We may find learning a second language so difficult: last week a junior told me he was struggling in the Spanish course, and he showed off a little bit to me that English is his first language. I don’t think English is tough, but it’s definitely harder to learn than my first language. Yet, we should realize that we learnt our mother tongue as little babies! When we just arrived in this world and cannot speak, don’t know anything, and lack the basic knowledge of everything that seem stupid to us today. However, we did it. With immense curiosity, which always spark flames of exploration in science, I determine to look up how babies complete such an impossible task and why we do better job learning a language as infants rather than as adults.

A study shows several essential elements in infants’ language learning, and first of all is “the discrimination of the acoustic events that distinguish phonetic units.” Eimas and colleagues showed that “young infants are especially sensitive to acoustic changes, including those of languages they have never heard, whereas adults cannot.” For instance, domain changes /b/ to /p/, and equivalently small differences in the frequency domain change /p/ to /k/. Infants can discriminate these subtle differences from birth, and this ability is essential for the acquisition of language.

Nevertheless, “Infants’ initial universal ability to distinguish between phonetic units must eventually give way to a language-specific pattern of listening. Werker and colleagues investigated when the infant ‘citizens of the world’ become ‘culture-bound’ listeners.” They showed that English-learning infants could easily discriminate Hindi and Salish sounds at 6 months of age, but that “this discrimination declined substantially by 12 months of age. English-learning infants at 12 months have difficulty in distinguishing between sounds that are not used in English. Yet at the same time, the ability of infants to discriminate native-language phonetic units improves.” The difference of capacity for learning mother tongue and a second language initiates here. 

Apart from the ability to distinguish phonetic units, categorization– “perceptually group different sounds that they clearly hear as distinct” is another skill babies must have. Basically, in a natural environment, infants hear sounds that vary on many dimensions (for example, talker, rate and phonetic context). At an early age, infants can categorize speech sounds despite such changes. If they are to imitate speech, this skill is necessary.

In addition, social learning plays a dominant part in language learning. Researchers conducted a speech experiment: “Nine-month-old American infants being exposed to Mandarin Chinese in twelve 25-min live or televised sessions.” After exposure, they were tested on a Mandarin phonetic contrast using the head-turn technique. (infants were treated to turn heads when perceiving difference between Mandarin phonetic sounds.)The results show “phonetic learning in the live-exposure group, but no learning in the TV- or audio-only group.” Below is a picture explaining the experiment.

As the last part, the effects of language learning on the brain are also significant. “Dehaene-Lambertz and colleagues used functional MRI to measure the brain activity evoked by normal speech and speech played backwards in 3-month-old infants.” They found that similar brain regions are active in adults and infants when listening to normal speech but that there are differences between adults’ and infants’ responses to backwards speech. Thus, distinct active brain region is also a reason why adults fall behind babies. 

Actually, there is still no definite conclusion of how exactly infants learn mother tongue and why adults are not as competent as babies regarding language learning. Nonetheless, through more and more hypothesis, data, observations, and experiments, we are more and more close to the core of truth. Science is a path of exploring.

Works cited: http://www.nature.com/nrn/journal/v5/n11/full/nrn1533.html