How many colors in this image? Here’s The Science Behind the Illusion That Shares Twitter

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Now that the 2020 bin-fire was in our rearview mirrors, social media is back to serious debates that really matter. Like how many colors a thing has. 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 up to 17. And tens of thousands of comments followed in a heated debate over what the “true” figure should be.

Here at ScienceAlert we don’t have a firm opinion on how many different bands are in the picture (there are 11 of them, right?). But we can help you provide information about what’s probably going on.

Although it is difficult to say for sure, the phenomenon in the work is probably due to an effect first described a century and a half ago by the Austrian physicist Ernst Mach, the same scientist who gave his name to the comparing unit. the speed of an object with the speed of sound.

Only in this case did Mach’s interest have less to do with speed and more to do with sight. 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 we all marvel at now: similar colors of slightly contrasting hues that are easily distinguished when touched, but more difficult to distinguish when separated.

Mach understood that something strange was happening inside the eyeball, specifically inside the photosensitive tissue that forms the retina. Later, these shaded strips will be known as Mach Bands in his honor.

Surprisingly, his speculations were pretty amazing. Research using a better technology than he ever expected to have access has since confirmed the mechanics of this strange eye trick as a retinal behavior called lateral inhibition.

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

If we imagine that two cells send two very similar signals to the brain, we could simply assume that they have the same shadow. Our brain loves shortcuts and, in a busy world, it really doesn’t have time to split hairs.

But nature has developed a clever trick to help our brain more easily distinguish patterns between similar nuances. Whenever a light-sensitive cell sends a signal, it tells its immediate neighbors to shut up.

This competition makes little difference between groups of cells that scream and roar as loudly as the others.

But when a quieter group of cells, reacting to a darker shadow, sits right next to strong cells, this inhibitory influence on the cells just at the limit forces them to respond in a way. unique, effectively improving the difference between the shadows.

diagram inhibition receptors(ScienceAlert)

The diagram above can help you understand what is going on. A brighter light causes the receptors to activate their corresponding nerve cell more intensely. At the same time, each light-sensitive cell dampens the nerves of its neighbors.

The result is nerves on the border between different shadows that send signals that improve the difference, providing a clear boundary signal for the brain to pick up.

This skill plays a role in a wide variety of optical illusions, including a mesh “twinkling grid” of dots that you can never stare at.

While lateral inhibition explains why our eyes can better distinguish similar shades when they are next to each other, it does not fully explain why some of us he can not differentiate the colors from the brightness with few differences, as in this illusion.

The inhibitory influences of our cells can be something we all experience to a great extent, but it is also unlikely to be the only factor that explains to our brain how to interpret an image. Many of which will be exclusive 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 cell composition of our retina will vary. Our brains will also add a level of correction to their unique way based on their experience and hard wiring.

Given so many variables, hopefully we won’t agree on exactly where one shade of rose stops and the next one begins.

All of this is fun and games on Twitter, but understanding more about how our retinas improve differences in the tones that fall into them can help us find ways to improve our vision.

Now, keep in mind, we don’t intend to be optics experts here at ScienceAlert. All this is the speculation of a scientific writer who has a deep love for the psychology of illusions.

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

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