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A rowdy cousin . . . an Eeyore T-shirt . . . a dog-shaped balloon.
Why we remember some scenes from early childhood and forget others has long intrigued scientists -- as well as parents striving to create happy memories for their kids. One of the biggest mysteries: why most people can't seem to recall anything before age 3 or 4.
Now, researchers in Canada have demonstrated that some young children can remember events from even before age 2 -- but those memories are fragile, with many vanishing by about age 10, according to a study in the journal Child Development this month.
Researchers asked 140 children, aged between 4 and 13, to describe their three earliest memories, and repeated the exercise two years later with the same children. On average, the 50 youngest children, aged 4 to 6 during the first interview, recalled events from when they were barely 2 years old, as verified by their parents. When they were interviewed two years later, only five of those 50 children mentioned the same earliest memory. By contrast, 22 of the 61 children who were 10 to 13 at the first interview were able to mention the same earliest memory when they were interviewed again two years later.
'By 10, those memories are crystallized. Those are the memories we keep,' says psychologist Carole Peterson at Memorial University of Newfoundland, the lead investigator. 'It's the memories from earliest childhood that we lose.'
The inability of adults to remember the earliest years of childhood -- also known as infantile amnesia -- has been the subject of speculation for more than a century.
Modern researchers think that storing and retrieving memories require language skills that don't develop until age 3 or 4. Others believe that while children can recall fragments of scenes from early life, they can't create autobiographical memories -- the episodes that make up one's life story -- until they have a firm concept of 'self,' which may take a few more years.
Researchers are finding intriguing cultural differences, too. In a study published in Child Development in 2009, Dr. Peterson and colleagues asked 225 Canadian children and 113 Chinese children, aged 8, 11 and 14, to write down as many early memories as they could in four minutes. The Canadian children were able to recall twice as many memories from their early childhoods, going back six months earlier, than Chinese children. What's more, the Canadian children's memories were much more likely to be about their own experiences, whereas the Chinese children focused on family or group activities.
The difference isn't in memory skills, experts believe, but in how experiences are encoded in children's brains, which is greatly affected by the attention adults pay to them. In this case, researchers concluded, the Western parents were more likely to savor and tell stories about moments when a child said something funny or did something unusual, underscoring their individuality, while Asian cultures value collective experiences.
Indeed, experts say that if parents want their children to remember particular events from their early lives, they should discuss them in as much detail as possible and help children see their significance. 'Talking over events with an adult gives a meaning to memories that children may not have before,' says psychologist Judith Hudson of Rutgers University who has studied how mother-child interactions influence memories. Ask a child, 'Remember when we went to the zoo? What did you see?' she suggests. 'Suddenly, it's something to talk about and share.'
Psychologist Robyn Fivush at Emory University, another early-memory expert, has shown that children whose mothers reminisce elaborately with them, eliciting their views and relating them to new experiences, at ages 3, 4 and 5, tend to have earlier first memories as well as better coping skills and higher self-esteem than those who mothers don't. 'We create a sense of who we are through these memories,' says Dr. Fivush.
Traumatic events, such as the 9/11 terrorist attacks, also tend to become seared in children's memories. In a study titled 'I Was Very, Very Crying,' published in Applied Cognitive Psychology last year, Dr. Peterson and colleagues interviewed 145 children aged 2 to 13 who were treated in a hospital emergency room for injuries. Children who recalled crying a lot at the time were more likely to remember specific details two years later.
Yet most early childhood memories are far more mundane, which baffles experts and parents alike. Dr. Peterson says that when she asked parents of children in her studies to verify that the events they recall were real, 'Many of them say, 'He remembered that? How interesting.''
Neuroscientists believe that there are different kinds of memories, stored in many different neural circuits. 'We can't go to a particular spot in the brain to see where our third birthday party is stored,' says Dr. Hudson.
Some memories are generic -- what your house, your street or your school looked like. Those get called up as background, like the sets of a movie. Others are semantic, for facts and other information. Still others are episodic, for events that took place.
Scientists think the brain's prefrontal cortex processes experiences, using sensory input from the eyes, ears, nose and mouth, sorts them into categories, and tags the various memory fragments with specific associations (smells of home, friends from camp, bugs, a pet, for example).
