According to PatricialKUHL, babies can learn so fast from 6 - 8 months old. The babies are sensitive for sound. For example, a Indiana mum talks to her 6-month-old child in Koro. This is a newly language in India. There is only 800 people speak Koro. However, her child can also understand what did she say. Also, language has critical period. Native babies can learn every language when they turn to 7-years-old because they will try to know what sound to use in their life. On the other hand, 15 - 39 years old people are the most difficult to learn now languages. Also, English is easlier than Japanese because English has lots of /r/ and /l/, but Japanese has /r/. Therefore, the 10 - 12 months old U.S. babies are better than Japanese babies. Then, the scientists also test the U.S .babies and Taiwanese babies in Mandarin and English. Finally, the U.S. babies didn't improve Mandarin, but Taiwanese babies get improvement. Therefore, the scientists want to find out what's mean to be human through the babies' brains.