Stage 3 of Sleep

The third stage of sleep is stage 3, which can also be called Delta Sleep. Sometimes, it is hard to differentiate between stages 3 and 4, but there is a trick - Stage 3 is known to have less than 50% of delta waves, while stage 4 has more than 50%.
Delta waves are the slowest, with the highest amplitude, brain waves. Stage 3 is known to have both delta waves, combined with occasional faster waves. Below is a picture of what the brain waves look like during stage 3 of sleep:
untitled.jpg(Hall, 1998)

During Stage 3

An interesting fact about stage 3 sleep is that it is the deepest sleep a person experiences. With that being said, it is the most difficult stage to wake a person up during. When a person is finally awoken during stage 3 of sleep, they may feel a bit groggy and disoriented for a few minutes. (Stibich, 2008)
Another interesting note is that it is during Stage 3 (and 4) that sleep-talking and sleep-walking will most likely occur. (Hall, 1998)


Hall, Richard (1998). Psychology World. Stages of Sleep. Retrieved on January 4, 2009, from
Stibich, Mark, Ph. D. (2008). The Stages of Sleep. Retrieved on January 4, 2009, from

Julie Kuberski
AP Psychology
January 4, 2009