Baylor College of Medicine

Refrigerator magnet colors are the new black: Fresh clues to understanding synesthesia

Graciela Gutierrez

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Houston, TX -
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Magnetic alphabet letters offer clue to researchers in the role the environment plays in synesthesia.
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A set of multi-colored magnetic letters that children used in the 1970s and 1980s to learn the alphabet have provided neuroscience researchers at Baylor College of Medicine, Stanford University and New York University a clue to the role of environment in synesthesia – a condition in which the senses are blended.

About three percent of the population has colored-letter synesthesia, a perceptual condition in which letters of the alphabet trigger color experiences. For example, J might trigger the experience of green, or M may trigger red.

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. (Winawer is now with New York University department of psychology.)

This finding opened the possibility that synesthetic associations can be shaped by associations in the environment, rather than simply resulting from random cross talk between brain areas. However, it was difficult to test the prevalence of such imprinting, given the challenge of finding and testing a sufficiently large population of synesthetes.

To address this challenge, Dr. David Eagleman collected data from 6,588 synesthetes. Eagleman is an assistant professor of neuroscience at Baylor College of Medicine, and a pioneer in researching the subtle differences in the synesthetic brain, from genetics to brain imaging. Eagleman’s laboratory developed the Synesthesia Battery, the gold standard test for measuring the condition. Through this online testing, Eagleman has rigorously verified the world’s largest collection of color-letter synesthetes.

“Often, if you want to understand a single human brain,” said Eagleman, “you have to study many thousands.”

Witthoft, Winawer and Eagleman collaborated to analyze this large data set, and their findings are forcing a re-evaluation of theories of synesthesia. Their results are published in the journal PLOS One this week.

They found that 6 percent of the synesthetes had 10 or more letters that matched the magnet set, much higher than could be expected by chance.

To see if their hypothesis about the magnet set was on track, the researchers then analyzed the birthdates of all the synesthetes. They found that no one born before 1967 matched the Fisher Price colors; all the “magnet synesthetes” were born 1967 or later. This was a crucial clue, because the Fisher Price magnet set went into production in 1971. Strikingly, for synesthetes born in certain time frames (for example, 1975-1980), almost 15 percent of them seem to have imprinted on the colors of the toy. For those synesthetes born after the magnet set went out of production in 1990, the percentage of magnet imprinting goes down, in parallel with the shrinking prevalence of the toy.

“It was entirely unexpected that we would find so many synesthetes with letter-color pairs that are traceable to the same external source,” Eagleman said. “Fifteen percent during the peak production of the toy—that’s more than anyone could have guessed.”

He is quick to point out that 15 percent needs to be considered a lower bound. It is possible that most or all of the synesthetes learned associations from their environment, but it would be infeasible for the researchers to identify the idiosyncratic displays in their homes and schools, such as posters, murals, quilts, and other letter toys. As surprising as 15 percent is, Eagleman noted, it presumably just scratches the surface.

“When combined with genetics and brain imaging, these findings open a powerful inroad into understanding the brain mechanisms of learning, memory and perception,” Eagleman said.

Eagleman is a co-author of a book on synesthesia, Wednesday is Indigo Blue: Discovering the Brain of Synesthesia (MIT Press). He is also the writer and host of a six-hour PBS series on the brain, airing in October 2015. Funding for the synesthesia research was provided by the Mind Science Foundation.

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