This is an interesting thread as it pertains to the visual trickery where putts seem to break uphill.
There is a road I drive on occasion that goes thru a small mountain range. In one section, there is a portion of the road where you swear you are going downhill, yet the water is running in the opposite direction verifying you are indeed driving uphill.
I noticed there are two ridgelines in the distance which are easily seen on this section of road. One is a few hundred feet away, and another ridgeline is perhaps a 1/2 mile away. Both of these ridge lines slope away from the driver, meaning its higher closest to me and drops down for the next mile or so. I'm guessing this is what gives the illusion that one is driving downhill by noticing these downward sloping ridgelines, even though still ascending the canyon.
I've tried to think of examples of how this is acheived on the course and Tom D describes it best I think....its a perception problem from what your eyes are telling you by looking across the horizon, and what you see by looking at the contours immediately in front of you.