Birds that are literally half-asleep-with one brain hemisphere alert and the other sleeping-control which side of the brain remains awake, according to a new study of sleeping ducks.
Earlier studies have documented half-brain sleep in a wide range of birds. The brain hemispheres take turns sinking into the sleep stage characterized by slow brain waves. The eye controlled by the sleeping hemisphere keeps shut, while the wakeful hemisphere's eye stays open and alert. Birds also can sleep with both hemispheres resting at once.
Decades of studies of bird flocks led researchers to predict extra alertness in the more vulnerable, end-of-the-row sleepers, Sure enough, the end birds tended to watch carefully on the side away from their companions. Ducks in the inner spots showed no preference for gaze direction.
Also, birds dozing(打盹)at the end of the line resorted to single-hemisphere sleep, rather than total relaxation, more often than inner ducks did. Rotaing 16 birds through the positions in a four-duck row, the researchers found outer birds half-asleep during some 32 percent of dozing time versus about 12 percent for birds in internal spots.
"We believe this is the first evidence for an animal behaviorally controlling sleep and wakefulness simultaneously in different regions of the brain," the researchers say.
The results provide the best evidence for a long-standing supposition that single-hemisphere sleep evolved as creatures scanned for enemies. The preference for opening an eye on the lookout side could be widespread, he predicts. He's seen it in a pair of birds dozing side-by-side in the zoo and in a single pet bird sleeping by mirror. The mirror-side eye closed as if the reflection were a companion and the other eye stayed open.
Useful as half-sleeping might be, it's only been found in birds and such water mammals(哺乳動物)as dolphins, whales, and seals. Perhaps keeping one side of the brain awake allows a sleeping animal to surface occasionally to avoid drowning.
Studies of birds may offer unique insights into sleep. Jerome M. Siegel of the UGLA says he wonders if birds' half-brain sleep "is just the tip of the iceberg(冰山)". He speculates that more examples may turn up when we take a closer look at other species.
16. Which of the following is evidence that TT is widely practiced?
A) TT has been in existence for decades.
B) Many patients were cured by therapeutic touch.
C) TT therapists are often employed by leading hospitals.
D) More than 100,000 people are undergoing TT treatment.
注：D為迷惑選項數字必轉化，C對應第二段末句。
17. Very few TT practitioners responded to the $1 million offer because ____________.
A) they didn't take the offer seriously
B) they didn't want to risk their career
C) they were unwilling to reveal their secret
D) they thought it was not in line with their practice
注：爭議題，B、C皆可。
18. The purpose of Emily Rosa's experiment was ____________.
A) to see why TT could work the way it did
B) to find out how TT cured patient's illness
C) to test whether she could sense the human energy field
D) to test whether a human energy field really existed
注：對應文章第三段首句
19. Why did some TT practitioners agree to be the subjects of Emily's experiment?
A) It involved nothing more than mere guessing.
B) They thought it was going to be a lot of fun.
C) It was more straightforward than other experiments.
D) They sensed no harm in a little girl's experiment.
注：對應文章第三段末句，no harm對應innocent，little girl對應fourth-grade
相關鏈接：新東方：四十天突破六級考試講義與筆記匯總
聽力材料渾身是寶 新東方名師曝四六級復習訣竅
大學英語四級考試完型填空做題拿高分的步驟
更多信息請訪問：考試吧四六級欄目
＞＞＞來四六級論壇看看吧
＞＞＞四六級博客圈，你開博了嗎？
