A radical empiricism underlies one of the tools Jan used to help people explore the world and themselves. What is often called 'self observation' was variously described by Jan to his students. Regardless of the emphasis in his descriptions, attention to the so-called inner world of man was critical. He carried the scientist's empiricism to the job of understanding one's internal thoughts.
This approach is unpopular in the scientific arena since often scientists are unwilling to credit this approach, labeling it as subjective. Had they tried it, the scientists of the physical external world would have realized that subjective is not a good adjective. Had they sincerely directed their curiosity on themselves they would have realized one's thoughts are not any kind of unique phenomena, in content, or in source.
The ordinary thoughts of one man are about as unique as one chicken in a noisy hen house.
The internal cackling is not subjective since it typifies a species. Is not the typical sound of species an interesting important and relevant field of study?? Just because with man there is an internal quieter side to the typical human chatter does not make it a less scientific subject. The internal chatter, if studied, reveals that man's internal life is not original, not autonomous, and not for the purpose the thinker assumes. The scientists of the external world miss these crucial facts, and since they have not turned a systematic attention to their own internal world, or wondering about the soundness of the positivistic aversion to internal study, their caveats about this approach lack intellectual weight.
There are complications to the intellectuals' interior experience also, which prevent them often pursuing the path of self-knowledge, but we can talk about that later. And later we can discuss Sagan's rather amazing contention that the human brain has stopped evolving. Oh really, and how could we test that statement? So check back.