Bilingual speakers who can switch languages easily are likely developing a higher level of mental flexibility than monolinguals, U.S. psychologists say. Fluent bilinguals seem to have both languages active at all times, whether both languages are consciously being used or not, researchers at Penn State report in the journal Frontiers in Psychology. Both languages are active whether either was used only seconds earlier or several days earlier, they said. Bilinguals rarely say a word in the unintended language, the researchers found, which suggests they have the ability to control the parallel activity of both languages and ultimately select the intended language without needing to consciously think about it. \"In the past, bilinguals were looked down upon,\" Judith F. Kroll, a professor of psychology and linguistics, said. \"Not only is bilingualism not bad for you, it may be really good. When you\'re switching languages all the time it strengthens your mental muscle and your executive function becomes enhanced.\"