LUCID DREAMING: AWAKE IN YOUR SLEEP?
                     
 
                     
                      By Susan Blackmore
                     
 
                     
           From Skeptical Inquirer, Vol. 15 Summer 1991
                     
                        pages 362-370
                     
 
                     
 
                     
    What could it mean to be conscious in your dreams? For most
                     
    of us, dreaming is something quite separate from normal life.
                     
    When we wake up from being chased by a ferocious tiger, or
                     
    seduced by a devastatingly good-looking Nobel Prize winner
                     
    we realize with relief or disappointment that "it was only
                     
    a dream."
                     
      Yet there are some dreams that are not like that. Lucid
                     
    dreams are dreams in which you know at the time that you are
                     
    dreaming. That they are different from ordinary dreams is
                     
    obvious as soon as you have one. The experience is something
                     
    like waking up in your dreams. It is as though you "come to"
                     
    and find you are dreaming.
                     
      Lucid dreams used to be a topic within psychical research
                     
    and parapsychology. Perhaps their incomprehensibility made
                     
    them good candidates for being thought paranormal. More
                     
    recently, however, they have begun to appear in psychology
                     
    journals and have dropped out of parapsychology - a good
                     
    example of how the field of parapsychology shrinks when any
                     
    of its subject matter is actually explained.
                     
      Lucidity has also become something of a New Age fad. There
                     
    are machines and gadgets you can buy and special clubs you
                     
    can join to learn how to induce lucid dreams. But this
                     
    commercialization should not let us lose sight of the very
                     
    real fascination of lucid dreaming. It forces us to ask
                     
    questions about the nature of consciousness, deliberate
                     
    control over our actions, and the nature of imaginary worlds.
                     
 
                     
    A Real Dream or Not?
                     
 
                     
    The term lucid dreaming was coined by the Dutch psychiatrist
                     
    Frederik van Eeden in 1913. It is something of a misnomer
                     
    since it means something quite different from just clear or
                     
    vivid dreaming. Nevertheless we are certainly stuck with it.
                     
    Van Eeden explained that in this sort of dream "the
                     
    re-integration of the psychic functions is so complete that
                     
    the sleeper reaches a state of perfect awareness and is able
                     
    to direct his attention, and to attempt different acts of free
                     
    volition. Yet the sleep, as I am able confidently to state, is
                     
    undisturbed, deep, and refreshing."
                     
      This implied that there could be consciousness during sleep,
                     
    a claim many psychologists denied for more than 50 years.
                     
    Orthodox sleep researchers argued that lucid dreams could not
                     
    possibly be real dreams. If the accounts were valid, then the
                     
    experiences must have occurred during brief moments of
                     
    wakefulness or in the transition between waking and sleeping,
                     
    not in the kind of deep sleep in which rapid eye movements (REMs)
                     
    and ordinary dreams usually occur. In other words, they could
                     
    not really be dreams at all.
                     
      This presented a challenge to lucid dreamers who wanted to
                     
    convince people that they really were awake in their dreams.
                     
    But of course when you are deep asleep and dreaming you cannot
                     
    shout, "Hey! Listen to me. I'm dreaming right now." All the
                     
    muscles of the body are paralyzed.
                     
      It was Keith Hearne (1978), of the University of Hull, who
                     
    first exploited the fact that not all the muscles are paralyzed.
                     
    In REM sleep the eyes move. So perhaps a lucid dreamer could
                     
    signal by moving the eyes in a predetermined pattern. Just over
                     
    ten years ago, lucid dreamer Alan Worsley first managed this is
                     
    in Hearne's laboratory. He decided to move his eyes left and
                     
    right eight times in succession whenever he became lucid. Using
                     
     a polygraph, Hearne could watch the eye movements for sign of
                     
    the special signal. He found it in the midst of REM sleep. So
                     
    lucid dreams are real dreams and do occur during REM sleep.
                     
      Further research showed that Worsley's lucid dreams most
                     
    often occurred in the early morning, around 6:30 A.M., nearly
                     
    half an hour into a REM period and toward the end of a burst
                     
    of rapid eye movements. They usually lasted for two to five
                     
    minutes. Later research showed that they occur at times of
                     
    particularly high arousal during REM sleep (Hearne 1978).
                     
