From brain to language to accent

Good article behind the science of accents.

The research was comparing the brains of native English, Chinese, and Bilingual speakers.

Good quote:

And it pays to start early. Research suggests that true native fluency in any language can only be gained in early childhood; some studies found that sensitivity to foreign accent goes down after age 1! It's not impossible to learn a new language late in life, but it does get more difficult: a 40-year-old will have a harder time than a 20-year-old, says Grant Goodall of the University of California, San Diego

From brain to language to accent - CNN

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