As previously mentioned in Part 1, Dr. Kuhl has proved infants' astonishing sensitivity to their mother tongue and the importance of "live" social interaction with surrounding people. Here, she introduces recent findings of research, which was conducted mainly in her laboratory, on two themes that are familiar to many child-rearing parents: the process of acquiring bilingualism and the influence of early language environment on the later language skills.

All parents hope their child will grow up to be a "better" person. The hope inscribed in the word "better" is surely different for each parent. For the parents who wish their child to become a successful athlete, it will be a superior physical ability, and for the parents who wish their child to become an international musician, it may be a good ear for music and sensitive touch. Some parents may want their child to have a gentle nature. In terms of number, however, most parents probably hope that their child will be a smart kid. Although intelligence quotient (IQ) clearly shows smartness, many previous studies have shown that intelligence is decided by both inherited factors and experiences. Genetic factors are already decided by genes inherited from parents. Many parents then try to improve their child's developmental environment, which can be changed. To choose a better education environment is the most workable method.

The problem is that many parents think along the same lines. As a result, it is understandable that they give "educational" encouragement to their child from infancy so that he or she will have an advantage over other children when entering school. This accounts for the emergence of early childhood education.

Dr. Kuhl addresses two main themes, which occupy the attention of parents and educators who are interested in early childhood education.

Longing for bilingualism

The first theme is bilingualism. The interest of parents in bilingualism is most commonly focused on how to make their child bilingual. If asked why they would like their child to become bilingual, many parents would answer that they want their child to become an adult who can actively participate in the world. Their hope reflects the memories of difficulties they experienced in studying English from junior high school or in travelling abroad.

Based on considerable experiences, it is known that children develop a ground for bilingualism if they spend a couple of years from 7 or 8 years old in an environment where two different languages are spoken. The reason why I refer to it as a ground is that it rapidly collapses if their environment changes from bilingual to monolingual (unilingual) after that. A family in which parents are always speaking in different languages, such as a family of internationally married couple, will be the environment where children can grow up to be bilingual.

However, many parents want to know how to make their children bilingual while staying in Japan. The most effective way is to send their children to international schools. As shown in the Dr. Kuhl's experiment in Part 1, learning foreign languages by listening to DVDs or tapes can help them understand foreign languages but it does not make them bilingual.

For me as a specialist of child development, bilingualism sometimes becomes a big problem. This is because children who grow up in a bilingual environment are often slow to acquire language. Many of my patients, the children of an international marriage, are brought by their parents who are concerned by their delayed speech.

Although this doesn't sound very scientific, I have explained that the delayed speech of a child raised in bilingual environment can be attributed to the capacity of a child's repository of language or "dictionary." When a child starts to acquire a language, vocabulary that can be stored in a child's brain is limited. For example, when the number of words stored in a brain is 100, a bilingual child can only store 50 words of each language. From the perspective of each parent, their child's vocabulary is half that of a monolingual child.

In the period when the total number of words from both languages is still small, this difference makes a big difference in conversational ability. However, it has been said that an adult's vocabulary is approximately 50,000 words, and even when it is halved to 25,000, it does not affect daily conversation. This is understandable when considering that the number of words required to pass the most difficult level of the Japanese Language Proficiency Test is 10,000.

Then, can it be said that the vocabulary of a bilingual person is twice that of a monolingual person? Interested in this question, I consulted the literature, but found it to be difficult to answer. The composition of a bilingual person's vocabulary is determined by the degree of exposure to each of the two languages and cannot be simply half and half. In the case of a person who spends his childhood in Japan and then many years in England later in life, his vocabulary may be 20% Japanese and 80% English, or 40% Japanese and 60% English, and cannot be decided uniformly.

The bilingual brain

Dr. Kuhl studied the problem by taking as a model the learning of speech sounds of different languages. Dr. Kuhl showed that children learn a speech sound by hearing it and statistically calculating its appearance frequency, and after hearing the speech sound a certain number of times, their understanding becomes fixed. After a speech sound is fixed, the ability to identify a less frequent speech sound rapidly decreases.

Bilingual children would be expected to hear a speech sound in each of the two languages a fewer number of times. Given that the ability to discriminate between sounds does not become fixed until the child hears a speech sound for a certain number of times (e.g. 10,000 times), bilingual children will have a longer unfixed "open" period. Using two methods, behavior observation and electroencephalogram (event-related potential), Dr. Kuhl successfully proved the above assumption by examining when the ability to discriminate between speech sounds becomes fixed.

The subjects of the study, children raised in a bilingual environment of English and French, were found to retain the ability to distinguish speech sounds in both English and French even at 20 months of age, well past 10 months of age when the ability to discern speech sounds is usually fixed. The perception level of their brain stayed high until they became familiar with the pronunciation and grammar of the two different languages.

Dr. Kuhl also concluded that bilingual people, not only children but also adults, had more advanced skills in performing tasks that require breaking rules and thinking flexibly.

Influence of early language environment on later language development

Finally, Dr. Kuhl confirmed how the infant's ability to learn speech sounds affected later language development by following up on the children who were found capable of comprehending speech sounds as infants until the age of five.

Dr. Kuhl again used behavior observation and brain scientific method (event-related potential) to measure infants' ability to distinguish their mother tongue, at 7 months and 11 months of ages. The infants were grouped into three groups: (1) infants who show excellent discrimination abilities at both ages, the high-high group, (2) infants who show poor abilities at 7 months but excellent performance at 11 months, the low-high group, and (3) infants who show poor abilities at both 7 and 11 months of ages, the low-low group. She followed up on these children and assessed correlation with their language skills at 5 years of age. The results were as expected. The children who showed excellent skills in distinguishing speech sounds at early age were later found at 5 years of age to be better at not only distinguishing but also expressing and understanding the spoken language.

Dr. Kuhl concludes that although verbal interaction between parents and infants in households is quite complex, it is clear that children's brains are literally "shaped" by external stimuli (language etc.) and further studies are needed.

Reference

• Early Language Learning and Literacy: Neuroscience Implications for Education by Patricia K. Kuhl from MIND, BRAIN AND EDUCATION, 10 August 2011. © 2011 the Author. Journal Compilation © 2011 International Mind, Brain, and Education Society and Blackwell Publishing, Inc. Republished with permission of John Wiley and Sons, Inc.