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What Causes Dreams?

A dream is a type of mental activity that occurs during sleep. A dream usually consists of visual images that tell a story, although the sequence of dream events is usually mystifying. Dreams may be influenced by internal physical factors such as hunger, thirst, or indigestion. External factors, too, may affect dreams; for example, the ringing of an alarm clock may be transformed in a dream into a telephone call, with the result that the dreamer does not awaken. Dreams are often an illogical combination of events from the past of the dreamer, from his daily life, and from his imagined future.

The realistic but bizarre quality of dreams has long led men to speculate about their meaning. An early example of the search for the hidden meaning of a dream is found in the Old Testament story of Joseph interpreting the dreams of the pharaoh. In ancient times, dreams were often thought to be supernaturally or divinely inspired and to represent the will of the gods. It was also believed that dreams could predict events. Some people still believe that dreams can foretell the future, but the belief has no scientific basis.

One of the first men in modern times to consider the dream worthy of scientific investigation was Sigmund Freud, the founder of psychoanalysis. In his famous book The Interpretation of Dreams (1900), Freud attempted to show that dreams are not meaningless but that they can be used to understand the workings of the unconscious mind. Freud believed that conscious control of the mind is reduced during sleep and that the thoughts, wishes, and conflicts that a person does not dare to recognize consciously are often expressed in his dreams. However, they are expressed through symbols so that the true meaning of the dreams may be hidden from the dreamer. For example, a cruel giant in a boy's dream may symbolically represent his bullying older brother. A dream of climbing a ladder may mean a desire to escape from an unhappy home or a craving for promotion in one's job or perhaps, in the case of an invalid, the yearning to be physically normal.

Recent research on dreams has been conducted by scientists using such instruments as the electroencephalograph, which is a machine that records the patterns of electrical brain waves, and a complicated apparatus for recording eye movements. The results of many tests with these instruments on sleeping subjects have made it possible to record when a person is dreaming and when he is not. The tests suggest that people dream for about 1 1/2 hours out of every 8 hours' sleep, that dreams vary in length but that the average duration of a dream is about 20 minutes, and that they occur at intervals all during the night. Furthermore, the direction of the eye movements during a dream appears to be related to the content of the dream. Thus, when vertical eye movements were recorded and the subject was awakened, he reported a dream in which he was looking up at a skyscraper. A dream of watching two people throwing tomatoes at each other was accompanied by horizontal eye movements.

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