http://www.scientificamerican.com/ar...-paper-screens
I think the "science" is at best exploratory at this point, and am skeptical on many levels about any of the 'conclusions' that are being suggested.
Digital reading is a skill, and digital reading systems and technologies are not all created equal. But the studies referred to don't appear to explore more than one digital reading system. Books aren't equal, either: they can be poorly typeset, cheap paper, or have unpleasant odors.
Also the subjects of the studies likely have a lifetime of experience reading books, but only a few years (if that) with digital reading. Again, it is a skill and brains need to rewire to do it well.
Without reading the methodology, it is impossible to know what they have experimental controls for.
I agree that ebook navigation is not what it ought to be, but digital reading is still in the early stages, and has yet to really tackle the higher-hanging fruit (textbooks, technical) that would really benefit from improved reading systems.