How the Brain Fools the Eye

By Carmella Van Vleet ~ Photos by Joshua Moglia

Scientists are exploring the mystery of “change blindness.”

My father had a mustache for twenty years. One day, he shaved it off and didn’t tell anyone. Everyone in the family could tell something was different, but we weren’t sure what. It took my mom a whole week to solve the mystery!

There is a simple explanation for why we didn’t see the change right away and why you might miss a change, too. It’s called change blindness.

A Trick of the Mind

Dr. Daniel Simons at the University of Illinois studies change blindness. He calls it a trick that our brains sometimes play on us.

“Change blindness is the surprising failure to see large changes to a scene,” he says. In other words, we can look at something but not notice that it’s new or different from what it was an instant ago.

Most of the time, change blindness is a good thing. Being able to block out distractions is important. If we couldn’t ignore the unimportant details and movements around us, we would have a hard time getting anything done.

But sometimes we miss changes that are right in front of our eyes. Our eyes see the changes, but our brains don’t keep track of each and every one.

Just how big can these changes be? You might be surprised.

“Now You See Me . . .”

Dr. Simons and Dr. Daniel Levin at Vanderbilt University did an experiment that showed that we can miss some big changes indeed.

In the experiment, a college student stood on a campus sidewalk and pretended to be lost. The student asked a stranger—either another student or a teacher—for directions. While the stranger was giving directions, two other people, carrying a door, walked between the student and the stranger.

While the door blocked the stranger’s view, another student took the place of the first student. After the door passed by, almost half of the people who were giving directions didn’t notice that they were talking to someone new.

People experienced change blindness in this experiment because their view was blocked. Having your view blocked for a moment is a common cause of change blindness. The thing that blocks your view doesn’t have to be as big as a door. It can be small, such as rain on the windshield of your car or someone waving a hand in front of your face. The block doesn’t have to last a long time. Even blinking can cause change blindness.

“Look! Over There!”

And the object doesn’t even have to be right in front of what’s changing. It just has to distract you from the thing that is changing.

Distractions cause change blindness because when something changes or disappears, our eyes are drawn to the movement. If a distraction causes us to miss the movement, we may miss the change.

Not paying attention to the right object can also cause change blindness. When we look at a picture or at the world around us, we usually pay attention to big, interesting things such as people or buildings. We don’t usually pay attention to smaller things, so we don’t notice when they change.

This is why puzzles in which you find the differences between two pictures (such as Check . . . and Double Check) can be challenging. Many of the changes are small.

Sometimes we miss a change because it happens over a long period of time. A tree takes years to grow. The growth is so slow that it doesn’t draw our attention. Then one day, we look out the window and wonder, “Where did that tree come from?”

How good our memories are may also play a role. Does change blindness happen because we don’t see many details in the first place or because we just can’t remember them well enough? Researchers are studying this question.

Most people believe they see everything around them. You might say, “Of course, I’d notice if my dad shaved his mustache or if I was suddenly talking to someone new.” But the more we learn about change blindness, the more we discover we can look at something but not really see it!

Four kids show how college students ran the experiment.
		2. Two people carry a big object between the two. 4. Will the girl notice the difference? Many people didn’t.
1. A boy asks a stranger for directions.
3. Behind the object, two boys switch places.
5. Would you have noticed?

Try This!
Will Anyone See the Change?

To see change blindness in action, try this experiment with your family. Without telling anyone what you’re doing, go to your room and change your shirt. When you come out, don’t draw attention to the shirt in any way. If no one notices that you’ve changed shirts, sneak off and change again. If you do it a few times and no one says anything, ask your family if they notice anything new about you. Or draw attention to the shirt. For example, you could say that it’s your favorite or that it makes you itchy.

How many times do you have to change shirts before someone notices?

Do brighter colors or wild patterns draw more attention?

Who notices the change first?

Does drawing someone’s attention to the shirt make it easier for him or her to notice that it has changed?

Art by Erin Mauterer