Perceived effort and people watching.

Have a look at this article from RunnersWorld.
A study revealed that male runners perceive less effort when they run with a woman watching.
I'm not going into the psychological and phisiological details on the subject and I can't report personal experiences because I'm not used to run/cycle/etc. with people watching (the occasional dog-walker or mushroom-hunter that you may meet in the woods does not count I suppose), but I think that it's similar to the feeling you get when you're pedalling on the bike lane and there is another cyclist some meters ahead and you feel the urge to cross over him. When you finally leave him behind you feel like you can relax and slow down but... he's crossing over you! So you speed up and don't let him pass so easy... then you both arrive at a traffic light, stop and have a good laugh together.
But in the moment that you feel you have to cross over, obviously you perceive less effort.
May it be considered a minor onset of agonistic trance?
Anyway, have a read to the article and try to focus on your own experiences on the matter. It's always useful to know the mental tricks that happen during training.