Perhaps there are futuristic science fiction scenarios in which humans have sufficient access to brain states that this situation could change, but then maybe it will be the case that cognitive content can at times be socially controlled. Maybe. After all, can a mental image of Abraham Lincoln really mean George Washington? (Adams & Aizawa, 2010, p. 73).
This last sentence seems a little cryptic to me now, but the idea is this. Suppose you have a mental representation of Abraham Lincoln, so that you are thinking of Abraham Lincoln. Could it really be the case that we can set up a convention so that when you get this mental image you are really thinking about George Washington rather than Lincoln? Maybe the convention could get the image to mean George Washington for lots of people who are party to the convention, but could the convention get the image to mean George Washington for you? Recall our earlier discussion of Thompson and Dretske regarding what something means for the subject? They have the idea that mental meanings have to be meanings for the subject. But, how could a public convention get a mental image to mean what it does for the subject?
Defending the Bounds of Cognition (with Fred Adams). (2010) In Menary, R., (Ed.). The Extended Mind, Cambridge, MA: MIT Press. (pp. 67-89).
* An animated Keanu Reeves in A Scanner Darkly.