Recent research [25] indicated that a Synesthesia Batteryconsistency score of 1.43 is an optimal cutoff score to discrimi-nate synesthetes from non-synesthetes. Thus, participants scoringbelow a threshold of 1.43 on any of the colored-sequence Batterytests (numbers, letters, weekdays, or months) were categorized asprobands. Those who either reported having no experience of CSSor scored above 1.43 on all of the colored-sequence Battery testswere categorized as unaffected. Eagleman et al. originally sug-gested a more conservative Battery score of 1.0 as the optimal cutoffscore; however, only four participants (representing three twinpairs) scored above 1.0 and would have been excluded at the moreconservative classification threshold (see Supplementary Tables 1a