There is really no reason why we should be able to read and yet here we are. If you consider the history of humans, reading is a relatively new skill that we’ve acquired. The Gutenberg Press is only about 560 years-old, to put that in perspective modern humans are about 150-200,000 years old.
When you read something you activate at least three distinct areas of your brain:
Your knowledge of a language (semantics), the way words sound (phonology), and how that word is supposed to properly appear within your known language (orthography)—work together to create the experience known as reading. This entire process takes around 300-400 milliseconds, but your brain has to decide to move onto the next word by the 100th millisecond. That’s not a whole lot of time.
Which is why when you read this sentence:
This little piggy went to market.
You see an image of a pig walking to a market in your head. You’re using everything you know, the word, your language, how you’ve seen those words used before, to create a mental image in your head.
According to NPR here is what is happening:
The brain appears to be taking words, which are just arbitrary symbols, and translating them into things we can see or hear or do.
Creating that imagery in your head is how you understand the abstraction that is a written word. When you are reading you also develop a physical landscape for the words. As Scientific American explains, a book has physical borders, and those help us root our reading and understanding of its contents. The tactile process of turning a page, of rifling through something, actually helps your brain maintain the organization and relative whereabouts of a book’s contents.
Reading online then presents us with a specific set of challenges. You can’t sort through that text in the same way. When you read on a computer the amount you can read, and the level of which you are reading is diminished. Your brain has to work harder to extract the information necessary to comprehend the text. This is because you can only ever really experience that text one page at a time. Your brain is trying to place that text within a structure that you just don’t know, and that’s no easy task (kind of like making a sand castle one piece of sand at a time).
Another challenge of web content is the light emanating from your computer, which we know causes visual fatigue. Your ability to read a text, to understand that text, depends on how easy that text is to read. This legibility is impacted (in part) by resolution, other light pollution, and contrast.
We also over-estimate our ability to understand text quickly when reading materials online. What you think you know and what you remember just isn’t the same when reading on a digital device. What you end up doing is not allowing yourself enough time to fully intake the information. Instead, you just end up moving to other information you assume is relevant. This is also known as scanning. You will be most drawn to the information that is important to you, looking for keywords that match this information. Often without even knowing it, you disregard the other text presented. Your reading becomes non-linear, it looks more like this:
You want to click on that text, scroll, find out what else is going on. You may even find (as people from this Washington Post article did) that they have difficulty reading books now. The book feels too long, the experience too passive for the digital consumer. This is what we would expect—it is what you would want from a brain that is constantly adapting, growing, and learning.
People have not stopped reading, they have just started to read and take in information differently. Humans are always adapting, and that’s not scary to me, that’s thrilling. Reading leaves us with new neural pathways, it allows us to understand our environment and our past experiences in new ways.
Each of us has a deeply personal and unique relationship to what we are reading. That is truly why we must treat how we present information with such care. You have the ability to create an experience that no one else can create. That is endlessly wonderful.
 “Beyond words: how to write for readability” by Andrea Ayres. Blog.