[CuriousSkeptic]

Actually, not at all. It's directly measurable http://www.ncbi.nlm.nih.gov/pubmed/17833905

"The pupil response not only indicates mental activity in itself but shows that mental activity is closely correlated with problem difficulty, and that the size of the pupil increases with the difficulty of the problem"

[reikonomusha]

My problem is precisely that these scientific methods are not used when "cognitive load" is being used as rationale. Wouldn't you agree that it would be a mistake for me to claim that cognitive load is an issue with something if e.g. I have not shown that pupils dilate (or some other reasonable experiment indicating correlation)? Unfortunately, doing these experiments is difficult, which justifies "hard to substantiate."

[CuriousSkeptic]

Yes I do think claims should be justified by experiments. Perhaps I'm reading the wrong fora but it seems to me that serious HCI-studies on language design should be happening a lot more than it does.