The Presence of One’s Own Smartphone Reduces Available Cognitive Capacity
Bards pre-literate-times in Greece purportedly could recite Homer's Odyssey themselves after one hearing.  Writing destroyed that all.  
(Maybe I don't have a citation right off, but I've read that on the web or heard it in some college class years ago ... in any case, ability to retain heard information has likely declined since then).  But ... few people complain about how books corrupt our memory.So we're the first generation shifting cognitive burden of some kinds of memory (all those phone numbers) elsewhere.  I welcome it.  My wife hates it, but she likes the books.  In a couple of generations it all will be irrelevant.