Understanding Synaesthesia: What colour is Wednesday?

By Samrah Siddiqi

Imagine being able to taste words or smell sounds. To many synesthetes, otherwise normal individuals, this is a daily experience. Their subjective and altered perception of the world, established from birth, is something quite remarkable for the average person – considered a type of superpower to many. Scientists, however, describe synaesthesia as an intriguing neurological phenomenon still yet to be fully understood. 

Unlike anaesthesia meaning “no sensation”, synaesthesia is defined by having “coupled or joint sensations”. This involves the complex joining of multiple sensory cognitive pathways resulting in different types of synaesthesia (TEDx Talks, 2018). For some, numbers have a personality (for example, 3 is sporty) and for Melissa McCracken, a synesthete herself, M is Magenta (TEDx Talks, 2018). The former and latter are both types of grapheme-colour synaesthesia. Individuals with grapheme-colour synaesthesia associate letters or numbers of letters with specific colours, or even personalities. An alternative type of synaesthesia is phoneme-colour synaesthesia. Individuals with phoneme-colour synaesthesia associate sounds with tastes and flavours (Ted-Ed, 2013). A slightly more complex and rare form of this is called Lexical-gustatory synaesthesia, which involves associating sounds and words with temperatures and textures (Wikipedia, n.d.). If synesthetes have one type of synaesthesia they are 50% more likely to have a second type (Cytowic R.E., 2018). Due to such a variety of experiences encountered by synesthetes, synaesthesia is used as a collective umbrella term for unique visual and cross-sensory experiences.

After the first documented case of synaesthesia in 1812, researchers began their investigation into how such a phenomenon could arise (Jewanski J., Day S.A. & Ward J., 2009). Interestingly, the root cause for synaesthesia involves the nature vs nurture debate. Through neuroimaging studies, researchers have discovered that there is an evident neural basis for synaesthesia, with anatomical differences between the brains of synesthetes and significant hyper connectivity between brain neurons (Ted-Ed, 2013). However, a genetic foundation for the phenomenon has also been investigated. It is thought that at the DNA level, a single nucleotide polymorphism (SNP) can alter perception, perhaps playing a role in synaesthesia (Ted-Ed, 2013). Additionally, it has been identified that synaesthesia is an inherited trait – the “synaesthesia genes” is present in approximately one in twenty-three individuals (Cytowic R.E., 2018). Nurture also plays a key role in the development of synaesthesia as individuals must be exposed to cultural artefacts such as calendars and food names in order to form and complete the neural connections (Ted-Ed, 2013).

As a congenital condition, scientists were intrigued as to whether synaesthesia could be acquired. A recent study (Bor et al., 2014) involved recruiting non-synesthetic adults to undertake memory and reading tasks to “reinforce thirteen specific letter-colour associations”. After 9 weeks of training, the non-synesthetic individuals showed genuine synaesthesia suggesting that later acquisition of synaesthesia is possible. However, it should be noted that it is difficult to determine whether the letter-colour associations acquired by the participating individuals directly equates to the sensations experienced by grapheme-colour synesthetes due to the ‘considerable heterogeneity in the form of phenomenology that genuine synesthetes report.’ Studies like this highlight the interplay between synaesthesia and memory, which is why individuals with synaesthesia usually have superior memories. 

Artificially-induced synaesthesia can also be exogenously introduced when individuals use psychedelic drugs such as psilocybin, LSD and mescaline (Schwartzman D.J. et al., 2019). However, there are significant differences between drug-induced and natural synaesthesia. Namely, the synaesthesia-like experiences induced by drugs are inconsistent, not automatic and are highly influenced by the individual’s present state of mind. By contrast, natural synesthetic experiences are involuntary, consistent and are not dependent on the individual’s present state of mind. 

The subjective and variable nature of this neurological condition provides difficulties when trying to diagnose the condition. To date, such methods include using fMRI (functional magnetic resonance imaging) to determine which neural areas are active during sensory perception (Simner J. & Ward J., 2006). Additionally, neuroscientist V.S. Ramachandran discovered a method called the galvanic skin response (GSR) which is used to determine the perceptual genuineness of individuals (due to the subjectivity of the condition). A high GSR would imply that an individual could be lying about having synaesthesia. Alternatively, no GSR would imply that the individual is telling the truth about their condition (Ramachandran V.S., 2011). 

As mentioned earlier, synaesthesia is more common than one might think. This union of senses has inspired many influential artists and composers, who are also synesthetes themselves, in order to shape the world in which we live in today. Notable synesthetes include Lady Gaga, Kanye West, Russian author Vladimir Nabokov, artists Vincent van Gogh and David Hockney and even Marilyn Monroe (Williams H., 2014). With their increased public outreach and scientists’ increased research into the condition, awareness of this spectacular phenomenon is growing worldwide.


Bor, D., Rothen, N., Schwartzman D. et al. (2014) Adults Can Be Trained to Acquire Synesthetic Experiences. Sci Rep. 4, 7089. Available from: DOI: https://doi.org/10.1038/srep07089 

Cytowic R.E. (2018) Synesthesia. London, The MIT Press. Available from: https://mitpress-mit-edu.iclibezp1.cc.ic.ac.uk/books/synesthesia [Accessed 24 August 2020]

Holly Williams. (2014) How synaesthesia inspires artists. Available from: https://www.bbc.com/culture/article/20140904-i-see-songs-in-colour

Jewanski J., Day S.A. & Ward J. (2009) A Colorful Albino: The First Documented Case of Synaesthesia, by Georg Tobias Ludwig Sachs in 1812. Journal of the History of the Neurosciences. 18:3, 293-303. Available from: DOI: 10.1080/09647040802431946

Ramachandran V.S. (2011) The tell-tale brain : a neuroscientist’s quest for what makes us human. New York, W.W. Norton. Available from: https://archive.org/details/telltalebrainneu0000rama [Accessed 25 August 2020]

Schwartzman D.J. et al. (2019) Neurophenomenology of induced and natural synaesthesia. Philosophical transactions of The Royal Society B – Biological Sciences. 374 (1787). Available from: DOI: https://doi.org/10.1098/rstb.2019.0030

Simner J. & Ward J. (2006) The taste of words on the tip of the tongue. Nature. 444 (438). Available from: DOI: https://doi.org/10.1038/444438a

TEDx Talks, (2018) Synesthesia and What It Has Taught Me | Melissa McCracken | TEDxUNC, Available from: https://www.youtube.com/watch?v=kvPd3wH21z8 [Accessed 24 August 2020]

Ted-Ed, (2013) What color is Tuesday? Exploring synaesthesia – Richard E. Cytowic, Available from: https://www.youtube.com/watch?v=rkRbebvoYqI [Accessed 24 August 2020]

Wikipedia, (n.d.) Lexical-gustatory synaesthesia, Available from: https://en.wikipedia.org/wiki/Lexical-gustatory_synesthesia#Possible_neural_basis [Accessed 24 August 2020]

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