Roger Ekirch is a historian at Virginia Tech whose 2001 article and 2005 book documented references in diaries, court records, medical texts, poems, and novels to "first sleep" and "second sleep" separated by a period of wakefulness of roughly an hour, during which people prayed, talked, had sex, or attended to chores. Ekirch draws evidence from more than 500 references to a segmented sleeping pattern in documents from the ancient, medieval, and modern world.

Other historians, such as Craig Koslofsky, have endorsed Ekirch's analysis.

Independent experimental support comes from a 1990s NIMH study by Thomas Wehr. In the early 1990s, a team headed by Thomas A. Wehr, MD, then a sleep researcher at the National Institute of Mental Health (NIMH), reported that when 8 healthy men had their light/dark schedule shifted from a typical modern photoperiod to 14 hours of darkness per night, their sleep spontaneously split into two bouts with a period of quiet wakefulness in between.

The theory is not without scholarly pushback. Roger Ekirch's theory that the people of the pre-industrial age split their sleep into two distinct periods, filling gaps of up to an hour inbetween with social activity or private meditation, has been widely accepted by historians, literary scholars and the general public in the two decades following its publication, but a 2023 paper by Niall Boyce in Medical History argues the pattern may not have been as universal or dominant as Ekirch's synthesis suggests, noting for example that early modern health manuals did not typically prescribe or describe such a pattern. Ekirch published a rebuttal in the same journal in 2024.