The human brain tends to process certain word sounds as either “round” or “sharp” and may match specific sounds with specific shapes, even abstract shapes. This tendency — known as the “bouba-kiki” effect — is so fundamental that it affects our perception before we are consciously aware of it, according to a new study published in the journal Psychological Science.
The bouba-kiki effect, originally reported over 85 years ago, shows that people consistently pair the soft-sounding nonsense word “bouba” with soft-looking, round shapes and the sharp-sounding nonsense word “kiki” with spiky-looking, angular shapes. This effect appears across many different cultures and age groups, suggesting that it may represent a universal mapping between different modes of perception.
The new findings reveal that the bouba-kiki effect operates on a deeper, more fundamental level than previously observed.
“This is the first report that congruence between a visual word form and the visual properties of a shape can influence behavior when neither the word nor the object has been seen,” said doctoral student Shao-Min (Sean) Hung of Duke-NUS Medical School in Singapore, first author on the research.
In one experiment, Hung and co-authors Drs. Suzy Styles (Nanyang Technological University) and Po-Jang (Brown) Hsieh (Duke-NUS Medical School) presented different images to participants’ left and right eyes. To participants’ dominant eye, the researchers presented a series of flashing images; to the nondominant eye, they presented a target image that gradually faded in. At first, participants were unaware of the target image and could only see the competing, flashing images.
In this experiment, the target image was a nonsense word — in this case “bubu” or “kiki” — inside of a shape. Sometimes the word (bubu) was congruent with the shape it was in (round) and sometimes it was incongruent with the shape (angular). The participants were asked to press a key whenever the target image became visible.
Timing data revealed that the target image broke through to conscious awareness faster when the word/shape image was congruent than when it was incongruent, suggesting that participants perceived and processed the association between word and shape before they were even consciously aware of it.
To make sure the volunteers were processing the roundness or angularity of the word sounds and not just the shapes of the letters in the written words, the researchers conducted a second experiment in which they taught participants to “read” two unfamiliar letters that were lacking any distinctive round or angular components as the words “bubu” and “kiki.” In other words, participants learned to arbitrarily associate the sounds “bubu” and “kiki” to these unfamiliar letters.
Again, the findings revealed that whichever letter was taught as “kiki” broke through into conscious awareness faster when it was inside the angular shape compared with the rounded shape; and whichever letter stood for “bubu” broke through faster when it was inside the rounded shape compared with the angular shape.
“The findings here show that once we have learned the sound of a letter, we are able to not only extract the sound without consciously perceiving the letter, but also map this unconsciously extracted sound to an unconscious shape,” said Hung.
A third experiment showed that the bouba-kiki effect operates outside of conscious awareness even when participants listen to word sounds. In this case, researchers presented a faint shape very briefly in between two images that masked the shape’s visibility.
The researchers varied the intensity of the shape to determine the level at which it became visible to the participants. Once again, they found that congruent sounds/shapes tend to speed up conscious awareness of the shape, lowering the threshold at which the participants reported seeing the shape.
“All these findings expand the limit of unconscious processing, demonstrating that crossmodal mapping occurs outside of the realm of conscious awareness,” said Hung.
Overall, these tests reveal that the bouba-kiki effect emerges unconsciously before we even have a chance to deliberately think about the relationship between sound and shape. That is, “a word can sound like a shape before the shape has been seen,” Hung concluded.