{{Short description|Neurological condition involving the crossing of senses}} {{Other uses}} {{Distinguish|Synthesia (disambiguation){{!}}Synthesia}} {{Use dmy dates|date=November 2015}} {{Use American English|date=December 2013}} <!-- Definition and symptoms --> {{Infobox medical condition | name = Synesthesia | image = Synesthesia.svg | alt = Picture of the word "synesthesia" and several numbers color-coded in a way a synesthete may see them. | caption = A person experiencing synesthesia may associate certain letters and numbers with certain colors. | pronounce = /ˌsɪn.əsˈθiː.zi.ə/ | specialty = Neuroscience, neurology, psychology | frequency = 4%<ref>[https://my.clevelandclinic.org/health/symptoms/24995-synesthesia]</ref> }}
'''Synesthesia''' (American English) or '''synaesthesia''' (British English) is a perceptual phenomenon in which stimulation of one sensory or cognitive pathway leads to involuntary experiences in other sensory or cognitive pathways.<ref name="isbn0-262-03296-1">{{cite book|last=Cytowic|first=Richard E.|author-link=Richard Cytowic|title=Synesthesia: A Union of the Senses |publisher=MIT Press |location=Cambridge, Massachusetts|year=2002 |isbn=978-0-262-03296-4 |oclc=49395033|edition=2nd}} {{page needed|date=January 2014}}</ref><ref name="isbn0-262-53255-7">{{cite book|last=Cytowic|first=Richard E.|author-link=Richard Cytowic|title=The Man Who Tasted Shapes |publisher=MIT Press|location=Cambridge, Massachusetts|year=2003 |isbn=978-0-262-53255-6 |oclc=53186027}} {{page needed|date=January 2014}}</ref><ref name="Cytowic_Eagleman2009">{{cite book|last1=Cytowic|first1=Richard E.|author1-link=Richard Cytowic|last2=Eagleman|first2=David M.|author2-link=David Eagleman|title=Wednesday is Indigo Blue: Discovering the Brain of Synesthesia|others=with an afterword by Dmitri Nabokov|publisher=MIT Press|location=Cambridge |year=2009 |isbn=978-0-262-01279-9}} {{page needed|date=January 2014}}</ref><ref name="isbn0-631-19764-8">{{cite book | vauthors = Harrison JE, Baron-Cohen S |title=Synaesthesia: classic and contemporary readings |publisher=Blackwell Publishing |location=Oxford|year=1996 |isbn=978-0-631-19764-5 |oclc=59664610}} {{page needed|date=January 2014}}</ref><ref>{{Cite web |title=Synesthesia|url=https://my.clevelandclinic.org/health/symptoms/24995-synesthesia|url-status=live|archive-url=http://web.archive.org/web/20250922172141/https://my.clevelandclinic.org/health/symptoms/24995-synesthesia |archive-date=2025-09-22 |access-date=2025-12-04 |website=Cleveland Clinic}}</ref> Synesthesia can manifest as a bridge between the five traditional senses, though it can also include other perceptions, such as nociception, thermoception, chronoception, and interoception.<ref name="Safran" /> People with synesthesia are referred to as synesthetes.{{Citation needed|date=January 2026}}
Awareness of synesthetic perceptions varies from person to person with the perception of synesthesia differing based on an individual's unique life experiences and the specific type of synesthesia that they have.<ref>{{Cite web |last=Henry |first=Paige |date=19 September 2003 |title=Synesthesia: Definition, Explanation, and More |url=https://www.betterhelp.com/advice/synesthesia/understanding-the-synesthesia-definition/|website=betterhelp.com}}</ref><ref name="campen2009">{{cite journal | vauthors = van Campen C|author-link=Cretien van Campen| date = 2009b | title = The Hidden Sense: On Becoming Aware of Synesthesia|journal=Revista digital de technologias cognitivas|issn=1984-3585|volume=1|pages=1–13|url=https://www.pucsp.br/pos/tidd/teccogs/artigos/pdf/teccogs_edicao1_2009_artigo_CAMPEN.pdf|url-status=dead|archive-url=https://web.archive.org/web/20090708013028/http://www.pucsp.br/pos/tidd/teccogs/artigos/pdf/teccogs_edicao1_2009_artigo_CAMPEN.pdf |archive-date=8 July 2009|type=final chapter of {{harvnb|van Campen|2007}}}}</ref> In one common form of synesthesia, known as grapheme–color synesthesia or color–graphemic synesthesia, letters or numbers are perceived as inherently colored.<ref>{{cite journal | vauthors = Rich AN, Mattingley JB | title = Anomalous perception in synaesthesia: a cognitive neuroscience perspective | journal =Nature Reviews. Neuroscience| volume = 3 | issue = 1 | pages = 43–52 | date = January 2002 | pmid = 11823804 | doi = 10.1038/nrn702 | type = Review | s2cid = 11477960}}</ref><ref name="Hubbard_2005">{{cite journal | vauthors = Hubbard EM, Ramachandran VS | title = Neurocognitive mechanisms of synesthesia | journal =Neuron| volume = 48 | issue = 3 | pages = 509–520 | date = November 2005 | pmid = 16269367 | doi = 10.1016/j.neuron.2005.10.012 | type = Review | s2cid = 18730779 | doi-access = free}}</ref> In spatial-sequence, or number form synesthesia, numbers, months of the year, or days of the week elicit precise locations in space (e.g., 1980 may be "farther away" than 1990), or may appear as a three-dimensional map (clockwise or counterclockwise).<ref name="galton1880b">{{cite journal| vauthors = Galton F |year=1880b|title=Visualized Numerals |url=https://zenodo.org/record/1429243 |journal=Nature|volume=21|issue=543|pages=494–495|doi=10.1038/021494e0|bibcode=1880Natur..21..494G|s2cid=4074444|doi-access=free}}</ref><ref>{{cite journal | vauthors = Seron X, Pesenti M, Noël MP, Deloche G, Cornet JA | title = Images of numbers, or 'When 98 is upper left and 6 sky blue'| journal =Cognition| volume = 44 | issue = 1–2 | pages = 159–196 | date = August 1992 | pmid = 1511585 | doi = 10.1016/0010-0277(92)90053-K | s2cid = 26687757}}</ref> Synesthetic associations can occur in any combination and any number of senses or cognitive pathways.<ref>{{Cite web|url=https://science.howstuffworks.com/life/inside-the-mind/emotions/synesthesia1.htm|title=How Synesthesia Works|date=1970-01-01|website=HowStuffWorks|access-date=2016-05-02}}</ref>
<!-- Cause --> Little is known about how synesthesia develops. It has been suggested that synesthesia develops during childhood when children are intensively engaged with abstract concepts for the first time.<ref name="MroczkoNikolic2014" />
<!-- History --> The earliest recorded case of synesthesia is attributed to the Oxford University academic and philosopher John Locke, who, in 1690, made a report about a blind man who said he experienced the color scarlet when he heard the sound of a trumpet.<ref name=OssianWard /> However, there is disagreement as to whether Locke described an actual instance of synesthesia or was using a metaphor.<ref name="Jewanski_2009">{{cite journal | vauthors = Jewanski J, Day SA, Ward J | title = A colorful albino: the first documented case of synaesthesia, by Georg Tobias Ludwig Sachs in 1812 | journal =Journal of the History of the Neurosciences| volume = 18 | issue = 3 | pages = 293–303 | date = July 2009 | pmid = 20183209 | doi = 10.1080/09647040802431946 | s2cid = 8641750}}</ref> The first medical account came from German physician Georg Tobias Ludwig Sachs in 1812.<ref name="Jewanski_2009" /><ref name="Herman_2018">{{Cite web|url=https://www.britannica.com/science/synesthesia|title=Synesthesia| vauthors = Herman LM |date=2018-12-28|website=Encyclopaedia Britannica|access-date=2019-01-25}}</ref><ref>{{Cite news |url=https://blogs.scientificamerican.com/literally-psyched/from-the-words-of-an-albino-a-brilliant-blend-of-color/ |title=From the words of an albino, a brilliant blend of color| vauthors = Konnikova M |date=2013-02-26|newspaper=Scientific American Blog Network |archive-url= https://web.archive.org/web/20160920114035/https://blogs.scientificamerican.com/literally-psyched/from-the-words-of-an-albino-a-brilliant-blend-of-color/ |archive-date=2016-09-20 |access-date=2019-01-25}}</ref> The term is from Ancient Greek {{lang|grc|σύν}} ({{lang|grc-Latn|syn}}, 'together') and {{lang|grc|αἴσθησις}} ({{lang|grc-Latn|aisthēsis}}, 'sensation').<ref name=OssianWard>Ward, Ossian (10 June 2006). [https://www.telegraph.co.uk/culture/art/3653012/The-man-who-heard-his-paintbox-hiss.html The man who heard his paint box hiss]. ''The Telegraph''. Retrieved 3 December 2018.</ref>
