Automatic Visual Smoothing

I wrote last time about how our brain receives a staggering amount of conflicting and imperfect information from our eyes, yet manages to sort it all out and provide us a reasonably accurate picture of our world. There's a similar task that our fabulous gray matter does, that helps us make sense or our world, in a slightly different manner. The brain receives a rapidly-varying amount of information. What keeps it from getting hopelessly lost in all the moment-to-moment jitter? Why doesn't the brain lose track of what our visual sense is trying to perceive, by getting confused with all the quivering information that comes in?

Recent research has discovered a key processing technique used by the brain, to keep from getting derailed by all the flickering data: our visual perception is strongly influenced by what we saw in the recent past—up to 15 seconds ago. The brain averages what's coming in at the moment with what it received 10-15 seconds ago. It's looking for consistency in our environment and throwing away the noisy, irrelevant stuff. It's smoothing or integrating the data, to pull out the necessary information that provides us a stable world.

By this process, the brain cleverly reduces the number of things we must deal with in our visual environment. Some researchers have dubbed it a “continuity field.” Think of approaching something on the ground when the light level is low. Is that a snake or coiled rope waiting there? As we cautiously proceed, many other visual signals get sent to the brain, but, remembering what we saw a few seconds ago, our attention hones in on the unknown object—ignoring extraneous information—until we see (whew!) that it's just a piece of rope. Our continuity field brought us the truth once again.

This phenomenon has another fascinating side to it. Because we pay attention to the one thing of interest, while we ignore the “clutter,” we become subject to what is sometimes referred to as “change blindness.” Trying to figure out if it's a snake or rope, we allow changes in our visual field—changes we're not expecting—to slip by unnoticed. We become blind to something that may, in fact, be intriguing, if not important.

For example, when movies are being filmed, numerous takes are often required by the director, to get the scene just right. The director—and later the editor—are focused on a particular desirable behavior of an actor, which they want to see. On the tenth take they may finally get it perfect—but something else has inadvertently slipped into the scene; an unexpected change that no one noticed. In take number 1, for example, the actor may have held a cup of tea, as he tried to respond to the director's guidance. By take number 10, the actor may now have his behavior perfect, but no one noticed that he now holds a glass of water. Change blindness has fooled everyone.

There's a famous psychological experiment in which subjects were directed to concentrate and count the number of times a basketball was passed between players with different colored shirts. Part way through the experiment someone dressed in a gorilla suit strolled slowly through the scene—even pausing to beat its chest. None of the participants ever saw the gorilla—so focused were they on counting. They had to be shown a film of the event to become convinced of their “gorilla blindness.”

Why do we miss the obvious? It's partly because of where our attention is directed, but also that our brain expects the world to follow certain rules—we believe that things don't arbitrarily change, while at the same time we know that inconsequential things can be ignored. But sometimes the world violates our rules, and because we're thinking so much about what happened 15 seconds ago, we miss an unexpected change. Be careful... next time that rope may actually be a rattlesnake.