Flooding
In the seen, just the seen. In the heard, just the heard. In the felt, just the felt. Let the senses arrive faster than they can be named.
Open everything at once. Eyes open, wide field — not focused on one thing, taking in the whole visual field together. Sound at the same time. Weight, temperature, contact, at the same time. Don't visit each sense in turn. Let all of it land together.
Don't name. The mind wants to label: car, bird, cold, that. Each label is a step back from the thing to a word about the thing, and the word is where the "I" gets attached. Let the raw sense arrive without the word. If naming happens, fine; notice it, and let the next moment arrive unnamed.
Noting, as a bridge. If unnamed experience is too slippery to stay with, use one word per moment — seen, heard, felt — and nothing more. One word, then the next moment. Training wheels: the point is to get fast enough that even the one word drops.
What goes wrong
Mechanical labeling. Noting that has become a chant, with a labeler sitting comfortably in the middle of it. Drop the labels and glance: who's noting? Go look.
Narrowing. Flooding collapses into concentration: one object, held. Widen. The whole field.
The sense gates fill up and no experiencer gets added. That's the outrun.
Where it comes from
The instruction is Bahiya's, from the Pali canon: in the seen, only the seen — and then there is no you there, no you here, no you in between. Mahasi-style noting in Theravada vipassana and Shinzen Young's See Hear Feel are the trained versions of it.