      It is sometimes said that discoveries in science happen when
                     
    the time is right for them. It was one of those odd things that
                     
    at just the same time, but unbeknown to Hearne, Stephen LaBerge,
                     
    at Stanford University in California, was trying the same
                     
    experiment. He too succeeded, but resistance to the idea was
                     
    very strong. In 1980, both Science and Nature rejected his first
                     
    paper on the discovery (LaBerge 1985). It was only later that it
                     
    became clear what an important step this had been.
                     
 
                     
    An Identifiable State?
                     
 
                     
    It would be especially interesting if lucid dreams were
                     
    associated with a unique physiological state. In fact this has
                     
    not been found, although this is not very surprising since the
                     
    same is true of other altered states, such as out-of-body
                     
    experiences and trances of various kinds. However, lucid dreams
                     
    do tend to occur in periods of higher cortical arousal. Perhaps
                     
    a certain threshold of arousal has to be reached before awareness
                     
    can be sustained.
                     
      The beginning of lucidity (marked by eye signals, of course)
                     
    is associated with pauses in breathing, brief changes in heart
                     
    rate, and skin response changes, but there is no unique
                     
    combination that allows the lucidity to be identified by an
                     
    observer.
                     
      In terms of the dream itself, there are several features that
                     
    seem to provoke lucidity. Sometimes heightened anxiety or stress
                     
    precedes it. More often there is a kind of intellectual
                     
    recognition that something "dreamlike" or incongruous is going
                     
    on (Fox 1962; Green 1968; LaBerge 1985).
                     
      It is common to wake from an ordinary dream and wonder, "How
                     
    on earth could I have been fooled into thinking that I was
                     
    really doing push-ups on a blue beach?" A little more awareness
                     
    is shown when we realize this in the dream. If you ask yourself,
                     
    "Could this be a dream?" and answer "No" (or don't answer at all),
                     
    this is called a pre-lucid dream. Finally, if you answer "Yes",
                     
    it becomes a fully lucid dream.
                     
      It could be that once there is sufficient cortical arousal it
                     
    is possible to apply a bit of critical thought; to remember
                     
    enough about how the world ought to be to recognize the dream
                     
    world as ridiculous, or perhaps to remember enough about oneself
                     
    to know that these events can't be continuous with normal waking
                     
    life. However, tempting as it is to conclude that the critical
                     
    insight produces the lucidity, we have only an apparent
                     
    correlation and cannot deduce cause and effect from it.
                     
 
                     
    Becoming a Lucid Dreamer
                     
 
                     
    Surveys have show that about 50 percent of people (and in some
                     
    cases more) have had at least one lucid dream in their lives.
                     
    (see, for example, Blackmore 1982; Gackenbach and LaBerge 1988;
                     
    Green 1968.) Of course surveys are unreliable in that many
                     
    people may not understand the question. In particular, if you
                     
    have never had a lucid dream, it is easy to misunderstand what
                     
    is meant by the term. So overestimates might be expected.
                     
    Beyond this, it does not seem that surveys can find out much.
                     
    There are no very consistent differences between lucid dreamers
                     
    and others in terms of age, sex, education, and so on (Green
                     
    1968; Gackenbach and LaBerge 1988).
                     
      For many people, having lucid dream is fun, and they want to
                     
    learn how to have more or to induce them at will. One finding
                     
     from early experimental work was that high levels of physical
                     
    (and emotional) activity during the day tend to precede lucidity
                     
    at night. Waking during the night and carrying out some kind of
                     
    activity before falling asleep again can also encourage a lucid
                     
    dream during the next REM period and is the basis of some
                     
    induction techniques.
                     
      Many methods have been developed (Gackenbach and Bosveld 1989;
                     
    Tart 1988; Price and Cohen 1988). They roughly fall into three
                     
    categories.
                     
      One of the best known is LaBerge's MILD (Mnemonic Induction
                     
    of Lucid Dreaming). This is done on waking in the early morning
                     
    from a dream. You should wake up fully, engage in some activity
                     
    like reading or walking about, and then lie down to go to sleep
                     
    again. Then you must imagine yourself asleep and dreaming,
                     
    rehearse the dream from which you woke, and remind yourself,
                     
    "Next time I dream this I want to remember I'm dreaming."
                     
