How does an optical illusion work?

We have all been fooled at one time or another by an optical illusion? This illusion transmits a distorted reality to us by disturbing our visual system.

But how exactly does it work?

The optical illusion is a visual construction that disturbs our visual system, from the eyes to the brain.  Indeed, our brain constantly adapts the light information of a point to what surrounds it. An erroneous interpretation of the information causes this illusion: our brain gets confused about the colour, the size or the straightness of a line.

This phenomenon would be linked to the evolution of our cognitive performance to ensure better survival of the species. So, the brain prefers to interpret information early, even if it is wrong, rather than too late.

Different types of optical illusions

There are several types of illusions:

  • Artistic illusions: where artists deliberately seek to deceive or sow doubt by using particular techniques. Painters such as Dali and Arcimboldo have used them in some of their works.
  • Geometric illusions: where the arrangement of points, lines or simple shapes leads to misinterpretation. For example, two identical objects look different because of what surrounds them.
  • Impossible illusions: where objects are represented that cannot exist because they are contrary to the physical laws we know.

Optical illusions, just a game?

If these illusions are often a form of entertainment, they also allow us to better understand how our visual system works and, in particular, how our brain processes information.

Indeed, in order to see reality, the brain is faced with two major obstacles:

  • First, it must understand the complexity of the world around it. Thus, objects that are partly hidden or intertwined with each other will be more challenging to interpret.
  • Furthermore, our sensors (eyes) and retina are not perfect, and their capacities are limited.

Consequently, to interpret the world and what is happening in it, the brain gradually builds a "toolbox." This toolbox brings together experience, culture and what surrounds what we are trying to interpret.