Whenever I read Runners World magazine or a running blog I subscribe to, I am often barraged by pieces of research showing brain games that runners listening to music tended to recover quicker or run more efficiently in some recent studies, and I listen to music a great deal when running, particularly on my longer runs, it helps me pass the time and I enjoy the absorption in the music - this is dissociation. It is me classically distracting myself from the detail of how I am really feeling, like when you are battling through fatigue or aches at mile 25 at the marathon and using whatever you can to get you through to the end. Music has other ways it helps us, with being uplifting and inspirational and having an emotional association that aids us, but it also can distract and aid dissociation.
However, the earlier mentioned study by Morgan (1977) showed that despite the prevalence of such these dissociation strategies were not the main "cognitive strategy" among elite runners. In fact, they tended to use an associative strategy.
So these elite marathon runners stated that they actually paid very close attention to their own bodies and especially noticed what happened within their legs and feet as well as monitoring their breathing closely.
They also did keep a note of time, heck these are elite runners, I watch my Garmin GPS watch a great deal, but these guys are watching it with more interest than I am! However, they generally stated that the pace they adhered to was dictated by how their body felt.
When marathon racing, these elite runners also tended to instruct themselves to relax and keep the muscles loose throughout the race. They tended to be people who dealt with anxiety very well outside of running and though there was much, much more to the research, these are the bits relevant to what I am writing about here.
It is far more common to think of runners using dissociative strategies, but these studies all do highlight the fact that runners who excel are mentally active in some shape or form while running. I hope you realize that and at the very least see the benefits of that.
One such cognitive strategy then, as already suggested here is that of 'association' and this is particularly prevalent with introverted elite distance runners. I suspect that most people who read this article are not elite runners, so we may not have as much awareness of ourselves when running. Those of you that have only been running for a short period of time may not know your own limits or how to spread out your exertions within your long runs as well as elite runners who rely on such awareness.