Yesterday, I did a quality two hour trainer workout. As a grad student, I felt obliged to try to get some studying in during the workout. This was no problem during the warmup and some of the early steady state stuff. But as soon as the tempo and power intervals started, I found my focus changing to the workout itself. It was unconscious, and every time I tried to refocus on anatomy, no matter how hard I tried to focus on the rotator cuff and its innervation, within two seconds my mind was back to the workout, either monitoring cues from my body or focusing on my cadence and power.
When you're running, there are a few different ways your mind can focus. Focus breaks down into two main categories, each involving two different types of focus: internal vs. external and association (tuning in) vs. dissociation (tuning out). Internal focus simply means focusing on something from your own mind or body, whereas external focus involves taking cues from outside yourself. Associating refers to focusing on the race or workout itself, and dissociating means distracting yourself from the workout with something unrelated. Therefore, examples of internally associating would involve focusing on things like your breathing, stride, or arm swing. Internally dissociating could involve playing music in your head or thinking about the day. Examples of externally associating are paying attention to lap splits or the time, focusing on your opponents, or monitoring speed and distance on a GPS watch or bike computer. Externally dissociating examples are focusing on the scenery or spectators.
Almost everyone's running involves some combination of the above methods of focus. I doubt anyone is able to use the same kind of focus for every run, workout, and race. Someone who internally associated every time they ran, including easy runs, would likely find themselves mentally burned out before too long. And someone who was only ever externally dissociated would never pay attention to any cues from their body and would probably not perform very well in workouts and races. When I'm racing, I'm usually associated, going between internal and external focus. I usually have a little bit of internal dissociation going on, when I play music in my head, though the better the race is going, the less I'll dissociate (and in my best races, there was nearly no dissociation involved). Quality workouts have a similar distribution, though there's usually a little more internal dissociation involved than during races. I almost never externally dissociate during races and workouts (no wonder studying was so impossible during the trainer workout!). Even when I'm doing a quality trainer workout with a trainer DVD or my iPod, it all fades into the background during the hard segments, and the focus is on the workout itself. On easy runs and recovery runs, the shift moves towards dissociation. I mainly internally dissociate, with some association when appropriate. The only times I actually externally dissociate are when I'm running with someone and talking or when I'm doing an easy trainer spin and watching TV. And once in a while if I'm doing an easy run somewhere really pretty, I'll externally dissociate. Most of the time I completely miss the scenery though, and afterward when someone asks how gorgeous it was, I'll make something up so they don't think I'm completely oblivious.
So what's the best way to focus to maximize performance during a race or hard workout? I'd say that's a pretty personal thing. While there are some very obvious benefits to focusing on the race or workout (both internally and externally), I can think of at least one elite runner who stated in a post-race interview that she sings to herself the entire race. Similarly, I've heard of people drawing strength from thinking of a loved one. Both of those are examples of internal dissociation (though it does raise the question as to whether it's truly dissociating if you're using the song for pacing reasons rather than distraction, as I would bet that the elite runner in question does). And many people say they get energy from the crowd, an example of external dissociation, unless the crowd is actually your coach giving splits or place information, in which case it becomes external association. Additionally, there is the hazard in association of getting feedback and using it in a negative instead of a positive manner. Someone whose breathing is labored or who gets splits that indicate that they're running too slowly can either use that information to modify their racing or can take that information and panic, deciding that their race is going poorly and destroying themselves mentally.
Disclaimer: I read something on this topic somewhere, probably either a Runner's World or Running Times article or something like that, but it was a long time ago (I haven't read RW in years, and it's been a while since I picked up an RT too), and I figure a lot of people haven't read anything about it. Unfortunately, I don't remember much of the article, so this is mainly going off of my own experience and what I learned in an Intro to Sport Psychology class I took senior year of college.