== Types == There are two overall forms of synesthesia: * Projective synesthesia: seeing colors, forms, or shapes when stimulated (the widely understood version of synesthesia) * Associative synesthesia: feeling a very strong and involuntary connection between the stimulus and the sense that it triggers For example, in chromesthesia (sound to color), a ''projector'' may hear a trumpet, and see an orange triangle in space, while an ''associator'' might hear a trumpet, and think very strongly that it sounds "orange".{{Medical citation needed|date=January 2026}}
Synesthesia can occur between nearly any two senses or perceptual modes, and at least one synesthete, Solomon Shereshevsky, experienced synesthesia that linked all five senses.<ref name="Schacter_1996">{{Cite book|title=Searching for Memory: The Brain, The Mind, And The Past| vauthors = Schacter D |author-link=Daniel Schacter|publisher=Basic Books|year=1996|isbn=978-0-465-07552-2|pages=[https://archive.org/details/searchingformemo00dani/page/81 81]|url=https://archive.org/details/searchingformemo00dani/page/81}}</ref> Types of synesthesia are indicated by using the notation {{nowrap|x → y}}, where x is the "inducer" or trigger experience, and y is the "concurrent" or additional experience. For example, perceiving letters and numbers (collectively called graphemes) as colored would be indicated as grapheme–color synesthesia. Similarly, when synesthetes see colors and movement as a result of hearing musical tones, it would be indicated as tone → (color, movement) synesthesia.{{Medical citation needed|date=January 2026}}
While nearly every logically possible combination of experiences can occur, several types are more common than others.{{Medical citation needed|date=January 2026}}
=== Auditory–tactile synesthesia === <!-- Auditory–tactile synesthesia redirects here. --> In '''auditory–tactile synesthesia''', certain sounds can induce sensations in parts of the body. For example, someone with auditory–tactile synesthesia may experience that hearing a specific word or sound feels like touch in one specific part of the body or may experience that certain sounds can create a sensation in the skin without being touched (not to be confused with the milder general reaction known as frisson, which affects approximately 50% of the population). Although it is one of the least common forms of synesthesia,<ref>{{cite journal |vauthors=Naumer MJ, van den Bosch JJ |date=July 2009 |title=Touching sounds: thalamocortical plasticity and the neural basis of multisensory integration |url=http://pdfs.semanticscholar.org/28e0/779e6d740192099466d629c490f93210eff5.pdf |journal=Journal of Neurophysiology|volume=102 |issue=1 |pages=7–8 |doi=10.1152/jn.00209.2009 |pmid=19403745 |s2cid=1712367 |archive-url=https://web.archive.org/web/20190220203234/http://pdfs.semanticscholar.org/28e0/779e6d740192099466d629c490f93210eff5.pdf |archive-date=2019-02-20}}</ref> a similar sensation can be evoked in many people known as ASMR.<ref>{{cite journal |last1=Simner |first1=Julia |last2=Mulvenna |first2=Catherine |last3=Sagiv |first3=Noam |last4=Tsakanikos |first4=Elias |last5=Witherby |first5=Sarah A. |last6=Fraser |first6=Christine |last7=Scott |first7=Kirsten |last8=Ward |first8=Jamie |display-authors=1 |year=2006 |title=Synaesthesia: the prevalence of atypical cross-modal experiences |url=http://sro.sussex.ac.uk/id/eprint/14073/1/p5469.pdf |url-status=live |journal=Perception|volume=35 |issue=8 |pages=1024–1033 |doi=10.1068/p5469 |pmid=17076063 |s2cid=2508540 |archive-url=https://web.archive.org/web/20220412005601/http://sro.sussex.ac.uk/id/eprint/14073/1/p5469.pdf |archive-date=12 April 2022 |access-date=2 July 2023}}</ref><ref>{{cite journal |last1=Banissy |first1=Michael J. |last2=Jonas |first2=Clare |last3=Cohen Kadosh |first3=Roi |display-authors=1 |date=15 December 2014 |title=Synesthesia: an introduction |journal=Frontiers in Psychology|volume=5 |issue=1414 |page=1414 |doi=10.3389/fpsyg.2014.01414 |pmc=4265978 |pmid=25566110 |doi-access=free}}</ref>
=== Chromesthesia === {{Main|Chromesthesia}}
Another common form of synesthesia is the association of sounds with colors. For some, everyday sounds can trigger seeing colors. For others, colors are triggered when musical notes or keys are being played. People with synesthesia related to music may also have perfect pitch because their ability to see ''and'' hear colors aids them in identifying notes or keys.<ref>{{Cite web|url=http://www.feinsteininstitute.org/robert-s-boas-center-for-genomics-and-human-genetics/projects/genetics-and-epidemiology-of-absolute-pitch-and-related-cognitive-traits/|title=Absolute Pitch and Synesthesia {{!}} The Feinstein Institute for Medical Research|website=The Feinstein Institute for Medical Research|language=en-US|access-date=2016-05-02|archive-date=13 December 2017|archive-url=https://web.archive.org/web/20171213201036/http://www.feinsteininstitute.org/robert-s-boas-center-for-genomics-and-human-genetics/projects/genetics-and-epidemiology-of-absolute-pitch-and-related-cognitive-traits/}}</ref>
The colors triggered by certain sounds, and any other synesthetic visual experiences, are referred to as ''photisms''.{{Citation needed|date=January 2026}}
According to Richard Cytowic,<ref name="Cytowic_Eagleman2009" /> chromesthesia is "something like fireworks": voice, music, and assorted environmental sounds such as clattering dishes or dog barks trigger color and firework shapes that arise, move around, and then fade when the sound ends. Sound often changes the perceived hue, brightness, scintillation, and directional movement. Some individuals see music on a "screen" in front of their faces. For Deni Simon, music produces waving lines "like oscilloscope configurations{{snd}} lines moving in color, often metallic with height, width, and, most importantly, depth. My favorite music has lines that extend horizontally beyond the 'screen' area."{{citation needed|date=April 2025}}
=== Emotional synesthesia === Emotional synesthesia is a rarely documented form of synesthesia in which emotions trigger a response in another sensation (such as smell, taste, color, and texture). Emotional synesthesia is estimated to make up about 1% of the synesthete population.<ref name="Schweizer et al">{{Cite journal |last1=Schweizer |first1=Tom A. |last2=Li |first2=Zeyu |last3=Fischer |first3=Corinne E. |last4=Alexander |first4=Michael P. |last5=Smith |first5=Stephen D. |last6=Graham |first6=Simon J. |last7=Fornazarri |first7=Luis |date=2013-07-30 |title=From the thalamus with love: A rare window into the locus of emotional synesthesia |url=https://www.neurology.org/doi/10.1212/WNL.0b013e31829d86cc |journal=Neurology|volume=81 |issue=5 |pages=509–510 |doi=10.1212/WNL.0b013e31829d86cc|pmid=23803316 |url-access=subscription }}</ref>
There is only one known case of acquired emotional synesthesia, which was caused by a focal thalamic lesion.<ref name="Schweizer et al" />
=== Grapheme–color synesthesia === {{Main|Grapheme–color synesthesia}}
[[File:Number Form--colored.jpg|thumb|From the 2009 non-fiction book ''Wednesday Is Indigo Blue'']] In one of the most common forms of synesthesia, individual letters of the alphabet and numbers (collectively referred to as "graphemes") are "shaded" or "tinged" with a color. While different individuals usually do not report the same colors for all letters and numbers, studies with large numbers of synesthetes find some commonalities across letters (e.g., A is likely to be red).<ref name="isbn0-19-516623-X" />
Some authors have argued that the term synaesthesia may not be correct when applied to the so-called grapheme–colour synesthesia and similar phenomena in which the inducer is conceptual (e.g. a letter or number) rather than sensory (e.g. sound or color). They have postulated that the term 'ideasthesia' is a more accurate description.<ref name="ideasthesia">{{cite journal |vauthors=Nikolić D |year=2009 |title=Is synaesthesia actually ideaesthesia? An inquiry into the nature of the phenomenon |url=http://www.danko-nikolic.com/wp-content/uploads/2011/09/Synesthesia2009-Nikolic-Ideaesthesia.pdf |journal=Proceedings of the Third International Congress on Synaesthesia, Science & Art, Granada, Spain, April 26–29}}</ref><ref name="defsyn">{{cite journal |vauthors=Simner J |date=February 2012 |title=Defining synaesthesia |url=https://www.pure.ed.ac.uk/ws/files/12435588/Defining_synaesthesia.pdf |journal=British Journal of Psychology|type=Review |volume=103 |issue=1 |pages=1–15 |doi=10.1348/000712610X528305 |pmid=22229768 |s2cid=9038571}}</ref>
