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Synesthesia: understanding the condition

Synesthesia occurs when two unrelated senses “cross over,” such as when someone consistently associates a particular letter with a particular color, or when a person “feels sounds.” But what causes synesthesia, and how many people have it?

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Dr. Thomas Tedeschi, Au.D.

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What is synesthesia?

Types

Causes

Diagnosis

Benefits and challenges

Key Takeaways

Synesthesia is a neurological condition where one sense involuntarily triggers another, such as seeing colors when hearing music or tasting words.
It’s not a disease or disorder, but a natural variation in the brain’s wiring, with research confirming physical and functional differences in the brains of individuals with synesthesia.
There are dozens of types, including grapheme-color synesthesia (associating colors with numbers or letters) and chromesthesia (seeing colors in response to sounds).
Synesthesia can be genetic or temporarily caused by factors like brain injury or drug use, but most cases are developmental and remain consistent over time.
While some challenges may arise, such as sensory overload, many synesthetes experience benefits like enhanced memory, creativity and empathy.

What is synesthesia?

People with synesthesia experience one sense being triggered by another, unrelated one. For example, someone with a synesthesia condition might “taste” colors or “see” music. Scientists have identified dozens of types of synesthesia so far, and research is ongoing. The common factor is that one of a person’s five senses—hearing, seeing, touching, smelling, tasting—crosses over with another sense.

A man on a colorful background wearing headphones

Is synesthesia a disease?

Synesthesia is not a disease, medical condition or mental disorder. Synesthesia is neurological, meaning it has to do with the brain’s pathways.

Is synesthesia real?

Synesthesia is real. This field of study has increased substantially in the past two decades or more, and there is now plenty of evidence to show neural and behavioral traits that are associated with synesthesia.¹ According to a 2016 paper by researchers at the University of Amsterdam, “Neuroimaging studies have shown functional and structural brain differences in synesthetes, as compared with non-synesthetes, in brain regions functionally related to emotion².”

Types of synesthesia

According to a 2011 article in the British Journal of Psychology, there are at least 61 different types of synesthesia³. Some synesthesia types are more common than others, but all fall under the same definition: it’s a condition where one sense triggers another, unrelated sense.

With grapheme-color synesthesia, people experience specific letters or numbers as specific colors. The letter F might be green, for example, or the number 3 might be orange.

Chromesthesia, or sound-color synesthesia, is when a person experiences a sound as a color, shape or movement. They might hear a car horn and see a burst of yellow, or they might hear the sound of wind through the trees and see swirls of purple and green.

If someone has lexical-gustatory synesthesia, they can “taste” words⁴. When this happens, there’s often a link between the taste and the word that triggers the taste. For example, someone with lexical-gustatory synesthesia might taste blueberry when they see the word “sky,” or the word “cat” might evoke the taste of radish, because both words include short-a sounds.

Mirror-touch synesthesia⁵ is sometimes described as akin to extreme empathy, but it’s more than just cringing if you see someone trip and fall. People with mirror-touch synesthesia feel what other people feel, literally. For example, if they see someone touch another person’s arm, they might get a feeling on the same place on their own arm.

Space-time synesthesia: People with space-time synesthesia see periods of time, such as days or months, as individualized spatial forms.⁶
Auditory-tactile synesthesia: If someone has auditory-tactile synesthesia⁷, sounds (such as a song, a particular musical note or an environmental noise) trigger a physical feeling in the body. These could include anything from a buzzing on the skin to feeling as if they’re holding an object in their hand.

What is the cause of synesthesia?

There are temporary types of synesthesia caused by factors such as drug use, injury to the brain or sensory deprivation. However, the most common category of synesthesia is genetic, or developmental^8,9.

Developmental synesthesia is:

Caused by more than one gene
Different for each person
Involuntary
Stable over time

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How do you know if you have synesthesia?

Pay attention to how you experience the world. Research the different types of synesthesia and see if any of them sound like something you experience regularly. Symptoms of synesthesia vary from person to person, but if your symptoms are automatic (involuntary) and consistent over time, you likely have synesthesia.

How synesthesia is diagnosed

There are online synesthesia tests available, but these aren’t always accurate. The most important factor is consistency, so if you choose the route of an online synesthesia test, consider taking the same test two weeks apart. That way, you will have forgotten your previous answers.

If your symptoms are on the intense end of the spectrum, you could start with your doctor. They might refer you to a mental health professional who can equip you with strategies that could help.

How common is synesthesia?

For years, researchers have estimated that 3–5% of the general population has heritable synesthesia⁸—that is, synesthesia that they inherited genetically from their parents. However, some researchers believe this number is low; in the past, some types of synesthesia were wrongly diagnosed as schizophrenia or other mental illnesses, leading synesthetes to hide their condition⁹. One study found an occurrence of 24% in its research sample¹⁰.

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Famous people with synesthesia

Many famous people with synesthesia are in the creative industries. Singer Olivia Rodrigo says she has chromesthesia, as do Billy Joel and Pharrell Williams. Painter Vincent Van Gogh⁹ and writer Vladimir Nabokov both claimed to have synesthesia, too.

