The entire field is like nutrition or fitness, 90% of it is bogus and made up. None of these studies have proper controlled experiments while still trying to appear as authoritative.
No one takes a step back and realize that physical books are an interface and so is your kitchen. Photons hitting your eyeballs have no clue if it came from a computer monitor or the world around you. Organizing visual information is far deeper than these "UI/UX" experts.