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Earlier studies showing that some of the eye movements of REM sleep corresponded to the reported direction of the dreamer's gaze (e.g., Roffwarg et al. 1962).LaBerge test this - asked subjects to carry out distinctive patterns of voluntary eye movements when they realized they were dreaming. The prearranged eye movement signals appeared on the polygraph records during REM, proving that the subjects had indeed been lucid during uninterrupted REM sleep (LaBerge 1990; LaBerge et al. 1981). Figure 1 shows an example.
Figure 1. A typical signal-verified lucid dream. Four channels of physiological data (central EEG [C3-A2], left and right eye-movements [LOC and ROC], and chin muscle tone [EMG]) from the last 8 min of a 30 min REM period are shown. Upon awakening the subject reported having made five eye movement signals (labeled 1-5 in figure). The first signal (1, LRLR) marked the onset of lucidity. Skin potential potential artifacts can be observed in the EEG at this point. During the following 90 s the subject “flew about” exploring his dream world until he believed he had awakened, at which point he made the signal for awakening (2, LRLRLRLR). This signal, made in non-lucid REM shows that the precise correspondence between eye movements and gaze is not an artifact of lucidity. After another 90 s, the subject realized he was still dreaming and signaled (3) with three pairs of eye movements. Realizing that this was too many, he correctly signaled with two pairs (4). Finally, upon awakening 100 s later he signaled appropriately (5, LRLRLRLR). [Calibrations are 50 microV and 5 s.]
Figure 2. Eye movement signal used by experimental subject to communicate to the experimenter during a lucid dream consisted of sets of quick horizontal movements separated by a brief pause. Upper trace (WEC) shows signal during wakefulness as 2 sets of left (L), right (R), left (L), center (C) sequences; lower trace (lucid) shows same signal during a lucid dream. Left and right eye movement electrodes (blue and red lines) are configured such that synchronous movements of the 2 eyes are displayed in opposite directions on the trace; this allows true eye movements to be discerned from muscle artifacts (green channel), which move in the same direction on the eye movement channels (From Voss, et al (2009), Sleep;32:1191-1200, figure 1).