Exploring touch-colour associations in achromatopsia: A case study

Crossmodal correspondences - systematic mappings between stimulus attributes in different modalities - are ubiquitous in the general population. For example, high-pitched (vs low-pitched) sounds are commonly associated with elevated (vs low) positions in space, and rounded (vs angular) shapes tend to be linked to the term 'Bouba' (vs 'Kiki'). There is still some debate about the role of immediate sensory experience versus conceptual colour understanding in crossmodal correspondences. In individuals with touch-colour synaesthesia - a rare condition in which colours are consciously experienced during haptic stimulation - associations are plausibly driven by sensory processes. However it is not known if touch-colour associations in non-synaesthetes also rely on sensory processes. Here, we tested the hypothesis that intact sensory (colour) processes are an optional, but not necessary, condition for crossmodal correspondences between touch and colour. We tested this hypothesis by comparing texture-colour associations in an achromatopsic observer, M.S., to those of matched controls. In a forced-choice task, M.S. (N = 1) reported associations between texture and colour that were very similar to control participants with typical colour vision (N = 17) when the response options were colour terms (words), but not when the response options were colour patches (hues). Our results indicate that typical (non-synaesthete) touch-colour associations can occur without sensory colour perception, suggesting that conceptual understanding of colour may be sufficient for touch-colour associations.