I make typos. A lot. It is amazing the number of people who believe there is a strong correlation between intelligence and typing accuracy. And that’s what we’re talking about, here; it often isn’t spelling that is at issue. There is no such connection.
Now, it’s not that I don’t think correct spelling is important, I do. No one gets more irritated at me that I get at myself when I make a typo, trust me. As much as it may amuse or exasperate you, I am ten times as angry at myself when I find them or have them pointed out. Plus humiliated. I want to spell things correctly.
And most of the time I do. And sometimes it is not spelling correctly that’s the problem…
I learned to type at an early age, using my mom's old typing class textbook. Which means that I spent hours typing sequences of words, each word correctly spelled, but the sequences were nonsense. The goal was muscle memory. All common words should be automatic. Rather than seeing, hearing, or thinking the word "what" and then thinking "double-u, aitch, aye, tee" as we type, you want to just think "what" and have lower level neural functions tell which fingers to go where.
The problem is that that lower brain function, in my case, filed lots of words really closely together. That, this, thus, their, they’re, there, the, to, two, and too seem to all be in the same compartment in my brain, so when I’m typing fast, if I intend to type one of the words on that list, it is just as likely that another word is what my fingers will type, instead.
Other words seem to be filed by sound. Certain words that sound sort of similar seem to be interchangeable as far as my fingers are concerned. Our and hour, for instance. When I make one of those errors, I sometimes joke that didn’t realize that my fingers have ears of their own. I know the truth is that language is stored as remembered sounds first. Most of us learn to speak and hear language before we learn spelling. For me, I hear the words in my head as I’m composing sentences. I’ve known people who say that they see the words in their imagination, but I have to stop and make myself do that. My natural process is to hear language in my imagination.
Then there are the words that are only off by a letter, often the final letter, such as show and shoe or an and and.
Another category are suffixes. When I am zooming along on the keys and am typing a word with a suffix (such as -ly or -ing or -ed) it’s like there’s a separate subroutine in my head for suffixes. I will think talking, for example, and my fingers may type talked. It makes for some interesting constructions.
One time I got into it with a guy who absolutely insisted that the word typo can only be used for errors when the keys on the keyboard are close together. On a qwerty keyboard, for instance, the R-key is right above the F-key and both are typed with the left index finger in standard typing, right? Which is why I am constantly typing or when I mean of and vice versa.
This guy was really, really insistent. And he absolutely did not understand the concept of whole words being in muscle memory. He was very skeptical, and even when several other people chimed in to explain that that is also how they learned to type, he seemed to think we were either all crazy, or lying just to mess with him.
This whole discussion occurred on an online forum, so people were posting links to sites about learning to type and such. As we attempted to convince him this was true, we somehow got on the topic of typing speeds. One thing led to another and then we all went to this one site where you could do a typing speed test. It used the standard speed test rules: 1) calculate your average words per minute as you retyped a passage it showed you, 2) subtract one word from your average for every mistake you made in the passage.
He was quite proud of himself for having a speed of 50 words per minute. Particularly since he had read someplace along the way that 40 words per minute was considered typical.
It was a good thing we weren’t in the same room, because I laughed out loud at his score.
Other people involved in the discussion posted their scores. And the folks who had talked about learning to type the way I had started posting their scores, and all of them were above 60.
And then I posted mine.
105 words per minute. And please note, that is after subtracting the errors.
Font Folly 
Thinking of the letters in a word tend to slow me down… So I completely understand the whole-word typing phenomena. I usually see words if I’m actively trying to write or am asked to spell. Otherwise, I can’t consciously tell how my brain is processing them. I’m used as a human dictionary at work, so quite often I’ll just sit down and type what I’m asked to spell, close my eyes and recite what I “see”, or even hand write… although that’s the least reliable of the methods. My parent’s best guess for how I learned to do that was reading at a very young age. Words it doesn’t work as well on are ones I’ve read first and invented my own pronunciation for. đŸ˜› Even if I’ve learned how to say them correctly later.