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From the publisher’s website: 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 descriptions, Oliver Sacks investigates the fundamental differences and similarities of these many sorts of hallucinations, what they say about the organization and structure of our brains, how they have influenced every culture’s folklore and art, and why the potential for hallucination is present in us all.

First Author: 
Oliver Sacks
Reviewed for SPR by: 
Tom Ruffles
SPR Review: 

Someone concerned with whether paranormal phenomena have any basis in reality might assume that a book devoted to hallucinations will have nothing to teach; after all, hallucinations are not what a psychical researcher wants to investigate.  But if you can’t tell one from another, you have a problem.  Oliver Sacks, the “Poet Laureate of Medicine” according to the New York Times, provides an accessible, if at times sketchy, overview of a complicated subject, and the implications for paranormal investigators are a cause for concern.  If you think you see a ghost, how do you decide whether it is veridical or subjective?  Hallucinations can affect all sense modalities, and while they run the gamut from realistic to outlandish, they can be remarkably convincing.  They may have their origin in neurological damage, often of the temporal or parietal lobes, but others affect neurologically healthy individuals.  Some types are extremely common.  Sacks gives an example of hypnopompic imagery recounted to him by a Mr. Fish:

“The most typical one would involve me sitting up in bed and seeing a person – often an old lady – staring at me at some distance from the foot of my bed. (I imagine that such hallucinations are thought to be ghosts by some people - but not by me.)  Other examples are seeing a foot-wide spider crawling up my wall; seeing fireworks; and seeing a little devil at the foot of my bed riding a bicycle in place.” (p.212)

Yes, seeing an old lady at the foot of the bed would be interpreted as a ghost by some, and it could be argued that Mr. Fish may have seen a ghost as well, but being of a sceptical bent chose to interpret the figure as a hallucination.  The spider though gives one pause as it would be an unlikely resident of his bedroom (though Mr. Fish is an Australian so a foot-wide spider sounds plausible).  The cycling devilette is doubtful too, and the fireworks definitely had no external reality, or he would have detected the residue afterwards.  If the fireworks weren’t real, why should the old lady be?

‘Lynn O.’ had hallucinations as part of a narcoleptic syndrome.  She told Sacks that she wished that she had received the narcolepsy diagnosis earlier, because previously she had interpreted her experiences as paranormal rather than as elements of a sleep disorder.  Her assumption that they were paranormal, that is external to her, had delayed her in seeking “more constructive” (i.e. medical) help, but that help had allowed her to come to terms with her condition.  As she wrote to Sacks, she had to reexamine those ‘paranormal’ experiences and readjust her view of the world: “It is like letting go of childhood or, rather, letting go of a mystical, almost magical view of the world.  I must say, perhaps I am experiencing a touch of mourning.” (p.223)  In other words, her earlier interpretation fulfilled a psychological need to make sense of her situation, albeit a maladaptive one.  Alternatively, did a form of liquid cosh block her psychic receptivity?  That remains a possibility.

Hallucinations are not restricted to ‘the external being experienced in here’; they can also involve the sense of ‘the internal being experienced out there’.  It might be a reasonable assumption that an out-of-body experience linked to taking LSD or accompanying migraine or an epileptic seizure is subjective, but in some situations the default interpretation could be a paranormal one.  OBEs can accompany narcolepsy and sleep paralysis, for example, and as the example of Lynn O. indicates, an experient might not be aware of their condition’s underlying pathology.  ‘Jeanette B’, with a history of narcolepsy and sleep paralysis, experienced OBEs and admitted that she “found it very difficult to believe it was a hallucination.” (p.255)  Moreover, the experiences became addictive to the point of her attempting to optimise the conditions required for them to occur, and refusing medication that she knew would have prevented them.

OBEs are also associated with near-death experiences, and Sacks deals with the latter as well in terms of hallucination caused by neurophysiological changes combined with stress arising from the extreme situation, though he passes over the subject in a couple of pages and does not engage with the extensive literature that has built up on it in recent years.  But then he does not feel he has to, because it is straightforward to interpret.  He notes a case where a surgeon was struck by lightning and had an NDE even though his heart had stopped for “little more than thirty or forty seconds.” (p.259)  In an interview in Skeptical Inquirer (‘Oliver Sacks on Hallucinations’, May/June 2013), Sacks again refers to this case (though in the interview the cardiac arrest victim’s experience now occupies only “twenty or thirty seconds”).  There he draws the conclusion that the surgeon’s “whole cosmic journey only occupied a matter of seconds”, which he uses to comment on the now-famous case documented by Eben Alexander in his recent book Proof of Heaven: A Neurosurgeon's Journey into the Afterlife that the claim of the reality of such a paranormal experience based on its complexity cannot be sustained because “a few seconds of altered consciousness as one emerges from coma would be enough to give him such a state.” (SI, Vol. 37, Issue 3, p.52).  We already know that hallucinations can feel intensely real.  This would mean that any talk of a flat EEG, such as in the even more famous Pam Reynolds case, is irrelevant because the NDE occurs in a very brief period on emergence from the period when the brain is inactive, but can seem convincing to the point of changing the experient’s life.

