It is a familiar fact that dreams are hard to recall. Because of this, memory alone is not a reliable indication of what they are like.
Consider the following examples. (1) Some people claim that they never dream. The truth is, psychologists assure us, that they do not remember having dreamt. Researchers say that they can tell when someone is dreaming, by his rapid eye movements (REM) and a certain pattern of brain waves recorded on an electroencephalograph (EEG). When a sleeper's eyes move rapidly, and he registers the appropriate pattern of brain-waves on the EEG, and then he is awakened, he almost always reports a dream. By this test, no one has yet been discovered who does not dream at all. In fact, psychologists have established that the average person has four to six periods of dreaming each night. (2) Some people say that they always dream in black and white, never in colour. Again, however, they have apparently forgotten the colours that occur in dreams, as is shown by the fact that most often, if we wake a sleeper in the middle of a dream, when it is still fresh in his mind, he then can report colours. (3) Another claim that some people make is that dreams never last more than a few seconds. This also seems to be a case of forgetting dreams, since periods of REM, together with EEG readings, indicate that dreams take longer than this; in fact they may last as long as thirty-five minutes. (4) Finally, it is a piece of folk wisdom that eating rich foods just before sleep causes nightmares. According to scientists, however, all that eating such foods can do is to cause a person enough bodily discomfort to wake him often during the night. This leads him to remember more of his dreams—and therefore more of their vividness and strangeness—than he usually does.