Supplementary material from "Echoes from the past: synesthetic colour associations reflect childhood gender stereotypes"

Grapheme–colour synesthesia is a neurological phenomenon in which linguistic symbols evoke consistent colour sensations. Synesthesia is believed to be influenced by both genetic and environmental factors, but how these factors interact to create specific associations in specific individuals is poorly understood. In this paper, we show that a grapheme–colour association in adult synesthetes can be traced to a particular environmental effect at a particular moment in childhood. We propose a model in which specific grapheme–colour associations are ‘locked in’ during development in children predisposed to become synesthetes, whereas grapheme–colour associations remain flexible in non-synesthetes. We exploit Western gender–colour stereotypes to test our model: we found that young girls in general tend to associate their first initial with the colour pink. Consistent with our model, adult female synesthetes are influenced by their childhood environment: they associate their first initial with pink. Adult female non-synesthetes do not show this bias. Instead, in our study, non-synesthetes tended to associate their first initial with their current favourite colour. The results thus support the ‘locking in’ model of synesthesia, suggesting that synesthetic associations can be used as a ‘time capsule’, revealing childhood influences on adult linguistic associations. Grapheme–colour synesthesia may thus offer an extraordinary opportunity to study linguistic development.This article is part of the discussion meeting issue ‘Bridging senses: new developments in synaesthesia’.