Anomalous Perceptual Experiences: Believing is Seeing is Believing

In modern Western cultures, hallucinations carry implications of abnormality. Faced with a patient who claims to have been visited by angels, dead souls, or extraterrestrials; or to have engaged in “astral travel”; or to have been possessed by unseen spirits, some physicians would consider these experiences pathological, suggesting the need for treatment. In any given instance, they may well be right, for hallucinations and delusions in nonintoxicated people can be signs of metabolic or endocrine diseases, psychoses, brain damage, or other serious neurological disorders. Hallucinations are not always pathological, however, and are not as uncommon in normal people as generally believed.1 If one were to call them religious visions, at least a sizeable minority would consider the perceiver somewhat privileged.

Reading media accounts of seemingly average citizens claiming to have had contacts of varying degrees of intimacy with space aliens, spirits of the dead, demons, or angels, it is tempting to question the honesty or the sanity of the contactees. People who report such experiences are probably neither fools nor psychotic or neurologically impaired. Although one cannot credit the objective reality of their experiences, most of the people describe what they believe to have been real events.

This review of hallucination by Dr Beyerstein is part of the Scientific Review of Alternative Medicine’s series on basic science subjects that are fundamental to the understanding of anomalous medical experiences and claims. We have been and will be exploring basic knowledge—from physics and chemistry to psychology and sociology, from logic to semantics and esoteric philosophies—in order to enable as broad an understanding as possible of the manifold aspects of nonrational, anomalous claims.

In this case, we intend for readers to relate the experience of “healing” to that of hallucinosis and other extraordinary experiences. “Healing,” as used in the parlance of sectarian medicine, is not the same as the phenomenon of recovery from disease. Disease recovery is an often slow and emotionally barren experience, devoid of physical or mental pleasure and devoid of elevated or transcendent experience, except perhaps in the recall and retelling (though the audience is more often bored than receptive). Healing may be nothing more than that—a slow adjustment to the unfortunate or the inevitable.

But another aspect of the healing phenomenon refers to an experience of insight or elevated, transcendent awakening—more than a mere accommodation to a traumatic health situation. Healing may refer to the events experienced at a religious ritual to those of emotional accommodation to loss or physical impairment. These experiences have not been well studied or even well defined.

Hallucination has been studied. It is familiar to every physician through experiences with alcohol withdrawal and drug toxicity, and the effects of isolation in acute medical units. Many are not aware of the rich research data on the subject. Because of hallucination’s relationship to other unusual mental states, and because so much is known about it, we think it appropriate to draw parallels between hallucination and the healing experience. They are both normal phenomena and both may be more common than is appreciated.

There are also obvious differences between an experience of healing and an experience of alien abduction—particularly, that the former can be objectively documented while the latter cannot. One does accommodate to disease. However, both have the aforementioned emotional components, and both may be affected by the interplay between sensory stimuli from external sources and material generated internally. Both are affected by memory and personal needs. Both can be at odds with observed fact. Recipients of healings often claim to be healed until death. In future articles we will present commentary from the experiential healing literature to support the relationship. Meanwhile, Dr Beyerstein’s comments should shine light on the entryway to this understanding. —Eds.


What is a physician to conclude when confronted with a patient describing such contacts and experiences? Harvard psychiatrist John Mack2 asserts that most “experiencers” (to use his preferred term) would not merit diagnoses of serious psychopathology by standard criteria. While other experienced therapists3 and researchers4 agree that most selfprofessed abductees are not psychotic, they have found that the individuals tend to exhibit a variety of less debilitating psychological peculiarities. Similarly, Spanos and his colleagues5 found a number of unusual cognitive traits in a sample of UFO abductees who responded to newspaper ads soliciting their participation in research on the abduction phenomenon. Many of these volunteers were found to hold unconventional cosmological beliefs that predated the episodes. In addition, the experiences typically involved an abrupt alteration in consciousness. Spanos5 recognized that sleep paralysis often includes hallucinations,6 and was the most prevalent association in the abductees. Rodeghier et al.4 also noted a fairly high incidence of sleep-related problems in their sample. A large proportion of subjects reported that their alleged abductions or occult visitations occurred in the borderland between sleep and full arousal.

