When Pavlov put food powder in the dog's mouth and saliva was generated, that's an unconditioned stimulus giving rise to an unconditioned response.

巴甫洛夫给狗喂食,狗会分泌唾液，这就是无条件刺激引起了无条件反应。

耶鲁公开课 - 心理学导论课程节选

What he would do is he'd put food powder in the dog's mouth to generate saliva.

他的做法是,给狗喂食，让狗分泌唾液。

耶鲁公开课 - 心理学导论课程节选