<P> Slow - wave sleep ( SWS ) , often referred to as deep sleep , consists of stage three ( combined stages 3 and 4 ) of non-rapid eye movement sleep . Initially , SWS consisted of both Stage 3 , which has 20 - 50 percent delta wave activity , and Stage 4 , which has more than 50 percent delta wave activity . However , as of 2008 , the American Academy of Sleep Medicine ( AASM ) has discontinued the use of Stage four as a separate stage . Thus , the two stages are now combined as `` Stage three '' or N3 . An epoch ( 30 seconds of sleep ) which consists of 20 % or more slow - wave ( delta ) sleep is now considered to be stage three . </P>
<P> Slow - wave sleep ( SWS ) , often referred to as deep sleep , consists of stage three ( combined stages 3 and 4 ) of non-rapid eye movement sleep . Initially , SWS consisted of both Stage 3 , which has 20 - 50 percent delta wave activity , and Stage 4 , which has more than 50 percent delta wave activity . However , as of 2008 , the American Academy of Sleep Medicine ( AASM ) has discontinued the use of Stage four as a separate stage . Thus , the two stages are now combined as `` Stage three '' or N3 . An epoch ( 30 seconds of sleep ) which consists of 20 % or more slow - wave ( delta ) sleep is now considered to be stage three . </P>
which stage of sleep is represented by delta waves
which stage of sleep is represented by delta waves
three
three