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Although we are not usually explicitly aware of the fact that we are dreaming while we are dreaming, at times a remarkable exception occurs, and we become conscious enough to realize that we are dreaming. "Lucid" dreamers (the term derives from van Eeden, 1913) report being able to freely remember the circumstances of waking life, to think clearly, and to act deliberately upon reflection, all while experiencing a dream world that seems vividly real (Green, 1968; LaBerge, 1985; Gackenbach & LaBerge, 1988). This is all in contrast to the usual past characterization of dreams as typically lacking any reflective awareness or true volition (Rechtschaffen, 1978).
In spite of the fact that most people have experienced lucid dreams, some theoreticians have considered them impossible and even absurd (eg, Malcolm, 1959). In the absence of empirical evidence bearing on the question, most sleep researchers were apparently inclined to accept Hartmann's "impression" that lucid dreams were "not typical parts of dreaming thought, but rather brief arousals" (Hartmann, 1975, p. 74; Berger, 1977). Schwartz and Lefebvre (1973) noted that frequent transitory arousals were common during REM sleep and proposed these "micro-awakenings" as the physiological basis for lucid dream reports. Although no one had put forward any evidence for this mechanism, it seems to have been the predominant opinion (cf. Foulkes, 1974) up until the last few years.
Empirical evidence began to appear in the late 1970s suggesting that lucid dreams occur during REM sleep. Based on standard sleep recordings of two subjects who reported a total of three lucid dreams upon awakening from REM periods, Ogilvie, Hunt, Sawicki, and McGowan (1978) cautiously concluded that "...it may be that lucid dreams begin in REM." However, no proof was given that the reported lucid dreams themselves had in fact occurred during the REM sleep immediately preceding the awakenings and reports. What was needed to unambiguously establish the physiological status of lucid dreams was some sort of behavioral response signaling to the experimenter the exact time the lucid dream was taking place.
We provided the necessary verification by instructing subjects to signal the onset of lucid dreams with specific dream actions that would be observable on a polygraph (i.e., eye movements and fist clenches). Using this approach, LaBerge, Nagel, Dement & Zarcone (1981) reported that the occurrence of lucid dreaming during unequivocal REM sleep had been demonstrated for five subjects. After being instructed in the method of lucid dream induction (MILD) described by LaBerge (1980b) the subjects were recorded from 2 to 20 nights each. In the course of the 34 nights of the study, 35 lucid dreams were reported subsequent to spontaneous awakening from various stages of sleep as follows: REM sleep 32 times, NREM Stage-1, twice, and during the transition from NREM Stage-2 to REM, once. The subjects reported signaling during 30 of these lucid dreams. After each recording, the reports mentioning signals were submitted along with the respective polysomnograms to a judge uninformed of the times of the reports. In 24 cases (90%), the judge was able to select the appropriate 30 second epoch on the basis of correspondence between reported and observed signals. All signals associated with lucid dream reports occurred during epochs of unambiguous REM sleep scored according to the conventional criteria (Rechtschaffen & Kales, 1968).
A later analysis extending these data with two additional subjects and 20 more lucid dreams produced identical results (LaBerge, Nagel, Taylor, Dement, & Zarcone, 1981). LaBerge et al. argued that their investigations demonstrated that lucid dreaming usually (though perhaps not exclusively) occurs during REM sleep. This conclusion is supported by research carried out in several other laboratories (Dane, 1984; Fenwick et al., 1984; Hearne, 1978; Ogilvie, Hunt, Kushniruk, & Newman, 1983).
Ogilvie et al. (1983) reported the physiological state preceding 14 spontaneous lucidity signals as unqualified REM in 12 (86%) of the cases; of the remaining two cases, one was "ambiguous" REM and the other appeared to be wakefulness. Keith Hearne and Alan Worsley collaborated on a pioneering study of lucid dreaming in which the latter spent 50 nonconsecutive nights in the Hull University sleep lab while the former monitored the polygraph. Worsley reported signaling in 8 lucid dreams, all of which were described by Hearne (1978) as having occurred during REM sleep.
However, demonstrations that signaling of lucid dreams occurs during REM sleep raises another kind of question: What exactly do we mean by the assertion that lucid dreamers are 'asleep?' Perhaps these 'dreamers' are not really dreamers, as some argued in the last century; or perhaps this 'sleep' is not really sleep, as some have argued in this century. How do we know that lucid dreamers are 'really asleep' when they signal? If we consider perception of the external world as a criterion of being awake (to the external world), we can conclude that they are actually asleep (to the external world) because although they know they are in the laboratory, this knowledge is a matter of memory, not perception. Upon awakening, they report having been totally in the dream world and not in sensory contact with the external world.
It might be objected that lucid dreamers might simply not be attending to the environment; rather than being asleep, perhaps they are merely absorbed in their private fantasy worlds as, for example, when deeply immersed in a novel or daydream. However, according to the reports of lucid dreamers (LaBerge, 1980a, 1985), if they deliberately attempt to feel the bedcovers they know they are sleeping in or try to hear the ticking of the clock they know is beside their bed, they fail to feel or hear anything except what they find in their dream worlds. Lucid dreamers are conscious of the absence of sensory input from the external world; therefore, on empirical grounds, they conclude that they are asleep.
If, in a contrary case, subjects were to claim to have been awake while showing physiological signs of sleep, or vice versa, we might have cause to doubt their subjective reports. However, when -- as in the present case -- the subjective accounts and objective physiological measures are in clear agreement, it is embarrassingly awkward to assert (as some critics have done) that subjects who reported being certain that they were asleep while showing physiological indications of unequivocal sleep were actually awake (cf. LaBerge, Nagel, Dement & Zarcone, 1981).
Some critics have suggested that "demand characteristics" might account for our results. It is true that our subjects were under demand to have, signal and report lucid dreams, but how could demand alone account for them doing all three things without having been lucid in the first place? If they merely unconsiously signaled, we would have found REM periods with signals without subsequent reports of lucidity -- but we did not. If they merely reported having signaled without actually having done so, we would have found reports without signals, which we did not. Further, by this account, where would the reported and observed signals have come from?
The evidence is clear: lucid dreaming is an experiential and physiological reality; though perhaps paradoxical, it is clearly a phenomenon of sleep.
lucidity
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