“What we found was that people on paper started to ‘know’ the material more quickly over the passage of time,” says Garland. “It took longer and [required] more repeated testing to get into that knowing state [with the computer reading, but] eventually the people who did it on the computer caught up with the people who [were reading] on paper.”
http://healthland.time.com/2012/03/14/do-e-books-impair-memory///cdn.embedly.com/widgets/platform.js
Intriguing! I wonder how these effects differ for fixed-format digital items, such as PDFs. I also think that free-format items with a rigid internal structure — particular poetry — would be equally memorable in either print or digital forms.
Tactile contact with a book is also part of reinforcing one’s memory of loci. I remember, I think, the locations of figures on a page and the relationship of text to them in part because I turned the page after lingering for a certain length of time. As touchscreen readers replace readers with buttons, I expect memory to improve slightly.