“The human eye sees things upside down, and the brain flips it.”

Many people are fascinated by the way our eyes capture the world around us, and it's a confirmed scientific truth that the lens of the human eye, much like a camera lens, inverts the image that falls onto the retina. This means the image projected onto the light-sensitive surface at the back of the eye is indeed upside down and reversed from left to right due to the basic physics of how convex lenses refract light. This optical phenomenon was famously demonstrated in the 17th century by René Descartes, who used an excised bull's eyeball to show the inverted image.

Despite the inverted image on our retinas, we don't consciously perceive the world upside down. This is thanks to the remarkable processing power of our brain. Rather than physically "flipping" the image, the brain interprets the complex patterns of nerve signals it receives from the retina. Through lifelong learning and by correlating visual input with other sensory information, the brain constructs our perception of an upright and correctly oriented reality. It simply understands what "up" and "down" mean based on consistent visual input.

The common belief that the eye sees things upside down and the brain then flips it stems from the seamless and automatic nature of this neural processing; we are never consciously aware of the initial inversion. Compelling evidence for the brain's role in interpretation comes from experiments where individuals wear special goggles that invert their vision. Initially, the world appears upside down, but after a few days, the brain adapts, and subjects begin to perceive things as upright again, demonstrating its incredible flexibility and ability to recalibrate our sense of orientation.