Optical illusion which is bigger

One of the most elegant demonstrations of how context effects size perception is the Ebbinghaus illusion. You can have a go at creating this illusion yourself. Draw around a 5 pence piece twice. Around one of the circles place a ring of very small circles. Around the other, draw around a 2 pence coin five or six times, as shown below. Do either of the two circles in the middle look bigger? Ask somebody else which of the two middle circles they think is bigger. Here is what the illusion typically looks like:.

Almost everyone who sees this image will say that the central circle on the left is smaller than the one on the right. Which line red or blue is longer? Of course, none - they are equal. The lower figure appears larger, however, both figures are identical.

Also called Titchener circles depicts relative size perception. Which central circle is bigger? The one on the right, right?

In reality, the pair are identical. From a lifetime of looking at things, we remember that smaller items tend to be farther away, while larger ones are closer. In this image, the brain reads the left ring of large, black circles as nearby and the right, smaller set as distant.

Simultaneously, the brain also groups the red circles with their black surroundings. Your eyes know your brain will rely on monocular cues! If you close one eye and look around, you can perceive depth, but size and distance are ambiguous. Now open both eyes. Another interesting point about the Ebbinghaus illusion is how much it relies on familiarity with cues in printed images.