The above linked article talks about an interesting project. How many people don’t have an internal monologue? It is interesting to try to understand what is going on in these people’s heads.
Along the same line, I was surprised to learn that many people don’t see a movie playing while they read. I have a full cast going in my head with the story I am reading. So many movies are ruined for me because the cast is not what I pictured in my head all along.