=== Kinesthetic synesthesia === Kinesthetic synesthesia is one of the rarest documented forms of synesthesia.<ref name="Types-of-Syn">{{cite web |title=Types-of-Syn |url=http://www.daysyn.com/Types-of-Syn.html |access-date=2016-01-26 |website=DaySyn.com}}</ref> This form of synesthesia is a combination of different types of synesthesia. Features appear similar to auditory–tactile synesthesia but sensations are not isolated to individual numbers or letters but complex systems of relationships.{{Medical citation needed|date=January 2026}}
=== Lexical–gustatory synesthesia === {{Main|Lexical–gustatory synesthesia}}
This is another form of synesthesia where certain tastes are experienced when hearing words. For example, the word ''basketball'' might taste like waffles. The documentary ''Derek Tastes of Earwax'' gets its name from this phenomenon, referring to pub owner James Wannerton who experiences this particular sensation whenever he hears the name spoken.<ref>{{cite web |title=Derek Tastes of Ear Wax |url=http://topdocumentaryfilms.com/derek-tastes-of-ear-wax |access-date=2 February 2015 |work=Top Documentary Films}}</ref><ref>{{cite web |title=BBC – Science & Nature – Horizon |url=https://www.bbc.co.uk/sn/tvradio/programmes/horizon/derek_prog_summary.shtml |access-date=2 February 2015 |work=bbc.co.uk}}</ref> It is estimated that 0.2% of the synesthesia population has this form of synesthesia, making it one of the rarest forms.<ref>{{Cite book |title=Encyclopedia of Neuroscience |vauthors=Simner J |publisher=Springer Berlin Heidelberg |year=2009 |isbn=978-3-540-23735-8 |pages=2149–2152 |chapter=Lexical-Gustatory Synesthesia |doi=10.1007/978-3-540-29678-2_2766}}</ref>
=== Mirror-touch synesthesia === {{Main|Mirror-touch synesthesia}}
This is a form of synesthesia where individuals feel the same/similar sensation as another person (such as touch). For instance, when such a synesthete observes someone being tapped on their shoulder, the synesthete involuntarily feels a tap on their own shoulder as well. Some research suggests people with this type of synesthesia have higher empathy levels compared to the general population.<ref>{{cite journal|last=Banissy|first=Michael|author2=Jamie Ward|title=Mirror Touch Synaesthesia is Linked with Empathy|journal=Nature Neuroscience|date=July 2007|volume=10|issue=7|pages=815–816|doi=10.1038/nn1926|pmid=17572672|s2cid=1345360}}</ref> This may be related to the so-called mirror neurons present in the motor areas of the brain, which some research links to empathy.<ref>{{cite journal |vauthors=Heyes C |date=March 2010 |title=Where do mirror neurons come from? |journal=Neuroscience & Biobehavioral Reviews|volume=34 |issue=4 |pages=575–583 |doi=10.1016/j.neubiorev.2009.11.007 |pmid=19914284 |s2cid=2578537}}</ref> However, other research finds no relationship between mirror-touch synesthesia and empathy.<ref>{{Cite journal |last1=Baron-Cohen |first1=Simon |last2=Robson |first2=Emma |last3=Lai |first3=Meng-Chuan |last4=Allison |first4=Carrie |date=2016-08-04 |title=Mirror-Touch Synaesthesia Is Not Associated with Heightened Empathy, and Can Occur with Autism |journal=PLOS One|language=en |volume=11 |issue=8 |article-number=e0160543 |doi=10.1371/journal.pone.0160543 |doi-access=free |issn=1932-6203 |pmc=4973977 |pmid=27490947|bibcode=2016PLoSO..1160543B}}</ref>
=== Number form === {{Main|Number form}}
[[File:Galton number form.svg|thumb|A number form from one of Francis Galton's subjects (1881).<ref name="galton1880b" /> Note how the first 4 digits roughly correspond to their positions on a clock face.]] A number form is a mental map of numbers that automatically and involuntarily appears whenever someone who experiences number-forms synesthesia thinks of numbers. These numbers might appear in different locations and the mapping changes and varies between individuals. Number forms were first documented and named in 1881 by Francis Galton in "The Visions of Sane Persons".<ref>{{Cite journal| vauthors = Seaton M |date=2013|title=The Visions of Sane Persons|journal=Ploughshares|volume=39|issue=1|pages=144–145|doi=10.1353/plo.2013.0012|s2cid=161837195|issn=2162-0903}}</ref>
=== Ordinal linguistic personification === {{Main|Ordinal linguistic personification}}
Ordinal-linguistic personification (OLP, or personification) is a form of synesthesia in which ordered sequences, such as ordinal numbers, week-day names, months, and alphabetical letters are associated with personalities or genders.{{sfn|Simner|Hubbard|2006}} Although this form of synesthesia was documented as early as the 1890s,{{sfn|Flournoy|2001}}<ref>{{cite journal|last=Calkins|first=M. W.|author-link=Mary Whiton Calkins|year=1893|title=A Statistical Study of Pseudo-chromesthesia and of Mental-forms|url=https://archive.org/details/sim_american-journal-of-psychology_1893-07_5_4/page/438|journal=American Journal of Psychology|issue=4|volume=5|pages= 439–464|doi=10.2307/1411912|jstor=1411912}}</ref> researchers have, until recently, paid little attention to it (see History of synesthesia research). This form of synesthesia was named "OLP" in the contemporary literature by Julia Simner and colleagues,<ref>{{cite journal | vauthors = Simner J, Hubbard EM | title = Variants of synesthesia interact in cognitive tasks: evidence for implicit associations and late connectivity in cross-talk theories | journal =Neuroscience| volume = 143 | issue = 3 | pages = 805–814 | date = December 2006 | pmid = 16996695 | doi = 10.1016/j.neuroscience.2006.08.018 | s2cid = 18922608}}</ref> although it is now also widely recognized by the term "sequence-personality" synesthesia. Ordinal linguistic personification normally co-occurs with other forms of synesthesia such as grapheme–color synesthesia.{{Medical citation needed|date=January 2026}}
=== Spatial sequence synesthesia === Those with spatial sequence synesthesia (SSS) tend to see ordinal sequences as points in space. People with SSS may have superior memories; in one study, they were able to recall past events and memories far better and in far greater detail than those without the condition. They can also see months or dates in the space around them, but most synesthetes "see" these sequences in their mind's eye. Some people see time like a clock above and around them, or perceive musical notes as occupying space in front and through them.<ref>{{cite journal |vauthors=Jonas CN, Price MC |date=2014-10-30 |title=Not all synesthetes are alike: spatial vs. visual dimensions of sequence-space synesthesia |journal=Frontiers in Psychology|volume=5 |page=1171 |doi=10.3389/fpsyg.2014.01171 |pmc=4214186 |pmid=25400596 |doi-access=free}}</ref><ref>{{MEDRS|date=January 2014}}[http://www.sciencemag.org/site/help/about/index.xhtml Do sequence-space synaesthetes have better spatial imagery skills? Maybe not], The National Center for Biotechnology Information</ref><ref>{{unreliable source?|date=January 2014}} [https://www.science.org/content/article/mind-touches-past A Mind That Touches the Past], Sciencemag.org</ref>
