What Are the McGurk and Bouba/Kiki Effects?

This week, trying to enjoy the strange 70-degree weather in the middle of November, I spent some time outside reading about two fun linguistic phenomena: the McGurk and Bouba/Kiki effects. The prior is an illusion that occurs when the sound of a phoneme and the lip movement of a different phoneme are overlapped, tricking the brain into hearing an entirely different sound. The latter is a phenomenon in which humans around the world have shown a tendency to match certain nonsense words to certain shapes, implying an inherent cognitive link between abstract meaning in shapes and words. In this post, I’d like to tell you a little bit more about both of these ideas in the hopes that you’ll find them as interesting as I did.

The McGurk effect was first discussed in a 1976 paper by Harry McGurk and John MacDonald. It was discovered by accident when the two researchers asked their lab technician to dub a child language acquisition experiment with his own pronunciations. To their amazement, when the pair reviewed the newly produced video, they heard neither the sound produced by the speaker nor the technician, but rather an entirely different phoneme. For example, let’s say the original speaker in the video makes the movements for ba-ba with their lips. Then, the technician dubs ga-ga over the original video. Instead of hearing one of the two patterns, a listener susceptible to the McGurk effect (it is my understanding that not everyone experiences it to the same degree) will actually hear da-da. Strange right?

The phenomenon is another great example of the imperfect nature of the human brain’s ability to process language. Garden path sentences and other semantic illusions demonstrate the same idea: the brain’s processing capabilities are pretty well-suited for language, but the multimodal nature of sensory input will always cause some confusion.

On a different note, the Bouba/Kiki effect brings us back to the question of linguistic and cognitive universals. First observed in 1924 by Dimitri Uznadze and then documented in 1929 by Wolfgang Kohler, the experiment has since been repeated with high rates of success. To exemplify the idea, let’s look at the two images below. I want you to match one of them to the word “bouba” and the other to the word “kiki.”

If you decided that the image on the left corresponds to kiki, you agree with around 95% of the experiment’s participants. Congrats! If you didn’t, then you’re breaking the norm, so congrats to you as well! Either way, the idea that humans tend to consistently match a certain word to a certain shape when neither has any real meaning is fascinating, indicating that the naming of words may not be as arbitrary as we think. fMRI scans of the participants’ brains showed higher prefrontal cortex activation during mismatch (spiky shape with bouba) than during match (rounded shape with bouba). Linguists have theorized that this has to do with the rounded nature of the mouth during the enunciation of bouba, which indicates that part of language development may have involved matching the shapes our mouth makes when creating certain phonemes to the shapes around us.

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