Synaesthesia in children

Synaesthesia is a developmental condition that triggers phantom sensations (e.g., colours or tastes) when exposed to everyday stimuli such as graphemes, music, and pain. Yet, despite synaesthesia being a developmental condition, there is very little work in children to date. In this thesis, I explore two types of synaesthesia in children aged 6-10 years old; grapheme-colour synaesthesia (letters and numbers elicit colours) and grapheme-personality synaesthesia (letters and numbers elicit personalities). I first use tests designed specifically for children to identify individuals with these types of synaesthesia. Here I tested children with and without synaesthesia who had been identified from a very large screening endeavour, called MULTISENSE (funded by the European Research Council; I played a central role in this project, but my thesis focuses on the children identified by this process, rather than the screening itself). Then once this cohort was identified I looked at group differences between synaesthetes and non-synaesthetes in two domains: personality and cognition (specifically, numerical cognition). Throughout the thesis I use tests targeted specifically for our child population. Where these did not already exist in Chapter 2 (e.g., suitable self-report personality measures for children) we created and validated them independently. In Chapter 3 I use some of these measures to identify whether synaesthetes have a different personality profile to non-synaesthetes. In the second half of the thesis I tested synaesthetes’ numerical cognition, and looked, too, at ‘synaesthesia-like’ phenomena in the general population. Here in Chapter 4 I explored whether a widely implemented maths tool that pairs numbers with colours aids non-synaesthete children in their numerical cognition. I then finally return to synaesthetes in Chapter 5 using the same tests of numerical cognition to determine if grapheme-colour synaesthetes show advantages in this domain. Overall, this thesis shows that child synaesthetes have a distinct personality profile, and show a pattern of differences in numerical cognition found also in ‘synaesthesia-like’ phenomena such as the educational colour-coding of numbers.