FIGURE 13-13 Sleeping and Waking over the Life Span The amount of time humans spend sleeping decreases with age. The proportion of REM sleep is especially high in the first few years of life.

Information from H. P. Roffward, J. Muzio, & W. C. Dement (1966). Ontogenetic development of the human sleep–dream cycle. Science, 152, 604–619.