The Real Experiment Behind Brain Games' Santa Test

Brain Games is a television show on NatGeo channel that explores the way our brains interpret our environment - which is often does in suprising, fascinating and unexpected ways. Optical illusions, for example, are illusions because our brains are attempting to make sense of something that, on the surface, doesn't make any.

A promo spot for Brain Games has been in heavy rotation on NatGeo in the run-up to the series' Christmas night special, with the focus on a test of perception and attentiveness. In a video, we see multiple people passing two basketballs back and forth; our task is to count how many times the people wearing white pass the ball. While we focus on doing that, a person wearing a Santa Claus outfit walks behind the scene. "Did you see the Santa?" viewers are asked when the clip ends.

That might not sound like much as I've described it, but it's a scenario based on a famous psychology test conducted by Daniel Simons and colleagues that has come to be known as "the gorilla experiment." Here, watch the original video, and play along:

Did you see the gorilla? What's being explored here is something called "inattentional blindness." In a post on, Simons says that half the viewers in his original gorilla experiment failed to see the gorilla! But how can that be? The gorilla walks right through the middle of the circle, the basketballs going right by it!

The original gorilla experiment became so famous (at least in psychology circles and on YouTube) that Simons made a second video. This one accounts for the fact that many people are now familiar with the test, and know to keep an eye out for the gorilla. But there's another test embedded within the larger test. Watch:

What, exactly, is the point? Why does this experiment matter? Well, for one, it shows just how shaky eyewitness testimony can be. If we care about a fair and just legal system, it's important to understand the limitations of our observational skills.

Simons writes on

How could they miss something right before their eyes? This form of invisibility depends not on the limits of the eye, but on the limits of the mind. We consciously see only a small subset of our visual world, and when our attention is focused on one thing, we fail to notice other, unexpected things around us—including those we might want to see.

... most of us are unaware of the limits of our attention—and therein lies the real danger. For instance, we may talk on the phone and drive because we are mistakenly convinced that we would notice a sudden event, such as a car stopping short in front of us.

In-between the two paragraphs I've quoted, Simons gives an example of a real court case that turned on whether or not it was believable when a police officer claimed not to have seen something that most of us would have a hard time believing could not have been seen by someone with his training. Yet a Simons experiment proved just how easy it was to miss this supposedly obvious thing.

If you find this as interesting as I do, you can delve much deeper into on Simons' website,, or buy the book co-written by Simons with Christopher Chabris and called The Invisible Gorilla: How Our Intuitions Deceive Us.