In search of the kiki-bouba effect

The kiki-bouba effect, where people map round shapes onto round sounds (such as [b] and [o]) and spiky shapes onto “spiky” sounds (such as [i] and [k]), is the most famous example of sound symbolism. Many behavioural variations have been reported since Köhler’s (1929) original experiments. These studies examine orthography (Cuskley, Simner, & Kirby, 2015), literacy (Bremner et al., 2013), and developmental disorders (Drijvers, Zaadnoordijk, & Dingemanse, 2015; Occelli, Esposito, Venuti, Arduino, & Zampini, 2013). Some studies have suggested that the cross-modal associations between linguistic sound and physical form in the kiki-bouba effect are quasi-synaesthetic (Maurer, Pathman, & Mondloch, 2006; Ramachandran & Hubbard, 2001). However, there is a surprising lack of neuroimaging data in the literature that explain how these cross-modal associations occur (with the exceptions of Kovic et al. (2010)and Asano et al. (2015)). We presented 24 participants with randomly generated spiky or round figures and 16 synthesised, reduplicated CVCV (vowels: [i] and [o], consonants: [f], [v], [t], [d], [s], [z], [k], and [g]) nonwords based on Cuskley et al. (2015). This resulted in 16 nonwords across four conditions: full match, vowel match, consonant match, and full mismatch. Participants were asked to rate on a scale of 1 to 7 how well the nonword fit the shape it was presented with. EEG was recorded throughout, with epochs timelocked to the auditory onset of the nonword. There were significant behavioural effects of condition (p