Superimposed flashed probes. The two discs, one red and one blue, always flash at the same location but when the moving frame is visible, they are pulled to the left and right by almost as much as the frame’s displacement. This is not affected much by fixation (try fixating the corners of the movie).
• The red and blue flashes are always at the same location.
• When the frame is present and moving, the blue flash may appear to be to the left of the red.
• The markers above are adjusted to match the perceived separation.
• The frame will fade out briefly to reveal that red is physically superimposed on blue.