She found that congenitally deaf people who learned American Sign Language as a first language in adulthood did far worse than people who lost their hearing from an accident or disease and learned it as a second language in adulthood. (Congenitally deaf adults who learned ASL as children were, as one would expect, best of all.) This confirms that adults are much worse than children at acquiring a language, but that the difference is masked by the fact that most adults are learning a second language, not a first one.
