Is synaesthesia really stable – or does it gradually consolidate?

Synaesthesia is a condition describing a perceptual variation where experience an additional concurrent following an inducer stimulus (Grossenbacher & Lovelace, 2001); some may experience that weekdays or letters have a specific colour, or that a number has a certain size or relate to a particular place in space. Often synaesthesia is linked to a genetic component, and it has been suggested to be the result of either increased cross- wiring or decreased lateral inhibition in certain areas of the brain (Hubbard & Ramachandran, 2005). Previous studies have revealed that synaesthesia can be established through experience during development (e.g. Witthoft & Winawer, 2006). Nevertheless, despite heroic attempts studies still fail to convincingly train non- synaesthetes to develop synaesthesia (see Colizoli, Murre, & Rouw, 2012; Bor, et al., 2014). One of the principle criteria for synaesthesia is that the associations are stable over time. However, here we present the case of AR, a colour-grapheme synaesthete who clearly demonstrate synaesthesia, but also a gradual consolidation over time (Sørensen, Nordfang, & Ásgeirsson, accepted). Also, AR does not demonstrate some of the typical modulations of attention found in synaesthetes (Ásgeirsson, Nordfang, & Sørensen, 2015), suggesting that these modulations may be the result of expertise.