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Relationship between the hypnagogic/hypnopompic states and reports of anomalous experiences.

A whole range of anomalous experiences (1) has been reported during the hypnagogic or hypnopompic states that surround periods of sleep. It is not uncommon for people to experience brief, vivid, and often strange imagery or to find themselves temporarily unable to move or speak during these periods between wakefulness and sleep. These brief sensations and the temporary paralysis are known as hypnagogic or hypnopompic imagery and sleep paralysis, (2) respectively (American Sleep Disorders Association [ASDA], 1990).

Recent surveys found that people who report more childhood experiences of hypnagogic/hypnopompic imagery or sleep paralysis also report a greater number of anomalous experiences during childhood or adulthood (Sherwood, 1999, 2000). More specifically, hypnagogic/hypnopompic imagery has been associated with reports of extrasensory perception (ESP), apparitions and communication with the dead, out-of-the-body experiences (OBEs), visions of past lives, and experiences involving extraterrestrials (e.g., Glicksohn, 1989; Gurney, Myers, & Podmore, 1886; Leaning, 1925; Mavromatis, 1983, 1987; McCreery, 1993; McKellar, 1957; Spanos, Cross, Dickson, & DuBreuil, 1993). In addition to the above anomalous experiences, sleep paralysis has also been associated with reports of psychokinesis (PK) and near-death experiences (NDEs) (Baker, 1992; Green & McCreery, 1994; Rose & Blackmore, 1996; Rose, Hogan, & Blackmore, 1997; Spanos et al., 1993; Spanos, McNulty, DuBreuil, Pires, & Burgess, 1995).

The question is: are the hypnagogic/hypnopompic states conducive to anomalous processes and events or are normal hypnagogic/hypnopompic features being misinterpreted? Perhaps both statements are true? The aim of this article is to consider evidence for each of these possibilities. First, it is necessary to outline the characteristics of the hypnagogic/hypnopompic states and the features of some of the experiences that can occur within them.

CHARACTERISTICS OF HYPNAGOGIC/HYPNOPOMPIC STATES

Most research, both experimental and survey-based, seems to have focused on the hypnagogic state (the period between wakefulness and sleep, i.e., just as a person is falling asleep). Comparatively little research has been carried out on the hypnopompic state (the period between sleep and wakefulness, i.e., just as a person is waking from sleep). Thus, this article focuses mainly on the hypnagogic state. The hypnagogic state, like the sleep state, is fairly complex and contains a number of steps and stages (Mavromatis, 1983; Rechtschaffen, 1994). Hori, Hayashi, and Morikawa (1994) concluded that the sleep onset period is unique and cannot be accurately categorised as either waking or sleeping. It is very difficult to determine the precise point of falling asleep, except by using arbitrary criteria, because the transition is gradual, because the changes are not always synchronised, and because there are large individual differences in when the changes occur (Lavie, 1996; Rechtschaffen, 1994).

During alert wakefulness, eye movements are fairly rapid, and the normal EEC trace consists of irregular waves of high frequency (Bray, Cragg, Macknight, Mills, & Taylor, 1992). As a person relaxes or becomes drowsy, there is an increase in alpha activity (8-12 Hz), and eye movements become slower and less frequent (Parker, 1975; Rechtschaffen, 1994). In fact, the presence of slow eye movements is considered to be an extremely accurate indicator of hypnagogic mentation (Schacter, 1976). Stickgold and Hobson (1994) found that as the period of eyelid movement quiescence lengthens, that is, as the eyelids move less, mentation becomes more dreamlike. This contrasts with the positive association between eyelid movements and dreamlike mentation during REM sleep. As a person passes through the hypnagogic period into the early stages of non-REM sleep, there is a decline in alpha activity and a concomitant increase in slower theta activity (4-7 Hz; Baddia, Wright, & Wauquier, 1994; Bray et al., 1992; Rechtschaffen, 19 94). A person is typically considered to be asleep once they reach Stage 2 sleep, which is characterised by theta activity and the appearance of sleep spindles (Lavie, 1996; Rechtschaffen, 1994). During the transition from wakefulness to sleep, there is also a decrease in muscle tone, a slowing of the heart and respiration rates, a reduction in blood pressure, and an increase in skin temperature (Mavromatis, 1983; Mavromatis & Richardson, 1984; Schacter, 1976). Upon awakening, these changes go in the opposite direction (Mavromatis, 1983).

During the hypnagogic/hypnopompic states, people can experience brief and vivid imagery or sensations in one or more different sensory modalities (e.g., Foulkes & Vogel, 1965; Hori et al., 1994; Mavromatis, 1987; Sherwood, 2001) or temporary paralysis (ASDA, 1990). Recall of hypnagogic imagery has been found to peak around the middle of standard Stage 1 sleep when the EEG mainly consists of theta activity (Hori et al., 1994).

Laboratory studies have also found that hypnagogic imagery and sleep paralysis can occur during sleep-onset REM periods (SOREMPs) and that isolated sleep paralysis is characterised by abundant alpha activity (Takeuchi, Miyasita, Inugami, Sasaki, & Fukuda, 1994; Takeuchi, Miyasita, Sasaki, Inugami, & Fukuda, 1992). SOREMPs have been associated with altered sleep schedules (Fukuda, 1994), which may predispose towards sleep paralysis (ASDA, 1990). Some consider REM sleep intrusions to be a necessary but not sufficient requirement for sleep paralysis (Takeuchi et al., 1992), though there is evidence to suggest that it is not inevitably associated with SOREMPs (see Ness, 1978). Although these SOREMP hallucinations are similar to other hypnagogic imagery, they seem to be more emotional, and there is a greater awareness of the surroundings (Takeuchi et al., 1992, 1994).