Spanos and his colleagues5 found that in their selfselected sample of alien abductees, the subjects were generally well-adjusted by conventional clinical criteria. (However, the recruitment method might have biased the sample toward those who were more normal, or wished to appear so.) But the investigators discovered a number of unusual thought patterns when they probed the volunteers more extensively. Virtually all of the many contactees who have approached me over the years have held quite unconventional cosmological beliefs. In their defense, the contactees would contend that their eccentric beliefs were adopted in response to their experiences. They said they had come to think the way they do because of some truly life-altering events that in a religious context might be called revelations. Many of them describe themselves as having been chosen for some higher purpose. Despite their protestations, it seems that their willingness to adopt paranormal explanations for anomalous, subjective experiences usually predates the particular episodes they described.

After subjecting their volunteer subjects to extensive testing, Spanos et al.5 concluded that neither a peculiar belief structure nor an anomalous subjective experience would be sufficient in itself to create the prototypical abductee. The sequence seems to be that someone with an affinity for unconventional speculations and beliefs experiences an unusual subjective event, such as sleep paralysis, hypnopompic imagery, an unusual drug effect, or an atypical migraine episode. A person with peculiar cosmological views would be strongly disposed to interpret and embellish the experience to be consistent with those views.

It seems that having both an eccentric metaphysical outlook and a rich fantasy life is conducive, but insufficient in itself, to mold someone into a contactee. But, given those predisposing attitudes and certain psychological needs, it becomes likely that an unexpected alteration of consciousness would unfold along these idiosyncratic lines. Contactees tend to reject that explanation, contending that they had no special interest in UFOs, religious lore, etc., prior to their visitations or abduction experiences. However, it is virtually impossible to avoid the stream of books, TV programs, and movies by or about people who say they were abducted by space aliens (the secular, high-tech theme) or who say they were visited by angels and demons (the religious counterpart). Even if people cannot recall being exposed to these narratives, the well-documented process known as “cryptomnesia” can leave unrecognized traces that will influence later experiences. Entertainment provides rich suggestive material for people seeking answers to existential dilemmas and difficulties in living. This provides the cultural license to embroider any warp in consciousness. Mack and other contactee supporters see the commonalities in contactee scenarios as grounds for accepting the objective truth of the experiences, rather than as evidence for a psychological basis for them.

Mack and others conduct support groups for experiencers. They argue that there are few payoffs for joining the ranks of the contactees, hence these experiences must be real. They say that these encounters are often horrific, and that those who admit to them incur many social costs as well. Why, then, they ask, would anyone make up such a story? In my opinion, the question misses the point. Most experiencers seem sincere; they describe something that felt real. That does not mean that their experiences were objectively real. It also does not exclude psychological payoffs associated with redefining oneself as a contactee. Apologists underrate the social advantages that accrue to someone who dons the mantles of victim and “chosen one.” Our society has spawned a cult of victimization that excuses, supports, and compensates people in a variety of ways—sometimes, unfortunately, by reinforcing their delusions.7,8 For someone with a weak sense of identity and self-worth, the rewards for adopting the contactee/abductee role can be substantial. A visitation from a superior being can satisfy a need for meaning and specialness that we all feel from time to time. It can also provide those in distress with existential support and explain why their lives are not productive and fulfilling.

Otherworldly messengers can allay anxiety by offering a hedge against fate or, if the experience is traumatic, it can supply a cloak of victimization that allows the troubled person to shift the blame for various personal shortcomings, or social or occupational reverses. Simply having an explanation—even if far-fetched— for disquieting emotions or memories, or difficulty in concentrating, applying oneself, or controlling one’s weight, can be a powerful incentive in itself. And for those of a more apocalyptic bent, comfort can be derived from the belief that somewhere, superior beings have apparently conquered the problems that humans seem helpless to overcome. Powerful entities that come at night from the sky have long had strong appeal for the worried and the perplexed.9,10,11

Humans try to make sense of sudden, emotionally charged experiences by fitting them into their social and philosophical leanings. In order to do so, they adorn raw sensations in ways that create a good fit. In much the same way psychedelic drug experiences develop, spontaneous shifts in consciousness can be strongly shaped by these psychosocial influences, called set and setting. “Set” refers to the knowledge, beliefs, expectations, aspirations, mood, and personality of the drug user. “Setting” includes the physical and social situation in which the experience occurs.12 Set and setting can have equally important influences on spontaneous and induced hallucinations. Ghost sightings are more frequently encountered by believers than by skeptics, and seem to be associated more with graveyards and musty, dark, Victorian residences than with well-lit, glass-and-steel skyscrapers.

