The psychologist’s “invisible gorilla” experiment demonstrates how we often miss major details when we’re concentrating on something else.

Question: Describe your "invisible gorilla" experiment.

Christopher Chabris: Dan Simons and I were teaching a course at Harvard University on research methods in the Psychology Department.  This is a course where students have to design their own psychology research projects and carry them out.  And as part of the course, we also thought it would be a good idea to have some group projects that everyone could participate in.  Dan had the idea to look at some work that had been done in the 1970’s, a somewhat famous experiment by Ulrich Neisser, one of the pioneers of cognitive psychology who had some people sort of play basketball passing balls around on an empty basketball court, and managed to get the groups of people to overlap by filming them with special mirrors.  And then while people were watching these basketball players, they’re supposed to count the number of times the ball gets passed.  About halfway through the video, a woman carrying an umbrella walks through the basketball court

The surprising finding of his experiment was that many people who were counting the basketball passes didn’t see the woman with the umbrella walking through and didn’t remember her being there at all.  The funny thing about the experiment though, was that since it was filmed using the special technique with mirrors, everyone was sort of invisible and transparent, and you could see through them.   It was a very unusual looking display.  It’s the kind of thing that nowadays you would do with digital video editing.  Back in the 1970’s, you used mirrors.

Some people had sort of dismissed the finding that people missed this very obvious and salient thing, like a woman walking through a basketball game because it was a strange-looking visual display.  So, we decided to try to do a new version of this experiment where all the action was live, and we had six people passing basketballs around, sort of choreographed to not run into each other and to not throw the ball in each other's face, and so on.  And that was a bit of a challenge insetting up this experiment, but that’s what we have students in the course for.  We managed to get it right. 

And then we had a woman walk through carrying an umbrella, just like Neisser did.  What was a little more amusing for us though was that one of the other professors in the department happened to have a gorilla suit lying around in his lab and we thought it would be fun to have someone walk though wearing the gorilla suit and see whether that was noticed. 

And we had first thought that people would notice the gorilla walking through the basketball game because there’s no longer this sort of transparency through display and the gorilla actually stayed on the screen for nine full seconds in one of the versions of our video. 

But when we ran the experiment and our students went out and tested people on the Harvard campus, we found that about half of the people did not at all notice the gorilla and, in fact, were very surprised they hadn’t noticed the gorilla.  There were actually two findings from this experiment.  One, you can miss very salient things, like a gorilla walking right in front of you, and two, that you’re shocked that you could miss it.  Most people seem to have the intuitive idea that they’re going to see this kind of thing and they’re really surprised when they find out that they don’t.

Question: What does this experiment demonstrate to us about selective attention?

Christopher Chabris: What this experiment shows is that when we’re paying attention to something, basically doing a task that demands our attention such as counting the passes of the basketball in this case, or really any other kind of really attention-demanding task that we do, we can seriously overestimate our ability to do other tasks at the same time and especially to notice and handle unexpected or surprising things.  We think that we’re going to notice unexpected things that come into our field of view and we think we’re going to pay attention to the things we should pay attention to, but in fact, when we’re focused on one task, we’re noticing and paying attention to a lot less than we really think. 

Question: What implications does this research have for real-world multi-tasking?

Christopher Chabris: This experiment implies a lot about our behavior in every day life.  For example, when we are driving and talking on a cell phone at the same time, we get the feeling that we are actually driving just a well as when we are not talking on the phone.  That’s part of why we do things like talk on the phone while we are driving, or send text messages or read our email, which are actually much worse.  But even talking on the phone while driving depletes a lot of your attention. 

Talking on the phone while you are driving is like counting the basketball passes in our experiment.  You can still drive, but what you’re going to have a problem with is noticing unexpected things.  And when you think about it, those are the really important things to notice when you are driving.  It’s one thing to just drive down an open highway at night, it’s another thing to drive in the suburbs when someone might be pulling out of their driveway right in front of you, or someone might be stopping short right in front of you and you won’t have the reaction time to be able to stop and not crash into them, or even worse, someone pushes a baby stroller out in front of the road.  So, we’re actually a lot worse at that than we think we are and we should, in fact, put down the cell phone while we are driving and perhaps even zip it up in a brief case or a purse or something like that. 

Those are some of the implications for everyday life.  But it’s not just driving; there are many other situations like this.  For example, the security screeners at airports... we sort of have the impression the are paying attention that’s in our suitcase, and our luggage and so on, but actually everybody has sort of an inflated impression of how much they are paying attention to, and we may not be as safe as we think we are even with trained and dedicated people doing that.  Lifeguards at swimming pools.  Radiologists looking at medical scans for anomalies and so on.  When you are looking for one thing and paying attention to one thing, it is easy to not notice other things and to not realize that you are not noticing those things.

Question: What is the funniest reaction you've gotten from your attention experiments?

Christopher Chabris: A TV news magazine that covered our research actually recreated the experiment for themselves in their own studios and they had a bunch of volunteers come in and look at the video tape and count the passes and missed the gorilla and they filmed the reactions of some of them.  And my favorite one of all was someone who said, “That bear didn’t go through there, did it?" ...

Did you notice that what I’m wearing actually changed several times during the course of this interview.  Some people might have noticed some of the changes, but it’s probably unusual to notice all of those changes.

Recorded May 13, 2010
Interviewed by Austin Allen