Still,Hyun's rejection of the North's explanation is a sign the South does not rule that possibility out.

VOA: standard.2009.09.09

It turns out that sign and--the developmental milestones of sign languages and the developmental milestones of spoken languages are precisely the same.

手语的发展阶段,和口语语言的发展阶段是完全相同的

耶鲁公开课 - 心理学导论课程节选

One of the real surprising findings in my field over the last ten/twenty years has been that the acquisition of sign languages has turned out to be almost exactly the same; in fact, as far as we know, exactly the same as the acquisition of spoken languages.

过去的十到二十年间,在我的研究领域里最令人吃惊的发现之一就是,各种手语的获得过程,被证明几乎是完全相同的,实际上据我所知,和口语语言的获得过程是完全相同的

耶鲁公开课 - 心理学导论课程节选