Optical and cognitive illusions are created by our brain taking shortcuts. These occur all of the time in a myriad of ways but can be highlighted through the visual tricks that we are all aware of. One fascinating theory about why they occur is the neural lag, the brain takes 1/10th second to create an image from the time that light hits our retina, so the brain compensates by generating images of what will happen 1/10 second into the future. Optical Illusions occur when it gets it wrong.
‘In a photo of a distant scene, all distant objects are perceived as smaller than when we observe them directly using our vision.
We don’t see a physical image of the world; we see objects, and the physical world is not itself separated into objects. We see it according to the way our brain organizes it. The names, colours, usual shapes and other information about the things we see pop up instantaneously from our neural circuitry and influence the representation of the scene. We “see” the most relevant information about the elements of the best 3D image that our neural networks can produce. The illusions arise when the “judgments” implied in the unconscious analysis of the scene are in conflict with reasoned considerations about it.’