Sign languages vary from country to country,and many are not well known internationally.

VOA: standard.2009.09.10

But these are important issues and these vary a lot from culture to culture and a good theory of psychology has to explain how these differences arise.

这些重要问题,在每个文化中都不一样,一个好的心理学理论必须能解释,这些差异是怎么产生的。

耶鲁公开课 - 心理学导论课程节选