Visual or auditory experiences during sleep are known as dreams. Every culture attributes some meaning to these dreams. Less vivid dreams occur during non-REM sleep. The brain is relatively insensitive to outside sensory input during this phase. The brain draws on internal images from memory during the sleep cycle. When a person is close to waking, he is more likely to dream about recent happenings. On the average, people dream several times a night for about 1 to 2 hours. A person can have an average of four to five dreams in a night.

 The painting to the left is The Persistance of Memory by Salvador Dali. Many of his works are thought to be influenced by his dreams.