Experiences similar to those related by abductees have been recorded throughout history,13 but every era adapts the basic scenario to conform to its prevailing worldview. Thus, fairies, leprechauns, incubi and succubi, and “old hags”—the night-time intruders of years gone by14,15—have been largely supplanted in today’s narratives by high-tech variants more acceptable to twenty-first-century sensibilities. Traditional religious themes appear to have withstood the social changes and still insert themselves in many accounts. Recent best-sellers and television documentaries celebrating guardian angel interventions attest to their periodic recurrence.


Anomalistic psychology is the study of peculiar subjective phenomena reported by ostensibly normal individuals.16,17,18 The field concentrates on those states of consciousness that have traditionally been considered mystical or supernatural. Workers in the discipline approach each investigation with the presumption that, unless there are clear indications of pathology or intent to deceive, informants’ narratives are probably a fairly accurate account of their experiences. While researchers recognize the impact and believability of these experiences, they assume that such episodes have naturalistic explanations. The episodes are presumed to be altered states of consciousness that are manifestations of unusual, though not necessarily pathological, states of the brain. They can be triggered by a variety of physical and psychosocial causes. In many instances, knowledge in psychology and neuroscience provide plausible explanations.19,20 As Reed17 points out, it is possible to be deluded without being psychotic. Researchers in anomalistic psychology hope that by studying these experiences, they will expand our knowledge of how the brain creates the mental model of the external world we call reality.

When one stops to consider that normal people typically spend about one-twelfth of their lives vividly hallucinating—that is to say, dreaming—it seems plausible that there could be occasional leakage of dreamlike activity into normal waking consciousness. Some describe mechanisms that suppress dreamlike mentation from entering awareness during wakefulness.21 They have suggested how the brain’s arousal and attention systems could allow visual images from memory to predominate during dreams, but not normally while awake. The neurochemistry of this proposed gating mechanism is affected by hallucinogenic drugs and abnormalities underlying organic hallucinations. Thus, in those and other circumstances, waking consciousness might be swamped by highly emotional, dreamlike imagery.22,23,24

Other researchers have shown that most people experience bouts of visual imagery periodically during the day.25,26,27 Ordinarily, these episodes are easily distinguished from real events, but for some people this kind of imagery can be so compelling that it temporarily supplants the sensory-driven model of reality.28 Understanding how such illusory but highly believable experiences contribute to belief in paranormal phenomena is a central interest of anomalistic psychology.


Hallucinations are perceptions that lack corresponding external stimuli, but nonetheless seem objectively real. The experience can be full or partial; i.e., it can be a complete but entirely self-generated experience of an external world, like a dream; or it can involve the perception of nonexistent objects interwoven with an otherwise accurate rendition of present surroundings. Fullblown hallucinations integrate imagery from all sense modalities, feel unwilled by the percipient, and have all the detail, vividness, and emotional impact that make them convincing.29

The term “vision” encompasses essentially what is meant by “hallucination,” but has the further connotation of mystical significance. According to occultists and some religious fundamentalists, “visions” (or “voices”) emanate from all-powerful, enlightened entities and are directed specifically to the recipient for his or her edification—i.e., a revelation. History records that many revered figures, such as Joan of Arc, Martin Luther, Saint Paul, Muhammad, and Mozart, felt they had been guided in this way. But history also warns that Adolf Hitler, Attila the Hun, Idi Amin, and Charles Manson also had experiences that made them feel similarly chosen by higher forces for special purposes. They all experienced their voices and visions as “coming from beyond.”30(p30) It is not equally apparent, however, that these events occurred outside the theater of their own minds.

Since ancient times, visions of ghosts, demons, angels, and deities have fueled supernatural beliefs and spawned new religions. A close relative is the “hallucination of presence,” in which one senses the nearness of unseen entities.17,31 Likewise, “transcendent,” “neardeath,” and “out-of-body” experiences have been taken as evidence for an afterlife, higher planes of existence, cosmic consciousness, and other mystical states, although they also have prosaic explanations.32 Occasionally, percept-like insertions can blend with accurate impressions of the environment, creating “sightings” of fairies and other phenomena—such as the space-age version, alien spacecraft, sometimes piloted by rapacious crews.

