Synaesthetic Interactions between Sounds and Colour Afterimages: Revisiting Werner and Zietz’s Approach

We ran a pilot experiment to explore, using a new psychophysical method, the hypothesis proposed by Zietz and Werner in the ’30s, that a sound presented simultaneously with an afterimage can change its phenomenal appearance in non-synaesthetes. The method we adopted is able to directly collect and visualise the apparent changes in intensity of the afterimages, by recording observers’ interactions with a physical feedback mechanism (the paths that the observers generated by moving a cursor), without referring to verbal descriptions. These first findings support some of the most meaningful observations reported by Werner (1934) and Zietz (1931), according to which the colours of the afterimages ‘disintegrate’ at the hearing of a low sound and ‘concentrate’ for a high sound. This relationship is particularly evident with the Yellow stimulus, where the perceived colour intensity of its afterimage seems to have a faster negative change with a low-pitched tone sound, and an increase in intensity and duration when perceived simultaneously with a soprano sound. These data are also coherent with the crossmodal correspondences between both pitch and loudness in audition and lightness and brightness in vision reported in the literature.