Other features of the sleep onset period include a decreasing awareness of observing the contents of one's own mind, increased absorption, a loss of volitional control over mentation, inaccurate time perception, a reduction of awareness of the environment, and a reduction in reality testing (Foulkes & Vogel, 1965; Mavromatis & Richardson, 1984; Rechtschaffen, 1994). Further features may also include the hypnagogic/hypnopompic speech phenomenon and sleep starts. The hypnagogic/hypnopompic speech phenomenon occurs when a person hears himself or herself uttering words, which can be nonsensical or irrelevant, just as he or she is falling asleep or waking from sleep (McKellar, 1989; Mavromatis, 1987). Sleep starts are sudden brief muscle contractions in one or more parts of the body that occur at sleep onset (ASDA, 1990). Sleep starts are sometimes associated with hypnagogic imagery such as illusory sensations of movement (Nielsen, 1992; Oswald, 1959).

Studies have shown that as one moves through the sleep-onset period, the amount of visual hypnagogic imagery tends to increase (Hori et al., 1994), it becomes more dreamlike (Foulkes & Vogel, 1965; Stickgold & Hobson, 1994), and the image quality, vividness, luminosity, and intensity of colour also increase (Mavromatis, 1987; Nielsen, 1992). McKellar (1989) suggested that the form of hypnagogic imagery also changes from sequences of objects, faces, or landscapes to more complex episodes or miniplays.

Although the hypnagogic state (and probably the hypnopompic) has unique behavioural, electrophysiological, and subjective characteristics (Hon et al., 1994), it is also highly variable, and there are large individual differences (Rechtschaffen, 1994; Tart, 1969, p. 73). Before going on to consider possible relationships with anomalous experiences, it is necessary to consider the experiential features of hypnagogic/hypnopompic imagery and sleep paralysis.

HYPNAGOGIC/HYPNOPOMPIC IMAGERY

Definition

The term hypnagogic ("hallucinations hypnagogiques") was provided by Maury (1848, p. 26) and was used to refer to hallucinations that begin shortly after one has gone to bed or when one is in need of a rest and when one's eyes are closed. The term hypnopompic imagery was introduced by Myers (1903), who defined it as "pictures consisting generally in the persistence of some dream-image into the first moments of waking" (p. 125).

Some writers distinguish between imagery that occurs in the hypnagogic and hypnopompic states (e.g., Glicksohn, 1989; McKellar, 1989) but others do not (e.g., Mavromatis, 1987; Mavromatis & Richardson, 1984). It is fair to say that both types are similar, and so many features will apply to both. However, certain features or experiences seem to be more common in the hypnagogic than in the hypnopompic state, and vice versa (Sherwood, 2001). For this reason, I think it is useful to maintain the distinction.

It has also been speculated that people may enter the hypnagogic state and experience hypnagogic phenomena at times other than just prior to nocturnal sleep (Mavromatis, 1983, 1987; Tart, 1969, p. 74). This has been supported by reports from a number of participants (McKellar & Simpson, 1954). Although hypnopompic imagery was originally defined as a persistence of dream imagery into wakefulness (Myers, 1903), it seems that the images are not always continuations of dreams because they can begin after the sleeper has awoken (e.g., Leaning, 1925; Mavromatis, 1987; Sherwood, 2001). Thus, hypnopompic images may not necessarily be the result of REM sleep continuation.

It is not easy to distinguish hypnagogic and hypnopompic imagery from dream imagery; some people consider them to be the same, whereas others consider them to be completely different. Any qualitative distinctions made will depend on the defining characteristics of hypnagogic/hypnopompic imagery and dreams (Mavromatis & Richardson, 1984), both of which would benefit from stricter definitions. However, there is some evidence that hypnagogic (and also hypnopompic) imagery tends to be more vivid and realistic, shorter, more passive, to have less emotion, and also to be more disorganised and irrelevant (Foulkes & Vogel, 1965; Mavromatis & Richardson, 1984; McKellar, 1989; McKellar & Simpson, 1954). McKellar (1989, p. 103) described how:

To use an analogy, dreaming resembles a lecture illustrated by slides which form part of it; hypnagogic imagery is more like a display of slides meant to illustrate some other lecture. Moreover, the slides have been mixed up, and follow one another in random.

With hypnagogic experiences, there also seems to be a greater awareness of the true situation and more reality testing compared with dream experiences (Mavromatis & Richardson, 1984). Some people also claim to be able to generate or control their hypnagogic/hypnopompic imagery to some extent (e.g., see Leaning, 1925, pp. 362-368; Mavromatis, 1987, pp. 71-77; McKellar, 1989, pp. 110-111). Necessary requirements seem to include a receptive attitude and passive volition.

Timing

It seems that episodes of hypnagogic/hypnopompic imagery often occur fairly sporadically although concentrated series of episodes can also occur (Mavromatis, 1987). Hypnagogic and hypnopompic images are typically very brief and dynamic and may last no more than a second or two (Nielsen, 1992).

