For years, I've been calling the phenomenon where my brain works faster than my mouth Progressive Dyslexia. The time delay that occurs between what I'm thinking, what's next and getting what I'd already thought to come out properly causes problems for me once in awhile. I'll transpose words, fumble syllables or flat out forget what I was going to say because my mind has already moved on.
I've noticed recently, that the same works for when I'm typing. I'm not sure whether I type too slow or think too fast, but I'll frequently type "me" when I meant "my" or, for instance, when I was typing something earlier today I said wrote "six months" when I distinctly heard my mind say "six weeks." But, I never catch those things unless I go back and proofread.
Strange. I'm a crazy grammar snob, so making these errors irks me to no end!
At least I don't mix up their/there, your/you're and its/it's. Maybe that's another thing that we should add a test for... you aren't allowed to participate online unless you know when to use the proper form of the word.
It took my years to learn how to spell commitment (committment) properly, but that's a whole different story. *wink*
LOOK, I just did that damn my/me thing in the last sentence! GRRRRRR.