How many colors in this image? Here is the science behind the illusion that divides Twitter

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Now that the trash fire of 2020 is in our rearview mirror, social media is returning to some serious talk that really matters. Like the number of colors of a thing. Again.

Earlier this month, a classic optical illusion was posted on Twitter with the question “How many colors do you see?” The poster saw three.

Others responded with numbers like high than 17. And tens of thousands of comments followed in a heated debate over what the “real” number should be.

At ScienceAlert, we don’t have a strong opinion on the number of distinct bands in the image (that’s 11, right?). But we can help you better understand what is likely going on.

While it’s difficult to say for sure, the phenomenon at work is most likely due to an effect first described about a century and a half ago by Austrian physicist Ernst Mach, the same scientist who lent its name to the unit comparing the speed of an object with the speed of sound.

Only in this case, Mach’s interest had less to do with speed and more to do with eyesight. While working as a professor of mathematics and physics at the University of Graz in the 1860s, he developed a deep interest in optics and acoustics.

In 1865, he became interested in an illusion similar to the one that amazes us all now – similar colors in slightly contrasting undertones becoming easily recognizable when touching, but more difficult to distinguish when separated.

Mach’s understanding was that something bizarre was going on inside the eyeball, specifically in the photosensitive tissue making up the retina. Later, these shaded bands would become known as the Mach bands in his honor.

Remarkably, his speculations were quite relevant. Research using technology better than what Mach was hoping to gain access to has since confirmed the mechanics behind this bizarre twist of the eye as a retinal behavior called lateral inhibition.

Here’s the 101: your retina is a bit like the movie screen, picking up the light projected through the pupil. This screen is covered with receptors, some of which will react more vigorously under brighter light and send a barrage of signals to the brain.

If we imagine two cells sending two very similar signals to the brain, we could just assume that they are of the same shade. Our brains love shortcuts, and in a busy world there really is no time to split our hair.

But nature has come up with a clever trick to help our brains more easily distinguish patterns among similar shades. Whenever an individual light-sensitive cell sends out a signal, it tells its immediate neighbors to shut up.

This competition makes little difference between groups of cells that are all screaming and whispering as loud as each other.

But when a quieter group of cells, reacting to a darker shade, are found right next to noisy cells, this inhibitory influence on cells right at the border forces them to respond in unique ways, effectively improving the difference between them. nuances.

inhibitory receptor diagram(ScienceAlert)

The diagram above can help to understand what is going on. Brighter light causes receptors to trigger the corresponding nerve cell more intensely. At the same time, each photosensitive cell deadens the nerves of its neighbors.

The result is that nerves on the border between different shades send signals that enhance the difference, providing a clear border signal that your brain can pick up.

This ability plays a role in a variety of optical illusions, including an infuriating “glittering grid” of dots you can never really focus on.

While lateral inhibition explains why our eyes can distinguish similar shades better when side by side, it doesn’t quite explain why some of us can not distinguish between colors of barely contrasting brightness, as in this illusion.

Inhibitory influences in our cells can be something we all experience to varying degrees, but it’s also unlikely to be the only factor that tells our brain how to interpret an image. Many of them will be unique to our eyes, brains, computer screens, and surrounding environments.

Surrounding light sources, differences in the brightness of our screens and monitors, and even the precise cellular makeup of our retina will vary. Our brains will also add a level of correction in their own way based on their experience and wiring.

Considering so many variables, it’s to be expected that we won’t all agree on exactly where one shade of pink ends and the next begins.

It’s all fun and entertaining on Twitter, but understanding more about how our retinas enhance the differences in the shades that fall on them can help us find ways to improve our vision.

Now keep in mind that we don’t claim to be the optics experts at ScienceAlert. These are all speculations from a science writer who happens to have a deep love for the psychology of illusions.

But we do know that beyond the questions of how many colors (or, more precisely, hues, tones, tints, and shades) are in the rectangle, there is a fascinating biology that can tell us a lot. on what we have in common.



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