Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Monday, February 11, 2013

Invisible lung gorillas

In recent posts, I've made the point more than once that eyewitness testimony is inherently flawed because of built-in inaccuracies in our perceptual apparatus.  Put simply, we are just poor observers.  Not only do our brains sometimes make stuff up, we also remember events inaccurately, and given appropriate priming, interpret things based on what we thought was happening

None of this is meant to malign our brains, honestly.  They are extraordinarily good at a great many things, and evolution has crafted them into a data-processing device that is orders of magnitude more complex than the best computer in the world.  The fact that they fail sometimes is only to be expected.

You can't be good at everything, after all.

However, a recent experiment, done by Trafton Drew, Melissa Vo, and Jeremy Wolfe of Brigham and Women's Hospital of Boston, has delivered yet another blow to our opinion of the brain's accuracy.  And this one is not just humbling, it's downright scary -- especially to anyone who has had to rely on the skills of medical professionals.  [Source]

The trio recruited a group of 24 trained radiologists as volunteers, and an equal number of average, non-medical types.  The volunteers were given a set of lung CT scans from five different patients to look at on a computer, and were instructed to click on any anomalous nodules they saw.  (The untrained group were given a brief description of what they were looking for.)  The nodules were small, and there were only ten of them in the hundreds of scans analyzed.

What they didn't tell any of the volunteers, however, was that hidden in the slides of the final patient was an image of a gorilla.  (The gorilla was chosen because of the seminal study of inattention, by Simons and Chabris -- see their famous video here.)  The gorilla image was huge by comparison with the nodules -- an estimated 48 times larger than the typical nodule size.

Twenty of the 24 radiologists, and all of the untrained volunteers, didn't see the gorilla.

And it wasn't hard to see.  Every single one of the people who didn't see the gorilla were shown the slide in question afterwards, and asked, "What is that?" and they all answered, "That's a gorilla."  Nevertheless, the vast majority of people who had analyzed the image closely didn't see what was right in front of their faces.  (The phenomenon has been named "inattentional blindness.")

Now, to their credit, the radiologists, who presumably would know that a gorilla in your lungs is abnormal, were better at spotting the anomaly than the average guy.  They were also (reassuringly) way better at finding the nodules.  But this once again punches a hole in our certainty that what we notice (and remember) is what is actually there.

I'm often asked -- usually apropos of UFO sightings, and less commonly about phenomena such as hauntings -- why I am so skeptical, when eyewitnesses report thousands of encounters every year.  It's not, honestly, that I think it's impossible that there is something weird out there; especially in the case of UFOs, I think that the likelihood of life elsewhere in the universe is near 100%, and I'd be mighty surprised if some of it didn't turn out to be intelligent.  (Why they'd want to come here, though, is a bit of a mystery.)  So, my beef isn't that I think the claim is impossible.  My problem is that eyewitness testimony is so inherently flawed that I need more than just your claim of having seen a UFO in order to believe it myself.  (In fact, I need more than just "I saw it," as well.  I don't trust my own brain any more than I trust yours.)  Our perceptual systems are simply too easy to fool, and too poor at remembering details, to be reliable recorders of data.

So, anyway, that's the latest from neuroscience.  More evidence of the inaccuracy of the human brain.  Makes me wonder what I'm missing, as I wander through my day -- all the stuff I'm not noticing.  Probably most of it is trivial, and it's just as well that my brain dismisses it -- but you have to wonder how many times something truly marvelous crosses your path -- the equivalent of an invisible lung gorilla -- and you don't see it.

1 comment:

  1. Though amusing, this doesn't seem like news to me. There's a game where you challenge someone to find a name on a map, and to stump them, you should choose a name that's printed large (unless, of course, they're on to this trick or the name is so large that it's known to them). When eyes are scanning for tiny print, they just don't see things that are at a different scale.
    On the picture posted with the NPR piece on this, the gorilla looks pretty obvious when you look at the whole picture at once. But I'm not sure how zoomed-in the people in this study were. I wouldn't have been surprised if the untrained volunteers had done better at spotting the gorilla, just because their brains hadn't been as trained to focus on the specific task.
    Maybe what's needed here is a combination human and software scanner. The software could have a larger set of patterns to look for, or a way to decide what looks like normal lung, and could highlight bits that someone needs to look at to decide whether they're a real abnormality, or a psychologist playing games with our heads.