss your own experiences of and theories on hallucinations, if you wish.

Hallucinations