Figure 1. Evidence for synesthesia.

Panel a shows within-session consistency in each subject’s color match for 26 letters and 10 numbers. Consistency score is the normalized geometric distance between RGB values for each of 3 matches for letters and numbers, summed over the 3 pairs of matches and averaged over graphemes during each subject’s first match session (Eagleman et al., 2007). All subjects perform well within the range typical of synesthetes with scores below 1 (indicated by the horizontal bar). Panel b shows subjects’ accuracy in a speeded letter-color recognition task, (Eagleman et al., 2007). Again all subjects perform above the threshold for synesthetes (90%, indicated by the horizontal bar). S5 was tested in the lab rather than using this method and data of this kind can be found in our previous paper (Witthoft & Winawer, 2006). Panel c shows the consistency in subject letter color matches across sessions. The y-axis shows the average circular correlation between hues in the first session and the second session. Subjects give highly consistent results even when test and retest are separated by nearly 8 years. The minimal delay was 54 days (Subject 6). There is no indication that matching consistency declines over time.