Hockenbury Discovering Psychology 5th txtbk

144 CHAPTER 4 Consciousness and Its VariationsIN FOCUSWhat You Really Want to Know About SleepWhy do I yawn?Researchers aren’t certain. But the notion thattoo little oxygen or too much carbon dioxidecauses yawning is not supported by research.Some evidence suggests that yawning regulatesand increases your level of arousal. Yawning istypically followed by an increase in activity level.Hence, you frequently yawn after waking up inthe morning, while attempting to stay awake inthe late evening, or when you’re bored.Is yawning contagious?Seeing, hearing, or thinking about yawningcan trigger a yawn. More than half of adultswill yawn when they’re shown videos of otherpeople yawning. Blind people will yawn morefrequently in response to audio recordings ofyawning. (Have you yawned yet?) Some psychologists believethat contagious yawning is related to our ability to feel empathyfor others. Interestingly, chimpanzees and macaques, bothhighly social animals, display contagious yawning. And so dodomestic dogs, which in a recent study were shown to“catch” yawns from human strangers. From an evolutionaryperspective, such observations lend support to the idea thatcontagious yawning may have evolved as an adaptive socialcue, allowing groups to signal and coordinate times of activityand rest.Why do I get sleepy?A naturally occurring compound in the body called adenosinemay be the culprit. In studies with cats, prolonged wakefulnesssharply increases adenosine levels, which reflect energy used forbrain and body activity. As adenosine levels shoot up, so doesthe need for sleep. Slow-wave NREM sleep reduces adenosinelevels. In humans, the common stimulant drug caffeine blocksadenosine receptors, promoting wakefulness.Sometimes in the morning when I first wake up, Ican’t move. I’m literally paralyzed! Is this normal?REM sleep is characterized by paralysis of the voluntary muscles,which keeps you from acting out your dreams. In a relativelycommon phenomenon called sleep paralysis, the paralysis ofREM sleep carries over to the waking state for up to 10 minutes.If preceded by an unpleasant dream or hypnagogic experience,this sensation can be frightening. Sleep paralysiscan also occur as you’re falling asleep. In eithercase, the sleep paralysis lasts for only a fewminutes. So, if this happens to you, relax—voluntary muscle control will soon return.Do deaf people who use sign languagesometimes “sleep sign” during sleep?Yes.Do the things people say when they talkin their sleep make any sense?Sleeptalking typically occurs during NREMstages 3 and 4. There are many anecdotes ofspouses who have supposedly engaged theirsleeptalking mates in extended conversations,but sleep researchers have been unsuccessful inhaving extended dialogues with people who chronically talk intheir sleep. As for the truthfulness of the sleeptalker’s utterances,they’re reasonably accurate insofar as they reflect whateverthe person is responding to while asleep. By the way, notonly do people talk in their sleep, but they can also sing or laughin their sleep. In one case we know of, a little boy sleepsang“Frosty the Snowman.”Is it dangerous to wake a sleepwalker?As a general rule, no, it’s not dangerous to wake a sleepwalker.Sleepwalking tends to occur during the first third of the nightwhen the deep, slow-wave sleep of stages 3 and 4 NREM isoccurring. Consequently, it’s difficult to rouse the person fromdeep sleep and, even if you do, the sleepwalker may be confusedand have no memory of sleepwalking. Although theirjudgment is impaired, most sleepwalkers usually respond to verbalsuggestions and can be guided back to bed.However, without realizing what they are doing, some sleepwalkerscan respond aggressively, even violently, if touched. Inthe Prologue, this occurred on a couple of occasions to Scott ashe was growing up. A little later, we’ll take a more detailed lookat sleepwalking and violent sleep behavior.Sources: J. R. Anderson & Meno (2003); J. R. Anderson & others (2004); Campbell &others (2009); Cartwright (2004); Empson (2002); Gallup & Gallup (2007); Landolt(2008); J. E. Moore (1942); Platek & others (2003); Platek & others (2005); Pressman(2007); Porkka-Heiskanen & others (1997); Provine (1989); Rétey & others (2005);Roenneberg & others (2003); Saper & others (2005); Spanos, McNulty, & others (1995a);Stickgold (2005); Takeuchi & others (2002).sleep paralysisA temporary condition in which a person isunable to move upon awakening in themorning or during the night.The newborn sleeps about 16 hours a day, though not all at once. Up to 8 hours—or 50 percent—of the newborn’s sleep time is spent in REM sleep. The rest is spentin quiet sleep that is very similar to NREM stages 1 and 2. It’s not until about thethird month of life that the deep, slow-wave sleep of NREM stages 3 and 4 appears.The typical 90-minute sleep cycles gradually emerge over the first few years oflife. The infant’s sleep during the first months of life is characterized by shorter60-minute sleep cycles, producing up to 13 sleep cycles per day. By age 2, the toddleris experiencing 75-minute sleep cycles. By age 5, the typical 90-minute sleepcycles of alternating REM and NREM sleep are established (Grigg-Damberger &others, 2007; Jenni & others, 2004).