Although previous studies have repeatedly shown the bouba/kiki effect that nonsense words including certain sounds are associated with particular shapes (round and sharp objects), the cognitive foundation of the effect still remains unclear because of the use of a very limited number of nonsense words. To clarify the relation between a larger set of speech sounds and visual shapes, we used a 7-point Likert scale to collect the data of roundness-sharpness ratings for Japanese 69 one-mora sounds. Both sighted and vision-impaired Japanese speakers rated the sonorants (/m/, /n/) more roundly than the unvoiced (/t/, /k/, /p/) and the voiced obstruents (/b/ /d/, /g/). Moreover, they rated the unvoiced obstruents more roundly than the voiced obstruents. This is inconsistent with the previous findings from English speakers who rated the voiced obstruents more roundly than the unvoiced obstruents (McCormick et al., 2015), suggesting a cross-linguistic difference in the consonant-roundness relation. The findings are discussed in light of a subtle difference in articulatory or acoustic characters and an orthographic system representing voiced obstruents.
