During the 16th century there was a transition in educational centers from using the natural and artificial memories to the methodical use of notebooks and commonplace books as a secondary memory saved by means of writing.

This allows people in some sense to "forget" what they've read and learned and be surprised by it again later. They allow themselves to create liminal memories which may be refreshed and brought to the center later. Perhaps there is also some benefit in this liminal memory for allowing ideas to steep on the periphery before using them. Perhaps combinatorial creativity happens unconsciously?

Cross reference: learning research by Barbara Oakley and Terry Sejnowski.