Benefits and challenges

Scientists are still working to understand the genetic basis for synesthesia, which will help them figure out why humans developed it—in other words, if there is an evolutionary reason for it.

There are dozens of types of synesthesia, each with its own benefits and challenges, but here are some of the more common ones.

Benefits

Some studies have shown that enhanced visual memory¹⁰ is linked with synesthesia. It’s unclear if this is because synesthetes’ associations enhance recall or because the neural pathways that cause the synesthesia enable better memory function.
Synesthetes show enhanced abilities in mental imagery^1,11.
People with space-time synesthesia could have enhanced organizational skills because they can “picture” time periods⁶.
One study found a correlation between mirror-touch synesthesia and heightened empathy skills¹².
Synesthetes tend to be attracted to the creative industries (writing, art, music)¹³.

Challenges

Variants such as mirror-touch synesthesia could be overwhelming, such as in crowded spaces.
People with auditory-tactile synesthesia could find events such as concerts too intense to enjoy.
Some synesthetes can feel isolated from the general population due to their unique experiences of the world.

If you experience any of these challenges, a mental health professional could help you adopt strategies that will ease your experience of synesthesia.

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Sources

1. Spiller, Mary & Jonas, Clare & Simner, Julia & Jansari, Ashok. (2015). Beyond visual imagery: How modality-specific is enhanced mental imagery in synesthesia?. Consciousness and Cognition. 31. 73-85. 10.1016/j.concog.2014.10.010. https://pubmed.ncbi.nlm.nih.gov/25460242/

2. Romke Rouw, H. Steven Scholte, Personality and cognitive profiles of a general synesthetic trait, Neuropsychologia, Volume 88, 2016, Pages 35-48.

https://doi.org/10.1016/j.neuropsychologia.2016.01.006.

3. Simner, J. (2012), Defining synaesthesia. British Journal of Psychology, 103: 1-15. https://doi.org/10.1348/000712610X528305

4. Ward, Jamie, and Julia Simner. “Lexical-gustatory synaesthesia: linguistic and conceptual factors.” Cognition vol. 89,3 (2003): 237-61. doi:10.1016/s0010-0277(03)00122-7 https://pubmed.ncbi.nlm.nih.gov/12963263/

5. Fitzgibbon, Bernadette M et al. “Mirror-sensory synaesthesia: exploring 'shared' sensory experiences as synaesthesia.” Neuroscience and biobehavioral reviews vol. 36,1 (2012): 645-57. doi:10.1016/j.neubiorev.2011.09.006 https://pubmed.ncbi.nlm.nih.gov/21986634/

6. Mann, Heather et al. “Time-space synaesthesia--a cognitive advantage?.” Consciousness and cognition vol. 18,3 (2009): 619-27. doi:10.1016/j.concog.2009.06.005 https://www.sciencedirect.com/science/article/abs/pii/S1053810009000932?via%3Dihub

7. Ali, SA, Ali SN and Khan R. "Sensing Sounds on the Skin: A Review of Auditory-tactile Synesthesia and Its Implications for Perception and Attention." J Neurol Disord. 11 (2023):565. https://www.hilarispublisher.com/open-access/sensing-sounds-on-the-skin-a-review-of-auditorytactile-synesthesia-and-its-implications-for--perception-and-attention.pdf

8. Brang D, Ramachandran VS (2011) Survival of the Synesthesia Gene: Why Do People Hear Colors and Taste Words? PLoS Biol 9(11): e1001205. https://doi.org/10.1371/journal.pbio.1001205

9. Safran, Avinoam B, and Nicolae Sanda. “Color synesthesia. Insight into perception, emotion, and consciousness.” Current opinion in neurology vol. 28,1 (2015): 36-44. doi:10.1097/WCO.0000000000000169 https://pmc.ncbi.nlm.nih.gov/articles/PMC4286234/

10. Rothen, N., Meier, B., & Ward, J. (2012). Enhanced memory ability: insights from synesthesia.Neuroscience & Biobehavioral Reviews, 36(8), 1952‐1963.

https://doi.org/10.1016/j.neubiorev.2012.05.004.

11. Barnett, Kylie J, and Fiona N Newell. “Synaesthesia is associated with enhanced, self-rated visual imagery.” Consciousness and cognition vol. 17,3 (2008): 1032-9. doi:10.1016/j.concog.2007.05.011 https://pubmed.ncbi.nlm.nih.gov/17627844/

12. Banissy, M., Ward, J. Mirror-touch synesthesia is linked with empathy. Nat Neurosci 10, 815–816 (2007). https://doi.org/10.1038/nn1926

13. Chun, C.A. and Hupé, J.-M. (2016), Are synesthetes exceptional beyond their synesthetic associations? A systematic comparison of creativity, personality, cognition, and mental imagery in synesthetes and controls. Br J Psychol, 107: 397-418. https://doi.org/10.1111/bjop.12146