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Grapheme-colour synaesthesia is a neurological trait that causes lifelong colour associations for letter and numbers. Synaesthesia studies have demonstrated differences between synaesthetes and non-synaesthetes in ways that extend beyond synaesthesia itself (e.g., differences in their cognition, personality, and creativity). This research has focused almost exclusively on adult synaesthetes, and little is known about the profiles of synaesthetic children. By and large, findings suggest advantages for synaesthetes (e.g., Chun & Hupé, 2016; Havlik, Carmichael, & Simner, 2015; Rothen, Meier, & Ward, 2012; Rouw & Scholte, 2016; Simner & Bain, 2018) although differences in mathematical ability are unclear: some research indicates advantages (e.g., Green & Goswami, 2008) whilst others suggest difficulties (e.g., Rich et al., 2005). In the current study, we tested numerical cognition in a large group of children with grapheme-colour synaesthesia. Synaesthetes with coloured numbers showed advantages over their peers in their sense of numerosity, but not in their curriculum mathematics ability. We discuss how our findings speak to models for synaesthesia, to methodologies for assessing number cognition (e.g., dot numerosity tasks), and to the wider educational practice of using coloured number-tools in schools (e.g., Numicon; Oxford University Press, 2018)., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Cognitive benefits associated with grapheme-colour synaesthesia in adults are well documented, but far less is known about whether such benefits might arise in synaesthetes as children. One previous study on a very small group of randomly sampled child synaesthetes found cognitive benefits in short-term memory and processing speed (the ability to quickly scan an array of images and discriminate between them), but was inconclusive for a test of receptive vocabulary. Using a stratified population sample ( Growing Up in Scotland Project, Edinburgh, UK: Scottish Executive, 2007), we investigated the performance of a large cohort of child grapheme-colour synaesthetes using four literacy measures taken at age 10 years. These were three verbal comprehension measures (expressive vocabulary, receptive vocabulary and sentence comprehension) and one measure of academic self-concept in reading (plus one measure of academic self-concept in numeracy as a comparison). After controlling for demographic differences between groups, synaesthetes showed significantly enhanced performance for expressive and receptive vocabulary compared to their peers, but no benefits in sentence comprehension. Child synaesthetes also reported significantly higher academic self-concept for reading, but not for numeracy. Finally, we found that synaesthetes made significantly more progress than controls across the primary school years, although they began school with no a priori advantage. Our study provides powerful new evidence that children with grapheme-colour synaesthesia show vocabulary and literacy differences, which we contextualize within a theory of synaesthetic development. This article is part of a discussion meeting issue 'Bridging senses: novel insights from synaesthesia'.

We developed the Sussex Cognitive Styles Questionnaire (SCSQ) to investigate visual and verbal processing preferences and incorporate global/local processing orientations and systemising into a single, comprehensive measure. In Study 1 (N = 1542), factor analysis revealed six reliable subscales to the final 60 item questionnaire: Imagery Ability (relating to the use of visual mental imagery in everyday life); Technical/Spatial (relating to spatial mental imagery, and numerical and technical cognition); Language & Word Forms; Need for Organisation; Global Bias; and Systemising Tendency. Thus, we replicate previous findings that visual and verbal styles are separable, and that types of imagery can be subdivided. We extend previous research by showing that spatial imagery clusters with other abstract cognitive skills, and demonstrate that global/local bias can be separated from systemising. Study 2 validated the Technical/Spatial and Language & Word Forms factors by showing that they affect performance on memory tasks. In Study 3, we validated Imagery Ability, Technical/Spatial, Language & Word Forms, Global Bias, and Systemising Tendency by issuing the SCSQ to a sample of synaesthetes (N = 121) who report atypical cognitive profiles on these subscales. Thus, the SCSQ consolidates research from traditionally disparate areas of cognitive science into a comprehensive cognitive style measure, which can be used in the general population, and special populations.