Infants Learn Vowels by 6 Months and Consonants by 1 Year; the First Pronunciation Habits Learned Persist the Longest (National Institute for Japanese Language and Linguistics)

Explanation

The National Institute for Japanese Language and Linguistics published an article on August 27, 2026, in its "Questions About Language" series, titled "Why Does a Dialect Accent Come Out Even When I Think I'm Speaking Standard Japanese?" by Haruo Kubozono (Professor Emeritus, Kobe University and the National Institute for Japanese Language and Linguistics).

According to the article, when people from regional areas speak the standard Japanese they learned later (second language = L2), features of the dialect of the area where they were born and raised (first language = L1) unconsciously emerge — a phenomenon called "native language interference." This is said to be the same in nature as the phenomenon in which a "Japanese accent" appears when Japanese people speak English. As examples from speakers of the Kagoshima dialect, the article cites the tendency to pronounce "yesterday" as KInoo instead of the correct kiNOo, and "London" as RONdon instead of ROndon (capital letters indicate the syllables pronounced with a higher pitch).

This interference is said to appear most readily not in the meaning of words but in "prosody," such as accent and intonation. Babies begin to perceive prosody immediately after birth, acquire the vowel system at around 6 months of age and the consonant system at around 1 year of age, and then go on to build their vocabulary. The article explains that, in line with the saying "the soul of a three-year-old lasts until one hundred," what is acquired first is the hardest to lose, and that interference from prosody, which is learned earliest, is what persists the longest.