A powerfully engaging essay on the nature of mind and the perception of time over on Edge by David M. Eagleman:
Try this exercise: Put this book down [or just stop reading the screen] and go look in a mirror. Now move your eyes back and forth, so that you’re looking at your left eye, then at your right eye, then at your left eye again. When your eyes shift from one position to the other, they take time to move and land on the other location. But here’s the kicker: you never see your eyes move. What is happening to the time gaps during which your eyes are moving? Why do you feel as though there is no break in time while you’re changing your eye position? (Remember that it’s easy to detect someone else’s eyes moving, so the answer cannot be that eye movements are too fast to see.)
Not only does our perception of time vary under different conditions, different sensory inputs do not slow down to the same subjective time:
Duration distortions are not the same as a unified time slowing down, as it does in movies. Like vision, time perception is underpinned by a collaboration of separate neural mechanisms that usually work in concert but can be teased apart under the right circumstances.
This is a fascinating and SF-mineworthy area of research.