发生的事情不过是，无条件刺激与条件刺激，铃声与食物，因为恰巧同时出现而联系在了一起。

So, what happens is the UCS and the CS, the bell and the food, go together because they happen at the same time.

youdao

比如，在条件作用形成之前，只是简单的存在着无条件刺激，即食物，以及无条件反应，即唾液。

Well, when Pavlov, for instance, started before conditioning there was simply an unconditioned stimulus, the food in the mouth, and an unconditioned response, saliva.

youdao

比如，在条件作用形成之前，只是简单的存在着无条件刺激，即食物，以及无条件反应，即唾液。

Well, when Pavlov, for instance, started before conditioning there was simply an unconditioned stimulus, the food in the mouth, and an unconditioned response, saliva.

youdao