Frequency

Generally speaking, hypnagogic imagery seems to be more common than hypnopompic imagery. Early surveys (e.g., Galton, 1883; Muller, 1848, cited in Mavromatis, 1987) estimated that about 2% of adults had experienced hypnagogic imagery of some form. More recent surveys have estimated that about 33% (Leaning, 1925), 61%-63% (McKellar, 1957; McKellar & Simpson, 1954), or about 75% (Glicksohn, 1989; Richardson, Mavromatis, Mindel, & Owens, 1981; Sherwood, 1999, 2000) of people have experienced it on at least one occasion compared with 2 1.4% (McKellar, 1957) to 67.6% for hypnopompic imagery (Richardson et al., 1981; Sherwood, 1999). One recent survey estimated that 37% (12.5%) of the U.K. population had experienced some form of hypnagogic (hypnopompic) imagery at least twice a week during the preceding year (Ohayon, Priest, Caulet, & Guilleminault, 1996).

Sensory Modalities

Although visual and auditory are two of the most common forms of both hypnagogic and hypnopompic imagery (Foulkes & Vogel, 1965; Hori et al., 1994; McKellar & Simpson, 1954), olfactory (smell), gustatory (taste), tactile, thermal, bodily movement, and synesthetic sensations (in which imagery in one modality triggers modality in a different modality) may also occur (e.g., Leaning, 1925; Mavromatis, 1987; Schacter, 1976). A sense of presence is also a common hypnagogic/hypnopompic feature (Sherwood, 2001).

Visual imagery typically occurs with the eyes closed though it can occur with eyes open (Gurney et al., 1886; Leaning, 1925; McKellar, 1957, 1989; McKellar & Simpson, 1954; Sherwood, 2001). It often begins with reports of clouds or mists of bright colours or a circle of light. Images may quickly change from one to another and may develop into progressively more complex images (Gurney et al., 1886; Leaning, 1925; Mavromatis, 1987; Sherwood, 2001). Occasionally, the images may be in black and white rather than in colour (McKellar, 1957; McKellar & Simpson, 1954; Sherwood, 2001). The images may sometimes be very small (micropsias) or gigantic (megalopsias), though changes in size and shape are possible (Leaning, 1925; Mavromatis, 1987; McKellar, 1957; McKellar & Simpson, 1954). A series of continuous repetitions (polyopsias) of the same image may also be experienced. Sometimes the images appear to be strangely illuminated or may be seen from a peculiar angle (Leaning, 1925; Mavromatis, 1987; McKellar, 1957).

Visual hypnagogic/hypnopompic imagery is often pleasant, even humorous, but it can also be terrifying (Mavromatis, 1987; McKellar & Simpson, 1954). Although hypnagogic and hypnopompic imagery are characterised by variety, Mavromatis (1987) modified Leaning's (1925) classification scheme and identified six recurrent themes: (a) formless (e.g., waves, clouds of colour); (b) designs (e.g., geometric and symmetrical patterns and shapes); (c) faces, figures, animals, and objects; (d) nature scenes (e.g., landscapes, seascapes, gardens); (e) scenes with people; and (f) print and writing (e.g., in real or imaginary languages). Sherwood's (2001) thematic analysis of imagery content supported the majority of these categories, although he suggested a separate category for "objects" and added categories associated with visions of falling or tripping and moving. Visual hypnagogic/hypnopompic imagery has often been referred to as "the faces in the dark phenomenon" because the seeing of faces is so common (McKellar, 1957).

Mavromatis (1987) provided a summary of auditory hypnagogic/hypnopompic phenomena:

Auditory hypnagogic [and also hypnopompic] phenomena include the hearing of crashing noises, one's name being called, a doorbell ringing, neologisms [new words or expressions], irrelevant sentences containing unrecognizable names, pompous nonsense, quotations, references to spoken conversations, remarks directed to oneself, meaningful responses to one's thought of the moment. (p. 81)

Other reported imagery includes music and singing, bangs, explosions, footsteps, motors and machinery, scratching, and humming (see Sherwood, 2001). Sometimes auditory hypnopompic imagery can take the form of a warning of impending danger or an important event; other times it may just be a feeling of foreboding (Mavromatis, 1987).

Sensations of smell (e.g., cigars, roses, burning), taste (e.g., bitter, sweet, metallic), sensations of actively touching or being passively touched by someone or something, and hot or cold sensations, sometimes moving along the body, have also been reported during the hypnagogic and hypnopompic states (Mavromatis, 1987; Sherwood, 2001).

A sensation of falling seems to be the most commonly reported sensation of movement (Sherwood, 2001). The experience is relatively common and is often associated with a bodily jerk and visual imagery, such as falling off a cliff (Oswald, 1959). Other sensations of movement may include floating, swinging, rocking, spinning, and being in or on a moving vehicle. Bodily sensations may include, for example, a feeling of energy flowing through the body, weightlessness, heaviness, tingling, numbness, shaking/vibrating, pain, and shrinking/elongation of the body (Sherwood, 2001). A sense of presence has also been reported (e.g., Ohayon et al., 1996) and may coincide with both imagery and sleep paralysis (Conesa, 1995; Hufford, 1982; Rose & Blackmore, 1996; Spanos et al., 1993, 1995). Feelings of foreboding or being under threat, or more general feelings of confusion and disorientation, have also been reported.

