Reading is typically an individual activity, done silently, although on occasion a person reads out loud for other listeners; or reads aloud for one's own use, for better comprehension. Before the reintroduction of separated text (spaces between words) in the late Middle Ages, the ability to read silently was considered rather remarkable. Reading for pleasure has been linked to increased cognitive progress in vocabulary and mathematics during adolescence. Sustained high volume lifetime reading has been associated with high levels of academic attainment.