It's worth distinguishing a few concepts: ① The qualia of the feeling. ② The physical equivalent of the feeling. ③ The causation between a stimulus and ②. ④ The behavior caused by ②.

If I show a person with a spider phobia an image of a spider for 5ms I might know more about what happens to them with ②, ③ and ④ then they do themselves.

In my experience the people who are really got at reading ②, ③ and ④ are generally strongly aware that they can't read ①.