Here is a good description of this exercise, used in Tibet from Alexandra David-Neel:
Seated in a quiet place, the disciple refrains as much as he can from consciously pointing his thoughts in a definite direction. He marks the spontaneous arising of ideas, memories, desires, etc., and considers how, superseded by new ones, they sink into the dark recesses of the mind.
He watches also the subjective image which, apparently unconnected with any thoughts or sensations, appears while his eyes are closed: men, animals, landscapes, moving crowds, etc.
During that exercise, he avoids making reflections about the spectacle which he beholds, looking passively at the continual, swift, flowing stream of thoughts and mental images that whirl, jostle, fight and pass away.
It is said that the disciple is about to gather the fruit of this practice when he loosens the firm footing he had kept, till then, in his quality of spectator.
He too – so he must understand – is an actor on the tumultuous stage. His present introspection, all his acts and thoughts, and the very sum of them all which he calls his self, are but ephemeral bubbles in a whirlpool made of an infinite quantity of bubbles which congregate for a moment, separate, burst, and form again, following a giddy rhythm.
The second exercise is intended to stop the roaming of the mind in order that one may concentrate it on one single object. Training which tends to (…)
There are four types of meditations-
1) A person is thinking constantly about particular subject,Suppose during the time of meditation,His/her mind is constantly thinking about one’s child in the hospital and consequences happening with thou over there. In that case, he is in the state of hurrying to the hospital.
2) The thoughts are forming and he has entangled himself with the thoughts.
3) The thoughts are forming but he is not entangled with them. But he is just watching the thoughts.
4) He does not know that whether thoughts were there or not during the state of meditation.
So, It depends on the various stages of the consciousness.