It's one of those things where you pick up these visual language elements without even realizing that you're doing it, just through sub-conscious exposure to them. Did you realize when you were five years old that you had a thousand-word vocabulary? I seriously doubt it. And when you were ten, did you realize you knew 3000 words? No- you just knew the words, without being aware that you knew those words, how many you knew, or why you knew the ones you did. Looking back from adulthood, you can spot moments where your vocabulary took a turn in a direction because you were exposed to an idea or experience (reading Shakespeare, studying chemistry, taking Spanish or French, learning photography) that developed an interest for you in some subject area. The same thing happens with visual imagery.