The Interesting Connection Between Autism and Synesthesia

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Written by: Amber Wu

Photo by: Robina Weermeijer on Unsplash

What colour is your Saturday? Which number has the worst temper? These might sound like strange questions to ask, but if you answered them without thinking, you may be a synesthete.

Synesthesia (or synaesthesia) is a perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to involuntary experiences in a second sensory or cognitive pathway (Cytowic, 2002). For people with synesthesia, ordinary sensory events, such as listening to music or reading text, can elicit experiences involving other senses, such as perceiving a taste or seeing a color.

At first glance, synesthesia and autism are two completely unrelated things: synesthesia is a blending of the senses, while autism is characterized by challenges with social skills, repetitive behaviors, speech, and nonverbal communication. However, studies have shown that the prevalence of synesthesia is almost three times higher in people with ASD (18.9%) compared to that of the general population (7.2%) (Baron-Cohen et al., 2013), which suggests some type of connection between the two conditions. Further research has shown that both conditions can be attributed to excessive neuro-connection and activities (Belmonte, 2004).

The genetic basis and the mechanism of both conditions are still unclear. However, in terms of brain connectivity, a predominance of local over global connectivity is a possible pattern in both autism and synaesthesia. A recent study by van (2020) pointed out that more studies involving synaesthetes are needed to confirm this hypothesis with direct comparisons between autism and synaesthesia. With regard to sensory processing, both groups show altered sensory sensitivity; and in perceptual tasks, evidence for an autistic-like, detail-oriented style in synaesthesia is accumulating.

To answer the two questions at the start of the article, my Saturday is sky blue, and number 8 has the worst temper. As an autistic female who also has multiple forms of synesthesia, this topic is very intriguing to me. I never thought that they can possibly be related in any way. Numbers and letters all have specific colours to me, I memorize people’s names, words, or phone numbers by their colours. Numbers also have age and gender, some even have their own characters. Music has colours, months are arranged in space in a very particular way… It might be hard to imagine without experiencing it yourself, but I think it’s a great reminder that everyone lives in their own reality.

Looking back, I see a lot of overlap between my autism and synesthesia. I was obsessed with memorizing pi because of how random and beautiful the colours those numbers make. Occasionally, adjacent numbers may have incompatible characteristics that almost act out as a play in my mind. You see, along with the ability to laser-focus on subjects I’m interested in (thanks to autism), I could easily go into my own world and enjoy the show, while to others I may just be staring at pages full of random numbers.

It is not surprising that there is also a lot of overlapping in sensory processing between autism and synesthesia. According to new research conducted by psychologists at the University of Sussex, both groups report heightened sensory sensitivity, such as an aversion to certain sounds and lights, as well as reporting differences in their tendency to attend to detail (Ward et al. 2017). When sensory alterations appeared as a new autism criterion in the newly minted fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), it was quickly recognized and accepted by professionals. And for some, it connected the dots.

Of course, I can only speak from my own experience. The point I’m trying to make is, there may be more to autism than what we see on the surface. New research has shown connections between Autism, Synesthesia and Savant syndrome (Riedel, A., Maier, S., Wenzler, K. et al., 2020), and by including related conditions into the scope of autism research, we may be able to see a bigger picture.

Additional Resources 

If you’re interested in this topic and would like to learn more about synesthesia, here are some of my favourite reads:

  • Born On A Blue Day: Inside the Extraordinary Mind of an Autistic Savant, by Daniel Tammet
  • Wednesday is Indigo Blue, by Richard Cytowic and David Eagleman (slightly more sciency)
  • A Mango Shaped Space, by Wendy Mass (fictional story based on the author’s encounter with a synesthete girl. A light and fun read)

Work Cited

Baron-Cohen, S., Johnson, D., Asher, J., Wheelwright, S., Fisher, S. E., Gregersen, P. K., & Allison, C. (2013). Is synaesthesia more common in autism?. Molecular autism, 4(1), 40.

Belmonte MK, Allen G, Beckel-Mitchener A, Boulanger LM, Carper R, Webb SJ. Autism and abnormal development of brain connectivity. J Neurosci. 2004;24:9228–9231. doi: 10.1523/JNEUROSCI.3340-04.2004.

Cytowic, Richard E. (2002). Synesthesia: A Union of the Senses (2nd ed.).

Jamie Ward, Claire Hoadley, James E. A. Hughes, Paula Smith, Carrie Allison, Simon Baron-Cohen, Julia Simner. Atypical sensory sensitivity as a shared feature between synaesthesia and autism. Scientific Reports, 2017; 7: 41155 DOI: 10.1038/srep41155

Riedel, A., Maier, S., Wenzler, K. et al. A case of co-occuring synesthesia, autism, prodigious talent and strong structural brain connectivity. BMC Psychiatry 20, 342 (2020).

Tessa M. van Leeuwen, Janina Neufeld, James Hughes & Jamie Ward (2020) Synaesthesia and autism: Different developmental outcomes from overlapping mechanisms?, Cognitive Neuropsychology, 37:7-8, 433-449, DOI: 10.1080/02643294.2020.1808455

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