user-1: 
Can anyone explain how 'stimulus / response' appears in Chinese or Japanese Buddhism? 
What does it mean?

I can recall barely nothing about it, but I do know that it features in Zhiyi's work, Chin Fa-hua-hsüan-i at least. I'm especially interested in how the terms, which I believe are paired, may have a universal meaning.

user13992: This is an extremely broad question, I will limit my response to Ch'an/Zen Buddhism.
Starting in the earliest schools of Ch'an in Sung China, we find the practice of a stimulus/response ritual the Japanese call sassho. It usually (but not necessarily) takes the form of a question-answer dialog between master and student and is used to both invoke and verify insight/realization. Some of these dialogs have become (in)famous and were compiled into Kung'An/Koan collections still used today.
The basic philosophy behind sassho is to verify whether the answer to a teacher's question is free-flowing or (pre)conceived. In the latter case, the answer would be rejected and the student would be requested to meditate further on the question.

-1: <ul>
<li><p>Can anyone explain how 'stimulus / response' appears in <a href="https://en.wikipedia.org/wiki/Chinese_Buddhism" rel="nofollow noreferrer"><em>Chinese</em></a> or <a href="https://en.wikipedia.org/wiki/Buddhism_in_Japan" rel="nofollow noreferrer"><em>Japanese Buddhism</em></a>? </p></li>
<li><p>What does it mean?</p></li>
</ul>

<p>I can recall barely nothing about it, but I do know that it features in Zhiyi's work, <em><a href="https://www.nichirenlibrary.org/en/dic/Content/P/109" rel="nofollow noreferrer">Chin Fa-hua-hsüan-i</a></em> at least. I'm especially interested in how the terms, which I believe are paired, may have a universal meaning.</p>
 13992: <p>This is an extremely broad question, I will limit my response to Ch'an/Zen Buddhism.</p>

<p>Starting in the earliest schools of Ch'an in Sung China, we find the practice of a stimulus/response ritual the Japanese call <em>sassho</em>. It usually (but not necessarily) takes the form of a question-answer dialog between master and student and is used to both invoke and verify insight/realization. Some of these dialogs have become (in)famous and were compiled into <a href="https://en.wikipedia.org/wiki/K%C5%8Dan#Classical_k%C5%8Dan_collections" rel="nofollow noreferrer">Kung'An/Koan collections</a> still used today.</p>

<p>The basic philosophy behind sassho is to verify whether the answer to a teacher's question is free-flowing or (pre)conceived. In the latter case, the answer would be rejected and the student would be requested to meditate further on the question.</p>
