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　　We all know that we don’t get enough sleep,。 But how much sleep do we really need,？ Until about 15 years ago， one common theory was that if you slept at least four or five hours a night,， your cognitive performance remained intact,； your body simply adapted to less sleep。 But that idea was based on studies in which researchers sent sleepy subjects home during the day — where they may have sneaked in naps and downed coffee,。

　　我們都知道自己睡眠不足,。但是我們真正需要多少睡眠呢？直到大約15年前,，有這樣一個(gè)理論：如果你每晚至少睡4或5小時(shí),，你的認(rèn)知表現(xiàn)依然保持完好；而你的身體只是適應(yīng)了較少的睡眠,。但是那種觀點(diǎn)是基于這樣研究：研究人員在白天把困倦的受試者送回家，而后者有可能在家里偷偷地小睡或者猛灌咖啡,。

　　Enter David Dinges,， the head of the Sleep and Chronobiology Laboratory at the Hospital at University of Pennsylvania， who has the distinction of depriving more people of sleep than perhaps anyone in the world,。

　　賓夕法尼亞大學(xué)醫(yī)院的睡眠與時(shí)間生物學(xué)實(shí)驗(yàn)室的負(fù)責(zé)人大衛(wèi),。丁格斯剝奪過(guò)很多人的睡眠，就人數(shù)而言世界上無(wú)人能比,。

　　In what was the longest sleep-restriction study of its kind,， Dinges and his lead author， Hans Van Dongen,， assigned dozens of subjects to three different groups for their 2003 study： some slept four hours,， others six hours and others， for the lucky control group,， eight hours — for two weeks in the lab,。

　　為了2003年的研究,，丁格斯和第一作者漢斯。凡東恩開(kāi)展了一項(xiàng)同類(lèi)研究中最長(zhǎng)的睡眠限制研究,，他們把受試者分成三組：一些人睡4小時(shí),，另一些人睡6小時(shí)，其他人則被幸運(yùn)地分進(jìn)了對(duì)照組,，睡8小時(shí)——他們?cè)趯?shí)驗(yàn)室里待了兩個(gè)星期,。

　　Every two hours during the day， the researchers tested the subjects’ ability to sustain attention with what’s known as the psychomotor vigilance task,， or P.V.T,。， considered a gold standard of sleepiness measures,。 During the P.V.T,。， the men and women sat in front of computer screens for 10-minute periods,， pressing the space bar as soon as they saw a flash of numbers at random intervals,。 Even a half-second response delay suggests a lapse into sleepiness， known as a microsleep,。

　　白天,，研究人員每隔兩小時(shí)就會(huì)使用精神運(yùn)動(dòng)警覺(jué)性任務(wù)來(lái)測(cè)試受試者持續(xù)集中注意力的能力。PVT被視為衡量困倦程度的黃金標(biāo)準(zhǔn),。參與PVT的男女需在電腦屏幕前坐10分鐘,，每當(dāng)看到不定時(shí)閃現(xiàn)的數(shù)字時(shí)，就要立刻按下空格鍵,。就算只滯后半秒,，也暗示著受試者陷入了睡眠之中，即微睡眠,。

　　The P.V.T,。 is tedious but simple if you’ve been sleeping well。 It measures the sustained attention that is vital for pilots,， truck drivers,， astronauts。 Attention is also key for focusing during long meetings,； for reading a paragraph just once,， instead of five times； for driving a car,。 It takes the equivalent of only a two-second lapse for a driver to veer into oncoming traffic,。

　　如果你的睡眠一直都很好，那么PVT就是一項(xiàng)乏味卻簡(jiǎn)單的任務(wù)。它衡量的是對(duì)飛行員,、卡車(chē)司機(jī)和宇航員來(lái)說(shuō)至關(guān)重要的持續(xù)性注意力,。在參加冗長(zhǎng)的會(huì)議時(shí)、在一次性閱讀一個(gè)段落,，而非看五遍時(shí),，以及開(kāi)車(chē)時(shí)，注意力同樣是保持專(zhuān)注的關(guān)鍵所在,。一名司機(jī)大約只要走神兩秒鐘,，就有可能沖入迎面而來(lái)的車(chē)流中。

　　Not surprisingly,， those who had eight hours of sleep hardly had any attention lapses and no cognitive declines over the 14 days of the study,。 What was interesting was that those in the four- and six-hour groups had P.V.T。 results that declined steadily with almost each passing day,。 Though the four-hour subjects performed far worse,， the six-hour group also consistently fell off-task。 By the sixth day,， 25 percent of the six-hour group was falling asleep at the computer,。 And at the end of the study， they were lapsing fives times as much as they did the first day,。

