Sleep and dreaming
LaBerge, Stephen The Lucidity Institute, Palo Alto, California.
Last reviewed:October 2016
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- Nature of sleep
- Sleep cycle
- Measuring sleepiness
- Evolution and function of sleep
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A state of rest in which consciousness and activity are diminished, and in which an involuntary series of visual, auditory, or kinesthetic images, emotions, and thoughts occur in the mind, which take the form of a sequence of events or of a story, having a feeling of reality but totally lacking a feeling of free will. Sleep is generally defined as an easily reversible, temporary, periodic state of suspended behavioral activity, unresponsiveness, and perceptual disengagement from the environment. Compared with other states of temporary unresponsiveness, including syncope (fainting) or coma, sleep is easily reversible with strong or meaningful sensory stimuli (for example, the roar of a nearby tiger, or a voice speaking the sleeper's name). Sleep researchers use various measures of the body's electrical activity to define the various stages and substages of sleep (Fig. 1). Still, sleep should not be considered a state of general unconsciousness. The sleeper is normally unconscious (but not always) of the nature of events in the surrounding environment; this is the meaning of perceptual disengagement: a lack of conscious perception and meaningful responsiveness to environmental stimuli. However, the sleeper's attention may be fully engaged in experiencing a dream. Furthermore, if reportability is accepted as a sufficient condition for conscious mental processes, any dream that can be recalled must be considered conscious. Dreaming, then, can be simply defined as the world-modeling constructive process through which people have experiences during sleep, and a dream is just whatever the dreamer experienced while sleeping. See also: Cognition; Consciousness; Perception
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