The standard theory is that synesthesia results from random over-wiring between brain areas—in this case, between regions that process letters and those that process color. This model of random connectivity predicts that each synesthete’s color associations will be different: Sue might have a yellow “B” while Tom’s “B” is red.

However, a suspicion about the standard model arose in 2006, when two Stanford scientists, Drs. Nathan Witthoft and Jonathan Winawer, found a synesthete whose colors had a distinctive pattern, cycling through red, orange, yellow, green and blue. When asked about the pattern, the synesthete pointed out that her colors matched those on the popular Fisher Price magnet set she had as a child—in which A is red, B is orange, C is yellow, D is green, and so on. By 2013, Winawer and Witthoft had found 10 more synesthetes whose colors echoed the Fisher Price magnet set.