An infant's very first step in their year-long journey to their first word is perhaps their most impressive. This first step is discriminating and categorising the basic sound components of the language they are hearing.
To get an idea how hard this might be think about listening to someone speaking a language you don't understand. Foreign languages can sound like continuous streams of noise in which it's very hard to pick up where one word starts and another word begins.
Young infants face an analogous challenge but not initially at the level of words, but at the lower level of pure noise. Their first struggle is to tell the difference between the most basic components of speech, the individual sounds we are making, the phonemes.
Noticing the difference between 'b' and 'p'
Until a classic study carried out by Peter D Eimas and colleagues from Brown University in 1971, psychologists were not sure how soon infants could discriminate phonemes.
Eimas and colleagues' study used infants aged between just 1 and 4 months old and tested their ability to discriminate between a 'b' sound and a 'p' sound (Eimas et al., 1971). To get an idea of how difficult this is, consider the fact there's only a 10ms difference in timing between the two. To be able to hear this difference, a baby has got to have a very fine-tuned ear.
The method they used for intuiting whether the infants had noticed a change from one sound to the other was pretty ingenious. They were hooked up to a fake nipple which measured their rate of sucking, the idea being that this was a proxy for how interested they were in what was going on around them. The more interested, the faster they suckled.
First, infants' suckling rates were measured while they were exposed to one repeated sound, say the 'b'. Initially infants found this interesting and sucked a bit faster. Then after a while they get bored and their suckling rate reduced.
Here's the crucial part: in some experimental conditions the sound is changed to a 'p', while in other conditions it continues with the same 'b'. The question is whether infants notice this change, as evidenced by an increased suckling rate, and thereby demonstrate that they can discriminate the tiny difference between a 'b' and a 'p' sound.
Innate ability to discriminate phonemes
What Eimas and colleagues found was that even the one-month old infants appeared to be able to tell the difference between a 'b' sound and a 'p' sound.
This findings, and more like it, suggests to many psychologists that infants are born with skills which enable them to categorise sounds that only slightly vary. This skill is one of the basic building blocks of language learning.
Most languages contain about 40 distinct phonemes and an infant's ultimate task is to master all of them. During their first three months of life infants make all kinds of sound, but none of them bear much resemblance to speech.
But, partly because of this innate ability to discriminate the components of speech, by 3 months they start producing vowel-like sounds. They've conquered their first few phonemes and are well on their way to their first words.
The first word
While infants seem to be born with an ear fine-tuned for language, this starts to subtly change at around 11 months of age. Subsequent findings have shown that adults cannot successfully distinguish as wider a range of phonemes as infants.
This is because until about 11 months of age infants are masters of discriminating phonemes used in all different types of languages. But after 11 months infants settle down with one set of phonemes for their first language, and lose the ability to discriminate the phonemes from other languages. Infants are beginning to specialise in their own language.
The specialisation at 11 months in one set of around 40 phonemes, along with other linguistic processes, is clearly crucial as it quickly brings a magical moment: the first word.
译文:
婴儿——如何结束咿呀之旅说出第一个字？
婴儿在冒出第一个字前的全年旅程是学说话的首要阶段，也可能是最让人难忘的阶段。在首要阶段中，婴儿 会对所听到的语言的基本声音成分进行区分和分类。
为更直观的了解，不妨回想一下你在听到某人用一种你不懂的语言说话时的情形：外语听上去就像连绵不断的噪音，很难弄清一个字是何时结束另一个又是何时开始的。
幼儿面对着类似的挑战，只不过一开始不是字而低一级的纯粹噪音。他们努力区分语言的最基本成分和我们所发出的单个声音即音素。
注意“b”和“p”的区别
要不是Peter D Eimas和他来自布郎大学的同事于1971年进行的一次著名的实验，心理学家们还不确定婴儿究竟多快就能区分音素。
Eimas和同事们的研究选择的是出生1-4月的婴幼儿来测验他们区分音素“b”和“p”的能力。要辨别二者不易，因为两者间转换时间只相隔10毫秒。要分辨出二者， 婴儿必须具备敏锐的听觉。
他们使用非常巧妙的方法来观察婴儿是否注意到了一个到另一个声音的变化。婴儿咬着用来测量吮吸速度的假奶嘴，并通过此奶嘴替代物被反映对周边事物的兴趣度。因为他们感兴趣程度越高，吮吸的速度会越快。
首先，婴儿当听到一个反复声音如“b”时，会被测量吮吸速度。起初，婴儿会对此感兴趣并由此加快吮吸速度。但过一会儿后，他们会厌倦并放慢速度。
接下来是关键的一步。在一些实验情况下，声音会被改成“p”，而在另一些情况下会继续“b”。问题是是否婴儿注意到此变化。如果吮吸速度增加，则证明他们能区分“b”和“p”发音的细微差别。
区分音素的天赋
Evimas和同事发现了甚至才一个月大的婴儿就能区分音素“b”和“p”的不同。
该实验结果，更多的是向心理学家们表明了婴儿天生就具有能区分仅些许差别声音的技能。而此技能就是语言学习的一块基石。
大多数语言包含有40种不同的音素，婴儿的最终任务就是要全部掌握它们。在婴儿出生的前三个月中，他们会发出各种声音，但都不是语言。
但部分由于这种能区分语言成分的天赋，三个月后他们就能开始发出类似元音的声音了。他们攻克了最初的几个音素于是便踏上将说出第一个字的旅途。
说出第一个字
尽管婴儿似乎天生具有对语言敏感的耳朵，但从大约11个月后，这种能力就会发生些许的改变。之后的实验表明，成人不能像婴儿那样成功的区分同样多的音素。
这是因为婴儿在大概11个月前擅长区分各种语言的音素，而11个月后则变成区分他们第一语言音素的里手，且失去了区分其他语言音素的能力。婴儿开始专攻他们的母语。
婴儿在前11个月里对约莫40个音素和语言产生的“钻研”，决定了他们说出第一个字的神奇一刻的到来。