How Your Eyes Make Sense of the World | Decoder

When you look at this painting, what do you see? A woman looking out a window? How about now? This famous painting by Salvador Dali is based on something called the “Lincoln illusion.” The effect shows how blurring pixelated images can make it easier to recognize faces. Optical illusions are fun to look at. But, they can also tell us a lot about our sense of sight.

So, how does the eye work exactly? And is it really true that seeing is believing? The human eye is pretty extraordinary. It has more than 2 million moving parts and can move faster than any other muscle, at less than 1/100th of a second. But when it comes to your vision, the way you perceive the world is actually thanks to your brain.

First, light enters the eye through the pupil. The muscles behind the iris squeeze and stretch the lens to focus the light onto the back of the eye. This is the retina. The retina is covered with sensitive photoreceptors called rods, for dim light, and cones, for bright light. The focused light hits the retina at a small pit called the fovea, which has the highest density of cone receptors.

We often compare our eyes to cameras, but they actually work quite differently. Our peripheral vision is very low resolution. We only see in full resolution at the small point of our fovea. But, we barely notice it because our eyes are constantly refocusing on what we want to see, like a high-resolution spotlight.

Pixels, or picture elements, are the tiny, illuminated squares that make up a digital display. If two pixels are close to your eye, the retina sends two signals for the brain to interpret. Farther away, two pixels prompt one signal. That’s why a TV screen can have a lower pixel density than a smartphone, but seen from farther away, it still appears seamless.

When stimulated, the rods and cones send signals to the optic nerve and back to the brain. Then, all of that visual information is processed to create the picture you see of the world. Unlike a camera, your brain can actually “fill in” missing information. For example, your eyes automatically blink every 3 to 4 seconds. In fact, that means your eyes are technically closed for roughly 10% of your waking hours.

Thankfully, your brain fills in those gaps, so you don’t feel like the lights are flickering on and off all day long. There’s a lot we still don’t understand about the complexities of our visual system. As technologies continue to innovate, the line between illusion and reality could start to blur. And when it comes to how we see the world, there might be more than meets the eye.