=== Ticker-tape synesthesia === Those with ticker-tape synesthesia mentally see written words when they are heard, sometimes on imaginary strips of paper.<ref>{{Cite journal |last1=Hauw |first1=Fabien |last2=El Soudany |first2=Mohamed |last3=Cohen |first3=Laurent|ref=none|date=2023-11-01 |title=The advantage of being a synesthete: The behavioral benefits of ticker-tape synesthesia |journal=Cortex|volume=168 |pages=226–234 |doi=10.1016/j.cortex.2023.08.011 |issn=0010-9452|doi-access=free |pmid=37832491}}</ref> It has been suggested that the name "subtitled synesthesia" would better describe the phenomenon.<ref>{{Cite journal |last1=Hauw |first1=Fabien |last2=El Soudany |first2=Mohamed |last3=Cohen |first3=Laurent|ref=none|date=2023-03-01 |title=Subtitled speech: Phenomenology of tickertape synesthesia |journal=Cortex|volume=160 |pages=167–179 |doi=10.1016/j.cortex.2022.11.005 |pmid=36609103 |issn=0010-9452|doi-access=free}}</ref> Research into people with ticker-tape synesthesia may help explain dyslexia.<ref>{{Cite journal |last=Makowski |first=Emily |date=July 2024 |title=Speech Transforms into Text I "See" |url=https://www.scientificamerican.com/article/my-synesthesia-transforms-speech-into-text-i-see-in-my-head/ |journal=Scientific American|volume=331 |issue=1 |page=90 |doi=10.1038/scientificamerican072024-7u4EbzmVYnR4vlcAgPF3SI |pmid=39017518 |bibcode=2024SciAm.331a..90M |issn=0036-8733|url-access=subscription}}</ref>
=== Other forms === Other forms of synesthesia have been reported, but little has been done to analyze them scientifically. There are at least 80 types of synesthesia.<ref name="Types-of-Syn"/>
In August 2017 a research article in the journal ''Social Neuroscience'' reviewed studies with fMRI to determine if persons who experience autonomous sensory meridian response (ASMR) are experiencing a form of synesthesia. While a determination has not yet been made, there is anecdotal evidence that this may be the case, based on significant and consistent differences from the control group, in terms of functional connectivity within neural pathways. It is unclear whether this will lead to ASMR being included as a form of existing synesthesia, or if a new type will be considered.<ref>{{cite journal | vauthors = Smith SD, Katherine Fredborg B, Kornelsen J | title = An examination of the default mode network in individuals with autonomous sensory meridian response (ASMR) | journal =Social Neuroscience| volume = 12 | issue = 4 | pages = 361–365 | date = August 2017 | pmid = 27196787 | doi = 10.1080/17470919.2016.1188851 | doi-access = free}}</ref>
== Signs and symptoms == Some synesthetes often report that they were unaware their experiences were unusual until they realized other people did not have them, while others report feeling as if they had been keeping a secret their entire lives.<ref name=campen2007>{{cite book|last=van Campen|first=Cretien|author-link=Cretien van Campen|title=The Hidden Sense: Synesthesia in Art and Science |publisher=MIT Press|location=Cambridge, Massachusetts|year=2007 |isbn=978-0-262-22081-1 |oclc=80179991 |url-access=registration |url=https://archive.org/details/hiddensensesynes0000camp}}{{page needed|date=January 2014}}</ref> The automatic and ineffable nature of a synesthetic experience means that the pairing may not seem out of the ordinary. This involuntary and consistent nature helps define synesthesia as a real experience. Most synesthetes report that their experiences are pleasant or neutral, although, in rare cases, synesthetes report that their experiences can lead to a degree of sensory overload.<ref name="isbn0-19-516623-X" />
Though often stereotyped in the popular media as a medical condition or neurological aberration,<ref name="Safran">{{Cite journal |last1=Safran |first1=Avinoam B. |last2=Sanda |first2=Nicolae |date=December 2014|title=Color synesthesia. Insight into perception, emotion, and consciousness |journal=Current Opinion in Neurology|volume=28 |issue=1 |pages=36–44 |doi=10.1097/WCO.0000000000000169 |issn=1473-6551 |pmc=4286234 |pmid=25545055}}</ref> many synesthetes themselves do not perceive their synesthetic experiences as a handicap. On the contrary, some report it as a gift{{snd}} an additional "hidden" sense{{snd}} something they would not want to miss. Most synesthetes become aware of their distinctive mode of perception in their childhood. Some have learned how to apply their ability in daily life and work. Synesthetes have used their abilities in memorization of names and telephone numbers, mental arithmetic, and more complex creative activities like producing visual art, music, and theater.<ref name="campen2007" />
Despite the commonalities which permit the definition of the broad phenomenon of synesthesia, individual experiences vary in numerous ways. This variability was first noticed early in synesthesia research.<ref name="isbn0-543-94462-X">{{cite book | vauthors = Flournoy T |title=Des phénomènes de synopsie (Audition colorée) |publisher=Adamant Media Corporation |year=2001 |isbn=978-0-543-94462-7}}{{page needed|date=January 2014}}</ref> Some synesthetes report that vowels are more strongly colored, while for others consonants are more strongly colored.<ref name="isbn0-19-516623-X" /> Self-reports, interviews, and autobiographical notes by synesthetes demonstrate a great degree of variety in types of synesthesia, the intensity of synesthetic perceptions, awareness of the perceptual discrepancies between synesthetes and non-synesthetes, and the ways synesthesia is used in work, creative processes, and daily life.<ref name="campen2007" /><ref name="dittmar2007">{{full citation needed|date=January 2014}} {{cite book | veditors = Dittmar A | date = 2007 | title = Synästhesien. Roter Faden durchs Leben? | trans-title = Synesthesia. A red thread through life? | language = German | location = Essen | publisher = Verlag Die Blaue Eule}}</ref>
Synesthetes are very likely to participate in creative activities.<ref name="dailey1997">{{cite journal |vauthors=Dailey A, Martindale C, Borkum J |year=1997 |title=Creativity, synesthesia, and physiognomic perception |journal=Creativity Research Journal |volume=10 |issue=1 |pages=1–8 |doi=10.1207/s15326934crj1001_1}}</ref> It has been suggested that individual development of perceptual and cognitive skills, in addition to one's cultural environment, produces the variety in awareness and practical use of synesthetic phenomena.<ref name="campen2009" /><ref name="dittmar2007" /> Synesthesia may also give a memory advantage. In one study, conducted by Julia Simner of the University of Edinburgh, it was found that spatial sequence synesthetes have a built-in and automatic mnemonic reference. Whereas a non-synesthete will need to create a mnemonic device to remember a sequence (like dates in a diary), a synesthete can simply reference their spatial visualizations.<ref>{{Cite web|url=http://www.synesthesiatest.org/blog/spatial-sequence-synesthesia#sthash.gan4VYDZ.dpuf|title=Investigating Spatial Sequence Synesthesia|date=2012-06-26|website=Synesthesia Test|language=en-US|access-date=2016-05-02}}</ref>
== Mechanism == {{Main|Neural basis of synesthesia}}
[[File:synaesthesiabrain.jpg|thumb|Regions thought to be cross-activated in grapheme–color synesthesia (green=grapheme recognition area, red=V4 color area).<ref name="ramachandran2001"/>]] As of 2015, the neurological correlates of synesthesia had not been established.<ref>{{cite journal | vauthors = Hupé JM, Dojat M | title = A critical review of the neuroimaging literature on synesthesia | journal =Frontiers in Human Neuroscience| volume = 9 | page = 103 | year = 2015 | pmid = 25873873 | pmc = 4379872 | doi = 10.3389/fnhum.2015.00103 | doi-access = free}}</ref>
Dedicated regions of the brain are specialized for given functions. Increased cross-talk between regions specialized for different functions may account for the many types of synesthesia. For example, the additive experience of seeing color when looking at graphemes might be due to cross-activation of the grapheme-recognition area and the color area called V4 (see figure).<ref name="ramachandran2001"/> This is supported by the fact that grapheme–color synesthetes can identify the color of a grapheme in their peripheral vision even when they cannot consciously identify the shape of the grapheme.<ref name="ramachandran2001"/>
