What is an example of a deception

Optical illusion

Our brain tries to interpret something into existing forms in order to make it easier for us to perceive the world. The brain measures what it perceives against what it already knows. In order to get as close as possible to what is known, the brain sometimes simply adds what is missing. This is a good example of this Kanizsa triangle (FIG 1). It is named after the Italian psychologist Gaetano Kanizsa, who studied how we perceive the world.

The amazing thing about the Kanizsa triangle is that there is no such thing as a triangle. There are only three circles, each of which is missing a corner. Since the brain is always looking for known shapes, we don't see three incomplete purple circles - which are there but which our brain does not recognize as a shape - but a non-existent white triangle - which is already known to us as a shape.

The brain always tries to put together a spatial image from the data it receives from the eyes. Sure - we live in a spatial world. This is expressed, for example, in the fact that people who approach us look small in the distance and get bigger as they approach. But we know: people are always the same size! Only spatial vision ensures that the differences in size arise.

That is also interesting Heringian illusion (FIG 2). The German scientist Ewald Hering also dealt with human perception and was the first to show this deception. You can see a lot of lines that cross at a center point and two lines that run horizontally. Are these horizontal lines straight or curved? Look closely! You are straight!

But why do we think they are curved? This has to do with the angles that are created at the points where the horizontal line and the others cross. Our brain has a preference for 90-degree angles, that is, for right angle. Obtuse angles, i.e. those that are larger than 90 degrees, we perceive a little smaller in order to approximate them to the right angles preferred by the brain.

Acute angle, i.e. those that are smaller than 90 degrees, we perceive somewhat larger for the same reason.
Hering's illusion creates a whole series of acute angles that the brain automatically enlarges. What happens then can be clearly seen on FIG 3: the red areas show what the brain is adding. And from these many small, slightly incorrect angle information, the brain calculates a curved (red) line - although it is actually dead straight.