When thought is transcended, that moment--it may be one millionth of a second--he can comprehend the truth about Brahman's transcending thought. For then the idea becomes the mind. At that moment the mind negates all thoughts. This is called the lightning flash in the Upanishads. You must watch vigilantly for it. When between two thoughts you catch this brief flash you have to understand that the thoughts were still in your mind whether they had appeared or vanished. The thought-gap is hidden. That gap is the see-er of the thoughts, that is, Drik, Mind, Brahman.
-- Notebooks Category 23: Advanced Contemplation > Chapter 8: The Void As Contemplative Experience > # 161