Series "Optical illusion" - Curved lines? - Germany / Federal Republic of Germany 2019 - 60 Euro Cent

There is no human being who is not occasionally fooled by an optical illusion. Whether it's the car wheels in the film, which seem to turn backwards, or roads which seem to go downhill, even though they actually lead uphill. The causes that fool the viewer are always to be found in disturbances of visual perception. In other words, all optical illusions are deceptions of perception. This also applies to the motif of this stamp from the special postage stamp series "Optical illusions", which offers a vivid example of the relativity of lines. Seeing something does not mean that what is seen (the "reality") is transferred one-to-one to the brain. Seeing is rather a visual interpretation of the environment, in which biological parameters and previous experiences also play a role. The recording and processing of optical stimuli are complex and susceptible processes in which information can be lost or added. Optical illusions are based on the resulting (mis)interpretations. The fact that the visual system sometimes makes false assumptions about the nature of a visual stimulus is impressively demonstrated by the motif of the stamp "Curved lines?". Do you see squares arranged like a chessboard that stretch out into a bubble in the middle? Far from it: the bubble is an optical illusion! The application of a ruler or a straight object proves that the seemingly curved lines run dead straight. How is this possible? The deception of perception is triggered by the small contrasts, the circles in the opposite colour in the corners of the individual squares. They "blur" the regular chessboard pattern, creating the impression that the dividing lines between the squares are curved. With this optical illusion it is not possible to perceive the chessboard pattern in its geometrically correct form.