For much of history, reading was a fairly noisy activity. On clay tablets written in ancient Iraq and Syria some 4,000 years ago, the commonly used words for "to read" literally meant "to cry out" or "to listen". "I am sending a very urgent message," says one letter from this period. "Listen to this tablet. If it is appropriate, have the king listen to it."
Only occasionally, a different technique was mentioned: to "see" a tablet - to read it silently.
Today, silent reading is the norm. The majority of us bottle the words in our heads as if sitting in the hushed confines of a library. Reading out loud is largely reserved for bedtime stories and performances.