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Our brains can recognize and convert numbers to letters pretty quickly automatically for the same reason that we can decipher messy handwriting. When we read, we process words and letters in a few steps; firstly, when reading a longer phrase, certain areas of our brain, namely the occipitotemporal cortex and superior-temporal cortex, work to predict what word comes next. Just by reading and talking to people regularly, you can predict how simple sentences might end. You understand there's a short list of words that can logically come next in a sentence which is why when you proof-read your own work, you're more likely to glaze over smaller mistakes. Next, your eyes recognize words as a chuck, not as individual letters. You'll see test this in longer words that we regularly see such as "difficulty" or "difficolties." When speed reading, you might not catch the misspelling of the second word. Now your brain takes other steps to turn the shapes into sounds and comprehend those words but we'll not talk about that in this article.

For a similar reason, your brain doesn't really care about letter ordering in words it recognizes. This is a very good thing seeing as people accidentally misspell words all the time. If our minds couldn't adapt to small changes, it'd likely struggle to read at all. Younger people seem to be better adapted to more easily read mistakes and letter swaps, likely due to the fact that they are more accustomed to more liberal spellings of words over texting and social media. This is just another reminder on how our brains can adjust for our carelessness and laziness brilliance and creativity.