quarter450

Hi, I was looking at experiment and I was wondering if somebody here could help clarify my understanding of it. I plan on presenting it to my class. It has to do with a pendulum and light filter for one eye (sunglasses). What you do is get friend to swing pendulum (side to side) about 2 meters away. Cover one eye with the filter and look at the swinging, instead of going side-to-side, it should be turning in an elipse. If you switch filters side over to the other eye, the pendulum elipse is swinging in the other direction. How come? I know it has to do with delayed reception of one eye (one w/ filter)vs other eye and then brain connecting the two together which causes the circle to appear, but I don't understand how it changes directions when you switch eyes. Can somebody explain that to me please. Thanks, Bryan