While it bases its test on reflex time, I'd suggest that a simpler demonstration of the same thing is the everyday vocabulary employed in novels and popular non-fiction. It is much larger, full of reference to standard works (Book of Common Prayer, Shakespeare, King James Bible, Pilgrim's Progress &c. &c.) most of which are now considered too difficult for highschool, which remains the final degree for the majority of the population. Thomas Hardy, Anthony Trollope, and George Meredith were major novelists, though the standard was Dickens. Thomas Carlyle is one of the most enjoyable non-fiction writers. In the US, Ralph Waldo Emerson and Henry James would be his opposite numbers. Take a moment and try them out. My trick is to have a pocket dictionary nearby, and make a pencil mark every time I have to look up a word: if I see something with 4 or more, I take time to write it out for myself. There may be other tricks that work as well when facing unfamiliar vocabulary.
What's discouraging about this is the direction of the change over time, and how poorly it is reflected in our popular understanding of ourselves. Reality. It takes work.