Mechanisms of Hallucinations

People often claim, “I saw it with my own eyes.” In so doing, one invites the inference that it existed “out there”—somewhere in the real world. If, instead, one had said, “I saw it with my own brain,” the statement, although closer to the truth, would have lost much of its intended force. That is because it would no longer demand the concession that one had perceived a tangible object “out there.”

Although the statement “I saw it with my own brain” may have an odd ring, it serves to remind us that the cerebral mechanisms of perception—where sensory events are really experienced—are at some remove from the scene of the action. Perceptions are transformations of environmental stimuli encoded in networks of active brain cells. Quite early in the process, the brain inserts memory and emotional and cognitive material into the perceptual stream. The input imparts names, meanings, and significance to the raw sensory information. This in turn sparks additional associations from memory that further enrich the experience. Thus, the exact placement of the boundary between raw sensation and the cognitive processes responsible for constructing our global awareness of the world is somewhat arbitrary. Perception has sometimes been referred to as “sensory reasoning,” as a way of acknowledging the fact that the final product owes more to cognitive interpretation and embellishment than commonly thought.33

The 19th-century psychologist Sir Francis Galton34 emphasized the continuity of all forms of visualization, whether stimulus-driven or memory-driven. Neurologically speaking, sensations, mental imagery, dreams, daydreams, and hallucinations are cut from the same cloth. Perceptions are cognitive constructions assembled from raw sense data, seamlessly combined with the images from memory that “flesh out” all conscious awareness. There is a constantly shifting relative preponderance of external (sensory) versus internal (memory) inputs to the cerebral mechanisms that cobble together our model of reality in awareness. Siegel35 has emphasized that there is competition between external and internal inputs for access to this central awareness system, and that hampering any of the contenders leaves the stage open for additional contributions from its rivals. Marks26 and Loverock and Modigliani36 have reviewed studies supporting the conclusion that the same cerebral mechanisms serve both perception and imagery. Schatzman37 reinforced this conclusion with electroencephalographic (EEG) data from people who can produce extremely vivid hallucinations at will. EEG recordings show that auditory hallucinations are correlated with activity in the brain areas that mediate perceptions of real sounds,38 and more recently this has been confirmed with PET scans.39,40

Because functionally equivalent states of the central awareness system can be built up with raw materials from either memory or sensory sources, it is possible for dreams, perceptual memories, fantasies, and hallucinations to become indistinguishable, on occasion, from perceptions of real events. Hallucinations result whenever internal events trigger a pattern of brain activity equivalent to that normally generated when sensory systems respond to a publicly observable event. Thus, if for any reason the brain’s awareness mechanisms were to be flooded by neural discharges from memory banks, the experience could feel just as real as if it had been engendered by actual events “out there.”

How we ordinarily distinguish perceived reality from vivid mental imagery or daydreams and why this ability should occasionally break down are central to an understanding of hallucinations.29 The ability of the brain to create illusory experiences so complete as to pass for reality can be seen as an occasional cost we incur in return for the ability to think and remember in complex images, to conjure up believable tableaux in our “mind’s eye.” In order for imagery to be useful in solving problems and testing out prospective actions in a mental “dry run,” we require neural systems capable of creating imagined models of the world with considerable veracity. That a representational system of this sophistication should occasionally fool us ought to surprise no one—it is a price we pay for being able to let our ideas die in our stead.

Predisposing Conditions

A diverse range of conditions can trigger hallucinations.41 Siegel,35 for instance, has combed the medical and psychological literature to find a number of obscure and fascinating causes for hallucinations that could explain otherwise baffling events. In some of these instances, he tried out his hypothesized precipitators on himself.

The probability of hallucinating rises with functional shifts within the brain’s awareness mechanisms.42 One predisposing factor is anything that prompts a shift from lexical (i.e., word-based) thinking to imagistic or pictorial thinking. Another is anything that turns the brain’s representational system toward internal sources of input (images from memory). This could arise because of a paucity of external stimulation (isolation). It also can occur because internal processing is amplified by strong motivation or a temporary weakening of the operations that suppress vivid imagery during waking (except, of course, when we are engaging in visual thinking or daydreaming).

