Wow, that sounds exactly like what I do. I can stare at something without really seeing it, the information goes in one eye and out the other. It's like I have to "try to see it" a couple times.

Just hearing about someone else having the same symptoms from marijuana actually helps clarify things for me. I also have some other anxiety related issues so it can be difficult for me to disentangle what is my problem vs. a substance causing some effect, but it sounds like in this case it might actually be the ol' cannabanoids doing work on my body chemistry.