      A second approach involves constantly reminding yourself to
                     
    become lucid throughout the day rather than the night. This is
                     
    based on the idea that we spend most of our time in a kind of
                     
    waking daze. If we could be more lucid in waking life, perhaps
                     
    we could be more lucid while dreaming. German psychologist
                     
    Paul Tholey suggests asking yourself many times every day,
                     
    "Am I dreaming or not?" This sound easy but is not. It takes
                     
    a lot of determination and persistence not to forget all about
                     
    it. For those who do forget, French researcher Clerc suggests
                     
    writing a large "C" on your hand (for "conscious") to remind
                     
    you (Tholey 1983; Gackenbach and Bosveld 1989).
                     
      This kind of method is similar to the age-old technique for
                     
    increasing awareness by meditation and mindfulness. Advanced
                     
    practitioners of meditation claim to maintain awareness through
                     
    a large proportion of their sleep. TM is often claimed to lead
                     
    to sleep awareness. So perhaps it is not surprising that some
                     
    recent research finds association between meditation and
                     
    increased lucidity (Gackenbach and Bosveld 1989).
                     
      The third and final approach requires a variety of gadgets.
                     
    The idea is to use some sort of external signal to remind
                     
    people, while they are actually in REM sleep, that they are
                     
    dreaming. Hearne first tried spraying water onto sleepers' faces
                     
    or hands but found it too unreliable. This sometimes caused them
                     
    to incorporate water imagery into their dreams, but they rarely
                     
    became lucid. He eventually decided to use a mild electrical
                     
    shock to the wrist. His "dream machine" detects changes in
                     
    breathing rate (which accompany the onset of REM) and then
                     
    automatically delivers a shock to the wrist (Hearne 1990).
                     
      Meanwhile, in California, LaBerge was rejecting taped voices
                     
    and vibrations and working instead with flashing lights. The
                     
    original version was laboratory based and used a personal
                     
    computer to detect the eye movements of REM sleep and to turn
                     
    on flashing lights whenever the REMs reached a certain level.
                     
    Eventually, however, all the circuitry was incorporated into
                     
    a pair of goggles. The idea is to put the goggles on at night,
                     
    and the lights will flash only when you are asleep and dreaming.
                     
    The user can even control the level of eye movements at which
                     
    the lights begin to flash.
                     
      The newest version has a chip incorporated into the goggles.
                     
    This will not only control the lights but will store data on
                     
    eye-movement density during the night and when and for how long
                     
    the lights were flashing, making fine tuning possible. At the
                     
    moment, the first users have to join in workshops at LaBerge's
                     
    Lucidity Institute and learn how to adjust the settings, but
                     
    within a few months he hopes the whole process will be fully
                     
    automated. (See LaBerge's magazine, DreamLight.)
                     
      LaBerge tested the effectiveness of the Dream Light on 44
                     
    subjects who came into the laboratory, most for just one night.
                     
    Fifty-five percent had at least one lucid dream this way. The
                     
    results suggested that this method is about as succesful as
                     
    MILD, but using the two together is the most effective
                     
    (LaBerge 1985).
                     
 
                     
     Lucid Dreams as an Experimental Tool
                     
 
                     
    There are a few people who can have lucid dreams at will. And
                     
    the increase in induction techniques has provided many more
                     
    subjects who have them frequently. This has opened the way to
                     
    using lucid dreams to answer some of the most interesting
                     
    questions about sleep and dreaming.
                     
      How long do dreams take? In the last century, Alfred Maury
                     
    had a long and complicated dream that led to his being beheaded
                     
    by a guillotine. He woke up terrified, and found that the
                     
    headboard of his bed had fallen on his neck. From this, the
                     
    story goes, he concluded that the whole dream had been created
                     
    in the moment of awakening.
                     
      This idea seems to have got into popular folklore but was very
                     
    hard to test. Researchers woke dreamers at various stages of
                     
    their REM period and found that those who had been longer in REM
                     
    claimed longer dreams. However, accurate timing became possible
                     
    only when lucid dreamers could send "markers" from the dream
                     
    state.
                     
      LaBerge asked his subjects to signal when they became lucid
                     
    and then count a ten-second period and signal again. Their
                     
    average interval was 13 seconds, the same as they gave when
                     
    awake. Lucid dreamers, like Alan Worsley, have also been able
                     
    to give accurate estimates of the length of whole dreams or
                     
    dream segments (Schatzman, Worsley, and Fenwick 1988).
                     
 
                     
    Dream Actions
                     
 
                     
    As we watch sleeping animals it is often tempting to conclude
                     
    that they are moving their eyes in response to watching a dream,
                     
    or twitching their legs as they dream of chasing prey. But do
                     
    physical movements actually relate to the dream events?
                     
