Thanks to Babbel for sponsoring this episode of SciShow Psych.

Click the link in the description to start learning a new language today. [♩INTRO]. You know how a dog goes “mung mung” and a cow goes “bu”?

Sure, that's pretty obvious — unless you didn't grow up in Korea or Hungary, where “woof” and “moo” may raise an eyebrow. Since Ancient Greece, we've been trying to figure out why people feel that some words just sound like the thing they refer to that is, why onomatopoeias exist. Like, does this only happen because of the cultures they were raised in, like with those animal sounds?

Or is there something more fundamental? Well, science says: maybe there is something fundamental here. And it could even go back to the beginning of language itself.

One famous study about all this was published in 1929, when German psychologist Wolfgang Köhler described what's now known as the bouba/kiki effect. Here's how it works. First, you show people — specifically, hearing folks — a lumpy shape and a jagged shape, and you tell them that, in Martian, one of those shapes is called “bouba” and the other is called “kiki.” And multiple experiments show that on average, 95% of people guess that “bouba” is the lumpy one and “kiki” refers to the spiky one.

Almost a century later, we know this effect works across languages and cultures. And it looks like this association is based on the sounds of the words, too, more than any similarity in the letters' shapes. We know this because research shows that the bouba/kiki effect happens no matter what writing system you grew up with, and even in cultures without a written language.

Researchers have also found it works just as well in infants as young as four months old, who mostly haven't had time to learn to read, what with their busy schedules. So it turns out that word lumpiness isn't subjective. And neuroscientific research also shows that this is a completely unconscious process.

So… what causes this connection? There are a handful of ideas. On the cognitive and linguistic side, some studies suggest this word-sound matching is based on the way people physically pronounce the words.

Like, the movement of someone's lips and tongue in some vowels maps onto the more rounded shape associated with “bouba” in the experiments. Other research shows that the bouba/kiki effect may actually be associated with the basic acoustic features of the sounds that make up those words like their amplitude and frequency. Meanwhile, on the brain side, scientists believe that bouba/kiki is an example of cross-modal perception.

That's when information from different senses is combined to form one coherent idea. One basic example is how you can still recognize what an object is through smell or touch even without the sense of sight. Another famous example is the McGurk effect.

That's when someone will hear the same speech sounds differently, based on how the person saying them is moving their lips. It happens because the brain is using multiple senses to understand what's going on like how someone uses sight and hearing to decide which shape is bouba or kiki. But as far as what causes this neurologically — we don't know.

Hypotheses point to the angular gyrus and the fusiform gyrus, which are structures in the brain responsible for things like understanding metaphors and integrating multiple sensory inputs. And experiments have shown that people with damage to those parts of the brain don't seem to experience the bouba/kiki effect anymore. Meanwhile, the reverse can be seen in synesthesia, where one type of sensory input activates another in a much more intense way than in run of the mill cross-modal perception.

For example, in grapheme-color synesthesia, people literally see letters in certain colors. So “A” may be bright blue, “B” may be chartreuse, and so on. At least some people with synesthesia have more neural connections in the fusiform gyrus, and they also tend to associate sounds and shapes more strongly in bouba/kiki experiments.

Still, the jury is officially out. The fascinating thing is, though, some scientists believe that cross-modal perception is more than a way to navigate the world. They think this could be the cognitive process that made it possible for us to develop language in the first place.

Essentially, some scientists point to these fundamental sound-shape mappings things like “kiki” equals “pointy” as the remnants of the very beginnings of language. They think that at some point, humans recognized that some sounds made other humans think of certain shapes. And then, that idea gradually expanded, until we had languages that could call up any type of mental image.

There are other ideas, of course, but this is about as likely as any other! Now, in general, not all word-sound associations are objective. Just like with “woof woof” versus “mung mung,” most of them are cultural.

For example, Japanese has multiple words that express the sounds of actions, objects, or feelings that may not sound like anything in another culture. Like, “guzu guzu” is the sound of procrastination, “peko peko” is the sound of being hungry, and so on. As another example,.

English has multiple words that have a negative connotation and all start with a “sl” sound, like slack, slouch, and sludge. But those less common, hard-wired cross-modal connections like bouba and kiki are where a lot of exciting research is taking place. Scientists have already discovered similar associations between speech sounds and the size of objects and even taste.

And the more we learn about the mechanics of cross-modal perception, the closer we get to revealing the origins of language and human cognition. If all this talk about language has gotten you wanting to learn a new one, you might be interested in Babbel. It's an app that helps you learn a new language and use it in real-world situations.

The lessons are specifically designed to take into account your native language, and the app also features personalized review sessions for you. So after as little as five hours of practice, you'll be ready to ask for directions, order at a restaurant, or just navigate around. Right now, Babbel offers 14 languages, including Russian, German,.

Spanish, Portuguese, and more. And as a SciShow viewer, you can get 50% off a six-month subscription. So if you want to check it out, you can download Babbel by clicking the link in the description below. [♩OUTRO].