A lucid dream is one in which the dreamer is aware of being in a dream state while the dream is still in progress. Lucid dreams can be extremely vivid and realistic, depending on the level of self-awareness during the dream. Most strikingly, lucid dreamers report being able to actively participate in and often manipulate experiences within the dream environment — that is, deliberately walk, fly, look around, handle objects, and interact with dream persons.

Lucid dreams provide a unique opportunity to find out more about the experience of dreaming — and, by extension, perhaps more about the experiences of shamans, and about other visionary experiences, including those related to ayahuasca.

It is clear, however, that dream reports, given after the dreamer awakens, have a number of methodological problems — problems with recall, conflation, censoring, exaggeration, and confabulation. Dream states are notoriously slippery and prone to being forgotten. Significant details are easily either lost or filled in; coherence is imposed on narrative; connections drawn later are understood as part of the dream itself; memory of the dream is subject to constant revision. People may fail to report the contents of dreams that they perceive to be too revealing, embarrassing, or in conflict with the dreamer’s waking persona.

Here is a simple example. Can a lucid dreamer perform mathematical calculations during a dream? If a lucid dreamer is instructed beforehand to calculate, say, the factors of sixteen while in a lucid dream, will the dreamer be able to do it? And — here is the methodological question — how would we know? The dreamer may misreport or misremember the dream content; the dreamer may dream that he or she had calculated the factors of sixteen without actually having done so.

What we would like, of course, is for the dreamer to answer the question during the dream, and somehow communicate that answer to the investigator.

Similarly, some lucid dreamers report being able to control events in their dreams. There is some reason to believe there are limits to this control — for example, that major changes in dream setting, or even sudden changes in ambient light, such as turning on or off a light switch, are beyond the power of a lucid dreamer. Interestingly, lucid dreamers almost universally are unable to read material of any complexity, being able to read only a few words, with longer sequences deteriorating quickly into gibberish. Again, we would like to have the dreamer both carry out and report the results of reading experiments while still dreaming.

So: Is there any way for a lucid dreamer to communicate with us while dreaming? The problem is that, during REM sleep, when lucid dreams seem most likely to occur, there is physical paralysis — known as REM atonia — and difficulty of arousal. However, we can take a look at several interesting possibilities.

Here we can distinguish between passive communication from the dreamer to the investigator, using such tools as electroencephalography, and active communication, in which the dreamer voluntarily initiates and controls the communication.

It is possible to use instrumentation to attempt to confirm at least some claims of experiences in lucid dreams. In one case, a female lucid dreamer claimed to be able voluntarily to initiate sexual activity in her lucid dreams, leading to orgasms of “profound” intensity. She was fitted with EEG, EOG, and chin-EMG measuring devices, as well as devices to measure respiration, heart rate, vaginal EMG, and vaginal pulse amplitude. She was able to signal, with eye movements, when she was initiating dream sexual activity, and reported upon awakening that she had had an orgasm while dreaming.

The instrumentation revealed that, at that time, her heart rate showed a moderate increase, and her respiration, vaginal blood flow, and vaginal muscle activity reached their highest point of the night. As a methodological issue, it is not clear whether — or by what criteria — those results count as a confirmation of an orgasm. It is reported that “comparable results were obtained with a male subject,” although presumably, in that instance, such elaborate instrumentation would be unnecessary, as would also concern over definitions.

This example raises important issues. To the extent that we are dealing with physiological correlates of internal states, when can it be said that instrumental verification of a physiological correlate confirms the reported state? Presumably what we would want to know about the female subject in the preceding paragraph is the state of her vaginal blood flow and muscle activity during a waking orgasm. Similar examples might include fear, excitement, sorrow, exaltation; to what extent can we claim to have confirmed such reports through physiological correlation? Can we legitimately generalize from physiological correlation of heart rate and fear, say, in waking life to a similar correlation in the course of a lucid dream?

The male volunteer raises similar questions. Since erections are regular concomitants of REM dream states in any event, to what extent does an erection confirm a report of voluntarily initiated sexual activity in a lucid dream? The question is generalizable, and once again raises the issue of baseline for particular dreamers.

But there are also ways in which the dreamer can voluntarily communicate while in the dream state. The most frequently used mechanism for voluntary communication from a dreamer is by eye movement. It appears that, when a lucid dreamer looks left or right in the dream, the physical eyes in fact make the corresponding motions, which can be picked up and measured by electrodes near the eye muscles. A number of ingenious experiments have been performed using these eye movements. Using such signals, experimenters can determine at what part of the sleep cycle lucid dreaming takes place, how long lucidity lasts, and the correlation of lucid dreams with REM and NREM sleep. Moreover, it has been possible to show that lucid dreamers can in fact remember tasks set for them before going to sleep and can carry out those tasks during the dream state.

For example, one lucid dreamer was instructed to draw triangles during the dream and follow the movement of his hands visually while doing so; and, indeed, the physical motions of his eyes while asleep corresponded to those that would have appeared had he been drawing a triangle while awake. Finally, eye movement has been used to show that a lucid dreamer’s sense of time is similar to his or her waking sense of time; instructed to signal with eye movements every ten seconds, lucid dreamers were about as accurate as their waking counterparts.

But eye signaling raises methodological issues of its own. While eye movement can signal that the dreamer is, in fact, lucid, it is difficult to use for more sophisticated communication. Moving the eyes apparently changes what the dreamer sees, and such changes in visual imagery apparently can on occasion be sufficiently disruptive to wake the dreamer. Further, there is a limit to the complexity of eye movement that can either be controlled by the dreamer or picked up by a polygraph, and, therefore, there seems to be a limit to the amount of information that can be transmitted by eye movement. Eye movement signaling is an information channel of very narrow bandwidth, usually confined, in experiments so far, to providing yes-no information.

In addition to eye movements, it is at least on occasion possible that nerve impulses generated by voluntarily walking during a lucid dream can be detected by electrodes placed at the feet. Apparently a lucid dreamer, when moving his or her legs in a dream, can actually cause nerve impulses to travel down the legs; although the legs do not actually move, these impulses can be detected. It is not clear that this can be done consistently, or to what extent this ability is found among lucid dreamers generally. It has also been reported that a lucid dreamer can affect the rate of breathing in the physical body by changing the rate of breathing during the dream.

The possibilities of such communication can be multiplied by the utilization of various current heads-up and virtual reality devices. For example, it is possible to detect, with relatively accessible technology, not only the movement but the position of the eyes; there are digital cameras available that use this technology to focus on what the viewer is looking at. Data-glove technology, used in virtual reality simulations, can similarly detect minute changes in the positions of the fingers. It should be possible, with proper training, to develop more elaborate codes than the simple yes-no eye-movement codes previously used in lucid dreaming experiments.

Such studies apparently remain to be performed.