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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.
参考译文：
一个吵闹的表兄弟或姐妹……一件印有Eeyore的T恤……一个小狗形状的气球。
为什么我们对幼儿时期发生的事件有些记得有些却忘了？这一直是让科学家及那些努力给孩子制造快乐回忆的父母深感好奇的问题。其中，最不可思议的一点是，为什么大多数人好像都无法记起三四岁之前的事情？
据《儿童发展》(Child Development)杂志本月刊登的一份研究报告显示，加拿大的研究人员现已证明，有些年幼的孩子甚至可记住两岁以前的事情，但那些回忆非常脆弱，很多在孩子10岁左右时就突然消失了。
研究人员让140名年龄在4岁至13岁的孩子描述自己所能记起来的最早的三个回忆，并在两年后让这些孩子对同样的问题进行描述。平均而言，第一次面谈时，年龄在4至6岁的50个最年幼的孩子可记起自己刚刚2岁时的事情，经向父母求证，他们说的事件属实。不过当两年后再问他们时，这50个孩子里只有五个提到的最早记忆与上次相同。相比之下，61个年龄在10至13岁的孩子中，有22个在两年后第二次接受提问时提到的最早记忆与第一次相同。
纽芬兰纪念大学(Memorial University of Newfoundland)的心理学家、这次研究的首席调查员彼得森(Carole Peterson)说，在10岁左右时，那些记忆会变得清晰，这是我们可保留的记忆，而那些最早的童年记忆却不见了。
成年人为何无法想起自己幼年早期的事情？这是一百多年来人们一直在思考的问题。这种现象也被称作婴儿期遗忘。
现代研究人员认为，记忆的储存和检索需要语言技巧，而这种技巧只有到人三四岁时才会逐渐被开发。还有人认为，虽然孩子可以记起儿时的事件片段，但他们无法形成自传性记忆(构成人生故事的经历)，直到他们有了牢固的“自我”概念，而这种概念的形成可能要再花几年时间。
研究人员还发现了有趣的文化差异。《儿童发展》2009年刊登的一份研究报告显示，彼得森和同事分别让年龄在8岁、11岁和14岁的225个加拿大儿童和113个中国儿童在四分钟内写下尽可能多的儿时回忆。加拿大儿童能写出的童年回忆(六个月以前的都算)是中国儿童的两倍。另外，加拿大孩子的回忆似乎更像是自己的经历，而中国儿童的回忆则主要是家人或集体活动。
专家认为，这种差异的出现与记忆技能无关，主要在于这些经历如何在孩子的大脑中编码，而成年人对事件的关注可极大地影响编码方式。研究人员在这项调查中得出的结论是，当孩子说一件事有趣或做了一件不寻常的事时，西方父母更有可能跟孩子讲述并回味那些事，重点是突出孩子的个性，而亚洲文化则看重集体经历。
专家说，其实如果父母想让孩子记住幼时的某些特定事件，就应该和孩子尽量详细谈论这些事，帮助孩子看到其中的意义。美国罗格斯大学(Rutgers University)曾研究过母子互动如何影响记忆的心理学家哈德森(Judith Hudson)说，和成年人一起讨论事情可给这些记忆赋予意义，而孩子以前可能并没有认识到这种意义。哈德森建议，大人可问孩子：还记得我们什么时候去的动物园吗？你当时都看到了什么？她说，这一下子就成了父母和孩子可以聊天和分享的事。
埃默里大学（Emory University）心理学家菲伍什（Robyn Fivush）也是一位早期记忆专家。他发现，在孩子三岁、四岁及五岁时，若母亲向孩子详细叙述往事、引导他们发表看法并将这些往事与新的经历相联系，他们往往比那些母亲没有这样做的孩子有更早的早期记忆，拥有更好的应对技巧和更强的自尊心。他说，通过这些记忆，我们建立了自我意识。
9•11恐怖袭击这样的创伤性事件往往也会给儿童记忆留下烙印。在去年发表的一份题为《I Was Very, Very Crying》的应用认知学研究报告中，彼得森和同事采访了145名在一间医院急诊室治伤的2至13岁的儿童。回忆自己当时大哭的孩子在两年后更有可能记得具体细节。
然而大多数幼儿时期记忆都单调得多，这令专家和家长都迷惑不解。彼得森说，当她要求研究中儿童的家长判断孩子回忆的这些事件是否属实时，许多人说，他记得那个？真有趣。
神经学家认为存在不同种类的记忆，储存在许多不同的神经回路中。哈德森说，我们无法进入大脑中某地去看我们第三个生日派对的记忆储存在什么地方。
有些是一般性记忆，比如你的房子、街道和学校是什么样子。这些被称为背景，就像一部电影中的场景。其他是语义性的，与事实和其他信息有关。还有一些是情节性的，与发生的事件有关。
科学家认为，大脑前额叶皮层通过眼睛、耳朵、鼻子和嘴巴的感觉输入来处理经历，将这些经历分门别类，对不同的记忆片段进行特殊关联，比如家的味道、营地的朋友、虫子、宠物等。
当一个记忆提示进来，大脑就会从神经回路中搜索相关片段，并将这些片段如拼图玩具一般组装起来。有些片段牵连着相关的片段，这就是为什么旧的记忆常常会引出其他记忆。纽约市专攻记忆问题的神经精神学家戴维（Gayatri Devi）说，味道和气味尤其能唤起记忆，有名的例子就是作家普鲁斯特（Marcel Proust）尝一个玛德琳小蛋糕就能完整的描述自己的童年。
每当人们提到同样的记忆，相关的片段和回路就会变得更强。戴维说，当你80岁时还记得你在幼儿园的日子，这事实上是记忆的记忆的记忆。
这可能会有助于解释儿童最早的记忆为何如此不稳定：他们的神经痕迹又弱又浅，而随着我们越来越大，不断回访的那些记忆会留下更深的痕迹。
不过，由于大脑在不断重组记忆片段，它们很容易扭曲。
哈德森说，有十分详细和生动的记忆，但对细节的记忆错误，这是有可能的。随着被扭曲的记忆被一再回忆，可能就很难判断这个记忆是真的还是假的。
一个知名的案例是，瑞士心理学家皮亚杰（Jean Piaget）有着两岁时在巴黎被绑架的生动记忆，还记得他的保姆被绑架者划伤了脸。几年后，这位保姆承认这个故事是她虚构的，但由于皮亚杰听到家人谈起过太多次，于是大脑形成了虚假的记忆。
有没有可能找回更多自己的童年记忆？有些研究人员认为，人们如果有正确的提示就有可能记起更多。与家人谈论往昔时光可以唤起记忆，还能提供不同的视角。
照片和信件也很有用；知道特殊的日子也会有助于将片段性记忆和时间联系起来，比如兄弟姐妹的生日或搬家的日子。
