"In the natural world, animal sleep states, aside from being classified as REM and NREM, can also be divided into two other types: BSWS, or bihemispheric slow-wave sleep, and USWS, or unihemispheric slow-wave sleep.
Humans experience bihemispheric slow-wave sleep, which is characterized by full immersion, with both cerebral hemispheres in a sleeping state.
Unihemispheric slow-wave sleep, on the other hand, is characterized by one cerebral hemisphere sleeping while the other remains alert,"
Li Ang said slowly. "The most notable examples are whales, dolphins, pigeons, and mallards.
Sperm whales, for instance, sleep 8-10 times a day for about 10 minutes each time, maintaining a vertical, suspended position in the sea.
Dolphins and mallards, meanwhile, will keep one eye open to watch the surroundings while in USWS. They move around vigilantly in a half-asleep, half-awake state, alert to predators."
PAT.
