They don't seem to mention if it is elective. An all or nothing mechanism might spell out words that the patient really didn't intend on others seeing (like "Ugh, that guy again! I can't stand the way he...")
It is pretty difficult to control your inner dialog against spontaneous and triggered thoughts.
I wanted to comment this HN entry with "people with intrusive thoughts sweating profusely" or something similar, but in truth are there people with no intrusive thoughts whatsoever?
I for one don't fight them, regardless how horrible they would be spoken out aloud, because so far I haven't seen any evidence of anyone reading my mind.
I also made a point of explaining to my child that her thoughts are hers and hers alone, so she can think whatever she likes.
I would rather not have to backtrack on any of this.