How Do Optical Illusions Work?

Surprising, astonishing, frustrating, and viral. Optical illusions have divided the Web over the color of a dress, but beyond the general disagreement, the question is: Why does this happen? How exactly do they work? As we have confirmed on previous occasions, it is a combination of the eyes with their natural limitations, and the brain that, in the name of speed begins to assume things incorrectly.

Some time ago we talked about the optical illusion of the twelve black dots that cannot all be seen at once. The official explanation is that this illusion challenges the limits of peripheral vision, but our brain also enters the equation, which concludes that the gray grid extends... when in reality that is not true. Why the need to “fill in”? Before moving on, we must first go through the so-called blind spot. We all have one, as do most animals, with the exception of squid and other mollusks.

The video gives us an excellent example to detect our blind spot. But why is it there? Let's say the eye is designed that way. The blind spot is the place where the optic nerve crosses the optic disc. That place lacks photoreceptor cells (cones and rods), so a small portion of the visual field becomes invisible. Consequently, the brain decides to cover the gaps, and its effect depends on the type of environment surrounding each object.

In the blind spot test we notice that the circle disappears; however, the brain decides that the line continues. This happens because of its tendency for “speed over precision”. The same applies to sentences with spelling mistakes or redundant words: despite the errors, comprehension of the text is not affected, and the brain's decision is to ignore what is wrong.

In short: the eyes-brain combo has evolved with the aim of improving our vision, but it makes assumptions based on memory, prior learning, and expectations. Optical illusions simply push those parameters to the limit, though they do not always succeed. Some people have proven to be almost immune to them...

Source: