Young infants can distinguish subtle contrasts that exist in speech sounds of all languages of all the world. English babies, for example, hear the difference between Zulu clicks, something that untrained English adults are hopeless at. This ability is lost as children zoom in on the distinctions made in their native language. Researchers at Stanford have built a model that suggests children learn vowel contrasts in their own language because of general, innate biases. These inborn tendencies allow young language-learners to work out how many different vowels exist in their language and where they lie with respect to each other. Moreover, the swooping, exaggerated way that parents speak to their children makes it easier for them learn the differences between vowels in their native language. PNAS.