Mavromatis (1987, p. 28) also pointed out that "very often hypnagogic [and hypnopompic] images are symbolic or metaphoric, and not infrequently autosymbolic, and therefore not always meaningless." The experient may sometimes become aware of the significance of the imagery (which may be known only by that person) during the experience or just afterwards. Such awareness is a characteristic of the "autosymbolic phenomenon," described by Silberer (1965, cited in Mavromatis, 1987), which is an experience in which one's thoughts or feelings at a given moment are translated into a symbolic form of imagery. However, Mavromatis (1987) added that "awareness of the significance of the symbolism is not always present, and in the majority of cases imagery remains a puzzle until one begins to pay attention to it and enters into a form of 'conversation' with it" (p. 59).

It is clear that hypnagogic/hypnopompic imagery may be extremely vivid, is characterised by variety, may evoke both positive and negative emotions, may occur in more than one sensory modality, sometimes simultaneously, and may have some significance for the experient.

SLEEP PARALYSIS

Definition

According to the ASDA (1990): "Sleep paralysis consists of an inability to perform voluntary movements either at sleep onset (hypnagogic or pre-dormital form) or upon awakening either during the night or in the morning (hypnopompic or post-dormital form)" (p. 166).

Timing

The sleep paralysis episode usually lasts from a few seconds to a few minutes, although a duration as long as 70 mm has been reported (Goode, 1962; Schneck, 1960; Spanos et al., 1995). The experience is sometimes preceded or accompanied by visual imagery that can be terrifying (Blackmore, 1996; Conesa, 1995; Goode, 1962; Penn, Kripke, & Scharff, 1981; Spanos et al., 1995; Takeuchi et al., 1992). The experience may end because of efforts to overcome it by the experient, the experience may be terminated by someone else either by touch or verbally, the experience may move into a dream (possibly lucid), or the episode may simply terminate spontaneously (Firestone, 1985; Goode, 1962; Schneck, 1960; Snyder, 1983).

Frequency

The hypnagogic form seems to be more frequent than the hypnopompic form (Conesa, 1995; Goode, 1962; Spanos et al., 1995; Sherwood, 2000), although the opposite has also been reported (Penn et al., 1981; Sherwood, 1999). The International Classification of Sleep Disorders estimates that isolated sleep paralysis (i.e., that which occurs independently of narcolepsy) occurs at least once in a lifetime in 40%-50% of normal people. Surveys have found that between 4.7% to 49% of people have reported sleep paralysis (of one or other or both forms), although the most frequent estimates range between 30% and 50% (Blackmore, 1996; Everett, 1962; Goode, 1962; Penn et al., 1981; Rose & Blackmore, 1996; Sherwood, 1999, 2000; Spanos et al., 1995).

Features

Accompanying features of sleep paralysis may include acute anxiety or terror, awareness of the surroundings, hypnagogic/hypnopompic imagery, a sense of presence, difficulty breathing or a sense of suffocation, pressure on the chest, a tendency to mentally or physically struggle to overcome it, a feeling of time distortion, sexual arousal (Blackmore, 1996; Cheyne, Newby-Clark, & Rueffer, 1999; Cheyne, Rueffer, & Newby-Clark, 1999; Conesa, 1995, 1997; Goode, 1962; Hufford, 1982; Liddon, 1967; Penn et al., 1981; Rose et al., 1997; Schneck, 1960, 1977; Snyder, 1983; Spanos et al., 1995; Takeuchi et al., 1992; Terrillon & Marques-Bonham, 2001).

INTERPRETATION OF HYPNAGOGIC/HYPNOPOMPIC EXPERIENCES

Personal beliefs and expectations, knowledge of normal sleep-related experiences, mental set, and the setting in which hypnagogic/hypnopompic experiences take place are all important factors that can influence how these experiences are interpreted (e.g., Leaning, 1925; Mavromatis, 1987; McKellar & Simpson, 1954). Some people pay little attention to their imagery and are unconcerned by it; others may find it rather puzzling and may be keen to find an explanation for it, particularly if they have not come across such experiences before, as this letter illustrates:

I'm writing about a recurring experience of mine in the hope that a reader might be able to offer an explanation. It happens when I'm asleep or half asleep--although it's so real at the time that I'm convinced I'm awake. My whole body buzzes or tingles, like a bad case of 'pins and needles'. I feel really scared, trapped and unable to move or speak. Sometimes I think I see or hear something. With concentration of strength I can escape from this state, although I always think I'm losing control. This only happens when I fall asleep on my back--which I now try to avoid! No-one I've spoken to has had the same experience. Any ideas? (Doubleday, 1996, p. 53)

Certainly there is evidence that some people consider their hypnagogic/hypnopompic experiences to have some kind of spiritual, paranormal, or supernatural significance (Sherwood, 2001). Mavromatis (1987) illustrated how, in some cases, "visual psi experiences are practically indistinguishable from those occurring in hypnagogia both in their content and in their nature. Also, the mental state of the subject appears to be the same" (p. 138). If psi does exist, then it seems that hypnagogic/hypnopompic experiences may be a vehicle for it but clearly there is room for misinterpretation. On a given occasion, a hypnagogic/hypnopompic experience may reflect genuine anomalous processes, but it may or may not be interpreted as such. On another occasion, a hypnagogic/hypnopompic experience may not reflect genuine anomalous processes, but it may be interpreted as if it does. Thus, false negatives and false positives are possible. Mavromatis (1987) did not really give much indication of how psi and non-psi hypnagogic/hyp nopompic experiences might be differentiated, but he did cite Roberts (see Mavromatis, 1987, p. 137), who suggested that, in relation to clairvoyance:

These experiences of the inward consciousness are often thought to be purely imaginative. There is one test by which the medium can prove whether they are psychic or imaginary: In imaginary pictures the thinker visualises the picture before it is seen; if the image is of psychic origin it is 'seen' first and then thought about-indeed the medium is often surprised by the fact that he (or she) has seen something which is so unexpected.

