
Bill Gates bought the Codex Leicester a notebook of Leonardo da Vinci's scientific observations and theories in 1994 from the estate of Armand Hammer for $30.8 million. Last year Gates loaned the work to Australia's Powerhouse Museum, which prepared this companion to its exhibition. No longer in codex form (the pages were bound in the 1600s, but Gates had the binding dismantled for digital reproduction), the manuscript ranges over topics from fossils to astronomy. Each recto of this edition reproduces one of Leonardo's pages, written in mirror-script Italian with sketches jotted in the margins; a discussion (but not a translation) appears on the verso. It includes an introduction to Leonardo's life, but no index.
For a long time I have a fascination for improving memory. It seems that visualization and memory are closely related, or even one and the same. Tony Buzan and Joshua Foer are authors that have written about this.
They write about techniques to learn a deck (or decks) of playing cards, names of people, long numbers, etc. The 'roman room' is one of these techniques, that is used for long speeches; and was also used by people like Seneca. See here a clip of how it works to learn a deck of cards: http://www.youtube.com/watch?v=X-xl7_hdWZo
The essence of these techniques is that you must create the most vibrant or bizarre imagery in your head about the subject. Not only visually, but by using all the senses: smell, taste, etc.
Da Vinci is also known for training his visualization skills by looking at an object for a moment and then trying to draw it from memory. I believe that is from Michael J. Gelb's book 'How to think like Leonardo'. (Which might not be the best source.)
For how consciousness and how we see things works this video by Susan Blackmore might be interesting, because it discusses with how much (or less) detail we can see with our eyes open in the first place: http://www.youtube.com/watch?v=sdMA8RVu1sk (from 40:00 or so)