An alternative possibility is disinhibited feedback or a reduction in the amount of inhibition along normally existing feedback pathways.<ref name="pmid11164734">{{cite journal | vauthors = Grossenbacher PG, Lovelace CT | title = Mechanisms of synesthesia: cognitive and physiological constraints | journal =Trends in Cognitive Sciences| volume = 5 | issue = 1 | pages = 36–41 | date = January 2001 | pmid = 11164734 | doi = 10.1016/S1364-6613(00)01571-0 | s2cid = 15092606}}</ref> Normally, excitation and inhibition are balanced. However, if normal feedback was not inhibited as usual, then signals feeding back from late stages of multi-sensory processing might influence earlier stages such that tones could activate vision. Cytowic and Eagleman find support for the disinhibition idea in the acquired forms<ref name="Cytowic_Eagleman2009" /> of synesthesia that occur in non-synesthetes under certain conditions: temporal lobe epilepsy,<ref>{{cite journal | vauthors = Neckar M, Bob P | title = Synesthetic associations and psychosensory symptoms of temporal epilepsy | journal =Neuropsychiatric Disease and Treatment| volume = 12 | pages = 109–112 | date = 11 January 2016 | pmid = 26811683 | pmc = 4714732 | doi = 10.2147/NDT.S95464 | doi-access = free}}</ref> head trauma, stroke, and brain tumors. They also note that it can likewise occur during stages of meditation, deep concentration, sensory deprivation, or with the use of psychedelics such as LSD or mescaline, and even, in some cases, marijuana.<ref name="Cytowic_Eagleman2009" /> However, synesthetes report that common stimulants, like caffeine and cigarettes do not affect the strength of their synesthesia, nor does alcohol.<ref name="Cytowic_Eagleman2009" />{{rp|137–140}}
A very different theoretical approach to synesthesia is that based on ideasthesia. According to this account, synesthesia is a phenomenon mediated by the extraction of the meaning of the inducing stimulus. Thus, synesthesia may be fundamentally a semantic phenomenon. Therefore, to understand neural mechanisms of synesthesia the mechanisms of semantics and the extraction of meaning need to be understood better. This is a non-trivial issue because it is not only a question of a location in the brain at which meaning is "processed" but pertains also to the question of understanding{{snd}} epitomized in e.g., the Chinese room problem. Thus, the question of the neural basis of synesthesia is deeply entrenched into the general mind–body problem and the problem of the explanatory gap.<ref>{{cite journal | vauthors = Gray JA, Parslow DM, Brammer MJ, Chopping S, Vythelingum GN, ffytche DH | title = Evidence against functionalism from neuroimaging of the alien colour effect in synaesthesia | journal =Cortex| volume = 42 | issue = 2 | pages = 309–318 | date = February 2006 | pmid = 16683506 | doi = 10.1016/s0010-9452(08)70357-5 | s2cid = 4475077}}</ref>
=== Genetics === {{Main|Genetics of synesthesia}}
Due to the prevalence of synesthesia among the first-degree relatives of people affected,<ref name=Baron-Cohen1996>{{cite journal | vauthors = Baron-Cohen S, Burt L, Smith-Laittan F, Harrison J, Bolton P | title = Synaesthesia: prevalence and familiality | journal =Perception| volume = 25 | issue = 9 | pages = 1073–1079 | date = 1 September 1996 | pmid = 8983047 | doi = 10.1068/p251073 | s2cid = 25954158}}</ref> there may be a genetic basis, as indicated by the monozygotic twins studies showing an epigenetic component.{{medical citation needed|date=May 2021}} Synesthesia might also be an oligogenic condition, with locus heterogeneity, multiple forms of inheritance, and continuous variation in gene expression.{{medical citation needed|date=May 2021}} While the exact genetic loci for this trait haven't been identified, research indicates that the genetic constructs underlying synesthesia are most likely more complex than the simple X-linked mode of inheritance that early researchers believed it to be.<ref name="Hubbard_2005" /> Further, it remains uncertain as to whether synesthesia perseveres in the genetic pool because it provides a selective advantage, or because it has become a byproduct of some other useful selected trait.<ref>{{cite journal | vauthors = Brang D, Ramachandran VS | title = Survival of the synesthesia gene: why do people hear colors and taste words? | journal =PLOS Biology| volume = 9 | issue = 11 | article-number = e1001205 | date = November 2011 | pmid = 22131906 | pmc = 3222625 | doi = 10.1371/journal.pbio.1001205 | doi-access = free}}</ref> Women have a higher chance of developing synesthesia, as demonstrated in population studies conducted in the city of Cambridge, England, where females were 6 times more likely to have it.<ref name=Baron-Cohen1996/> As technological equipment continues to advance, the search for clearer answers regarding the genetics behind synesthesia will become more promising.{{Medical citation needed|date=January 2026}}
Although often termed a "neurological condition", synesthesia is not listed in either the ''Diagnostic and Statistical Manual of Mental Disorders'' IV (1994) or the International Classification of Diseases (ICD) since it usually does not interfere with normal daily functioning.<ref>{{cite journal | vauthors = Hubbard EM | title = Neurophysiology of synesthesia | journal =Current Psychiatry Reports| volume = 9 | issue = 3 | pages = 193–199 | date = June 2007 | pmid = 17521514 | doi = 10.1007/s11920-007-0018-6 | s2cid = 13370073 | url = https://www.hal.inserm.fr/inserm-00150599/file/Hubbard_CurrPsychReports.pdf}}</ref> Indeed, most synesthetes report that their experiences are neutral or even pleasant.<ref name="isbn0-19-516623-X">{{cite book | vauthors = Sagiv N, Robertson LC |title= Synesthesia: perspectives from cognitive neuroscience |publisher=Oxford University Press |location=Oxford |year=2005 |isbn=978-0-19-516623-1|oclc=53020292}} {{page needed|date=January 2014}}</ref> Like perfect pitch, synesthesia is simply a difference in perceptual experience.{{Medical citation needed|date=January 2026}}
thumb|Reaction times for answers that are congruent with a synesthete's automatic colors are shorter than those whose answers are incongruent.<ref name="Cytowic_Eagleman2009" /> The simplest approach is test-retest reliability over long periods of time, using stimuli of color names, color chips, or a computer-screen color picker providing 16.7 million choices. Synesthetes consistently score around 90% on the reliability of associations, even with years between tests.<ref name="isbn0-262-03296-1" /> In contrast, non-synesthetes score just 30–40%, even with only a few weeks between tests and a warning that they would be retested.<ref name="isbn0-262-03296-1" />
Many tests exist for synesthesia. Each common type has a specific test. When testing for grapheme–color synesthesia, a visual test is given. The person is shown a picture that includes black letters and numbers. A synesthete will associate the letters and numbers with a specific color. An auditory test is another way to test for synesthesia. A sound is turned on and one will either identify it with a taste or envision shapes. The audio test correlates with chromesthesia (sounds with colors). Since people question whether or not synesthesia is tied to memory, the "retest" is given. One is given a set of objects and is asked to assign colors, tastes, personalities, or more. After some time, the same objects are presented and the person is asked again to do the same task. The synesthete can assign the same characteristics because that person has permanent neural associations in the brain, rather than memories of a certain object.{{Medical citation needed|date=June 2021}}
[[File:synaesthesiatest.jpg|thumb|The automaticity of synesthetic experience. A synesthete might perceive the left panel like the panel on the right.<ref name="ramachandran2001">{{primary source inline|date= January 2014}} {{Dead link|date=January 2014}}{{cite journal|vauthors=Ramachandran VS, Hubbard EM|title=Synaesthesia: A window into perception, thought and language |journal=Journal of Consciousness Studies|volume=8 |issue=12 |pages=3–34 |year=2001 |url=https://psy.ucsd.edu/~edhubbard/papers/JCS.pdf |archive-url=https://web.archive.org/web/20060527085838/http://psy.ucsd.edu/~edhubbard/papers/JCS.pdf |archive-date=27 May 2006}}</ref>]] Grapheme–color synesthetes, as a group, share significant preferences for the color of each letter (e.g., A tends to be red; O tends to be white or black; S tends to be yellow, etc.)<ref name="isbn0-19-516623-X"/> Nonetheless, there is a great variety in types of synesthesia, and within each type, individuals report differing triggers for their sensations and differing intensities of experiences. This variety means that defining synesthesia in an individual is difficult, and the majority of synesthetes are completely unaware that their experiences have a name.<ref name="isbn0-19-516623-X"/>