Sacks briefly touches on the phenomenon of the bereaved experiencing the return of loved ones, though he sceptically examines these cases as aspects of “The Haunted Mind” rather than the haunted person, the ‘reappearance’ for him representing a compulsive return to the past during a time of emotionally-charged turmoil.  These appearances can be so vivid that it is hard to believe that the deceased has not returned, and they are mostly, though not always, comforting.  Unfortunately Sacks skims over this important phenomenon, and does not offer an adequate analysis of what might be happening.  That they do not always occur in a context of intense grief is indicated by the account supplied by ‘Malonnie K’ who ‘saw’ her seventeen-year-old cat the day after it died while she was getting ready for work.  The routine may have induced a mild altered state of consciousness which was a carrier for the longing she felt to have her pet back, but there is no suggestion that she was experiencing the sort of acute emotion that would be caused when a spouse dies.  It is a puzzle why she hallucinated her cat, assuming it was a hallucination of course, while many people who have been married for a long time do not experience the return of their spouse after death (though it is possible that such incidents are under-reported, and some spouses doubtless are more relieved than devastated by their loss).  The closest Sacks comes to an explanation is when he muses that “bereavement causes a sudden hole in one’s life, a hole which – somehow – must be filled.  This presents a cognitive problem and a perceptual one as well as an emotional one, and a painful longing for reality to be otherwise.” (p.231)  He seems to be saying that the brain is ‘filling in’ for the missing person in much the same way that it would fill in for an amputated limb which the amputee can still feel.

Unfortunately, experiences are not always benign.  Sleep paralysis accompanied by hallucinations is surprisingly common, affecting perhaps a third to a half of the general population, and can be “vivid, elaborate, multimodal and terrifying” (p.226).  The ‘Old Hag’ phenomenon is well known to psychical researchers, but for those suffering “the sense of terror and doom” it brings with it, it is easy to believe that they are being persecuted by a supernatural being against which they are literally powerless to act.  That class of hallucination shows how difficult it can be to tell, while it is occurring, whether an experience is hallucinatory or has an objective reality when it seems so real.  You might dismiss an event as a hypnagogic (ie when falling asleep) because it occurred with closed eyes, in the dark, but Sacks notes that hypnopompic hallucinations can be seen in bright illumination with open eyes, and seem solid.  They can have a strong emotional impact, much as one might have if confronted with a ghost.  Sacks considers this very point:

“Indeed, one must wonder to what degree the very idea of monsters, ghostly spirits, or phantoms originated with such hallucinations.  One can easily imagine that, coupled with a personal or cultural disposition to believe in a disembodied spiritual realm, these hallucinations, though they have a real physiological basis, might reinforce a belief in the supernatural.” (p.215)

He briefly discusses Frederic Myers, one of the founders of the SPR, who coined the term ‘hypnopompic’.  Sacks dismisses both Phantasms of the Living (of which Myers was a co-author) and Myers’ own Human Personality and its Survival of Bodily Death on the grounds that “one feels” the majority of the psychical experiences recounted in them are actually hallucinations arising from “states of bereavement, social isolation, or sensory deprivation, and above all in drowsy or trancelike states.” (p.216)  One might want to discount Sacks’ verdict on the grounds that having a feeling is not providing evidence, but one feels in turn that he may have a point (even while somewhat sceptical that he has read both those lengthy works from end to end).

Given all the complications, think how hard it is for an investigator, interviewing a witness who claims to have had an anomalous experience, to get at the truth.  The witness may well be supplying an honest account, not realising how easy it is for our brains to fool us into thinking that something is there when it isn’t.  Sacks would argue that the lesson of Hallucinations is that you may think it is difficult to discriminate between an objective and subjective experience, but actually the experience is always subjective, the ghost never has an external reality.  The standard answers in the psychical research literature revolve around reliance on shared experiences, or the transfer of veridical information, but this is a field beset with uncertainty.  The witness may well have seen a ghost, but the investigator recording their story cannot rule out possible counter-explanations in terms of hallucination.

This then is a book that should be read by psychical researchers because they need to be aware of the many ways in which we can be tricked by our cognitive apparatus.  It should not though be read uncritically.  Sacks makes the somewhat sweeping statement that “Any consuming passion or threat may lead to hallucinations in which an idea and an intense emotion are embedded.” (p.231), but it cannot be that simple.  His book is crammed with examples of hallucinations that could be construed as having a paranormal component, but this he refuses to countenance on the grounds that we are all susceptible to suggestion.  He considers that if we believe a house can be haunted, even though naturally the proposition is “scoffed at by the rational mind” (p.250), and the belief is combined with emotional arousal in a setting of ambiguous stimuli, then hallucinations may result.  That’s hauntings disposed of in under a page.  Children’s imaginary friends? Hallucinations.  One feels that he is not giving the matter much attention as he assumes that hallucination obviously has to be the correct conclusion.  Towards the end he cites the hypothesis that the ‘feeling of presence’ is part of our biological inheritance, an evolutionary adaptation relating to threat that is controlled within the temporal lobe (p.291).  It may well be, and one can see the advantages in such a mechanism.  What might trigger this in someone who is sitting around, so not experiencing a sense of threat, when a ghost appears Sacks does not address, and one feels that there is likely to be more involved than the activation of a circuit in the temporal lobe.  Whether a complete explanation should invoke the paranormal is another matter.


A separate review of Hallucinations by Robert A. Charman appeared in the July 2014 issue of the SPR’s Journal.

Reference Information: 
Hallucinations. Picador, November 2012. ISBN-13: 978-0307957245