There are at least a few in every college dorm: students who seem to exist in their own time zone, in bed hours before everyone else and awake again at daybreak, rested and prepared for the morning's first lecture.

    Sleep researchers refer to these early risers as larks （midnight-oil-burners are known as owls）, and new data presented this week at the annual Associated Professional Sleep Societies suggest that a student's preferred sleeping schedule has a lot to do with his or her grade-point average in school. In one study, psychologists at Hendrix College in Arkansas found that college freshmen who kept night-owl hours had lower GPAs than early birds. Another group at the University of Pittsburgh revealed that poor sleep habits among high-schoolers led to lower grades, particularly in math.

    It's no surprise that poor sleep habits may negatively impact academic performance - anyone who's been exhausted enough to doze off during class knows that's detrimental to learning. And dozens of studies have linked an increase in nightly sleep to better cognition and alertness. The new research, however, goes a step further, quantifying the impact of erratic or inadequate sleep on grades. "These findings are more tangible than saying that if you get more sleep, you'll feel better," says Jennifer Cousins, a fellow at the University of Pittsburgh and author of one of the studies. "They connect sleep and how you sleep to the real world of daily activities."

    In the study of night owls, psychologist Jennifer Peszka asked a group of 89 incoming Hendrix College freshmen ages 17 to 20 to fill out a questionnaire about their sleep preferences prior to arriving on campus. Regardless of how much they actually slept, Peszka asked them whether they considered themselves owls, larks or, in the case of those who were neither very late or very early sleepers, robins. Students also answered questions about their sleep "hygiene" - factors that contribute to quality of sleep, such as adhering to a regular bedtime, waking up at the same time every day, or exercising or drinking caffeine before trying to sleep. One year, Peszka asked the same students to fill out another similar questionnaire to determine whether their sleep schedules were associated with GPA.

    The owls, it turned out, averaged a 2.84 GPA at the end of their freshman year. Larks and robins both averaged 3.18. That means high-quality sleep may have contributed to one group of students' B average, while inadequate shut-eye pushed owls into the C range. Peszka also compared the students' high school GPAs with their college scores, and found that owls had lost an entire GPA point once entering college - larks and robins also saw their grades drop （a common phenomenon as students transition from high school to university）, but not as much. "Not only did they flat out have a lower freshman GPA," she says of the owls, "but they also dropped their grades more."

    The study did not delve into the details of why owls may perform worse in school, but Peszka suspects it may boil down to "an owl living a lark's schedule." Students with late bedtimes still end up taking early morning classes, which means they often end up feeling sleepier and less alert during the day. In fact, in Peszka's study, night owls slept 41 minutes less each night than the other students, but were still attending early classes, during which they reported sleepiness and inability to concentrate, which, unsurprisingly, led to lower scores at exam time.

    That's precisely what University of Pittsburgh researchers found in their study of 56 teens ages 14 to 18. Jennifer Cousins, a postdoctoral fellow in psychiatry, asked the adolescents to fill out sleep diaries for one week and wear a special activity monitor on their wrist, which recorded when the students were asleep or awake. Overall, teens with poor sleep habits - those who woke up frequently during the night, spent more hours in bed （whether or not they were sleeping） and reported feeling tired in the morning - received lower grades than students who stuck with a more regular sleep routine.

    Interestingly, Cousins also found that different sleep habits had different effects on the student's school performance: those who woke up more often during the night and reported poorer sleep quality did worse in math, for example, while those who slumbered peacefully through the night tended to get better grades in English. "These findings bring up new questions about teasing out the specifics of what is important about sleep that impacts learning," says Cousins. "Does sleeping more help our ability to deal with abstract concepts found in math, or does sleep quality increase creativity? We don't know the answers, and don't want to draw those conclusions yet. But this helps us understand more about how sleep helps the things we do in daily life."

    Both groups of researchers are quick to point out that academic performance is the product of many different factors - from I.Q. to study habits and effort, and not just sleep - but the new findings suggest that catching good quality z's certainly doesn't hurt, and may even help boost your GPA.

    在大學(xué)宿舍都至少有一小撮學(xué)生：他們似乎生活在自己的時(shí)區(qū)，在其他人上床前幾小時(shí)就睡覺然后在黎明醒來，休息一下并準(zhǔn)備上午的第一堂課。

    睡眠研究人員提及這些早起的人稱他們?yōu)?quot;云雀"（最能熬夜的午夜燃燒器是貓頭鷹）,最新的發(fā)表在這周的《年度相關(guān)專業(yè)睡眠協(xié)會》的數(shù)據(jù)表明：學(xué)生首選的睡眠時(shí)間表與他或她在學(xué)校的平均學(xué)分積有很強(qiáng)的相關(guān)。在一項(xiàng)研究中，阿肯色州里克斯學(xué)院的心理學(xué)家發(fā)現(xiàn)，大學(xué)新生中那些"夜貓子"式的作息方式的學(xué)生們比早起的"云雀"平均學(xué)分積低。另一組美國匹茲堡大學(xué)的研究發(fā)現(xiàn)，高中學(xué)生劣質(zhì)的睡眠作息方式導(dǎo)致較低的學(xué)習(xí)成績，特別是數(shù)學(xué)成績。