Neurologist Richard Cytowic identifies the following diagnostic criteria for synesthesia in his ''first'' edition book. However, the criteria are different in the second book:<ref name="isbn0-262-03296-1" /><ref name="isbn0-262-53255-7" /><ref name="Cytowic_Eagleman2009" />
# Synesthesia is involuntary and automatic # Synesthetic perceptions are spatially extended, meaning they often have a sense of "location". For example, synesthetes speak of "looking at" or "going to" a particular place to attend to the experience # Synesthetic percepts are consistent and generic (i.e., simple rather than pictorial) # Synesthesia is highly memorable # Synesthesia is laden with affect{{Medical citation needed|date=January 2026}}
Cytowic's early cases mainly included individuals whose synesthesia was frankly projected outside the body (e.g., on a "screen" in front of one's face). Later research showed that such stark externalization occurs in a minority of synesthetes. Refining this concept, Cytowic and Eagleman differentiated between "localizers" and "non-localizers" to distinguish those synesthetes whose perceptions have a definite sense of spatial quality from those whose perceptions do not.<ref name="Cytowic_Eagleman2009" />
== Prevalence == Estimates of the prevalence of synesthesia have ranged widely, from 1 in 4 to 1 in 25,000–100,000. However, most studies have relied on synesthetes reporting themselves, introducing self-referral bias.<ref name="auto">{{cite book| veditors = Simner J, Hubbard EM |title=Oxford Handbook of Synesthesia|date=2013|publisher=Oxford University Press|location=Oxford, UK|isbn=978-0-19-960332-9|pages=13–17|chapter-url=https://books.google.com/books?id=WXq9AgAAQBAJ&q=Oxford+Handbook+of+Synesthesia|access-date=25 February 2018|language=en|chapter=A brief history of synesthesia research}}</ref> In what is cited as the most accurate prevalence study so far,<ref name="auto"/> self-referral bias was avoided by studying 500 people recruited from the communities of Edinburgh and Glasgow Universities; it showed a prevalence of 4.4%, with 9 different variations of synesthesia.<ref name="Simner_2006">{{cite journal | vauthors = Simner J, Mulvenna C, Sagiv N, Tsakanikos E, Witherby SA, Fraser C, Scott K, Ward J | display-authors = 6|ref=none| title = Synaesthesia: the prevalence of atypical cross-modal experiences | journal =Perception| volume = 35 | issue = 8 | pages = 1024–1033 | date = 2006 | pmid = 17076063 | doi = 10.1068/p5469 | s2cid = 2508540 | url = http://sro.sussex.ac.uk/id/eprint/14073/1/p5469.pdf}}</ref> This study also concluded that one common form of synesthesia{{snd}} grapheme–color synesthesia (colored letters and numbers){{snd}} is found in more than one percent of the population, and this latter prevalence of graphemes–color synesthesia has since been independently verified in a sample of nearly 3,000 people in the University of Edinburgh.<ref>{{cite journal | vauthors = Carmichael DA, Down MP, Shillcock RC, Eagleman DM, Simner J | title = Validating a standardised test battery for synesthesia: Does the Synesthesia Battery reliably detect synesthesia? | journal =Consciousness and Cognition| volume = 33 | pages = 375–385 | date = May 2015 | pmid = 25734257 | pmc = 5047354 | doi = 10.1016/j.concog.2015.02.001}}</ref>
The most common forms of synesthesia are those that trigger colors, and the most prevalent of all is day–color.<ref name="Simner_2006" /> Also relatively common is grapheme–color synesthesia. Prevalence refers to both how common is synesthesia (or different forms of synesthesia) within the population, or how common are different forms of synesthesia within synesthetes. So within synesthetes, forms of synesthesia that trigger color also appear to be the most common forms of synesthesia with a prevalence rate of 86% within synesthetes.<ref name="Simner_2006" /> In another study, music–color is also prevalent at 18<ref name="Safran"/>–41%.<ref>{{Cite journal |last1=Niccolai |first1=Valentina |last2=Jennes |first2=Janina |last3=Stoerig |first3=Petra |last4=Van Leeuwen |first4=Tessa M. |date=2012 |title=Modality and variability of synesthetic experience |journal=American Journal of Psychology|volume=125 |issue=1 |pages=81–94 |doi=10.5406/amerjpsyc.125.1.0081 |pmid=22428428}}</ref> Some of the rarest are reported to be auditory–tactile, mirror-touch, and lexical–gustatory.<ref name="Safran" />
Some studies suggest that the likelihood of having synesthesia is greater in autism.<ref>Baron-Cohen S, Johnson D, Asher J, Wheelwright S, Fisher SE, Gregerson PK, Allison C, "Is synaesthesia more common in autism?", Molecular Autism, 20 November 2013</ref><ref>{{cite journal | vauthors=((Neufeld, J.)), ((Roy, M.)), ((Zapf, A.)), ((Sinke, C.)), ((Emrich, H. M.)), ((Prox-Vagedes, V.)), ((Dillo, W.)), ((Zedler, M.)) | journal=Frontiers in Human Neuroscience| title=Is synesthesia more common in patients with Asperger syndrome? | volume=7 | page=847 | date= 2013 | doi=10.3389/fnhum.2013.00847 | pmid=24367321 | pmc=3856394 | doi-access=free}}</ref> Another study claims that synesthesia is specifically more common in the subset of autistic people who self-report unusual skills not ordinarily found in the general population, which study authors describe in terms of savant syndrome.<ref>{{cite journal | vauthors=((Hughes, J. E. A.)), ((Simner, J.)), ((Baron-Cohen, S.)), ((Treffert, D. A.)), ((Ward, J.)) | journal=Multisensory Research | title=Is synaesthesia more prevalent in Autism Spectrum Conditions? Only Where There Is Prodigious Talent | volume=30 | issue=3–5 | pages=391–408 | date= 2017 | doi=10.1163/22134808-00002558 | pmid=31287074}}</ref> The relationship between autistic traits and synesthesia appears to be primarily driven by shared genetic underpinnings.<ref>{{cite journal | vauthors=((Taylor, M. J.)), ((Van Leeuwen, T. M.)), ((Kuja-Halkola, R.)), ((Lundström, S.)), ((Larsson, H.)), ((Lichtenstein, P.)), ((Bölte, S.)), ((Neufeld, J.)) | journal=Proceedings of the Royal Society B: Biological Sciences| title=Genetic and environmental architecture of synaesthesia and its association with the autism spectrum—a twin study | volume=290 | issue=2009 | article-number=20231888 | date=25 October 2023 | issn=1471-2954| doi=10.1098/rspb.2023.1888 | pmid=37876199 | pmc=10598415}}</ref>
Prior research also reports that sensory hyperresponsiveness,<ref name="Ward_2017">{{cite journal | vauthors=((Ward, J.)), ((Hoadley, C.)), ((Hughes, J. E. A.)), ((Smith, P.)), ((Allison, C.)), ((Baron-Cohen, S.)), ((Simner, J.)) | journal=Scientific Reports | title=Atypical sensory sensitivity as a shared feature between synaesthesia and autism | volume=7 | article-number=41155 | publisher=Nature Publishing Group | date= 2017 | issn=2045-2322 | doi=10.1038/srep41155 | pmid=28266503 | pmc=5339734 | bibcode=2017NatSR...741155W}}</ref><ref>{{cite journal | vauthors=((van Leeuwen, T. M.)), ((Wilsson, L.)), ((Norrman, H. N.)), ((Dingemanse, M.)), ((Bölte, S.)), ((Neufeld, J.)) | journal=Cortex| title=Perceptual processing links autism and synesthesia: A co-twin control study | volume=145 | pages=236–249 | date= 2021 | issn=0010-9452 | doi=10.1016/j.cortex.2021.09.016 | pmid=34763130 | hdl=2066/239905 | hdl-access=free}}</ref> and according to one study also sensory hyporesponsiveness,<ref name="Ward_2017"/> are more common in people with synesthesia (as well as autistic people) than in control participants. Researchers have also suggested that synesthesia may be related to misophonia, a specific type of heightened responsiveness to sensory stimulation in which certain trigger sounds can evoke distressing emotional responses.<ref>{{cite journal |vauthors=Edelstein M, Brang D, Rouw R, Ramachandran VS |year=2013 |title=Misophonia: physiological investigations and case descriptions |journal=Frontiers in Human Neuroscience|volume=7 |page=296 |doi=10.3389/fnhum.2013.00296 |pmc=3691507 |pmid=23805089 |doi-access=free}}</ref> A study exploring whether individuals with misophonia reported chromesthesia, grapheme–colour synesthesia, number form synesthesia, or other kinds of synesthesia reported 9–17% experienced each type; although the study did not include a comparison group of people without misophonia, the study authors noted this prevalence would be higher than previously found in the general population.<ref>{{cite journal | vauthors=((Rouw, R.)), ((Erfanian, M.)) | journal=Journal of Clinical Psychology | title=A large-scale study of misophonia | volume=74 | issue=3 | pages=453–479 | date= 2018 | doi=10.1002/jclp.22500 | pmid=28561277| hdl=11245.1/c9c45e84-3c70-407e-aa2f-782ccdb79791 | hdl-access=free }}</ref> However, research exploring whether synesthesia and misophonia are linked remains very limited.{{Medical citation needed|date=January 2026}}
