For fifteen years now, The Neural Correlate Society (NCS), a non-profit organisation that promotes scientific research on the neural correlates of perception and cognition, and the Bethlem Museum of the Mind in Beckenham (England) have been selecting the best optical illusions of the year. These simple shapes continue to be a fun way to fool our eyes and brains.First prize: ‘Schröder's staircase in 3D’This staircase by Schröder, named after the mathematician who designed it, is an ambiguous 2-D figure: depending on how the steps are looked at, they appear as normal or upside down. In the case of Kokichi Sugihara's staircase, a Japanese mathematician and artist, winner of the 2020 prize, the staircase is in 3D. The stairs go down and then up in the blink of an eye. Two interpretations that are nevertheless particularly visible when the object is rotated 180 degrees. Second prize: ‘The real thing?’Second prize went to Matt Pritchard from Britain (@sciencemagician on Instagram) for his series of illusions. The spectator perceives the reflection of a Coca-Cola can in a mirror. But this is all a misinterpretation. The point of reflection here is an empty frame in which a second can is placed. But even when the elements of the design intended to deceive the eye are removed, the illusion of the mirror persists for a brief moment. A phenomenon that ‘is not yet fully understood,’ the author admits. Third prize: ‘Impossible grid typeface’Created by the Dutch graphic and motion designer Daniël Maarleveld (@daniel_maarleveld on Instagram), the squared shapes seem to be in 3D. However, on closer inspection, ‘nothing seems to add up,’ notes the inventor. Are they rigid or flexible? In which direction do they turn? Difficult to say. The bottom becomes the top, the back becomes the front. Some parts of the letters even seem to turn in opposite directions, in an ‘illogical logic,’ he continues on his site. So, what do you think of the winners this year?