When a memory cue comes in, the brain searches its circuits for related fragments and assembles them like a jigsaw puzzle. Some fragments bring associated fragments along, which is why one old memory often leads to others. Tastes and smells are particularly evocative, which is how Marcel Proust was famously able to construct a whole discourse on his childhood just by tasting a Madeleine, says Gayatri Devi, a neuropsychiatrist who specializes in memory problems in New York City.
Each time people bring up the same memory, those related fragments and circuits become stronger. 'When you are 80 years old, remembering your kindergarten days, it's really the memory of a memory of a memory,' says Dr. Devi.
That may help explain why children's earliest memories are so unstable: Their neural traces are weak and shallow, whereas the few memories we revisit as we get older lay down stronger traces.
Still, because the brain is constantly reassembling the fragments, they are vulnerable to distortion.
'It's possible to have a very detailed and vivid memory and be wrong about the details,' says Dr. Hudson. As the distorted memory is repeatedly recalled, it can be very difficult to tell is the memory is or isn't real.
In one famous case, the Swiss psychologist Jean Piaget had vivid memories of being kidnapped at age 2 in Paris, complete with the kidnappers scratching his nurse's face. Years later, the nurse confessed to fabricating the story -- but Piaget had heard his family discuss it so often that his mind created a false memory.
Is it possible to recall more of your own childhood memories? Some researchers believe that people can access more if they have the right cues. Discussing past times with family members can jog the memories as well as offer different perspectives.
Photographs and letters are also helpful; knowing specific dates like the birth of a sibling or a move to a different house can help place fragmentary memories in time.
參考譯文：
一個吵鬧的表兄弟或姐妹……一件印有Eeyore的T恤……一個小狗形狀的氣球。
為什么我們對幼兒時期發生的事件有些記得有些卻忘了？這一直是讓科學家及那些努力給孩子制造快樂回憶的父母深感好奇的問題。其中，最不可思議的一點是，為什么大多數人好像都無法記起三四歲之前的事情？
據《兒童發展》(Child Development)雜志本月刊登的一份研究報告顯示，加拿大的研究人員現已證明，有些年幼的孩子甚至可記住兩歲以前的事情，但那些回憶非常脆弱，很多在孩子10歲左右時就突然消失了。
