By: Urvashi Balasubramaniam.
“All that we see or seem is but a dream within a dream.”
― Edgar Allan Poe
Everything you have ever seen in your life is a figment of your imagination.
Neuroscience proves that our sensory experience is constructed entirely by our brains, and by the same parts concerned with dreams, hallucinations and memory failure. So how much of what we see is real, and is any of it?
Our brain paints a picture of the world around us with incomplete information, and it does so without us noticing. The brain uses prior knowledge and assumptions to construct a logical piece and finish the jigsaw puzzle of sight. This remarkable process helps us see without staring at our noses all day, and covers up gaps in our vision like the famous 'blind spot' where the optic nerve blocks the retina of the eye.
Interestingly, if it weren't for the brain fixing images on the go, we would see the entire world upside down. It's true! René Descartes, a French philosopher and scientist with gorgeous luscious locks, actually proved that since our retinas are concave lenses, the images produced on it are inverted, or flipped upside down. The brain turns these images right-side-up while simultaneously performing thousands of other functions like keeping you alive and making sure you don't forget your car keys.
Over the centuries, however, we've discovered a few glitches where the almost perfect functioning of our senses go awry. A quick litmus test to see one of these glitches is an optical illusion, in which our brains misinterpret a picture based on informational clues in it.
The first image here shows a gradient bar surrounded by a gradient background, but if you cover the background you'll notice that the bar is monochromatic. Why? Your brain thinks there are two light sources in the image, deducing that the left end of the bar is a light grey object in dim lighting and the right end is a well-lit darker object. This explanation also holds true for the muffin holder in the second image.
You need to be able to determine what protrudes and what caves in to survive in the wild. Sharper objects look different under light, and so you're brain behaving this way isn't a quirk, but an ability.
Optical illusions operate on cues that our brains pick up from visuals and form assumptions around. The odd and exciting quality of illusions, though, is that even if we are aware that what our brain is perceiving is false, we see it that way anyway. For better or worse, there are certain ways that we see the universe that we simply cannot influence or correct.
We recognise illusions when they're presented to us, but we experience so many illusions in life that we take for granted. Ever wondered why artwork of still life looks like, well, an actual still life? Shading, colour and brightness significantly affect how we see depth, which is why we can look at a flat, two-dimensional image and see it as three-dimensional.
Knowledge of how the brain perceives the world is a growing field, and we’re yet to find out what applications it could have in the future. Could we manipulate the world around us for our own benefit? Definitely. Artists and designers have already discovered how illusions can be elements of joy in our mundane urban spaces. One of its interesting applications is in safety. The zebra-crossing illusion (on the right) uses colour and shading to make it seem that the crossing is a solid set of objects levitating above the ground, causing the driver to stop while making a statement about the importance of road safety.
What about colour? If you’re like most people, you have a retina, a paper-thin layer of cells at the back of your eyeball, with two light-detecting types of cells, or ‘photoreceptors’ in it - rods and cones. Rods work in low-light conditions to help you see, but since they don’t have colour-specific light detectors, you can’t see any colour in the dark. Cones, however, are of three kinds roughly corresponding to the colours red, blue and green. When you look at a colour, the cone that corresponds to it sends a distinct signal to your brain for it to recognize.
From a physics aspect, colour depends on the frequency of a light wave, and so the frequency of yellow light is what makes it yellow. But here’s where it gets tricky. We don’t have specific cones to detect yellow light in our eyes, so what do we do? Well, yellow is kind of close to both red and green, so both the red and green cones in your retina send signals to the brain and you see the colour yellow. This is true whether you’re looking at an actual yellow light or the overlap of red and green light, which is why overlapping the colours on a screen can look like a new colour altogether.
People suffering from colour blindness have a weakness in their photoreceptors, usually green, so they lose the corresponding sensitivity to the shades of green that they would otherwise be able to distinguish. Some may also be 'tetrachromats', meaning 'four colours', characterised by a heightened sense of colour owing to their extra colour photoreceptor.
Colour illusions like the infamous dress illusion, however, are based on how the brain interprets its setting and a concept called ‘colour constancy’. Colour constancy is when your brain interprets colours differently under varying conditions of illumination. It’s what helps your brain distinguish between (or sometimes fail to distinguish between) actual dark colours and shadows.
So is anything you see real if it's all in your head? To paraphrase JK Rowling, of course it is happening inside your head, but why on earth should that mean it isn't real? This may comfort you or shock you, but there is something truly magical in the fact that no one in the universe can see it from your eyes.
Thomson, G. and Macpherson, F. (September 2017), "Ebbinghaus Illusion" in F. Macpherson (ed.), The Illusions Index. Retrieved from https://www.illusionsindex.org/ir/ebbinghaus-illusion.