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The everyday meaning of the word "consciousness" corresponds fairly closely to how most psychologists use the term. To be conscious is to be aware.
Most of the time, we are aware of whatever activity happens to be at the center of our current attentional focus. For example, in order to read this sentence the readers need to focus their attention on the appropriate line on the page, and concentrate on extracting meaning from what they are reading. Such conscious attention is, however, very selective. Research has demonstrated that a great deal of our mental activity is performed outside of conscious awareness. Consciousness is like the tip of an iceberg. It allows us to exert purposeful control over our current activities, and to communicate our mental states to others. We selectively attend to only a small fraction of the stimulation to which we are constantly exposed. We ignore many sources of external information, but can be made instantly aware of them. Upon reflection, it is obvious that we are operating at various levels of consciousness throughout the day. Do students daydream in class, and later wonder what the teacher said? When people brush their teeth, are they thinking about how clean they are getting them? There are a variety of states or levels of consciousness that have been studied extensively by psychologists. A few of them are described below.
Perhaps the most frequent and conspicuous altered state of consciousness is experienced during sleep. Sleep is typically studied by means of an electroencephalograph. It produces a visual record (called an EEG) of the changes in electrical activity in the brain that occur during sleep. Changes in muscle activity and eye movements are also monitored. There are four major stages of sleep that are distinguished from one another on the basis of the electrical activity associated with each. There is also a distinctive fifth stage, known as REM (rapid eye movement) sleep. During this phase the brain's electrical activity is similar to that of the waking state. The sleeper's eyes dart about rapidly, even though the lids remain closed. Apart from the occasional twitch, there is a total suppression of muscle movement. The sleeper is essentially paralyzed. Because the brain's motor cortex is active during this stage, REM sleep is sometimes referred to as "paradoxical sleep." There is considerable internal activity, but an external calmness. REM sleep is the stage during which almost all dreaming occurs. REM sleep is usually accompanied by genital arousal in both males and females, although such arousal is unrelated to dream content. Regardless of the stage of sleep, there is no evidence that any substantive learning can take place during sleep. Despite extravagant claims, listening to a foreign language while sleeping is not going to make someone bilingual.
Author Info: Timothy E. Moore PhD, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Nursing and Allied Health, 2002
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