M. A. Carskadon and W. C. Dement, “Sleep studies on a 90-minute day,” Electroencephalography and Clinical Neurophysiology 39 (1975), pp. 145–155; M. A. Carskadon and W. C. Dement, “Distribution of REM sleep on a 90-minute sleep-wake schedule,” Sleep 2 (1980), pp. 309–317.