Pulfrich Phenomenon - in Detail

This is a top-down view of the swinging pendulum. The viewer's eyes are at the bottom of the screen. The covered eye's signal to the brain is delayed slightly, and thus it sees the ball at a previous position. This disparity causes the viewer's eye to converge on points either in front of, in back of, or on the plane of motion, depending on the eye that is covered and the direction of the ball's motion. Click near either eye to change the location of the filter. Note the movement of the intersection point when each eye is covered.