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When you imagine a walrus, you probably picture it way smaller than it actually is. It’s because our brains meddle with our senses in more ways than you might expect.

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Take a moment to picture a walrus in your mind. You got it?

Now picture a polar bear. Which is bigger? Did you picture the bear as roughly the same size, or even bigger, maybe, than the walrus?

If so, sorry, but that is very wrong. Walruses are huge — like, two or three times the size of an adult polar bear. Which, by the way, are among the largest land carnivores on the planet.

I almost guarantee you that, no matter how big an animal you imagined, walruses are bigger than that. And it's not just walruses. You're probably underestimating the size of wombats, and overestimating platypuses.

But that's not because you're animal-size illiterate or something. It's because our brains meddle with our senses in more ways than you might expect. You don't really see the world as it is.

Everything you perceive is filtered and biased by your brain in subtle, and not-so-subtle, ways. For example, size judgments can depend on how big you are. That's because you instinctively measure things against your own body, like by using your eye-height as a ruler of sorts.

So some things appear larger to a small observer, and smaller to a large observer. That's just one of many biases your brain throws into the mix when you're judging the size of something you're looking at. And if the information you use to estimate the size of animals isn't totally correct, then your mental image of them may be bigger or smaller than the animals actually are.

Of course, those visual biases can affect how we size up all kinds of objects. It turns out, though, living thing s are subject to a few additional ones. Like, that being in motion makes animals look bigger.

A study from 2017 illustrated this by asking participants to judge the size of ‘point-light walkers' — patterns of dots that mimic the biological motion of an animal — which was, in this case, a human. They found that point-light walkers consistently seemed bigger than static point-light figures, even though nothing other than their movement could lead people to that conclusion. So, your estimate of that walrus's size might vary depending on if you saw it swimming or sitting still.

And, how an animal moves can matter, too. We automatically assume faster walking gaits mean that animals are smaller, for instance. Animal size estimations also hinge on how much of a threat we think the animal is.

Negative emotions like fear can make animals appear larger. Researchers think that's because what we're afraid of captures our attention, and that creates attentional bias in our perception of its size. That bias makes sense from an evolutionary perspective, because presumably, the things you are afraid of are actually threats.

They're a “bigger” deal when it comes to your survival, which means it's more important to spot them quickly and keep an eye on them than it is for harmless objects of comparable size. In other words, they're the things you really should pay attention to — and because of how our brains process visual information, the more something grabs your attention, the bigger it looks. This has been shown with a lot with specific phobias, especially spiders, but it also applies to animals more generally.

If you're looking at a polar bear laying down, for example, you're likely to perceive it as smaller than one sitting upright, even if both of them are perfectly still. That's presumably because the upright one could jump into action more readily. And this bias might explain why we overestimate the size of predators — so, why you were predisposed to thinking a polar bear is bigger than a walrus.

Though, if you have ever been unlucky enough to encounter a walrus in the wild and really learn firsthand how dangerous they can be, your estimate might have been a bit more accurate. Now, those of you who go to zoos all the time might be thinking that all of this doesn't really apply to you. Seeing something a number of times in a nice, chill environment would give you a much better idea of its size, right?

Well... not necessarily, because you're still having to rely on your memory. And — surprise surprise! — memories are pretty unreliable, even when we're super familiar with the thing we're remembering. In a study published in 2000, for instance, researchers asked participants to estimate the size of several everyday objects they knew well, like a key and a VHS tape — which, hey, back then, actually was a common thing in people's houses.

They also were asked to size up pieces of wood, cardboard, and paper that were cut and painted to match the size, shape, and overall color of familiar objects. And weirdly, they gave more accurate size estimates for the objects made from random materials than the ones they knew well. And the researchers thought that might be because they weren't actually looking at them — they were guessing the sizes from their memories instead.

And in a follow up experiment, they found that size estimations from memory were less accurate than those made when directly looking at something. That's at least partly because memories change over time. For example, your memories of animals might be vulnerable to category effects.

That refers to the tendency to bias judgements across a whole category of things toward an average. So if you are thinking of, say, seals and their kin, you might be more prone to thinking that small species like harbor seals are bigger than they are, while bigger ones, like walruses, are a little smaller. All things considered, there are a ton of cognitive quirks that might have made your walrus and polar bear guesses more than a little off.

Which is actually fine, because knowing the /exact/ size of different animals super accurately isn't all that essential a skill. But it does show that the line between “seeing” and “thinking” is kind of blurry — and maybe a bit blurrier than we usually realize. Thanks for watching this episode of SciShow Psych!

We hope you enjoyed today's insights into your brain and its weird quirks. And if you did, you might consider clicking that subscribe button. Also, there's a little bell next to it.

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