Which is bigger illusions

Which of the two red circles 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. So the left one is also seen as nearby, and the right one farther away.

From the scans, they were able to assess the size of the visual cortex. They found that people with a smaller visual cortex experienced the Ebbinghaus illusion more strongly. Schwarzkopf suggests that this is because the circuits in the visual cortex responsible for the illusion are the same size in everyone, but cover a greater proportion of a smaller visual cortex, causing a stronger effect.

The team also found that people with a smaller visual cortex tended to have bigger brains overall, though it is not clear why.

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.

The illusion rests on the fact that the visual-attention system uses context to determine the size of objects. The orange circle on the left is surrounded by larger circles, making it seem small by comparison.

The one on the right is surrounded by smaller circles, making it seem big. Interestingly, adults who fall for the illusion visually tend not to succumb if asked to reach for the two objects.

Although their eyes are telling them that the circles are different sizes, their grip size is the same in both cases. This has been used as evidence that there are two separate pathways for vision in the brain, one used for identifying objects and the other used for action.

The illusion feels fast and automatic yet is surprisingly susceptible to individual differences. Although most people across cultures experience the illusion, it is stronger for those from Japan than those from the UK. This cultural difference interacts with other factors: the effect is stronger on average in women than men though there is massive overlap and in social scientists than in mathematicians. These differences are thought to rest on processing style.