Explained: How human brain perceives optical illusions 

Look carefully at the image that you just saw. The columns initially appear to be chess pieces for a board game. However, if you focus on the empty area between them, you can see that the space resembles human beings. This is what we call an optical illusion. The Phaeno Science Centre in Wolfsburg, Germany, is home to these columns. In 1989, David Barker, an English physician, created them for the first time. 

Optical illusions trick our brains into seeing false images using colour, light, and patterns. Our brains are developed to recognise patterns and make associations through interactions with the real-world environment. It is a survival instinct! Science experiments around optical illusions reflect that our brain associates visual inputs like shapes, sizes, colours, and geometric patterns with the reality of the physical and interprets them accordingly. Let us dive deep into three well-reckoned optical illusions to figure out how our brain perceives them. 

Ames Window 
This is an optical illusion experiment, created by Adelbert Ames, Jr., an American scientist sometime around the 1950s. Here, a trapezoid (a geometrical shape with four sides with one pair of parallel sides) window rotates on a vertical axis with the help of an electric motor. The motor is connected to the window via a rod on which the window is mounted. However, the window appears rectangular when observed from the front. Moreover, if you look at it with both eyes from a distance of 6 metres, your brain perceives it to be oscillating, reversing its direction once every 180 degrees. However, the reality is that it is rotating in a single direction without any change. Well, what does this indicate? Our brain interprets things that the eyes see in a way that is closer to reality. In the real world, windows are rectangular, not trapezoid. Also, they oscillate on a windy day, moving back and forth. But they are never seen to rotate, isn’t it? 

Troxler Effect  
You may have seen posts on Instagram telling you to keep your eyes fixed at the centre of a hazily visible area without blinking. So, what do you observe when you wait a short while? Does the image start to disappear? And you only see the point of focus? This is called the Troxler Effect, which explains the brain’s ability to focus on one thing and eliminate the clutter around it! In 1804, Ignaz Paul Vital Troxler, a Swiss physician, initially identified this visual phenomenon and it was named after him. It illustrates how the optical system responds to sensory information. It happens because neurons stop responding when a stimulus is constant. In this case, the static hazy image in the background causes the image to disappear from your consciousness! 

Kanizsa Triangle  
In this optical illusion, your brain sees a white upright triangle with three equal sides where none exists! Also, the imaginary triangle is brighter despite having the same luminance as the background. This phenomenon, described by Italian researcher Gaetano Kanizsa in 1955 is called the Kanizsa Triangle! According to Kanizsa, this illusion demonstrates how we often look for completeness in our visual perception. The foundation of this experiment is that our brain automatically fills in spaces between forms and lines. It thinks of space as an object even when there are none present. In other words, Kanizsa’s triangle serves as an example of how experiences, rather than only sensory input, shape our view of the world. It’s amazing!