Don't recall, but I found some links to the subject that have a lot more "information" (that's in quotes, because there are some contradictory claims). Also, there is an alarm watch that claims to track your sleep cycle by your body movements, using an accelerometer....

http://www.harvardmagazine.com/on-line/070587.html
http://en.wikipedia.org/wiki/Polyphasic_sleep
http://en.wikipedia.org/wiki/Sleep#Patterns_and_disruptions