R sounds are rough, and L sounds are smooth, according to cross-cultural study

People around the world associate a trilled R sound with a rough texture and a jagged shape, and an L sound with smooth texture and a flat shape, according to the findings of a new study. Researchers believe this association may be more universal than the famous bouba/kiki effect.

New research from the University of Birmingham (UK), published today (20^th Nov) in the Journal of the Acoustical Society of America, has found one of the strongest cases ever documented of “sound symbolism” – a direct link between speech sounds and meaning.

Marcus Perlman, Associate Professor in Linguistics and Communication at the University of Birmingham said: “Our research shows that speech sounds have texture and shape to them. In a previous study, we found that across languages, R sounds are more common in adjectives describing rough as opposed to smooth surfaces. This could be due to a kind of iconicity – a resemblance between the sound of the word and the texture to which it refers. In this study, we wanted to see if there was a perceptual connection between the trilled R sound and roughness.

“The most famous example of sound symbolism in spoken language is the bouba/kiki effect, where nonsense words like ‘bouba’ are matched to round shapes, as opposed to words like ‘kiki’, which are matched to angular shapes. In a comparable experiment, we previously demonstrated the bouba/kiki effect with speakers of different languages, but the R/L effect appears much stronger and more consistent across cultures. These kinds of cross-modal correspondences might have influenced the evolution of spoken languages, shaping the words we use to talk about texture and shape.”

From Albanian to Zulu

The researchers conducted their study through online and field experiments involving 1030 adults who spoke a total of 28 different languages, including Zulu, Albanian, Danish, English, Greek, Italian, Farsi, Spanish, Russian, Japanese, Korean, Mandarin Chinese, Thai, Daakie and Palikúr. Participants were presented with images of two lines – one jagged and one straight – and were asked to imagine running their fingers along each. They were then played a recording of a speaker producing a trilled R (a rolled “R” sound, like in Spanish) and an L-sound and matched each sound to one of the lines.

The research showed that the great majority of participants displayed a strong tendency to match R with the jagged line and L with the straight line, regardless of which was presented first. The pattern was strongest for matching the trilled R to the jagged line (94% on independent trials), but it was also very strong for matching L to the straight line (84% on independent trials). Speakers of languages including Estonian and Finnish had the highest match rate of 100%, with the lowest at 70% for speakers of languages including Albanian and Mandarin Chinese.

The trilled R connection to roughness appeared across speakers of all languages regardless of whether the sound was used in that language or not. For example, speakers of Palikúr, a language that is completely lacking in a trilled R, performed matching at 100%. Together with the evidence from languages which do not regularly use the trill, such as Mandarin Chinese and Japanese, this shows that even when speakers cannot produce sound, they still perceive it to be rough and jagged.

Near-universal link between speech and texture

The results are the strongest case ever documented of an iconic correspondence between speech sounds and properties related to our senses of touch and vision.

Bodo Winter, Professor of Linguistics at the University of Birmingham commented: “Overall the findings from our experiments are even more consistent than in the cross-cultural investigation of the bouba/kiki effect. Nearly all participants in our study thought R is rougher than L, about 15% more than for the bouba/kiki effect. This pattern was exceptionless across cultures: every single language group showed the same association. This is different from bouba/kiki, which doesn’t work in some languages. It seems that the connection between R/L and roughness/smoothness may be one of the most cross-culturally robust cases of sound symbolism documented to date.”

The researchers also found that, while there was an overall high average match rate across languages, participants whose native language primarily uses the alveolar trill R had a slightly lower proportion of correct matches (86.6%) compared to those whose native language does not use this sound as the primary variant (89.8%). This suggests that the conventional use of the sound diminishes its iconic power.

Dr Perlman concluded: “The trilled R is among the most fascinating of speech sounds. It is notoriously difficult for speakers to produce, and some languages even have a word for people who cannot ever learn to produce this sound ("Erre moscia" in Italian). And yet trilled Rs are surprisingly common across languages. It’s a mystery why such a difficult sound would be so prevalent. We think the iconicity of R has something to do with it. The sound can convey such a strong sense of texture and shape, and it has this extraordinary expressive value that drives people to use the sound even when it’s relatively hard to articulate. Also, it’s a very exciting sound and a lot of fun to produce!”