I have heard that silent reading was almost unheard of before seventh century. Is this notion true? If so, what was the cause? One of my philosophy professors also made a sidenote (during a greek philosophy lecture) that thinking in your head was also rare in those times but I'm not sure if this has any basis in fact at all.
This is an often-repeated but false myth inspired by a single anecdote in Augustine's Confessions about St. Ambrose reading out loud. The idea that silent reading was unusual in the ancient world is debunked by a pair of articles in a 1997 issue of Classical Quarterly that discuss ancient testimony of silent reading.