Consider Mary, the super-scientist of Knowledge Argument fame. She has never seen red and yet knows everything there is to know about the physical nature of red and the brain processing related to color experience. Now, as a twist, suppose we show her red subliminally (say with backward masking or something). She sees a red fire hydrant and yet denies that she saw anything except the mask (say). Yet we can say that she is primed from this exposure (say quicker to identify a fire truck than a duck subsequently or something). Does she learn what it is like to see red from this? Does she know what it is like to see red and yet not know that she knows this?
It seems to me that views which accept phenomenological overflow, and allow that there is phenomenal consciousness in the absence of any kind of cognitive access, have to say that the subliminal exposure to red does let Mary learn what it is like for her to see red (without her knowing that she has learned this). But this seems very odd to me and thus seems to me that this is a kind of a priori consideration that suggests there is no overflow.
Of course I have had about 8 hours of sleep in the last week so maybe I am missing something?
Richard Brown 
I think a proponent of the overflow thesis would have to argue that there’s something it’s like for Mary to see red, even though she doesn’t *know* what it’s like to see red. We acquire phenomenal knowledge through introspection, and introspection requires the possibility to access a content. So if you cannot access a content, then you cannot introspect it, and if you cannot introspect it then you cannot acquire phenomenal knowledge. It seems to me that proponents of the phenomenal overflow thesis would have to accept that an inattentional-Mary or a primed-Mary would not acquire phenomenal knowledge, even if there would be something it’s like for inattentional-Mary to see colors. Jesse Prinz wrote an article with a case like this in order to argue that a kind of mental pointing must constitute phenomenal knowledge (Prinz, 2007 “Mental Pointing”): “My intuition (for what it’s worth) is that we would not credit a person who merely experienced something with knowledge of what that experience is like, but, when that person focuses on the experience in a top-down way, we do credit her with knowledge of what it’s like.”
Hi Matthias, thanks for the comment and sorry for the delay in getting back to you!
I had forgotten about that section of Jesse’s paper! I guess I was assuming that having the conscious experience=knowing what it is like but I can see that is something people can disagree on! I’ll have to think about the arguments a bit more…