Stress-induced arousal also can trigger hallucinations; e.g., during life-threatening accidents, natural disasters, terrorist attacks, or torture.35,43 The same is true of the tension and fatigue of sustained military operations44,45 or the anguish of recent bereavement. Strong desire can also play a role, as in those who fervently seek reassurance that deceased loved ones survive in another realm and see their ghosts as a result.46 The roles of suggestion and classical (i.e., Pavlovian) conditioning have also been investigated in this regard.29 Conditioned stimuli have been found to be able to evoke hallucinatory images as conditioned responses.

While fears and conflicts often slip into consciousness via the imagistic mode, hopes and aspirations can also bring on more welcome hallucinations—e.g., “visions” are sought in some settings as a source of inspiration, a rite of passage, or a way of solemnifying occasions and conferring special status. Prolonged meditation, drug intoxication, sensory bombardment to the point of physical and emotional exhaustion, various kinds of self-denial, and even self-mutilation are all routes pursued in search of transcendent states.16,20,43

Precipitants also include sensory understimulation or sensory overload (especially with intense, repetitive stimuli), extended fasting, dehydration, social isolation and prolonged sexual abstinence, toxicities and diseases of the brain, oxygen deprivation, hyperventilation, hypoglycemia, overdoses of common nonprescription drugs, delirium, and extreme pain. Certain abnormalities in the visual system that prevent normal inputs from reaching higher visual centers can also trigger rich hallucinatory experiences, generated elsewhere within the brain, that fill in the missing sectors. An interesting example of this is the Charles Bonnet syndrome, which suggests a model and possible mechanisms that could be useful in explaining other cases of hallucinations that occur in those who show no detectable psychopathology or disturbance of normal consciousness.47

Aberrations of the brain’s arousal system are also common triggers for hallucinations: e.g., extended sleep loss,44,45 extreme fatigue, prolonged monotony, hypnagogic and hypnopompic states (hallucinatory reveries occurring at the boundaries between sleep and waking),48 narcolepsy,49,50 and other disturbances of the sleep-waking system.51,52 Many of these precipitants were present during the long solo flight of Charles Lindbergh, the solitary global circumnavigations of Joshua Slocum and Sir Francis Chichester, and the polar expeditions of Admiral Richard Byrd—all of whom reported vivid hallucinations during their epic journeys.53

Just as psychedelic drugs can trigger hallucinations, so can occasional spontaneous eruptions in the electrical activity of the brain. The auras that precede epileptic attacks, particularly of the type known as complex partial seizures or temporal lobe epilepsy, can produce prolonged dreamy states with extremely lifelike hallucinations, intense meaningfulness, and feelings of losing one’s autonomy to unseen entities. Similarly, a migraine aura can produce vivid perceptual and emotional effects.20 Odd sensory, cognitive, and emotional events of the migraine prodrome can precede the headache by as much as a day or more.54 Some experience the perceptual distortions, hallucinations, visceral phenomena, and emotional upheavals of the migraine aura without the headache. In cases such as these, where headache does not follow the aura immediately, supernatural causes could well be entertained.

Overwhelming the Reality-Checking Processes

As mentioned, hallucinations can be facilitated by factors such as sleeplessness, fatigue, and monotony, on the one hand; and strong emotion and arousal, panic, or extreme needs, on the other. Any or all of these can hinder the cognitive strategies we normally rely upon to check the veracity of perceptions. These checks include comparison between sense modalities: “I see it, but can I also reach out and grasp it?” Likewise, we can check against memory: “Does this seem familiar?” Or we can check with cognitive appraisals: “Does this make sense?” And, as a last ditch, we can enlist the aid of others: “Did you see that?

Just as some people experience more intense and detailed imagery,26 others seem to be poorer at judging the differences between real and imagined events. Situational variables can also make the task of reality testing more difficult for everyone under certain conditions. Bentall29 and Reed17 provide good reviews of research on how these cognitive misattributions can come about, leading hallucinators to mistake their own private mental processes for publicly observable events.

