That’s still just asking people, which isn’t exactly the most scientific method. If you were to stop me and ask what I was thinking, a lot of the time I wouldn’t be able to tell you - but that doesn’t mean I wasn’t thinking. Thinking without being consciously aware of it is basically what I’m doing all day, every day. It's mostly when I try to just be and let the world come to me that I become aware of how quickly I get lost in thought.