I found a great article on Quora called "Why Do I Misread Words?":
Most of us don’t read everything word-for-word, much less letter-for-letter. In fact, in a letter written by Graham Rawlinsin in 1999 (a specialist in child development and educational psychology), he said that:
“randomizing letters in the middle of words had little or no effect on the ability of skilled readers to understand the text."
As an example of this, the article provides this exercise:
What this demonstrates is that our minds can assume what is being said through context. Although we perceive ourselves to be reading everything one word at a time, this is not always the case.
So, when you "see" the word undeserved, it might actually be that you just assume it to be that because it's a more natural fit for what you're used to reading and for what you have been reading in the sentence up until that point. It's only when you continue past that word, and realize that things aren't making sense, that you back up in order to discover your error.
The Wired article "What's Up With That: Why It's So Hard to Catch Your Own Typos" also discusses this:
Generalization is the hallmark of all higher-level brain functions. It's similar to how our brains build maps of familiar places, compiling the sights, smells, and feel of a route. That mental map frees your brain up to think about other things. Sometimes this works against you, like when you accidentally drive to work on your way to a barbecue, because the route to your friend's house includes a section of your daily commute. We can become blind to details because our brain is operating on instinct. By the time you proof read your own work, your brain already knows the destination.
A good word is used in that passage: generalization. It's this generalization that helps you decipher the gibberish passage above—but which also, sometimes, prevents you from correctly interpreting what you're reading.
I know of no real scientific word for what you've described, but I'm going to call it generalization.
Generalization is one of the reasons that copyeditors need to have their own work edited. I happen to be a copyeditor and I'm very good at spotting problems in other people's work. But while I make fewer mistakes than some others might, I still miss more errors in my own writing that I do in anybody else's.
The reason for this is that when I'm writing, I already know what I intend to say. So, my mind automatically assumes that what I've written is correct. Even after the fact, when I proofread myself, I might still assume that I've written underserved (and read it that way because it's what I expect to read) even though, in actually, my fingers had inadvertently typed undeserved as the more common of the two words.
