And what this is in a very general sense is the learning of an association between one stimulus and another stimulus, where stimulus is a technical term meaning events in the environment like a certain smell or sound or sight.

一般来说,经典条件作用是指在一个刺激,和另一个刺激之间形成联结，这里的刺激是一个专业术语,意思是环境中出现的事件,比如某种味道，声音或景观。

耶鲁公开课 - 心理学导论课程节选

Use "When" whenever you want to ask about the timing of a certain event or series of events.

当你想要询问一个或一系列事件的具体时间时，你可以用“When”句型。

When 课堂 - SpeakingMax英语口语达人