First, observe the alignment of the red circles as they move in a straight vertical path, up and down. Then keep your gaze on one of the three Xs in the middle. What do you notice?
The red circles seem to drift away from their true physical trajectories, as if they were following the curves of the static lines. This perceptual shift is known as the “Mainz-Linez Illusion“.
When you keep your gaze on the central X, the moving dots shift into peripheral vision, where spatial resolution is limited and detail is reduced. The visual system compensates by interpolating missing information based on contextual cues and prior experience. As a result, the dots become perceptually “bound” to the nearby curved lines, as if threaded on them, and their straight vertical motion is misread as oscillating.
The Mainz-Linez phenomenon reflects a broader principle: peripheral vision is largely constructive. Under certain conditions, this predictive filling-in can also distort motion judgments in real-world tasks—such as driving—where events in the periphery may be misperceived.