Typography and ease of use

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…It’s helpful to understand one of the basic mechanicals of reading: saccades. Instead of moving smoothly across the page when we read, our eyes actually make discrete jumps between words, fixating on one word for a short period of time before making a ballistic movement to another one. We call these movements saccades.”

“But despite their “ballistic” nature, these rapid eye movements actually improve our reading capabilities. While we process the words immediately within our focus, we use the additional information just outside of it to further guide our reading. As readers, our time to comprehension is aided by the context of adjacent words-to the extent that we are often able to automatically process (and thus skip over) shorter functional words like and, the, of, and but.

From: Setting Type for User Interfaces