This is a guest post by Jonathan Leathers, one of Greta’s top student writers for Spring 2007.
Take a look at this word:
What color do you see? Red? Blue?
While you may see nothing unusual, some people report being able to perceive colors associated with different days of the week when they are written down or heard in conversation. This ability is attributed to a phenomenon known as synesthesia, previously thought to be extremely rare. In synesthesia, the human brain interprets one set of sensory stimuli in terms of another; in other words, two senses cross. But synesthesia goes beyond metaphorically stating that one feels blue on Mondays. Previous sampling methods relied on self-referral, placing the percentage of people with synesthesia roughly around 0.05%. But, a recent study led by Julia Simner has shown that the number is actually much higher — about 88 times higher!
There are many different forms of synesthesia, each one a product of different senses crossing — word-color, taste-shape, music-color, people-smell — all were included in Dr. Simner’s study of synesthesia’s prevalence in a population. Students at the Universities of Glasgow and Edinburgh (327 women and 173 men) were asked which, if any, forms of synesthesia applied to them by drawing a line from a list of “triggers” (smells, sounds, words etc.) to a list of corresponding “experiences” elicited (for example: colors, shapes or tastes). Those who had indicated to having some form of synesthesia, 120 in all, were then presented randomly with a trigger and instructed to record whatever they experienced. After 70 trials, the order of the stimuli would be re-randomized and each subject re-tested. After a period of several months, the students were asked to return again and complete a third test; this was done in order to ensure the consistency and validity of their answers and to verify that they were, in fact, synesthetic. Here are the results:
Subjects had to be able to consistently choose the same response to at least 19 questions on which senses were triggered by which stimuli, in order to be considered synesthetic. About 1 percent of those completing the study met this requirement and were classified as synesthetes. This may not seem like much, but the most recent estimate had indicated that just 0.024 percent of the population was synesthetic.
Not only was the prevalence of synesthesia in the sample population much higher than previously thought but the results also failed to support the widely held belief of a gender bias in the occurrence of synesthesia. Prior studies on the subject had reported that women were as much as six times more likely to experience synesthesia as males were. Simner’s team, however, found that the female to male ratio was really in the range of 1.1 to 1, not a statistically significant difference between sexes. By using more effective methods of sampling, the researchers were able to debunk two of the longest running misperceptions about synesthesia. Look again at the top of the page; are you sure you didn’t see a color when you read the word “Monday”?
Simner, J., Mulvenna, C., Sagiv, N., Tsakanikos, E., Witherby, S.A., Fraser, C., Scott, K, & Ward, J. (2006). Synesthesia: The prevalence of atypical cross-modal experiences. Journal of Perception, 35, 1024-1033.