I believe that I asked here (I can't imagine a better stackexchange for the subject matter, and I can't find any trace of where I would have asked elsewhere) a question requesting references to research on the effectiveness of "phrasing things in a hard way to force the reader to struggle with understanding the content." The examples furnished were from a mathematics author whose work I have been researching.
After feedback this was revised a bit to specify "memory retention" as the measure of effectiveness, and someone did come through with a related reference to a study where something like bad typeface improved retention rates, or something like that.
I haven't had time to follow up until now... but I can't find it! I think the question was closed, and that opens up the chance it was deleted. If someone could just recover the reference from the deleted post, I'd be very grateful.