Thus there is a suggestion that clairvoyant imagery tends to be unrelated to ongoing thought processes and is particularly involuntary and spontaneous. If reliable differences could be identified, then this might help the experient make better judgements. Further investigation of this question of how to differentiate psi from non-psi imagery is warranted. Qualitative investigations of self-proclaimed psychics might throw up some useful hypotheses that could then be tested in a more quantitative fashion.

EVIDENCE FOR CONDUCIVENESS OF HYPNAGOGIC/HYPNOPOMPIC STATES TO ANOMALOUS PROCESSES

So what evidence is there to suggest that hypnagogic/hypnopompic states are conducive to anomalous processes or agencies? The hypnagogic state is considered to be "unusually receptive" (Schacter, 1976, p. 468) and shares features of the psi-conducive state such as physical relaxation, reduction in sensory distraction, and increased internal attention (Braud & Braud, 1975; Honorton, 1977; Mavromatis, 1987). According to Mavromatis (1983), support for a relationship between psi and hypnagogia (his generic term for hypnagogic and hypnopompic imagery) comes from the practices and literature on occultism and spiritualism, the literature on controlled psi experiments, and spontaneous cases of psi during hypnagogic practices.

Some experimental studies have found that hypnagogic/hypnopompic imagery seems to be conducive to telepathy (Gertz, 1983; Schacter & Kelly, 1975), perhaps more so than dreaming (Braud, 1977; White, Krippner, Ullman, & Honorton, 1971). The ganzfeld technique, which has provided some of the best evidence for ESP, is believed to induce a hypnagogiclike state (Bertini, Lewis, & Witkin, 1969). Palmer, Bogart, Jones, and Tart (1977) reported a ganzfeld study that found significant correlations between ESP z performance (psi-hitting or psi-missing) and scoring on altered state of consciousness/hypnagogic imagery scales.

Bem and Honorton (1994) reviewed ganzfeld studies carried out up until the Hyman (1985) and Honorton (1985) meta-analyses, and also a group of subsequent studies carried out by Honorton that were designed to meet the more stringent standards specified by Hyman and Honorton (1986). Bem and Honorton (1994) concluded that Honorton's studies had met the required standards and had produced results consistent with the previous ganzfeld studies, though they also acknowledged the need for further replication by a broader range of investigators. Milton and Wiseman (1999) conducted a meta-analysis of other ganzfeld studies reported since the joint Hyman-Honorton guidelines were published and concluded that these studies failed to confirm the earlier research and the overall performance was not significantly better than chance expectations. Milton and Wiseman (1999) suggested that this failure to replicate could have been a result of better methodological controls used in these studies or that the autoganzfeld studies m ay have been conducted in psi-conducive conditions that were not apparent in the later studies. Milton and Wiseman's (1999) meta-analysis has been criticised for the inclusion of what some researchers consider to be nonstandard ganzfeld studies (e.g., those involving musical targets), but there seems to be a lack of agreement over what the standard features of a ganzfeld study actually are (Milton, 1999; Schmeidler & Edge, 1999).

Milton (1999) later reported an updated version of the Milton and Wiseman (1999) meta-analysis that included studies published up until March 1999. The revised database did show a statistically significant small effect (Stouffer z = 2.28, p = .011, one-tailed), but this was maintained only by the inclusion of one very successful study by Dalton (1997). However, Milton (1999) pointed out that the effect size had still not been replicated and in fact was significantly lower than that obtained in earlier meta-analyses. As with the Hyman (1985) and Honorton (1985) meta-analyses, there are disagreements over the interpretation of the results (see Schmeidler & Edge, 1999) of the Milton and Wiseman (1999; Milton, 1999) meta-analyses, and these relate partly to the way the meta-analysis itself was conducted (see also Storm & Ertel, 2001, and reply by Milton & Wiseman, 2001). Milton (1999) suggested that future meta-analyses ought to be prospective; and specific criteria for the inclusion/exclusion of studies should b e made in advance in the hope of establishing whether studies, conducted by a broad range of investigators at different laboratories, that meet the Hyman and Honorton (1986) guidelines can replicate the statistical effect and also the effect size found in earlier meta-analyses.

Bem, Palmer, and Broughton (2001) recently updated the Milton and Wiseman (1999) meta-analysis and added a further 10 studies. Analysis of ratings assigned to the updated database by three independent raters revealed a significant positive correlation between effect size and the extent to which studies adhered to the "standard ganzfeld protocol." They also found that "standard" studies produced replicable effect sizes that were similar in magnitude to a database of previous studies and Bem and Honorton's (1994) summary of autoganzfeld studies. As the "standardness" seems to be an important predictor, Bem et al. (2001) argued that this should be considered in any future meta-analyses.

