Illusion – Fixed objects move before your eyes

Sandrine Ceurstemont, video producer


You may think it’s easy to perceive an object’s location. But a new illusion created by Peter Tse from Dartmouth College, New Hampshire and his team shows that surrounding motion can trick our brain.

While looking at the animation above, pay attention to the moving layer of black dots while keeping your eyes fixed on the blue dot in the middle. When a pair of red dots is flashed on screen, how are they aligned? Now switch your focus to the spinning white layer. Do the red dots appear in the same place? Finally, look at the blue dot without focussing on either spinning layer and note the position of the red dots.

When paying attention to the black layer, the red dots should appear slanted to the left and when looking at the white layer they appear to be skewed to the right. But when the layers are ignored, the dots seem to be aligned vertically – which is in fact their true position in every case.According to the researchers, the illusion is the strongest example to date for how attention can affect our perception of an object’s location.


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By using an identical stimulus with different layers to pay heed to, it clearly demonstrates how an object in a fixed place can appear to move around. For the effect to occur, the objects must be presented very briefly, there must be motion around them and they should appear at the moment when the surrounding motion is reversed.The researchers haven’t yet figured out why we perceive this illusion but Tse has a theory. When we look at a scene where there is movement, he thinks that our brain accounts for the motion to compute the location of objects. So if an object quickly appears before our eyes, it’s unclear whether it’s part of the moving scene or not. Tse says:In a sense the motion information sweeps the computed position along with it. If the object appears for a longer period of time, our brain is able to determine its correct position since there is no ambiguity about whether it’s part of the moving surface or not.

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This illusion was one of the finalists in this year’s Illusion of the Year contest, held in Naples, Florida. You can see more illusions from the contest here.





New Scientist TV: Friday Illusion: Fixed objects move before your eyes.

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