Generally my young children don't let me get a full night of uninterrupted sleep. Due to their colds, they have woken me numerous times the past couple nights. Sometimes I'd wake up wide awake; it's as if I'm on alert while asleep. I don't know how I'm doing that, or how I'm functional. But I've noticed the cognitive hit pretty much since the first one was born.
@dronenumberPI: Actually, anyone can function on 4 hours of sleep/day, the technique is called "phasic sleep" or more commonly, "catnapping." If you sleep for 30 minutes out of every 3 hours, that's 4 hrs sleep/day. Your body learns to drop into REM state [which drives the need for sleep; higher brain functions need down time for R&R] almost immediately; times up, you wake up and voila, you're good to go for another few hours. The down side is that if you sleep past about 45 minute mark & get woken up between then & about 1.5 hours of sleep, you're more tired than before you went to sleep! BTDTGTTS&IS [Been there, done that, got the t-shirt & it SUX!]
@rxantos I think I have seen you before on Family Guy: http://answers.yahoo.com/question/index?qid=20100403202219AAdCCPY
@ewood Everyone is different, but if you look at the distrobution of sleep required of people from various studies you will find it is a bell curve with a very small standard deviation and the mean is just over 8 hours. The people who function at the 4 hours level are at the 5 or 6 sigma range.