Coloured Letters and Numbers (CLaN): A reliable factor-analysis based synaesthesia questionnaire Nicolas Rothen a,⇑ , Elias Tsakanikos b,c , Beat Meier d , Jamie Ward a a School of Psychology and Sackler Centre for Consciousness Science, University of Sussex, Brighton, United Kingdom b Institute of Psychiatry, King’s College London, United Kingdom c Centre of Research in Individual Differences (CRID), Department of Psychology, University of Roehampton, United Kingdom d Institute of Psychology and Center for Cognition, Learning and Memory, University of Bern, Switzerland article info Article history: Received 23 April 2013 Keywords: Synaesthesia Colour Questionnaire Factor analysis Consistency Stroop abstract Synaesthesia is a heterogeneous phenomenon, even when considering one particular sub-type. The purpose of this study was to design a reliable and valid questionnaire for grapheme-colour synaesthesia that captures this heterogeneity. By the means of a large sample of 628 synaesthetes and a factor analysis, we created the Coloured Letters and Numbers (CLaN) questionnaire with 16 items loading on 4 different factors (i.e., localisa- tion, automaticity/attention, deliberate use, and longitudinal changes). These factors were externally validated with tests which are widely used in the field of synaesthesia research. The questionnaire showed good test–retest reliability and construct validity (i.e., internally and externally). Our findings are discussed in the light of current theories and new ideas in synaesthesia research. More generally, the questionnaire is a useful tool which can be widely used in synaesthesia research to reveal the influence of individual differences on various performance measures and will be useful in generating new hypotheses. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction Synaesthesia can be described as extraordinary perceptual experiences associated with normal sensory or cognitive pro- cess. For instance, in grapheme-colour synaesthesia a letter printed in black triggers a highly specific and consistent colour experience. So far, many different forms of synaesthesia have been identified in scientific work, including spatial associations with days and months (time–space synaesthesia; Simner, Mayo, & Spiller, 2009; Smilek, Callejas, Dixon, & Merikle, 2007), tactile experiences elicited from observing touch (mirror-touch synaesthesia; Banissy & Ward, 2007; but see Rothen & Meier, 2013), and even colours evoked by swimming styles (swimming-style colour synaesthesia; Nikolic ´ , Jürgens, Rothen, Meier, & Mroczko, 2011; Rothen, Nikolic ´, et al., 2013). Not only do many different forms exist, but also the heterogeneity within a particular form is large. For instance, synaesthetic experiences may be perceived in the mind’s eye (often referred to as asso- ciator synaesthetes) or as if projected onto the synaesthesia inducing stimulus (often referred to as projector synaesthetes) (Dixon, Smilek, & Merikle, 2004; Ward, Li, Salih, & Sagiv, 2007). Yet, by means of conventional statistical analyses (e.g., factor analysis) no psychometrically sound questionnaire exists to assess how different aspects of the heterogeneity of synaesthetic experiences influence performance in various tasks and its underlying neural activation. It is our aim to provide the field of synaesthesia research with such an instrument using standard statistical techniques. 1053-8100/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.concog.2013.07.005 ⇑ Corresponding author. Address: School of Psychology and Sackler Centre for Consciousness Science, University of Sussex, Falmer, Brighton BN1 9QH, United Kingdom. E-mail address: nicolas.rothen@gmail.com (N. Rothen). Consciousness and Cognition 22 (2013) 1047–1060 Contents lists available at SciVerse ScienceDirect Consciousness and Cognition journal homepage: www.elsevier.com/locate/concog