However, although the ganzfeld procedure is often assumed to induce a hypnagogic state, the extent to which it does resemble the naturally occurring hypnagogic state is not clear (Braud, Wood, & Braud, 1975; Schacter, 1976). In fact, in a recent study, Wackermann, Putz, Buchi, Strauch, and Lehmann (2000) compared the EEG activity of participants in waking, ganzfeld, sleep onset, and sleep Stage 2 conditions to see if the ganzfeld truly did induce a state resembling the hypnagogic state. They concluded that "Contrary to the common belief, the ganzfeld does not necessarily induce a true hypnagogic state, and will surely not do so in most ganzfeld settings" (p. 302). Brain activity during the ganzfeld condition was more similar to the relaxed waking condition, and there was no evidence of a shift towards slower EEG frequencies, such as theta and delta, which is characteristic of sleep onset. However, one should note that in Wackermann et al.'s (2000) ganzfeld condition, participants did not undergo any form of progressive relaxation procedure and did not provide a continuous report of their mentation. These are features of many ganzfeld ESP studies, and it is not clear whether these may be important in facilitating induction of a hypnagogic state. Although this study requires replication, it does suggest that the ganzfeld technique does not induce a hypnagogic state, and therefore ganzfeld studies probably cannot provide experimental support for the psi-conducive nature of the hypnagogic state.

In terms of spontaneous cases, there are a number of well documented cases of ESP and crisis apparitions that have occurred during the hypnagogic/hypnopompic states (e.g., Gurney et al., 1886, Chapter IX, "Borderland" Cases, pp. 251--285). For example, a father reported a hypnopompic image involving his son:

I was suddenly awoke by hearing his voice, as I fancied, very near me. I saw a bright, opaque, white mass before my eyes, and in the centre of this light I saw the face of my little darling, his eyes bright, his mouth smiling. The apparition, accompanied by the sound of his voice, was too short and too sudden to be called a dream: it was too clear, too decided, to be called an effect of imagination. So distinctly did I hear his voice that I looked around the room to see whether he was actually there. (p. 277)

The father received a letter the following day informing him that his son was ill but later found out that his son had died at the time of the apparition.

Another well-documented spontaneous case involving hypnagogic/hypnopompic phenomena was the haunting of the Mill House at Willington in northeast England (MacKenzie, 1982). The haunting lasted for about 13 years, it was well documented (partly by a diary kept by the owner), and phenomena were observed at different times and in different locations by a variety of witnesses, sometimes simultaneously. Hypnagogic/hypnopompic phenomena included shadowy figures, apparitions, the sound of footsteps, strange voices and doors opening, people feeling pressure on parts of their body as they lay in bed, and, in particular, the feeling of the bed and/or bedclothes being moved up and down.

Some writers believe that hypnagogic visions might be an early form of ESP (Leaning, 1925; Mavromatis, 1983). In support of this, developing psychics often experience an increase in hypnagogic phenomena (Mavromatis, 1987). Gifted subjects also use hypnagogic imagery (White, 1964); for example, well-known psychics, such as Garrett and Northage, have described personal examples of telepathy and clairvoyance during the hypnagogic and hypnopompic states (Mavromatis, 1987).

Moody (with Perry, 1993) also described a number of cases of visionary encounters with departed loved ones inside a psychomanteum chamber that share characteristics of hypnagogic imagery. OBEs also tend to occur spontaneously during the hypnagogic/hypnopompic states (Mavromatis, 1983); McCreery (1993) found a positive relationship between number of hypnagogic imagery episodes and number of OBEs. Mavromatis (1983, 1987) also listed a number of hypnagogic phenomena that have been reported during OBEs: sensations of floating, sinking, and drifting; seeing lights, images, and landscapes; hearing noises, music, and name being called; and sensation of being touched.

Rose et al. (1997) found that sleep paralysis has been associated with reports of a number of anomalous experiences, such as ESP, PK, OBEs, NDES, apparitions, past life experiences, and extraterrestrials. It is possible that anomalous experiences and sleep paralysis episodes might be related to each other because they might both be affected by a third variable such as the earth's geomagnetic field. A number of studies have found that subjective (e.g., Persinger, 1985) and experimental GESP experiences (Berger & Persinger, 1991) and sleep paralysis (Gonesa, 1995, 1997) tend to occur when geomagnetic activity is relatively low.

If the hypnagogic state is conducive to anomalous processes, perhaps this could be due to the initial increase in alpha or the later increase in theta activity (Healy, 1986) that occurs during this period (e.g., Baddia et al., 1994; Davis, Davis, Loomis, Harvey, & Hobart, 1938). Experienced meditators have also been found to show the alpha-theta progression that characterises the transition through the hypnagogic state towards sleep (Mavromatis, 1987). Meditation has been associated with reports of a variety of anomalous experiences (Eysenck & Sargent, 1993).

There is evidence that alpha activity might be conducive to anomalous processes and experiences. Tart (1968) found that Miss Z's OBEs tended to occur during Stage 1 sleep, which was dominated by alphoid activity. Laboratory episodes of sleep paralysis have also been found to be characterised by abundant alpha activity (Takeuchi et al., 1992). In terms of theta, Stanford and Stevenson (1972, cited in Healy, 1986) found some evidence to suggest that lower EEG activity, such as theta, might facilitate telepathy performance. Unusual theta activity has also been found in individuals who report mediumship ability or OBEs (Nelson, 1970; Palmer, 1979; Tart, 1967, 1968; all cited in Healy, 1986).