== History == {{Main|History of synesthesia research}}
The interest in colored hearing dates back to Greek antiquity when some theorists wondered whether the color (''chroia'', what we now call timbre) of music was a quantifiable quality of sound, together with pitch and duration. Additionally, one kind of musical scale (''genos'') introduced by Plato's friend Archytas of Tarentum in the fourth century BC was named ''chromatic''. The late sixth century BC kitharist Lysander of Sicyon was said to have introduced a more 'colorful' style, even before the development of the ''chromatic'' scale itself. In Plato's time, the description of melody as 'colored' had become part of professional jargon, while the musical terms 'tone' and 'harmony' soon became integrated into the vocabulary of color in visual art.<ref name=Gage1993>{{cite book |url=https://books.google.com/books?id=oq_GtjmoTNgC&q=chroia=frontcover |title=Colour and Culture. Practice and Meaning from Antiquity to Abstraction |vauthors=Gage J |date=1993 |publisher=Thames & Hudson |location=London|isbn=978-0-520-22225-0}} p.227</ref> Isaac Newton proposed that musical tones and color tones shared common frequencies, as did Goethe in his book ''Theory of Colours''.<ref>{{Cite book|title=Theory of Colours| vauthors = Goethe JW |publisher=J. Murray|year=1840}}</ref> There is a long history of building color organs such as the clavier à lumières on which to perform colored music in concert halls.<ref name="Peacock, Kenneth 1988">{{cite journal | vauthors = Peacock K | title = Instruments to Perform Color-Music: Two Centuries of Technological Experimentation | journal =Leonardo| volume = 21 | issue = 4 | date = 1988 | pages = 397–406 | doi = 10.2307/1578702 | jstor = 1578702 | s2cid = 54178977 | url = http://www.matchtoneapp.com/images/instrumentstoperformcolor.pdf}}</ref><ref>{{cite book | veditors = Jewanski J, Sidler N | title = Farbe – Licht – Musik. Synaesthesie und Farblichtmusik. | location = Bern | publisher = Peter Lang | date = 2006}} {{page needed|date=January 2014}}</ref>
The first medical description of "colored hearing" is in an 1812 thesis by the German physician Georg Tobias Ludwig Sachs.<ref>{{cite journal | vauthors = Mahling F | year = 1926 | title = Das Problem der 'audition colorée': Eine historisch-kritische Untersuchung | journal =Archiv für die gesamte Psychologie| volume = 57 | pages = 165–301}}</ref><ref name="Jewanski_2009" /><ref name="Herman_2018" /> The "father of psychophysics", Gustav Fechner, reported the first empirical survey of colored letter photisms among 73 synesthetes in 1876,<ref>{{cite book | vauthors = Fechner G | date = 1876 | title = Vorschule der Aesthetik | location = Leipzig | publisher = Breitkopf und Hartel | url = https://archive.org/details/vorschulederaest12fechuoft}}</ref><ref>{{cite journal | vauthors = von Campen C|author-link=Cretien van Campen| year = 1996 | title = De verwarring der zintuigen. Artistieke en psychologische experimenten met synesthesie | journal = Psychologie & Maatschappij | volume = 20 | issue = 1| pages = 10–26|language=nl}}</ref> followed in the 1880s by Francis Galton.<ref name="galton1880b" /><ref name="galton1880a">{{cite journal | vauthors = Galton F |title=Visualized Numerals |journal=Nature|volume=21 |issue= 533|pages=252–256|year=1880a|doi= 10.1038/021252a0|bibcode=1880Natur..21..252G |doi-access=free}}</ref><ref name="galton1883">{{cite book | vauthors = Galton F |title=Inquiries into Human Faculty and Its Development |publisher=Macmillan |year=1883 |url=http://galton.org/books/human-faculty/ |access-date=2008-06-17}} {{page needed|date=January 2014}}</ref> Carl Jung refers to "color hearing" in his Symbols of Transformation in 1912.<ref>{{cite book | vauthors = Jung CG | chapter = The Transformation of Libido | title = Symbols of Transformation | location = London | orig-date = 1912 | date = 1956 | publisher = Routledge & Kegan Paul | page = 237}}</ref>
In the early 1920s, the Bauhaus teacher and musician Gertrud Grunow researched the relationships between sound, color, and movement and developed a 'twelve-tone circle of colour' which was analogous with the twelve-tone music of the Austrian composer Arnold Schönberg (1874–1951).<ref name=harmonisation>[https://www.bauhaus100.com/the-bauhaus/training/curriculum/classes-by-gertrud-grunow/ Bauhaus100.Curriculum. Harmonisation theory 1919–1924] {{Webarchive|url=https://web.archive.org/web/20190705104412/https://www.bauhaus100.com/the-bauhaus/training/curriculum/classes-by-gertrud-grunow/ |date=5 July 2019}}. Retrieved 2 December 2018</ref> She was a participant in at least one of the ''Congresses for Colour–Sound Research'' (German:''Kongreß für Farbe-Ton-Forschung'') held in Hamburg in the late 1920s and early 1930s.<ref>''Farbe-Ton-Forschungen. III. Band. Bericht über den II. Kongreß für Farbe-Ton-Forschung'' (Hamburg 1. – 5. Oktober 1930). Published 1931.</ref>
Research into synesthesia proceeded briskly in several countries, but due to the difficulties in measuring subjective experiences and the rise of behaviorism, which made the study of ''any'' subjective experience taboo, synesthesia faded into scientific oblivion between 1930 and 1980.{{citation needed|date=December 2018}}
As the 1980s cognitive revolution made inquiry into internal subjective states respectable again, scientists returned to studying synesthesia. Led in the United States by Larry Marks and Richard Cytowic, and later in England by Simon Baron-Cohen and Jeffrey Gray, researchers explored the reality, consistency, and frequency of synesthetic experiences. In the late 1990s, the focus settled on grapheme → color synesthesia, one of the most common<ref name="isbn0-19-516623-X" /> and easily studied types. Psychologists and neuroscientists study synesthesia not only for its inherent appeal but also for the insights it may give into cognitive and perceptual processes that occur in synesthetes and non-synesthetes alike. Synesthesia is now the topic of scientific books and papers, Ph.D. theses, documentary films, and even novels.{{citation needed|date=December 2018}}
Since the rise of the Internet in the 1990s, synesthetes began contacting one another and creating websites devoted to the condition. These rapidly grew into international organizations such as the American Synesthesia Association, the UK Synaesthesia Association, the Belgian Synesthesia Association, the Canadian Synesthesia Association, the German Synesthesia Association, and the Netherlands Synesthesia Web Community.{{citation needed|date=December 2020}}
== Society and culture ==
=== Notable cases === {{Main|List of people with synesthesia}}
Solomon Shereshevsky, a newspaper reporter turned mnemonist, was discovered by Russian neuropsychologist Alexander Luria to have a rare fivefold form of synesthesia,<ref name="Schacter_1996"/> of which he is the only known case. Words and text were not only associated with highly vivid visuospatial imagery but also sound, taste, color, and sensation.<ref name="Schacter_1996" /> Shereshevsky could recount endless details of many things without form, from lists of names to decades-old conversations, but he had great difficulty grasping abstract concepts. The automatic, and nearly permanent, retention of every detail due to synesthesia greatly inhibited Shereshevsky's ability to understand what he read or heard.<ref name="Schacter_1996" />