研究人員讓140名年齡在4歲至13歲的孩子描述自己所能記起來的最早的三個回憶，并在兩年后讓這些孩子對同樣的問題進行描述。平均而言，第一次面談時，年齡在4至6歲的50個最年幼的孩子可記起自己剛剛2歲時的事情，經向父母求證，他們說的事件屬實。不過當兩年后再問他們時，這50個孩子里只有五個提到的最早記憶與上次相同。相比之下，61個年齡在10至13歲的孩子中，有22個在兩年后第二次接受提問時提到的最早記憶與第一次相同。
紐芬蘭紀念大學(Memorial University of Newfoundland)的心理學家、這次研究的首席調查員彼得森(Carole Peterson)說，在10歲左右時，那些記憶會變得清晰，這是我們可保留的記憶，而那些最早的童年記憶卻不見了。
成年人為何無法想起自己幼年早期的事情？這是一百多年來人們一直在思考的問題。這種現象也被稱作嬰兒期遺忘。
現代研究人員認為，記憶的儲存和檢索需要語言技巧，而這種技巧只有到人三四歲時才會逐漸被開發。還有人認為，雖然孩子可以記起兒時的事件片段，但他們無法形成自傳性記憶(構成人生故事的經歷)，直到他們有了牢固的“自我”概念，而這種概念的形成可能要再花幾年時間。
研究人員還發現了有趣的文化差異。《兒童發展》2009年刊登的一份研究報告顯示，彼得森和同事分別讓年齡在8歲、11歲和14歲的225個加拿大兒童和113個中國兒童在四分鐘內寫下盡可能多的兒時回憶。加拿大兒童能寫出的童年回憶(六個月以前的都算)是中國兒童的兩倍。另外，加拿大孩子的回憶似乎更像是自己的經歷，而中國兒童的回憶則主要是家人或集體活動。
專家認為，這種差異的出現與記憶技能無關，主要在于這些經歷如何在孩子的大腦中編碼，而成年人對事件的關注可極大地影響編碼方式。研究人員在這項調查中得出的結論是，當孩子說一件事有趣或做了一件不尋常的事時，西方父母更有可能跟孩子講述并回味那些事，重點是突出孩子的個性，而亞洲文化則看重集體經歷。
專家說，其實如果父母想讓孩子記住幼時的某些特定事件，就應該和孩子盡量詳細談論這些事，幫助孩子看到其中的意義。美國羅格斯大學(Rutgers University)曾研究過母子互動如何影響記憶的心理學家哈德森(Judith Hudson)說，和成年人一起討論事情可給這些記憶賦予意義，而孩子以前可能并沒有認識到這種意義。哈德森建議，大人可問孩子：還記得我們什么時候去的動物園嗎？你當時都看到了什么？她說，這一下子就成了父母和孩子可以聊天和分享的事。
埃默里大學（Emory University）心理學家菲伍什（Robyn Fivush）也是一位早期記憶專家。他發現，在孩子三歲、四歲及五歲時，若母親向孩子詳細敘述往事、引導他們發表看法并將這些往事與新的經歷相聯系，他們往往比那些母親沒有這樣做的孩子有更早的早期記憶，擁有更好的應對技巧和更強的自尊心。他說，通過這些記憶，我們建立了自我意識。
9•11恐怖襲擊這樣的創傷性事件往往也會給兒童記憶留下烙印。在去年發表的一份題為《I Was Very, Very Crying》的應用認知學研究報告中，彼得森和同事采訪了145名在一間醫院急診室治傷的2至13歲的兒童。回憶自己當時大哭的孩子在兩年后更有可能記得具體細節。
然而大多數幼兒時期記憶都單調得多，這令專家和家長都迷惑不解。彼得森說，當她要求研究中兒童的家長判斷孩子回憶的這些事件是否屬實時，許多人說，他記得那個？真有趣。
神經學家認為存在不同種類的記憶，儲存在許多不同的神經回路中。哈德森說，我們無法進入大腦中某地去看我們第三個生日派對的記憶儲存在什么地方。
有些是一般性記憶，比如你的房子、街道和學校是什么樣子。這些被稱為背景，就像一部電影中的場景。其他是語義性的，與事實和其他信息有關。還有一些是情節性的，與發生的事件有關。
科學家認為，大腦前額葉皮層通過眼睛、耳朵、鼻子和嘴巴的感覺輸入來處理經歷，將這些經歷分門別類，對不同的記憶片段進行特殊關聯，比如家的味道、營地的朋友、蟲子、寵物等。
當一個記憶提示進來，大腦就會從神經回路中搜索相關片段，并將這些片段如拼圖玩具一般組裝起來。有些片段牽連著相關的片段，這就是為什么舊的記憶常常會引出其他記憶。紐約市專攻記憶問題的神經精神學家戴維（Gayatri Devi）說，味道和氣味尤其能喚起記憶，有名的例子就是作家普魯斯特（Marcel Proust）嘗一個瑪德琳小蛋糕就能完整的描述自己的童年。
每當人們提到同樣的記憶，相關的片段和回路就會變得更強。戴維說，當你80歲時還記得你在幼兒園的日子，這事實上是記憶的記憶的記憶。
這可能會有助于解釋兒童最早的記憶為何如此不穩定：他們的神經痕跡又弱又淺，而隨著我們越來越大，不斷回訪的那些記憶會留下更深的痕跡。
不過，由于大腦在不斷重組記憶片段，它們很容易扭曲。
哈德森說，有十分詳細和生動的記憶，但對細節的記憶錯誤，這是有可能的。隨著被扭曲的記憶被一再回憶，可能就很難判斷這個記憶是真的還是假的。
一個知名的案例是，瑞士心理學家皮亞杰（Jean Piaget）有著兩歲時在巴黎被綁架的生動記憶，還記得他的保姆被綁架者劃傷了臉。幾年后，這位保姆承認這個故事是她虛構的，但由于皮亞杰聽到家人談起過太多次，于是大腦形成了虛假的記憶。
有沒有可能找回更多自己的童年記憶？有些研究人員認為，人們如果有正確的提示就有可能記起更多。與家人談論往昔時光可以喚起記憶，還能提供不同的視角。
照片和信件也很有用；知道特殊的日子也會有助于將片段性記憶和時間聯系起來，比如兄弟姐妹的生日或搬家的日子。