It has been suggested that it is not so much altered states per se that are psi-conducive but the degree or the rapidity of the transition from one state to another (e.g., Honorton, 1973; Honorton, Davidson, & Bindler, 1971; Murphy, 1966; all cited in Parker, 1975). Physiological monitoring of participants in the hypnagogic/hypnopompic states might be useful in that it could potentially identify the precise point, or at least the optimal physiological conditions, at which psi processes might operate. However, it is recognised that this might be difficult to investigate experimentally given that, for many people, hypnagogic/hypnopompic imagery and sleep paralysis may occur only sporadically and tend to be rather involuntary when they do occur.

In summary, evidence for the conduciveness of the hypnagogic/hypnopompic states to anomalous processes comes from the fact that these states have physiological and psychological features believed to be psi-conducive in other contexts, from experimental studies using both naturally occurring and induced states, from spontaneous case reports of a variety of different phenomena, and from biographical accounts of gifted subjects and psychics.

EVIDENCE FOR MISINTERPRETATION OF HYPNAGOGIC/HYPNOPOMPIC EXPERIENCES

Hypnagogic/hypnopompic experiences may also have been misinterpreted as ESP, apparitions, visions of previous lives or other worlds, alien abductions, witchcraft, or attacks by evil spirits or demons (Baker, 1992; Blackmore, 1996; Dahlitz & Parkes, 1993; Hufford, 1982; Leaning, 1925; Liddon, 1967; McKellar, 1957, 1989; Reisner, 2001; Spanos et al., 1993, 1995; Wilson & Barber, 1983; Wing, Lee, & Chen, 1994; Zusne & Jones, 1989). Such experiences may initiate or sustain beliefs in the paranormal and the supernatural and may have contributed to mythology and folklore (Fukuda, Miyasita, Inugami, & Ishihara, 1987; Liddon, 1967; Mavromatis, 1983; McKellar & Simpson, 1954; Ness, 1978). Blackmore and Rose (1996) found that many people were scared by sleep paralysis, and some were worried that they were going mad or being visited by supernatural entities. It is also possible that knowledge and beliefs may influence the content of hypnagogic/hypnopompic experiences (Hufford, 1982; Spanos et al., 1993).

Assuming that the hypnagogic/hypnopompic experiences do not reflect anomalous processes, are there any general characteristics of the hypnagogic/hypnopompic states that might facilitate misinterpretations, regardless of individual knowledge, beliefs, and expectations? There may be reduced sensory input from the environment and some ambiguity of external stimuli, especially if the person is in bed and it is dark. This may interfere with accurate reality testing (Spanos et al., 1993), which also tends to reduce during the sleep-onset period (Foulkes & Vogel, 1965). It is sometimes difficult, subjectively, to distinguish wakefulness from sleep (Rechtschaffen, 1994); false awakenings and lucid dreams are a good illustration of this (Green & McCreery, 1994). One of the features of hypnagogic/hypnopompic imagery that may lead people into believing in their reality and veracity may be that they feel awake throughout. In their survey of hypnagogic experiences, McKellar and Simpson (1954) found that:

Among the reasons given for believing oneself to be awake were: being able to have ordinary perception at the same time (the commonest reason given); being able to have separate thoughts; being able to engage in conversation; being able to open eyes, close them, and continue with the image, etc. (p. 270)

Awareness of the surroundings may be reduced during the hypnagogic/hypnopompic states to some extent (Foulkes & Vogel, 1965; Rechtschaffen, 1994), but it is an important feature, particularly during sleep paralysis episodes (e.g., Conesa, 1995; Goode, 1962; Liddon, 1967; Schneck, 1960). As Mavromatis (1987) noted: "The 'sense of reality, of life-likeness' pointed out by many subjects in reference to their hypnagogic imagery often expands into 'feelings of heightened reality'" (p. 30). Visual imagery can sometimes contain more detail than one might observe in more usual circumstances (Leaning, 1925). Hypnagogic/ hypnopompic imagery and sleep paralysis are also spontaneous, vivid, realistic, intense, and often frightening (Conesa, 1995; Schacter, 1976; Zusne &Jones, 1989). The unfamiliarity and involuntary nature of the imagery might facilitate external attributions.

Evidence for possible misinterpretation of normal hypnagogic/ hypnopompic experiences is perhaps best illustrated by example. The "Old Hag attack," well-known in the Canadian province of Newfoundland, is believed, by some people, to be caused by a supernatural creature, by a human in spirit form (e.g., a witch), or a combination of the two (Firestone, 1985; Hufford, 1982; Ness, 1978). The main features of an Old Hag attack are an impression of wakefulness and an accurate perception of the real environment, paralysis, and fear; secondary features, which may be experienced with eyes open or closed, include a sense of presence, imagined sounds, visual images of a human (e.g., an old woman) or nonhuman attacker, a sense of motion, pressure (e.g., on the chest), difficulty breathing, odours, and other bodily sensations (Hufford, 1982). Experiences with similar phenomenology have also been reported in Japan and China. These experiences are known as kanashibari and ghost oppression attacks, respectively, and are bel ieved by some to be caused by evil spirits or possession by a ghost (Fukuda et al., 1987; Wing et al., 1994). However, there is evidence to suggest that such beliefs may be more common among people who have not had the experiences themselves (Wing et al., 1994).

