The term is pace recognition. The professionals are exceptionally good at it, the not-so-professional are hit and miss. The experts will say it is because we have become so reliant on the pace indicators on our watches that we have lost our innate ability to gauge our speed over long distances. I'm not sure I was ever that good prior to my Garmin, but I do know that I find myself looking to my wrist about every .2 of a mile, just to reassure and readjust my pace. That can't be good.
One sign of how bad I am at nailing the right pace without my watch, is how good it feels when I do run a few miles completely tuned in to a consistent rhythm. The watch's pace per lap never changes and the miles are within a second or two. I think that must be how the greats feel over the course of a full race.
So what to do about it? Well, like most everything we do, if we want to improve we practice. If you can resist the temptation, (and I confess, I have hard time doing it), wear the watch, but DON'T LOOK! Run a 6 miler and then study the splits. Think about keeping an even effort throughout. Eventually you will know how a 9:00 pace feels, or a 7:30, or whatever pace you are trying to maintain.
Of course, as seen with my pace chart below, even while wearing and watching the Garmin, it takes discipline and focus to run the splits you have trained for. If you were to compare the range of splits on my run below with those of the Olympic Marathoners, it would be night and day. Mine are all over the place, while they can hammer out mile after mile after mile of split times that are within 5 seconds of each other. I guess that's why I have a day job, and they are Olympic Marathoners, huh?