Sound symbolism in sighted and blind. The role of vision and orthography in sound-shape correspondences

Non-arbitrary sound-shape correspondences (SSC), such as the "bouba-kiki" effect, have been consistently observed across languages and together with other sound-symbolic phenomena challenge the classic linguistic dictum of the arbitrariness of the sign. Yet, it is unclear what makes a sound "round" or "spiky" to the human mind. Here we tested the hypothesis that visual experience is necessary for the emergence of SSC, supported by empirical evidence showing reduced SSC in visually impaired people. Results of two experiments comparing early blind and sighted individuals showed that SSC emerged strongly in both groups. Experiment 2, however, showed a partially different pattern of SSC in sighted and blind, that was mostly explained by a different effect of orthographic letter shape: The shape of written letters (spontaneously activated by spoken words) influenced SSC in the sighted, but not in the blind, who are exposed to an orthography (Braille) in which letters do not have spiky or round outlines. In sum, early blindness does not prevent the emergence of SSC, and differences between sighted and visually impaired people may be due the indirect influence (or lack thereof) of orthographic letter shape.