I do not know if you have ever noticed that when you give total attention there is complete silence.

And in that attention there is no frontier, there is no center, as the “me” who is aware or attentive.

That attention, that silence, is a state of meditation.

~ J Krishnamurti

Krishnamurti had quite a lot to say about nondual perception. You can find some excerpts at the awakened eye website, along with links to sites connected with his work and places to purchase his books.