Can you hear colors? Can you see sounds? Do words have colors or images associated with them? It may sound impossible, but there are many documented cases of people who experience all these things. We’ve discussed it before on Cognitive Daily, and even found some limited evidence of similar phenomena among the general population. Collectively, these experiences are called synesthesia. Perceptions have many modalities corresponding to different ways of experiencing the world. The most well-known modalities are the five senses, but “words” or “numbers,” or “colors” may also be considered separate modalities. So to experience synesthesia is to perceive things with multiple modalities simultaneously.
The most common forms of synesthesia involve associations of words, letters, or numbers with colors. Some estimates say that as many as 1 in 200 people may have word-color synesthesia.
By contrast, there have only been five documented cases in the past century of “word-gustatory synesthesia,” where hearing or seeing a word evokes an involuntary taste association. Mathew Gendel spent several months working with a woman with this type of synesthesia who goes by the initials “TD.”
Since synesthesia is a completely internal process, it’s sometimes hard to believe it exists at all. It’s particularly difficult to demonstrate that it exists when only one or two people currently living experience it, so Gendel focused his efforts on determining if TD’s description of her synesthesia was real.
For more common (or rather, less uncommon) forms of synesthesia, the most convincing evidence that it’s real comes from studies showing that synesthetic associations are stable. If “A” is associated with the color blue now, it will still be associated with blue six months from now. What’s more, sometimes the letter-color associations are the same for different people. With only one example to study, this type of evidence is harder to come by, but at least Gendel could test TD at different times and see if her associations were stable.
Gendel presented TD with 806 randomly selected words, and 222 nonsense words created from English-language sounds. She was asked to write down what taste (if any) she associated with each word, and rate the strength of the association. Then the test was repeated three months later. Almost 50 percent of the time, TD experienced a taste sensation accompanying the word. In those cases, 88 percent of the time that sensation was identical or nearly identical three months later. Stronger taste sensations were significantly more likely to be repeated at the end of the study.
For comparison, a group of nine women without synesthesia were given a similar, shorter test. There was no correlation between the strength of the taste sensations they reported and accuracy three months later.
This seems to suggest that TD’s synesthesia is genuine. But this case is a bit more complicated than that. With non-words, synesthetic responses were much less common for TD, as this graph illustrates:
With non-words, TD had a taste association both times she saw the word just 12 percent of the time, compared to 47 percent of the real words. While in those cases she was quite accurate, it’s possible that the associations were acquired through experience, rather than being an innate part of her perceptual system.
It’s also possible that TD has developed a very good memory for associating tastes with words — that the association has nothing to do with perception, but instead is just a memory trick.
In a separate experiment, Gendle selected 23 words and 23 non-words for which TD said initially that she had no taste association. TD and nine others were asked to invent tastes to associate with each word, and then try to remember those associations two weeks later. Here are the results:
Even though TD had said that she didn’t spontaneously associate a taste with these words, she still performed significantly better than the others. This suggests that she might just have a better memory than others, or have developed a habit of associating tastes with words in order to remember them better.
Whether or not TD is an authentic synesthete, her case is fascinating. The tastes she associates with each word are remarkably vivid. She even has a list of 28 “ugly words” that she avoids using or writing (including Cincinnati, number, portable, squirm, and phony) because of the disgusting tastes she says she experiences along with them.
Mathew H Gendle (2007). Word – gustatory synesthesia: A case study. Perception, 36 (4), 495-507 DOI: 10.1068/p5654