National Geographic Channel
National Geographic Channel

5 Color Illusions and Why They Work

National Geographic Channel
National Geographic Channel

Think colors are objective facts? Think again! Color is more subjective than you might expect—it’s really all in your head. These illusions show you how.

1. Checkerboard Illusion

In this illusion, both block A and B are the same color.

Don’t believe it? Check this out.

It’s all because of color constancy, which helps the brain recognize objects regardless of the amount of light being reflected. Cone cells in our eyes help us see color. As these cones register different wavelengths of light, special neurons in the visual cortex try to make sense of the cone activity. Seeing that Square B is under a shadow, your brain assumes that the square must be even lighter than it really is.

2. Chubb Illusion

Another example of color constancy: the left inner box appears darker than the box on the right—although they’re the same color. Both squares reflect the same amount of light into your eyes, but they still appear different because of the context.

3. Scintillating Grid Illusion

This one is pretty trippy. Dark dots rapidly appear and disappear at the intersections. However, if you stare at one intersection, the crossroad remains white.

Scientists are still trying to put a finger on this one. One theory, called lateral inhibition theory, suggests that several photoreceptors in the eye send information to a retinal ganglion cell in the brain. As your brain interprets these signals, the most active brain cells inhibit and reduce the activity in neighboring cells, making them less excited. This creates an unequal black-white contrast.

4. The Cornsweet illusion

Lateral inhibition strikes again! Both panels are the same color. Just cover the fold with your finger to see it.

5. The Bezold Effect

Wilhelm von Bezold discovered that a color may appear darker depending on its context. In this picture, there’s only one shade of red, although the right side appears darker.

Scientists are still puzzled by this one. Some think lateral inhibition is to blame, although many disagree.

What Makes Our Brains Feel Trust?

Trust is part of your brain’s default setting, but the feeling may not be as noble as your teachers made it out to be. Neuroscience has an explanation that relies on a lot of fascinating biochemistry.

In one study, scientists asked 49 participants to play a two-person game of trust. One participant had to act as a broker while the other worked as a trustee. Working together, the two built up a pot of money by investing in each other. But to amp up the risk—and the trust—there was one major caveat: One of the participants could steal all of the money at any moment.

Before playing the game, some of the participants snorted a nasal spray laced with oxytocin. Best known for being the “love hormone,” the scientists suspected that oxytocin also had a hand in making us trustworthy. It seems they were right. Participants who sniffed the oxytocin spray ended up investing more money than those who had inhaled a placebo. It seems the burst of oxytocin had increased their trust.

But the takeaway isn’t so warm and fuzzy. As participants trusted each other more and more, a brain area called the caudate nucleus—one of the brain’s pleasure centers—lit up. As their trust solidified, the caudate became active earlier and earlier. That is, they started taking the benefits for each investment for granted. The researchers concluded that we don’t trust people because it’s some universal moral force. We trust people because it rewards one of the brain’s pleasure-seeking centers. Our brain simply likes getting that oxytocin-laced caudate kick.  

Trust us. You'll want to tune in to Brain Games Mondays at 9/8c on the National Geographic Channel to discover all the astonishing things your brain can do.

Can Stress Be a Good Thing?

It’s an accepted fact that stress is bad for you. But don’t drown in all the hype. In some cases, a little bit of stress can be good for your brain.

Stress May Not Make You Sick

A study of a whopping 29,000 people found that stress isn’t really taking years off your life. Rather, the belief that stress is bad is the problem. Stress, they discovered, doesn’t kill you—your viewpoint does. The study found that people who believed stress is bad had a 43 percent increased risk of death. People who did not believe stress was bad were far less likely to die. So stress may not be making you sick. How you deal with it is.

Stress Helps You Learn

A 2013 study found that a boost of corticosterone (a stress hormone) may help neural stem cells grow in the hippocampus, the brain’s learning center. The team discovered that stressful events could improve the mental performance of rats. From a survival standpoint, that makes sense. In the animal world, remembering a stressful event can help a critter avoid similar, life-threatening events in the future.

Stress Saves Your DNA and RNA

A little dose of stress tells your body to dial up antioxidants to fight free radicals, those pesky molecules that make us age. Ends up, with all that help, acute stress can help reduce damage to your body’s DNA and RNA. (Chronic stress, though, does the opposite. So don’t stress too much.)

Stress Boosts Your Immune System

Although chronic stress wreaks havoc on your immune system, an acute “fight or flight” stress attack can stimulate your immune system, making it more responsive. (Your body’s stress response, after all, is there to save you—not make you sick.) One study on rats found that moderate stress makes immune cells more aggressive.

Stress Can Be Alleviated With Charity

Of course, it’s still a good idea to avoid stress. But if you can’t, remedy it by donating to charity. A study of 850 people found that your risk of death increases 30 percent after a major stressful event, like the loss of a loved one. But there’s a treatment: People who helped others—especially by giving—practically eliminated that risk.

Learn more about the inner workings of that beautiful machine between your ears! Tune in to Brain Games Mondays at 9/8c on the National Geographic Channel.


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