Imagine being able to see smells, taste colors, or hear sights. Imagine counting to ten, and simultaneously seeing flashes of vibrant colors take over your vision. Imagine listening to a symphony and being taken over by feelings all across your body that correspond with each instrument being played. This is real life for the four percent of our population that have a condition dubbed synesthesia, or “a union of the senses” (Carpenter 2001).
I first learned about this condition after discovering the vibrant world of mantis shrimp. Somehow, seeing what mantis shrimp see with their sixteen photoreceptors got me thinking, if these creatures are able to see colors unthinkable to humans, what are the extents to which our bodies can see, hear, taste, feel, or smell things in different ways. Synesthesia caught my eye immediately. I could not imagine a world where someone was able to conjoin their senses to get a whole new view of their surroundings. It is amazing what the human body can do.
The cause of synesthesia is a topic heavily debated in the scientific field. The three main theories are as follows. Baron-Cohen et al. (1987) suggests that synesthesia is caused due to an overabundance of neural connections in the brain. It is known that the five senses are localized in different areas of the brain. Baron-Cohen states that in cases of synesthesia, these different areas become conjoined through neural connections which may cause the senses to blend together, explaining “seeing smells” or “tasting colors”. The second theory, proposed by Grossenbacher et al. (2001) suggests synesthesia is rooted in “feed-backwards” loop in multisensory areas of the brain. These areas, most notably the insula, are places where multiple senses are processed in the same location. Grossenbacher states that in the brains of synesthetes, senses are unable to be distinguished in these multisensory areas, and thus become mixed together. Finally, Maurer et al. (2009) proposes that all humans are adept with the neural connections needed to experience synesthesia, however think most humans lose those connections over time.
Synesthesia can present itself in over eighty known ways documented across the world. These types are categorized into two groups; associative synesthesia, where the synesthete feels a strong, involuntary connection to a stimulus and the sense that is triggered in its presence, and projective synesthesia, where the synesthete sees colors or figures when interacting with a stimulus (Carpenter 2001). Some of the more common types of synesthesia are described below.
- Grapheme-color synesthesia: occurs when letters and numbers have a certain color strongly associated with them.
- Chromesthesia: occurs when sounds, such as those occurring in the natural world or musical notes, are strongly associated with colors.
- Auditory-tactile synesthesia: occurs when certain sounds or notes induce sensations in different parts of the body.
Autism Spectrum Disorder has been an interest of mine ever since I got involved in the growing community in my district. I started a boot camp for kids on the autistic spectrum, and after interacting with up to eight kids on a weekly basis, I began to wonder what actually goes on inside their amazingly creative, thoughtful, and caring minds. After some research, I found that synesthesia, another interest of mine, has been found to be a common comorbid disorder in those on the autistic spectrum.
Because there is not a lot of knowledge on what causes autism, nothing can be linked between neural connections that are found in synesthetes and those on the autistic spectrum. However, it has been found, especially in savants, or those who have special and significant abilities in subjects such as art, math, or memorization, synesthesia is common (“Sensory Links between Autism”). There has been research done in the past few years linking some sensory details between autism and synesthesia including sound and light aversion and attention to detail. More research could be done regarding the rates of comorbidity between autism and synesthesia, as well as the similarities between rates of diagnosis between genders. Autism is a predominantly male dominated disorder, with nearly five males being diagnosed for every one female (“Sensory Links between Autism”). However current research suggests this ratio is flipped for synesthesia, with almost six females being diagnosed for every one male (in the United States). This would be an interesting and potentially important topic to research regarding diagnosis and treatment of ASD.
Baron-Cohen, Simon, et al. “Hearing Words and Seeing Colours: An Experimental Investigation of a Case of Synaesthesia.” Perception, vol. 16, no. 6, 1987, pp. 761–767., doi:10.1068/p160761.
Carpenter, Siri. “Cover Story: Everyday Fantasia: The World of Synesthesia.” American Psychology Association, vol. 32, no. 3, Mar. 2001, doi:10.1037/e303592003-024.
Grossenbacher, Peter G., and Christopher T. Lovelace. “Mechanisms of Synesthesia: Cognitive and Physiological Constraints.” Trends in Cognitive Sciences, vol. 5, no. 1, Jan. 2001, pp. 36–41., doi:10.1016/s1364-6613(00)01571-0.
“Sensory Links between Autism and Synesthesia Pinpointed.” ScienceDaily, University of Sussex, 7 Mar. 2017, www.sciencedaily.com/releases/2017/03/170307100346.htm.
Spector, Ferrinne, and Daphne Maurer. “Synesthesia: A New Approach to Understanding the Development of Perception.” Developmental Psychology, vol. 45, no. 1, 2009, pp. 175–189., doi:10.1037/a0014171.