I was watching a short documentary the other day on this very topic, and it was rather interesting and applicable to combat sports in a number of ways.
Now the actual program was focused on the revolutionary treatment method for people who have had strokes or accidents denying them the function of a limb for example, were being taught to regain function in that limb by immobilizing the working limb and being forced to use affected limb, thereby forcing the brain to create new neural pathways. (or as I understood it)
Half way through the program there was a section where they were talking about a study that had a control group practice playing a piano with the goal of rapidly improving the speed at which they could press the keys. The 2nd group was sat down in front of a piano, not to play, but to visualize themselves doing the task of the other group. After a few weeks both groups showed significant improvement in their key speed.
This lead to a expert talking about how just through imaging yourself doing an activity, you were slowly creating new neural pathways. (again as I understood it :P)
Now I've never been a big on visualization/meditation but this does lend some credibility to the concept in my mind. Although I do still think crap like "visualize yourself with your hand held up at the end of the fight" is a waste of time, but visualizing yourself performing techniques or dodging etc may have some merit.