The color of touch: A case of tactile-visual synaesthesia

We report a single-case study, EB, who experiences synaesthetic sensations of color from tactile stimulation. Developmental synaesthesia is typically characterized by the consistency of synaesthetic pairings over time, in that stimuli tend to generate the same synaesthetic responses on different occasions. Here we demonstrate that EB's touch-color associations are significantly more consistent over time compared to a group of non-synaesthete controls, but that this comes in the face of surprisingly high consistency among non-synaesthetes themselves, for certain tactile stimuli. We show, too, that EB's touch-color correspondences are guided by an implicit rule system, and that this system is shared by non-synaesthetes. Both synaesthetes and non-synaesthetes are sensitive to tactile qualities such as smoothness and softness, and these qualities are systematically related to the luminance and chroma of associated colors. This research was supported by VUL's Huygens Scholarship Programme award by the Dutch Ministry of Education, Culture and Science. We are grateful to EB for her kind participation and to our anonymous reviewers for their helpful comments. We are grateful also to Areesa Chinoy, Cristina Dunare, Charlotte Dobson, Carly Pattinson, Sarah Bates, Jonathan Murnane, Alexandra Hatt, and Cathy Tran for their help in control testing and materials generation.