      Early sleep researchers occassionally reported examples like
                     
    a long series of left-right eye movements when a dreamer had
                     
    been dreaming of watching a ping-pong game, but they could do
                     
    no more than wait until the right sort of dream came along.
                     
      Lucid dreaming made proper experimentation possible, for the
                     
    subjects could be asked to perform a whole range of tasks in
                     
    their dreams. In one experiment with researchers Morton Schatzman
                     
    and Peter Fenwick, in London, Worsley planned to draw large
                     
    triangles and to signal with flicks of his eyes every time he
                     
    did so. While he dreamed, the electromyogram, recording small
                     
    muscle movements, showed not only the eye signals but spikes
                     
    of electrical activity in the right forearm just afterward.
                     
    This showed that the preplanned actions in the dream produced
                     
    corresponding muscle movements (Schatzman, Worsley, and Fenwick
                     
    1988).
                     
      Further experiments, with Worsley kicking dream objects,
                     
    writing with umbrellas, and snapping his fingers, all confirmed
                     
    that the muscles of the body show small movements corresponding
                     
    to the body's actions in the dream. The question about eye
                     
    movements was also answered. The eyes do track dream objects.
                     
    Worsley could even produce slow scanning movements, which are
                     
    very difficult to produce in the absence of a "real" stimulus
                     
    (Schatzman, Worsley, and Fenwick 1988).
                     
      LaBerge was especially interested in breathing during dreams.
                     
    This stemmed from his experiences at age five when he had
                     
    dreamed of being an undersea pirate who could stay under water
                     
    for very long periods without drowning. Thirty years later he
                     
    wanted to find out whether dreamers holding their breath in
                     
    dreams do so physically as well. The answer was yes. He and
                     
    other lucid dreamers were able to signal from the dream and
                     
    then hold their breath. They could also breathe rapidly in
                     
    their dreams, as revealed on the monitors. Studying breathing
                     
    during dreamed speech, he found that the person begins to
                     
    breathe out at the start of an utterance just as in real speech
                     
    (LaBerge and Dement 1982a).
                     
 
                     
    Hemispheric Differences
                     
  
                     
    It is known that the left and right hemispheres are activated
                     
    differently during different kinds of tasks. For example,
                     
    singing uses the right hemisphere more, while counting and
                     
    other, more analytical tasks use the left hemisphere more. By
                     
    using lucid dreams, LaBerge was able to find out whether the
                     
    same is true in dreaming.
                     
      In one dream he found himself flying over a field. (Flying
                     
    is commonly associated with lucid dreaming.) He signaled with
                     
    his eyes and began to sing "Row, row, row your boat...."
                     
    He then made another signal and counted slowly to ten before
                     
    signaling again. The brainwave records showed just the same
                     
    patterns of activation that you would expect if he had done
                     
    these tasks while awake (LaBerge and Dement 1982b).
                     
 
                     
    Dream Sex
                     
 
                     
    Although it is not often asked experimentally, I am sure plenty
                     
    of people have wondered what is happening in their bodies while
                     
    they have their most erotic dreams.
                     
      LaBerge tested a woman who could dream lucidly at will and
                     
    could direct her dreams to create the sexual experiences she
                     
    wanted. (What a skill!) Using appropriate physiological
                     
    recording, he was able to show that her dream orgasms were
                     
    matched by true orgasms (LaBerge, Greenleaf, and Kedzierski
                     
    1983).
                     
      Experiments like these show that there is a close
                     
    correspondence between actions of the dreamer and, if not real
                     
    movements, at least eletrical responses. This puts lucid
                     
    dreaming somewhere between real actions, in which muscles work
                     
    to move the body, and waking imagery, in which they are rarely
                     
    involved at all. So what exactly is the status of the dream
                     
    world?
                     
 
                     
    The Nature of the Dream World
                     
 
                     
    It is tempting to think that the real world and the world of
                     
    dreams are totally separate. Some of the experiments already
                     
    mentioned show that there is no absolute dividing line. There
                     
    are also plenty of stories that show the penetrability of the
                     
    boundary.
                     
      Alan Worsley describes one experiment in which his task was
                     
    to give himself a prearranged number of small electric shocks
                     
    by means of a machine measuring his eye movements. He went to
                     
    sleep and began dreaming that it was raining and he was in a
                     
    sleeping bag by a fence with gate in it. He began to wonder
                     
    whether he was dreaming and thought it would be cheating to
                     
    activate the shocks if he was awake. Then, while making the
                     
    signals, he worried about the machine, for it was out there
                     
    with him in the rain and might get wet (Schatzman, Worsley,
                     
    and Fenwick 1988).
                     