Fantasy-Prone Personalities

For as much as 4% of the healthy population, vivid hallucinations are an everyday occurrence. In an attempt to characterize the best-hypnotizable persons, Wilson and Barber28 serendipitously uncovered a group of individuals who fantasize with great realism during a large portion of their waking lives. Their hallucinations are sufficiently controllable that they tend not to interfere with their safety, jobs, or family lives. Wilson and Barber dubbed these individuals “fantasy-prone personalities” (FPPs). While fantasizing, they exhibit a reduced awareness of time, place, and personal identity, much as if deeply hypnotized, all without formal induction procedure. FPPs “see,” “hear,” “smell,” and “touch” (for all intents and purposes, they live in) the worlds they fantasize. Their experiences seem so real that FPPs can reach orgasm without physical stimulation, just by imagining a sexual encounter. Most learn early in life to conceal their heavy involvement in their fantasy lives for fear of being thought weird or escapist. Because they frequently confuse fantasy and reality, FPPs are apt to hold various paranormal beliefs. Not surprisingly, they are well represented among the mystics, sensitives, mediums, healers, and channelers who claim access to higher realities.

Cognitive Embellishment and Suggestion

When trauma, drugs, meditative exercises, etc., disrupt the prevailing reality model in consciousness and release a flood of internal imagery, the brain immediately begins to marshal these elements into more natural scenarios and to categorize them, much as we do when we see recognizable objects in smoke, tea leaves, or clouds.55 In this way, observers can impose on a few flashes of light in the night sky visions of space vehicles, complete with portholes and pilots, and turn a wind-rustled curtain into a menacing ghost. In other contexts, it has been pointed out how people with strong imagistic abilities could be influenced by some overly suggestive therapists to create false, but detailed and believable, perceptual memories of ritual satanic abuse, childhood incest, and alien abductions.56,57 As products of active minds, these reveries often reflect the hallucinator’s needs, problems, and preoccupations. The novelist Ambrose Bierce recognized this when, in his Devil’s Dictionary, he defined a ghost as “the outward and visible sign of an inward fear.”58 By the same token, the resurgence of angel sightings in recent years might be termed an outward manifestation of an inward hope.

A century of psychological research has demonstrated that factors as diverse as attention, arousal, belief, desire, context, suggestion, expectancy, fatigue, boredom, stress, and even personality can strongly influence what we perceive. In light of this and the many payoffs for engaging in “wishful thinking,” it should, by now, seem less controversial to assert that “believing is seeing” is, in many instances, just as true as the old adage “seeing is believing.”


When cues that help distinguish internally generated images from externally perceived reality become blurred, others most often dismiss the accounts as hallucinatory. The dismissal is frequently rejected with the counterclaim that the experience seemed to be of greater than ordinary realness. That is, it couldn’t have been illusory because it actually felt more real than reality itself. This hyperreal quality of many hallucinations demands an explanation. But first, perhaps we should step back for a moment and ask the more fundamental question of why anything ever feels real.

The job of consciousness is to construct a mental model of reality from the various inputs at its disposal, for use in guiding our behavior. To accomplish this, the brain assembles an internal representation of those aspects of the environment that have some biological utility. In the process, it takes the fragmentary shorthand notes provided by the senses and “fills in” the gaps to produce our global experience of existing in the world around us. In a poorly understood way, it also uses some learned and some innate processes to project the whole experience into 3-dimensional space, so that it feels like there is a world “out there,” rather than merely a bunch of stimuli impinging on sense organs at the periphery of the body.59 Interestingly, hallucinations are imparted with this same quality of being “out there.” As part of the exercise, this awareness system also constructs a mental model of one’s own body and the self that seems to inhabit it.60

If the brain mechanisms that assemble those models become disrupted, this carefully crafted sense of a self dwelling within a physical body, distinct from the rest of the universe, breaks down. While this could be highly disturbing if it happened spontaneously (which it sometimes does), this feeling of “oneness with the universe” is the ultimate goal of many forms of mystical contemplation. Without understanding why their rituals work, many esoteric movements have independently stumbled upon similar physical rituals and meditative manipulations that affect the brain to produce these experiences.16,20,43 Known to acolytes as “transcendence,” “cosmic consciousness,” or “nirvana,” these experiences are labeled by psychologists and psychiatrists as “depersonalization” and “derealization.” Perhaps because of the accompanying emotional content, these phenomena typically have an urgency about them that makes them, temporarily, feel more real than everyday perceptions of the world. The resulting feeling of clarity and portentousness is in part responsible for the fact that many who experience them take them to be transcendent—i.e., supernatural—events.

Why Do We Sometimes Confuse Fantasy with Reality?