It is also possible that hypnagogic/hypnopompic imagery and sleep paralysis may account for some intense UFO reports and abductions (e.g., Baker, 1992; Blackmore, 1998; Sherwood, 2000; Spanos et al., 1993). Abductions are often reported around the time of sleep and may feature paralysis, awareness of surroundings, a sense of presence, bright lights and figures in the room, humming and buzzing sounds, and sensations of floating (e.g., Baker, 1992; Mack, 1994; Spanos et al., 1993).

Visual hypnagogic/hypnopompic imagery might also facilitate interpretations in terms of ghosts or apparitions (Wilson & Barber, 1983). Faces may be experienced that range from the beautiful and the pleasant to the hideous and the terrifying (Leaning, 1925; Mavromatis, 1987; McKellar, 1957). These faces are often characterised as being extremely lifelike and often seem to be looking at the observer (Gurney et al., 1886; Leaning, 1925). These faces can also develop into figures that may move towards the observer. Such faces or figures can be singular or in groups, of known or unknown, living or dead persons and may sometimes seem to represent particular moods and emotions (Leaning, 1925; Mavromatis, 1987). The experients may also hear their name being called, which might be interpreted as attempts at communication by deceased persons.

Features that are similar to OBE and NDE accounts (see Sherwood, 2000) include feelings of floating or weightlessness, sensations of movement, changes in body image, awareness of the surroundings, and experiencing visual images such as landscapes/seascapes or faces/figures (perhaps from an unusual angle).

There are also hypnagogic/hypnopompic features that might facilitate ESP interpretations. Hypnopompic imagery, in particular, tends to anticipate forthcoming daily events, and in connection with actual later events it may be considered to be precognitive (Zusne &Jones, 1989). Hypnopompic imagery may also appear to be warning of imminent or future danger. Visual imagery involving complex scenes characterised by movement and life may also be experienced (Leaning, 1925; Mavromatis, 1987).

In summary, it seems possible that features of the hypnagogic/hypnopompic states can facilitate possible confusions between reality and imagination in some instances. There are also a number of specific features that may facilitate anomalous interpretations. This maybe more likely if a person has little knowledge of normal hypnagogic/hypnopompic features, or if a person is within a group or culture that has certain explanations for particular phenomena, or if the person already believes in anomalous phenomena.

In conclusion, it is possible that the hypnagogic/hypnopompic states may be both conducive to, and also misinterpreted as involving, anomalous processes and agencies. In the absence of more objective information, the decision as to which interpretation is taken may depend on the individual and the context in which the experiences take place. Further research that addresses the decision-making processes involved in interpreting these kinds of experiences would be useful. Ideally, more naturalistic, experimental testing of participants who regularly experience hypnagogic/hypnopompic experiences is required. The boundary structure (Hartmann, 1991) and transliminality (Thalbourne, 2000; Thalbourne & Delin, 1994) personality dimensions might aid the selection of suitable participants. The available evidence suggests that people who have thin boundary or highly transliminal personality types find it easier to enter and become absorbed in altered states of consciousness, experience a lot of imagery and dreams, and may spend a lot of time fantasising and daydreaming. These personality types also pay a lot of attention to their internal state and often try to make sense of it, and they can move easily from one state of consciousness to another, possibly experiencing mixed states of consciousness (Sherwood, 2000, pp. 68-77). More attention to the hypnopompic state and the extent to which experimentally induced states are physiologically and psychologically equivalent to the naturally occurring states would also be beneficial. More attention to the physiology, features, and content of the hypnagogic/hypnopompic states may enable us to identify, with a greater degree of accuracy, if and when anomalous processes are operating.

I would like to acknowledge the financial assistance (No. R00429534380) provided by the Economic and Social Research Council. This article is based on an earlier version presented at the 41st Annual Convention of the Parapsychological Association, August 1998, Halifax, Nova Scotia, Canada. I would also like to acknowledge the referees of this article for their helpful comments and suggestions.

(1.) I have chosen to use the term anomalous experiences for two reasons: (a) It is fairly neutral and does not carry as many implicit assumptions as other terms, such as paranonnal and parapsychological, and it places the emphasis on the experience rather than the explanation for it; (b) it is broader and allows the inclusion of experiences involving phenomena, such as UFOs, that are not usually considered to be paranormal. Jam using the term to refer to experiences that, at least to those concerned, have some unusual, atypical, or abnormal aspect to them that may cause the individual to wonder what is happening and why. Some anomalous experiences might also be paranormal but not necessarily so.

(2.) Hypnagogic/hypnopompic imagery and sleep paralysis can be possible symptoms of narcolepsy, a sleep disorder that is characterised by excessive sleepiness and is typically associated with cataplexy. However, it is important to note that such imagery and sleep paralysis may also occur in an isolated form independently of narcolepsy (ASDA, 1990).

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Title Annotation:sleep
Author:Sherwood, Simon J.
Publication:The Journal of Parapsychology
Geographic Code:1USA
Date:Jun 1, 2002
Words:9228
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