      This kind of interference is amusing, but there are dreams
                     
    of confusion that are not. The most common and distinct are
                     
    called false awakenings. You dream of waking up but in fact,
                     
    of course, are still asleep. Van Eeden (1913) called these
                     
    "wrong waking up" and described them as "demoniacal, uncanny,
                     
    and very vivid and bright, with ... a strong diabolical light."
                     
    The French zoologist Yves Delage, writing in 1919, described
                     
    how he had heard a knock at his door and a friend calling for
                     
    his help. He jumped out of bed, went to wash quickly with cold
                     
    water, and when that woke him up he realized he had been
                     
    dreaming. The sequence repeated four times before he finally
                     
    actually woke up - still in bed.
                     
      A student of mine described her infuriating recurrent dream
                     
    of getting up, cleaning her teeth, getting dressed, and then
                     
    cycling all the way to the medical school at the top of a long
                     
    hill, where she finally would realize that she had dreamed it
                     
    all, was late for lectures, and would have to do it all over
                     
    again for real.
                     
       The one positive benefit of false awakenings is that they can
                     
    sometimes be used to induce out-of-body-experiences (OBEs).
                     
    Indeed, Oliver Fox (1962) recommends this as a method for
                     
    achieving the OBE. For many people OBEs and lucid dreams are
                     
    practically indistinguishable. If you dream of leaving your
                     
    body, the experience is much the same. Also recent research
                     
    suggests that the same people tend to have both lucid dreams
                     
    and OBEs (Blackmore 1988, Irwin 1988).
                     
      All of these experiences have something in common. In all
                     
    of them the "real" world has been replaced by some kind of
                     
    imaginary replica. Celia Green, of the Institute of
                     
    Psychophysical Research at Oxford, refers to all such states
                     
    as "metachoric experiences."
                     
      Jayne Gackenbach, a psychologist from the University of
                     
    Alberta, Canada, relates these experiences to UFO-abduction
                     
    stories and near-death-experiences (NDEs). The UFO abductions
                     
    are the most bizarre but are similar in that they too involve
                     
    the replacement of the perceived world by a hallucinatory
                     
    replica.
                     
      There is an important difference between lucid dreams and
                     
    these other states. In the lucid dream one has insight into
                     
    the state (in fact that defines it). In false awakening, one
                     
    does not (again by definition). In typical OBEs, people think
                     
    they have really left their bodies. In UFO "abductions" they
                     
    believe the little green men are "really there"; and in NDEs,
                     
    they are convinced they are rushing down a real tunnel toward
                     
    a real light and into the next world. It is only in the lucid
                     
    dream that one realizes it is a dream.
                     
      I have often wondered whether insight into these other
                     
    experiences is possible and what the consequences might be.
                     
    So far I don't have any answers.
                     
 
                     
    Waking Up
                     
 
                     
    The oddest thing about lucid dreams - and, to many people who
                     
    have them, the most compelling - is how it feels when you wake
                     
    up. Upon waking up from a normal dream, you usually think,
                     
    "Oh, that was only a dream." Waking up from a lucid dream is
                     
    more continuous. It feels more real, it feels as though you
                     
    were conscious in the dream. Why is this? I think the reason can
                     
    be found by looking at the mental models the brain constructs
                     
    in waking, in ordinary dreaming, and in lucid dreams.
                     
      I have previously argued that what seems real is the most
                     
    stable mental model in the system at any time. In waking life,
                     
    this is almost always the input-driven model, the one that is
                     
    built up from the sensory input. It is firmly linked to the
                     
    body image to make a stable model of "me, here, now." It is
                     
    easy to decide that this represents "reality" while all the
                     
    other models being used at the same time are "just imagination"
                     
    (Blackmore 1988).
                     
      Now consider an ordinary dream. In that case there are lots
                     
    of models being built but no input-driven model. In addition
                     
    there is no adequate self-model or body image. There is just
                     
    not enough access to memory to construct it. This means, if my
                     
    hypothesis is right, that whatever model is most stable at any
                     
    time will seem real. But there is no recognizable self to whom
                     
    it seems real. There will just be a series of competing models
                     
    coming and going. Is this what dreaming feels like?
                     