Research suggests that the brain can work simultaneously, outside awareness, on several “candidate” models that are constantly jockeying for acceptance as “reality.” In deciding what is really concrete and “out there,” the executive mechanisms of consciousness confer the accolade of “reality” on that mental representation which is currently the most stable, complex, and coherent, and serve that particular rendition up to conscious awareness. Under ordinary circumstances, when we are awake and our attention is outwardly directed, that will usually be the model that is most richly supplied with external sense data. Selection among models is necessary because the brain’s representational systems not only guide our overt behaviors, but also provide the wherewithal for our flights of fancy. In daydreams and reveries we can call up images of objects, activities, and places that are not physically present. We can control the action. We can place images of our own bodies in the scene and watch events unfold in bird’s-eye view. If need be, we can even conjure up images of things like unicorns, dragons, and space monsters that never could have been “out there.” Given the ease with which we construct detailed mental tableaux that never happened, and the variety of things that can derail the reality-checking processes, it should hardly seem mysterious that the brain could occasionally mistake a self-generated experience for reality. After all, our nightly dreams often seem terrifyingly real.

Brain Mechanisms of Perception, Imagery, and Hallucination

The neural systems involved in creating the reality model include parts of the cerebral cortex as well as the more primitive limbic system. As I have discussed elsewhere,1,20 subcortical limbic structures serve memory, imagery, motivation, emotion, and the spatiotemporal mapping of self and environment. They are responsible for the sense of familiarity and personal meaningfulness that makes some mental representations feel more “real” than others. If those mechanisms, which both assemble the reality model and weigh its significance, were to spring into action spontaneously, they could concoct a convincing mental panorama and infuse it with a feeling of special realness and importance. Electrical stimulation of these parts of the brain in awake neurosurgical patients and, more recently, electromagnetic stimulation from outside the head in normal volunteers61,62,63 can elicit otherworldly visions suffused with an ineffable but profound sense of meaningfulness and cosmic importance. It can also precipitate feelings of déjà vu, ecstasy or foreboding, as well as estrangement from the body, where patients are convinced they are looking down at their bodies from above. Interestingly, the limbic system is one of the most electrically volatile parts of the brain, increasing the likelihood that it might spontaneously erupt occasionally, even in normal people.64 The fact that memories and dreams often occur in a similar bird’seye perspective is one of the reasons for concluding that out-of-body and near-death experiences are really complex, memory-driven hallucinations.32,55

Blackmore55 notes that the mental model dubbed “reality” is that which is most stable and complex. The candidate with greatest clarity and coherence is ordinarily the model richest in sense data. Under severe psychological stress, physiological trauma, or attentional manipulations such as meditation, sensory deprivation, or hypnosis, the brain’s representational apparatus may lose access to the sense data that are ordinarily its most predictive and useful inputs. So deprived, it begins to search for the next best alternative, usually images stored in memory banks (see the discussion of the Charles Bonnet syndrome, above). In this way, a model from memory can become “real” for the time being. If, as during nightly dreams, the brain’s reality-checking processes are also disengaged, the strangeness of the temporary model (i.e., hallucination) is less likely to cause its immediate rejection.


In this paper I have argued that hallucinations are best explained as unusually vivid images experienced when normal reality-checking processes are temporarily impaired. Since photography and videotape recorders have become commonplace, people have come to assume that our senses record everything in the same passive, one-toone fashion. In fact, perception is much more constructive than this, fleshing out from memory and inference the frugal outlines provided by the sense organs. The job of consciousness is not only to record but also to infer, predict, and make sense of the world. In so doing, this system, which works tolerably well most of the time, can occasionally manufacture and make sense of things that aren’t really there. Anything that temporarily impedes the representational system’s ability to model the world based on external sense data will send it scurrying about for an acceptable replacement; most often this will be perceptual memories. Any of a number of social and psychological factors that can hinder one’s usual means of checking the reality status of one’s flow of experience can lead one to accept, temporarily, that this self-generated scenario is real. This imagined world can seem real for the time being, but when external sensory data reassert their primacy, it, too, will pass—but not always before its dramatic impact has left the experiencer literally changed for life.

Faced with a probable instance of hallucination, the prudent physician should, of course, try to eliminate the various organic and psychopathological causes that can cause such experiences. If none should emerge, however, diagnosticians ought to remember that there are more reasons than is often believed as to why normal people might experience the occasional hallucination. Their impact can be profound. For it is true, as Brierre de Boismont reminded us, that “traces of hallucinations are written on every page of history.”30(p1)


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