次の英文の中のある箇所の意味について教えてください
The study suggests people who speak two languages may find it easier to pay attention than those who can speak only one language. It found differences in the way bilingual brains and the brains of people who speak one language process speech sounds. Bilingual people are better at picking out a syllable such as “da” or “ta”, even when other people are talking at the same time.
That difference in hearing also seems to improve the attention and memory of those who speak more than one language, they say. “Because you have two languages in your head, you become very good at choosing what is relevant and what is not. You are a mental juggler,” says Nina Kraus, a professor of neurobiology at Northwestern, who was part of the study team.
１．4～5行目のBilingual people are better at picking out a syllable such as “da” or “ta”の意味はわかるのですが、いまいちピンときません。da, taの音節を識別するというのは具体的にどういうことですか？
２．第二段落３～４行目のyou become very good at choosing what is relevant and what is not.の意味がよくわかりません。relevantはここではどういう意味で、what is relevant and what is notを選ぶのがうまくなるというのはどういう意味ですか？
わかる方解説のほどよろしくお願いします。