      Finally, we know from research that in the lucid dream there
                     
    is higher arousal. Perhaps this is sufficient to construct a
                     
    better model of self. It is one that includes such important
                     
    facts as that you have gone to sleep, that you intended to
                     
    signal with your eyes, and so on. It is also more similar to
                     
    the normal waking self than those fleeting constructions of
                     
    the ordinary dream. This, I suggest, is what makes the dream
                     
    seem more real on waking up. Because the you who remembers
                     
    the dream is more similar to the you in the dream. Indeed,
                     
    because there was a better model of you, you were more
                     
    conscious.
                     
       If this is right, it means that lucid dreams are potentially
                     
    even more interesting than we thought. As well as providing
                     
    insight into the nature of sleep and dreams, they may give
                     
    clues to the nature of consciousness itself.
                     
 
                     
    References
                     
 
                     
    Blackmore, S. J. 1982. Beyond the Body. London: Heinemann.
                     
    ---------        1988. A Theory of lucid dreams and OBEs.
                     
                     In Conscious Mind, Sleeping Brain, 373-387, ed.
                     
                     J. Gackenbach and S. LaBerge. New York: Plenum.
                     
    Delage, Y. 1919. Le Reve. Paris: Les Presses Universitaires de
                     
                     France.
                     
    Fox, O. 1962.    Astral Projection. New York: University Books.
                     
    Gackenbach, J., and J. Bosveld. 1989. Control Your Dreams.
                     
                     New York: Harper & Row.
                     
    Gackenbach, J., and S. LaBerge, eds. 1988. Conscious Mind,
                     
                     Sleeping Brain. New York: Plenum.
                     
    Green, C. E. 1968. Lucid Dreams. London: Hamish Hamilton.
                     
    Hearne, K. 1978. Lucid Dreams: An Electrophysiological and
                     
                     Psychological Study. Unpublished Ph.D. thesis,
                     
                     University of Hull.
                     
    ---------  1990. The Dream Machine. Northants: Aquarian.
                     
    Irwin, H. J. 1988. Out-of-body experiences and dream lucidity:
                     
                     Empirical perspectives. In Conscious Mind,
                     
                     Sleeping Brain, 353-371, ed. J. Gackenbach and
                     
                     S. LaBerge. New York: Plenum.
                     
    LaBerge, S. 1985. Lucid Dreaming. Los Angeles: Tarcher.
                     
    LaBerge, S. and W. Dement. 1982a. Voluntary control of respiration
                     
                     during REM sleep. Sleep Research, 11:107.
                     
    ---------  1982b. Lateralization of alpha activity for dreamed
                     
                     singing and counting during REM sleep.
                     
                     Psychophysiology, 19:331-332.
                     
    LaBerge, S., W. Greenleaf, and B. Kerzierski. 1983. Physiological
                     
                     responses to dreamed sexual activity during lucid
                     
                     REM sleep. Psychophysiology, 20:454-455.
                     
    Price, R. F., and D. B. Cohen. 1988. Lucid dream induction: An
                     
                     empirical evaluation. In Conscious Mind, Sleeping
                     
                     Brain, 105-134, ed. J. Gackenbach and S. LaBerge.
                     
                     New York: Plenum.
                     
    Schatzman, M., A. Worsley, and P. Fenwick. 1988. Correspondence
                     
                     during lucid dreams between dreamed and actual
                     
                     events. In Conscious Mind, Sleeping Brain,
                     
                     155-179, ed. J. Gackenbach and S. LaBerge.
                     
                     New York: Plenum.
                     
    Tart, C. 1988. From spontaneous event to lucidity: A review of
                     
                     attempts to consciously control nocturnal
                     
                     dreaming. In Conscious Mind, Sleeping Brain,
                     
                     67-103, ed. J Gackenbach and S. LaBerge.
                     
                     New York: Plenum.
                     
    Tholey, P. 1983. Techniques for controlling and manipulating
                     
                     lucid dreams. Perceptual and Motor Skills,
                     
                     57:79-90.
                     
    Van Eeden, F. 1913. A study of dreams. Proceedings of the Society
                     
                     for Psychical Research, 26:431-461.
                     
 
                     
    Susan J. Blackmore is with the Perceptual Systems Research Centre,
                     
    Department of Psychology, University of Bristol, and the School
                     
    of Social Sciences, University of Bath.
                     
                     

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