I read The Man Who Tasted Shapes by the neurologist Richard Cytowic in the mid-1990s. Whenever the man ate something, he felt sensations on his skin. For example, eating chicken caused him to feel like his skin was being poked by pointy things. If the chicken was a little underdone, the points were more rounded. The sensation was so strong for him that he decided what to eat based not on the taste, but based on what he wanted his skin to feel like. Synesthesia has been a topic in my Intro Psych course ever since. I usually first cover it when we talk about how the cerebral cortex processes sensation, but it often comes up again in the sensation and perception chapter. Synesthesia is a powerful reminder that our experience of the world is entirely subjective.
Several years ago in class, after covering synesthesia, a student raised her hand. She said, “I have that, but I just learned that a few months ago.” A friend of hers who was taking my Intro Psych course was talking with his friends about synesthesia. This young woman was in that group conversation, and she said, “Doesn’t everyone experience that?” Silence—and they all turned to face her. That’s when she learned that the colors she sees when she hears sounds is not experienced by everyone else.
Synesthesia historians mark 1812 as the year synesthesia came to light. (For a complete history of synesthesia research, see Jörg Jewanski’s chapter, “Synesthesia in the Nineteenth Century: Scientific Origins” in the Oxford Handbook of Synesthesia. Yes, I, too, was surprised to learn that there is an Oxford Handbook of Synesthesia.) Despite this 200-year start on the research, modern research didn’t really take off until Cytowic met the man who tasted shapes in the 1990s. “Sir Francis Galton, the cousin of Charles Darwin, described some synesthetes in his work Colour associations. The interest and attention on this field raised and some publications followed. The US-scientist Mary Calkins introduced the term synesthesia or synaesthesia at the end of 19ths [sic] century” (Mächler, n.d.).
How many people have synesthesia? We have no idea. That’s not true. We do have an idea. We know it’s more than one person. The problem lies in how to test for synesthesia in all of its forms from an appropriate population sample. For a good explanation of the challenges in determining prevalence see Watson, et.al.(2017).
Consider using Cytowic’s 4-minute TEDEd video to introduce synesthesia. He points out that we frequently use one sensation to describe another, such as using a skin sensation word like sharp to describe taste or sound, so we all may be, in essence, synesthetes.
(Shout out to Ruth Frickle for sending me this video!)
If you’d like to explore the topic of synesthesia yourself—and amass some examples—check out these books among many that have been written about synesthesia. They are listed in no particular order.
The Man Who Tasted Shapes (1993) by Richard Cytowic
This is the book that launched modern-day synesthesia research. The first half of the book is about the synesthetic experience. In the second half, he waxes philosophically on the meaning of it all.
Blue Cats and Chartreuse Kittens (2001) by Patricia Lynn Duffy
Written by someone with grapheme-color synesthesia—perhaps one of the most common forms of synesthesia—Duffy shares what it’s like to have sounds produce color.
The Tale of the Dueling Neurosurgeons (2014) by Sam Kean
Kean, in the “Wiring and Rewiring” chapter, spends a few pages discussing synesthesia. Mostly, I will take any opportunity to plug this book. If you teach Intro Psych—and especially if neuroscience is a weakness for you—you must read this book. It’s non-negotiable.
Synesthesia (2018) by Richard Cytowic
This is Cytowic’s newest book. I haven’t read it yet, but my local library system is routing it to me as I type. I trust that this will contain the most current research on the topic.
References (excluding the above book recommendations)
Mächler, M.-J. (n.d.). History of synesthesia. Retrieved April 24, 2019, from https://synesthesia.com/blog/synesthesia/science-of-synesthesia/history-synesthesia-research/
Watson, M. R., Chromý, J., Crawford, L., Eagleman, D. E., Enns, J. T., & Akins, K. A. (2017). The prevalence of synaesthesia depends on early language learning. Consciousness and Cognition, 48, 212–231.