I listened to a talk, though I may not be able to find it now, about our ability to hear elements of language. They played consonant sounds used in different languages and I could not distinguish between some of them them at all. Apparently if as a child you are not exposed to them by the age of about 4 you will never be able to.
It is driving me mad that I can't remember where I heard it. It would be great if someone knows.