Why do we see illusions? This question has sparked a lot of curiosity and research over the years. I’ve delved into this topic and found some intriguing insights that challenge what we might commonly read in textbooks. Let’s take a look at one of the classic visual illusions, for example.

Consider two parallel lines that appear to bow outwards at their centers. When you examine them, you notice that where the radial lines intersect, your visual field perceives the distance to be wider at the center than the parts above and below. This is fascinating because it’s a simple image: just a bunch of straight lines. Yet, our complex brain struggles to interpret it correctly.

To understand why this happens, we need to dive into what these lines signify to our brains. Our brains aren’t just processing lines—they are evolved to process natural stimuli from our environment. This particular illusion mimics what we experience every day when we move forward. When we move, objects in our vision create an optic flow, much like how stars streak past in a sci-fi warp drive sequence. These objects create blur lines on our retina, which mini-neurons process to indicate movement.

Cartoonists cleverly use these blur lines to show motion. While you might not see blur lines in real life, the stimuli hitting the back of your eye create these optic blurs. This tells your brain that you’re moving. As you move forward, your eyes take quick snapshots, creating a flowing outward effect. This effect aids in motion perception.

But there’s more to the story. Our brains don’t instantly create perceptions when light hits our eyes—it takes about a tenth of a second. This delay is significant, especially when you’re moving. Without correction, you’d perceive everything with a delay, which would be quite problematic.

To cope, our brains predict the near future. It’s not just reacting passively; it actively creates a guess of what will happen next. When you perceive something, your brain has already predicted where the object will be a tenth of a second later. This way, your perception is perfectly timed with the present.

In the case of our illusion with the parallel lines, your brain thinks you’re moving towards the center of those radial lines. As you get closer, like approaching a grand cathedral doorway, the sides of the doorway start to bow outwards in your visual field. This change happens because, as you move closer, your perspective shifts, altering the geometry of what you see.

This prediction mechanism explains why static images can trick your brain into seeing motion where there is none. Your brain expects motion and compensates for its perceptual delay, causing illusions. It’s a fascinating glimpse into how our brains strive to make sense of the world around us.

These illusions are essentially failed future perceptions. The static images don’t match up with real-life dynamics, making your brain’s predictive efforts go a bit haywire. So next time you get fooled by an illusion, remember: it’s just your brain working hard to keep up with the fast pace of reality.