　　在為期14天的研究中,，每天睡8小時(shí)的人幾乎沒(méi)走過(guò)神，也沒(méi)有出現(xiàn)認(rèn)知能力下降的問(wèn)題,，這并不令人意外,。有趣的是，睡4小時(shí)和6小時(shí)的那些人的PVT測(cè)試成績(jī)幾乎逐日穩(wěn)步下降,。雖然睡4小時(shí)的受試者的表現(xiàn)要差得多,，但是睡6小時(shí)的受試者也常常分心。到了第六天,，睡6小時(shí)的那組人中有25%會(huì)在電腦前睡著,。而在研究的收尾階段，他們走神的次數(shù)達(dá)到第一天的5倍,。

　　The six-hour subjects fared no better — steadily declining over the two weeks — on a test of working memory in which they had to remember numbers and symbols and substitute one for the other。 The same was true for an addition-subtraction task that measures speed and accuracy,。 All told,， by the end of two weeks， the six-hour sleepers were as impaired as those who,， in another Dinges study,， had been sleep-deprived for 24 hours straight — the cognitive equivalent of being legally drunk。

　　在對(duì)工作記憶的測(cè)試中，受試者必須記住一些數(shù)字和符號(hào),，并用一個(gè)代替另一個(gè)——睡6小時(shí)的受試者沒(méi)有更好的表現(xiàn)——而是在兩周之內(nèi)穩(wěn)步下降,。在測(cè)量速度和準(zhǔn)確度的加減運(yùn)算任務(wù)中，情況也是如此,�,？傊瑑芍芙Y(jié)束時(shí),，睡6小時(shí)的受試者的能力被削弱了,，就像丁格斯的另一項(xiàng)研究中整整24小時(shí)沒(méi)有睡過(guò)覺(jué)的人一樣——其認(rèn)知能力跟那些在法律上會(huì)被認(rèn)定為醉酒的人差不多。

　　Not every sleeper is the same,， of course： Dinges has found that some people who need eight hours will immediately feel the wallop of one four-hour night,， while other eight-hour sleepers can handle several four-hour nights before their performance deteriorates。（But deteriorate it will,。） There is a small portion of the population — he estimates it at around 5 percent or even less — who,， for what researchers think may be genetic reasons， can maintain their performance with five or fewer hours of sleep,。（There is also a small percentage who require 9 or 10 hours,。）

　　當(dāng)然，睡眠者的情況并非千篇一律：丁格斯發(fā)現(xiàn),，一些需要睡8小時(shí)的人如果有一晚只睡4小時(shí),，情況立刻就會(huì)變得很糟，而另外一些需要睡8小時(shí)的人在好幾晚只睡4小時(shí)之后,，表現(xiàn)才會(huì)變差,。（但終究會(huì)變差。）有一小部分人——據(jù)他估計(jì)約為5%,，甚至更低——可以在只睡5小時(shí),，甚至更短時(shí)間的情況下維持其表現(xiàn)，研究人員認(rèn)為這是遺傳原因,。（還有一小部分人需要睡9或10小時(shí),。）

　　While it’s tempting to believe we can train ourselves to be among the five-hour group — we can’t， Dinges says — or that we are naturally those five-hour sleepers,， consider a key finding from Van Dongen and Dinges’s study： after just a few days,， the four- and six-hour group reported that， yes,， they were slightly sleepy,。 But they insisted they had adjusted to their new state。 Even 14 days into the study,， they said sleepiness was not affecting them,。 In fact,， their performance had tanked。 In other words,， the sleep-deprived among us are lousy judges of our own sleep needs,。 We are not nearly as sharp as we think we are。

　　人們很容易就會(huì)認(rèn)為,，我們可以把自己訓(xùn)練成只需睡5小時(shí)的人——丁格斯說(shuō)我們其實(shí)做不到——除非我們天生就是只需睡5小時(shí)的人,，看看凡東恩和丁格斯的研究得出的一個(gè)關(guān)鍵結(jié)論：僅僅幾天過(guò)后，睡4小時(shí)和6小時(shí)的人就會(huì)報(bào)告說(shuō),，沒(méi)錯(cuò),，他們感覺(jué)有點(diǎn)兒困倦。但是他們堅(jiān)稱(chēng)已經(jīng)適應(yīng)了自己的新?tīng)顟B(tài),。即便參加研究已經(jīng)有14天了,，他們還是說(shuō)困倦對(duì)他們沒(méi)有造成影響。事實(shí)上,，他們的表現(xiàn)已然大打折扣,。換句話說(shuō)，我們當(dāng)中的睡眠不足者難以準(zhǔn)確判斷自身的睡眠需求,。我們遠(yuǎn)遠(yuǎn)不像自己所認(rèn)為的那樣敏銳,。(外研社)

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