    毫不奇怪，劣質(zhì)的睡眠作息習(xí)慣會對學(xué)習(xí)成績產(chǎn)生不利的影響。那些已經(jīng)累到在課堂上打盹的人都知道，這樣對學(xué)習(xí)很不好。其他幾十個(gè)研究表明夜間睡眠時(shí)間的增加與更好的認(rèn)知和警覺感覺相聯(lián)系。然而，這項(xiàng)新的研究更進(jìn)了一步，它量化了睡眠的影響，探索了不穩(wěn)定或睡眠不足對于學(xué)習(xí)成績的影響。"比起那些空洞的說法說：如果你獲得更多的睡眠，你會感覺更好。這些調(diào)查結(jié)果更為具體。"詹妮弗�？ㄔ�斯說。他們將睡眠和你在現(xiàn)實(shí)世界的日�；顒又腥绾嗡�眠聯(lián)系起來。

    在對那些"夜貓子"的研究中，心理學(xué)家詹妮弗。佩茲卡讓來自里克斯大學(xué)89名17-20歲的大一新生填寫了一張問卷調(diào)查他們在進(jìn)入大學(xué)之前的睡眠偏好。無論他們自己的睡眠偏好如何，詹妮弗都會讓他們自己評價(jià)自己認(rèn)為自己是"夜貓子","云雀",還是睡得不早也不晚介于中間角色的"知更鳥".大學(xué)生們還回答了關(guān)于自己睡眠的"衛(wèi)生"--影響睡眠質(zhì)量的因素，比如堅(jiān)持固定的上床時(shí)間，每天同樣的時(shí)間點(diǎn)起床，在睡前運(yùn)動，喝咖啡等等。一年之后，佩茲卡讓他們再填寫相同的問卷，以此來考察他們的睡眠時(shí)間表與平均學(xué)分積是否相關(guān)。

    研究表明，那些"夜貓子"們，在他們的大一學(xué)年末有2.48的平均學(xué)分積；而"云雀"有3.18的平均學(xué)分積。這表明高質(zhì)量的睡眠很可能對學(xué)生B的平均學(xué)分積有貢獻(xiàn)。佩茲卡同時(shí)還對比了那些學(xué)生在高中時(shí)候的學(xué)分積，發(fā)現(xiàn)那些熬夜的"貓頭鷹"們自從進(jìn)入大學(xué)之后平均學(xué)分積下降了一個(gè)積點(diǎn)--"云雀"和 "知更鳥"的學(xué)分積也都有下降（這是學(xué)生從高中到大學(xué)的普遍情況）,但不會有這么多。"他們的成績不僅低于新生的平均水平，"她說，"而且他們的成績下降更多。"

    這項(xiàng)研究并沒有深入研究為什么夜貓子在學(xué)習(xí)成績上的表現(xiàn)差的細(xì)節(jié)。但佩茲卡懷疑原因可以歸結(jié)為"夜貓子"仍然按照"云雀"的時(shí)間表生活。那些晚睡的學(xué)生仍然早起上課，這意味著他們最終往往在白天感覺很困倦，警覺性降低。事實(shí)上，在佩茲卡的研究，"夜貓子"比其他的學(xué)生們每晚少睡41分鐘，但仍早起上課，在此期間，意料之中地，他們報(bào)告嗜睡和精神無法集中，這些都導(dǎo)致考試期間較低的分?jǐn)?shù)。

    這恰恰是美國匹茲堡大學(xué)的研究人員在對56位14歲至18歲的少年們進(jìn)行研究發(fā)現(xiàn)的。詹妮弗�？ㄔ�斯--心理咨詢的博士后人員，要求青少年填寫為期一周的睡眠日記，并要求在他們手腕上帶上特殊的活動監(jiān)測器，記錄時(shí)學(xué)生們?nèi)胨�或醒來的情況�？傊�，具有較差的睡眠習(xí)慣的青少年--那些在夜間睡眠時(shí)經(jīng)常醒來，花很多時(shí)間賴在床上（不管它們是不是睡眠）和在早晨報(bào)告感覺疲累--獲得的成績比那些堅(jiān)持規(guī)律睡眠的學(xué)生更低。

    有意思的是，卡曾斯發(fā)現(xiàn)不同的睡眠習(xí)慣對學(xué)生們的成績表現(xiàn)有不同的影響：那些在睡覺時(shí)經(jīng)常醒來并報(bào)告睡眠質(zhì)量很差的學(xué)生在數(shù)學(xué)表現(xiàn)不好，而那些在整個(gè)晚上睡得很平靜的學(xué)生容易獲得更好地英語成績，"這些發(fā)現(xiàn)帶來了新問題，那就是關(guān)于具體厘清影響學(xué)習(xí)的睡眠哪個(gè)過程是重要的？"卡曾斯說道，"睡眠是否對于我們處理在數(shù)學(xué)中的抽象問題更為有益？或者睡眠質(zhì)量是否增加了創(chuàng)造性？我們不知道這些問題的答案，而且我們還不想下定論。但這些幫助我們對睡眠在日常生活中對哪些事情有益有更多的了解。"

    這兩組研究人員正在迅速指出，學(xué)習(xí)成績是許多不同的因素共同作用的結(jié)果--從智商學(xué)習(xí)習(xí)慣和努力程度，而不僅僅是睡眠--但新的研究結(jié)果表明，追求優(yōu)質(zhì)的睡眠肯定沒有壞處，甚至可能有助于提高您的成績。