We have a new paper out in Language:

Dingemanse, Mark, Will Schuerman, Eva Reinisch, Sylvia Tufvesson, and Holger Mitterer. 2016. “What Sound Symbolism Can and Cannot Do: Testing the Iconicity of Ideophones from Five Languages.” Language 92 (2): e117–33. doi:10.1353/lan.2016.0034

The basic finding is this: people are sensitive to the meaning of ideophones they’ve never heard, even when they are produced out of context by a computer voice in a difficult forced choice task. Yet there is also reason for caution: the effect is not nearly as strong as what people have found for pseudowords like bouba and kiki.

As we note in the introduction, “there appears to be a tendency to either underplay or exaggerate the significance of iconicity in the study of language and mind”. In this paper we chart a middle way between these extremes. Here’s a quick summary in 3×3 points:

What we did:

1. Sound symbolism (iconicity in spoken language) is usually studied using hand-crafted pseudowords in binary forced choice experiments (think bouba and kiki, as reviewed here), but there are three problems with such experimental designs: (i) they run the risk of inflating effect sizes, (ii) it is unclear how they relate to natural languages, and (iii) they usually don’t control for prosody.
2. We designed a study to tackle these problems by (i) adjusting the binary choice task to be more realistic and harder, (ii) using real words and meanings from natural languages, and (iii) teasing apart prosody and segmental features. Essentially, we bring linguistic insights to bear on the psychological study of sound symbolism.
3. We take 203 ideophones —lexical sound-symbolic words— from 5 languages and 5 semantic domains and present them to 80 participants in 4 versions: (i) full original recording, (ii) full speech synthesized version, (iii) prosody-only condition and (iv) phonemes-only condition. The versions help us control for variation due to different speakers and help us examine the contributions of prosody and segmental features.

What we found:

1. People can choose the correct translation of ideophones at a level significantly above chance. So ideophones in Japanese, Korean, Semai, Ewe and Siwu are not fully arbitrary, as is normally assumed of words; they contain iconic cues that even people who don’t speak these languages can pick up.
2. Sound ideophones are easiest to guess, but the other semantic domains (movement, texture, color/visual appearance, and shape) come out significantly above chance as well. However, the effect is much more modest than most bouba/kiki studies: in the best versions, people score 57.2% on average (where 50% would be chance level) — quite different from the 95% that has sometimes been claimed for pseudoword studies.
3. Performance for the original and resynthesised stimuli is indistinguishable, so our speech synthesis method works. Performance is significantly better for the full versions (i-ii) than for the reduced versions (iii-iv), so both prosody and phonemes contribute to the effect (and neither alone is sufficient).

What we conclude:

1. Findings based on pseudowords like bouba/kiki cannot be automatically translated into claims about natural languages. Ideophones combine iconicity and arbitrariness, and lexical iconicity in ideophones is best characterised as a weak bias, which is supported by multimodal performances in actual use and which may be amplified in cultural evolution (cf our TiCS paper).
2. Prosody is just as important as segmental information in supporting iconic interpretations (as predicted here). Prior work, which has rarely controlled for prosody, likely overestimates the role of speech sounds and underestimates the role of intonation, duration and other prosodic cues.
3. Speech synthesis offers a viable way to achieve experimental control in the study of sound symbolism. To stimulate its wider use we’re making available all stimulus materials, including the diphone synthesis source files we used to create them. Get them at MUSE or OSF.