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As a SciShow viewer, you can  keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. If you’ve ever taken a psychology class, chances are you’ve learned about the so-called “gorilla experiment”.

Maybe you’ve even done it, yourself. In this study, participants are asked to watch a video of two “teams” passing a couple basketballs around, and count the passes made by just one team. And many people, including myself, were so focused on that task, that they somehow miss the human in a gorilla suit that shows up halfway through the video to stroll right through the scene.

Scientists have been researching this  strange kind of blindness for decades. And much like a video with a gorilla hiding in plain sight, there’s still more to see. [ ♪ intro jingle ♪] The gorilla experiment was  first published back in 1999, So I saw it when I was in college like a year after it came out

but it was a variation on a type of experiment from the 1970s and 80s that featured a woman carrying an open umbrella, instead of a woman in a gorilla suit. But instead of having her walk through the scene, the video of this Umbrella Lady was superimposed over the video of the basketball players, so both she and the players were all a little transparent.

That’s not exactly a sight we encounter in the real world. So some follow-up research was needed to get a better sense of why so many people didn’t see her, and what tweaks to the scenario might make her more or less likely to stand out. Enter a couple of dudes from Harvard.

In addition to having a woman with an umbrella actually walk through the basketball players, they added an alternative condition that was… a little more amusing. And there were a few other  parameters to the experiment. Like, half of the participants were told to monitor the  team wearing white shirts, and half monitored the team wearing black.

Meanwhile, a different half only had to count the total number of passes, while the rest had the more difficult task of remembering how many passes were thrown and how many were bounced. And people were more likely  to notice the interruption if they were doing the easier task. It was also easier for people  to spot the black gorilla when they had been instructed to count passes between the black shirt team.

That suggests humans are more  likely to notice unexpected things that are more similar to the task at hand. Maybe that’s why more people noticed the human carrying an umbrella than the non-human gorilla suit. But out of the nearly 200  participants in this study, 46% of them completely missed either the Umbrella Lady or Gorilla Lady walking through the scene.

It was a perfect demonstration of what scientists call inattentional blindness, or the failure to perceive something simply because you’re not paying attention to it. And to understand how this  inattentional blindness actually works, we’ve got to understand where it happens inside of us. Because visual processing takes several steps.

Sure, light hits our retinas and a signal gets sent from our eyes to the brain. But the brain takes a few steps of its own, too. First, it figures out the  basic features of an image, like orientation of lines, color, and direction of motion.

Then, it starts to organize  those into general shapes. Those shapes get put together, the bigger picture starts to emerge, and we start to apply our previous  knowledge to figure out what things are. And finally, it enters our conscious awareness and we actually perceive the image.

But unfortunately, these  steps aren’t entirely linear. Information that’s processed in later steps, like how much attention you’re paying, is often sent back to previous steps for another round of updated processing. So inattentional blindness arises at some point in this big, loop-filled process, but scientists are still working  on finding exactly where.

One hypothesis is that when  you’re focused on one thing, like counting basketball passes, you literally don’t even look at others, like a wayward gorilla. Your eyes just skip over it. However, one study from 2006 tracked where 21 German children were looking while they watched  a gorilla experiment video.

And the kids who didn’t see  the gorilla looked at it for the same amount of time as the children who did report seeing it. So it’s probably happening somewhere in the brain. It could be that feedback from a  later processing step loops back around to the start and tells your brain to not even bother processing the gorilla, because it isn’t important right now.

Maybe the brain processes that  there’s totally a gorilla there, but the news gets filtered out right before you can become  consciously aware of it. Or maybe you do actually perceive the gorilla, but your focus on basketball passes makes you less likely to remember you did. These are all things researchers  are trying to figure out.

In a 2023 paper, this year, a long time after the experiment, one team considered that other  attention studies demonstrate we tend to see objects moving really fast through our field of vision or things that just pop up and disappear. So they repeated the 1999  experiment, but with a few changes. In one version, they had the gorilla move faster, taking 2 or 6 seconds to move across the screen instead of the 10 seconds in the original video.

They also had a version where the  gorilla leapt across the scene, more like an actual gorilla would move. And sure enough, people who  were counting passes made by the white shirt team were more likely to report seeing the gorilla the faster it was moving, as well as when it was leaping. For participants counting  passes by the black shirt team, a speed boost didn’t matter as much.

But that’s probably because the  gorilla was already easy enough for them to spot in the original conditions. Because the basic features of movement like direction and speed are handled in some of the earliest  stages of visual processing, this new study would suggest the blindness part comes in at a later stage, and we’re at least unconsciously  aware that the gorilla is there. Which would make sense, because while inattentional  blindness might help us focus and perform better on tasks, zero processing of other things would leave us vulnerable to external dangers.

Whether it’s a tiger trying  to eat you in the wild, or your kid about to stick a  metal fork in an open socket. So instead, this study supports the idea of a flexible attention hierarchy. More important things get more attention, but since the brain can’t  always know ahead of time what things are going to be important, it has to be able to reorder that  hierarchy at a moment’s notice.

And that might be what movement does. If the movement is slow, the  attentional hierarchy carries on as is. If it’s fast, that early visual  processing step signals the brain to reorder the hierarchy and pay  attention to the speeding gorilla.

So clearly, there are a lot more details to  understand about inattentional blindness. And It’s important research, because while a rogue gorilla at a  basketball game is a bit unlikely, inattentional blindness does have real world and potentially deadly consequences. But it might be getting harder to do, because now a ton of people know  about the gorilla experiment.

And people who know about it are  more likely to see the gorilla. So while this amusing experiment has served us well for over two decades, we might need to try something new if we want to see the unexpected. Inattentional blindness is a  part of our everyday lives.

So to help you understand  these everyday science topics, Brilliant has a Physics of the Everyday course. It covers topics like car collisions and traffic that can be outcomes of inattentional blindness, along with things like spinning  and flipping in gymnastics, which you might miss in a video created  to study inattentional blindness. And Brilliant courses are designed to focus and keep your attention on the subject at hand, through interactive puzzles  and real-world examples.

This online learning platform includes thousands of interactive lessons in math, science, and computer science, with bonus puzzles in each of those categories. To try them out for yourself free for 30 days, you can visit Brilliant.org/SciShow or click the link in the description down below. That link also gives you 20% off an annual premium Brilliant subscription.

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