Neuroscientist and author V. S. Ramachandran studied the case of a grapheme–color synesthete who was also color blind. While he couldn't see certain colors with his eyes, he could still "see" those colors when looking at certain letters. Because he did not have a name for those colors, he called them "Martian colors".<ref>{{cite web| vauthors = Carroll S |date=5 November 2007|title=Martian Colors – Cosmic Variance|url=https://www.discovermagazine.com/the-sciences/martian-colors|access-date=12 April 2018|website=Discover}}</ref>
=== Art === {{Main|Synesthesia in art}}
Other notable synesthetes come particularly from artistic professions and backgrounds. Synesthetic art historically refers to multi-sensory experiments in the genres of visual music, music visualization, audiovisual art, abstract film, and intermedia.<ref name="campen2007" /><ref name="campen1999">{{cite journal|year=1999|title=Artistic and psychological experiments with synesthesia|journal=Leonardo|volume=32|issue=1|pages=9–14|doi=10.1162/002409499552948| vauthors = Campen C|author-link=Cretien van Campen|s2cid=57568389}}</ref><ref name="berman1999">{{cite journal | vauthors = Berman G |title=Synesthesia and the Arts |journal=Leonardo|volume=32 |issue=1|pages=15–22 |year=1999 |doi= 10.1162/002409499552957|s2cid=57565862}}</ref><ref name="isbn3-7913-2082-3">{{cite book | vauthors = von Maur K |title=The Sound of Painting: Music in Modern Art (Pegasus Library) |publisher=Prestel |location=Munich |year=1999 |isbn=978-3-7913-2082-3}} {{page needed|date=January 2014}}</ref><ref name=Gage1993 /><ref>{{cite book| vauthors = Gage JD |title=Color and meaning: art, science, and symbolism|publisher=University of California Press |location=Berkeley |year=1999 |isbn=978-0-520-22611-1}} {{page needed|date=January 2014}}</ref> Distinct from neuroscience, the concept of synesthesia in the arts is regarded as the simultaneous perception of multiple stimuli in one gestalt experience.<ref>{{cite book | vauthors = van Campen C|author-link=Cretien van Campen| date = 2009 | chapter = Visual Music and Musical Paintings. The Quest for Synesthesia in the Arts. | veditors = Bacci F, Melcher D | title = Making Sense of Art, making Art of Sense. | location = Oxford | publisher = Oxford University Press}}{{page needed|date=January 2014}}</ref> Neurological synesthesia has been a source of inspiration for artists, composers, poets, novelists, and digital artists.{{Citation needed|date=January 2026}}
==== Writers ==== Vladimir Nabokov wrote explicitly about synesthesia in several novels. Nabokov described his grapheme–color synesthesia at length in his memoir, ''Speak, Memory'':<ref>{{cite book |last1=Bouchet |first1=Marie |last2=Loison-Charles |first2=Julie |last3=Poulin |first3=Isabelle |title=The Five Senses in Nabokov's Works |date=19 June 2020 |publisher=Springer Nature |isbn=978-3-030-45406-7 |url=https://books.google.com/books?id=T2jsDwAAQBAJ |language=en |pages=255–256}}</ref> <blockquote>I present a fine case of colored hearing. Perhaps "hearing" is not quite accurate, since the color sensations seem to be produced by the very act of my orally forming a given letter while I imagine its outline. The long ''a'' of the English alphabet (and it is this alphabet I have in mind farther on unless otherwise stated) has for me the tint of weathered wood, but the French ''a'' evokes polished ebony. This black group also includes hard ''g'' (vulcanized rubber) and ''r'' (a sooty rag being ripped). Oatmeal ''n'', noodle-limp ''l'', and the ivory-backed hand mirror of ''o'' take care of the whites. I am puzzled by my French ''on'' which I see as the brimming tension-surface of alcohol in a small glass. Passing on to the blue group, there is steely ''x'', thundercloud ''z'', and huckleberry ''k''. Since a subtle interaction exists between sound and shape, I see ''q'' as browner than ''k'', while ''s'' is not the light blue of ''c'', but a curious mixture of azure and mother-of-pearl.</blockquote>
Daniel Tammet wrote a book on his experiences with synesthesia called ''Born on a Blue Day''.<ref name="BlueDay">{{cite book |url=https://archive.org/details/bornonbluedayins00tamm |title=Born on a Blue Day |vauthors=Tammet D |publisher=Free Press |year=2007 |isbn=978-1-4165-3507-2 |url-access=registration}} {{page needed|date=January 2014}}</ref> Joanne Harris, author of ''Chocolat'', is a synesthete who says she experiences colors as scents.<ref>{{cite news |date=7 April 2010 |title=Chocolat author Joanne Harris talks about her latest novel Blue Eyed Boy |newspaper=Metro |url=http://metro.co.uk/2010/04/07/chocolat-author-joanne-harris-talks-about-her-latest-novel-blue-eyed-boy-226133/}}</ref> Her novel ''Blueeyedboy'' features various characters with synesthesia.{{Citation needed|date=January 2026}}
==== Painters and photographers ==== [[File:Music, Pink and Blue No. 2, by Georgia O'Keeffe.jpg|thumb|upright|''Music, Pink and Blue No. 2'' (1918), Georgia O'Keeffe]] Wassily Kandinsky (a synesthete) and Piet Mondrian (not a synesthete) both experimented with image–music congruence in their paintings. Georgia O'Keeffe gave titles to several of her paintings, e.g. ''Blue and Green Music'' (1919–1921), using music–color associations.<ref>{{cite book|last=Cytowic|first=Richard E.|year=2018|title=Synesthesia|page=15|publisher=MIT Press|isbn=9780262346290}}</ref> Contemporary artists with synesthesia, such as Carol Steen<ref name="Steen">{{cite journal |vauthors=Steen C |year=2001 |title=Visions Shared: A Firsthand Look into Synesthesia and Art |journal=Leonardo|volume=34 |issue=3 |pages=203–208 |doi=10.1162/002409401750286949 |s2cid=57570552}}</ref> and Marcia Smilack<ref>[http://www.marciasmilack.com/synethesia-intro.php Marcia Smilack Website] {{Webarchive|url=https://web.archive.org/web/20210227092455/http://www.marciasmilack.com/synethesia-intro.php |date=27 February 2021}} Accessed 20 August 2006.</ref> (a photographer who waits until she gets a synesthetic response from what she sees and then takes the picture), use their synesthesia to create their artwork. Linda Anderson, according to NPR considered "one of the foremost living memory painters", creates with oil crayons on fine-grain sandpaper representations of the auditory-visual synaesthesia she experiences during severe migraine attacks.<ref>{{Cite web |date=2019-04-07 |title=Linda Anderson|url=https://mocaga.org/collections/permanent-art-collection-artists/linda-anderson/ |archive-url=https://web.archive.org/web/20190407003637/https://mocaga.org/collections/permanent-art-collection-artists/linda-anderson/ |archive-date=7 April 2019 |access-date=2021-12-27|publisher=Museum of Contemporary Art of Georgia}}</ref><ref>{{Cite web |date=2019-04-07 |title=Linda Anderson |url=http://www.gpb.org/stateofthearts/term/anderson |archive-url=https://web.archive.org/web/20190407003642/http://www.gpb.org/stateofthearts/term/anderson |archive-date=7 April 2019 |access-date=2021-12-27 |website=NPR}}</ref> Brandy Gale, a Canadian visual artist, experiences an involuntary joining or crossing of any of her senses{{snd}} hearing, vision, taste, touch, smell and movement. Gale paints from life rather than from photographs and by exploring the sensory panorama of each locale attempts to capture, select, and transmit these personal experiences.<ref>{{cite web |title=Coastal Synaesthesia: Paintings and Photographs of Hawaii, Fiji and California by Brandy Gale – Gualala Arts Center exhibit: January, 2015 |url=http://www.gualalaarts.org/Exhibits/Gallery/2015-01-Coastal-Synaesthesia.html |archive-url=https://web.archive.org/web/20150202215117/http://www.gualalaarts.org/Exhibits/Gallery/2015-01-Coastal-Synaesthesia.html |archive-date=2 February 2015 |access-date=2 February 2015 |work=gualalaarts.org}}</ref><ref>{{cite web |author=EG |title=The Wondrous Sensory Spectrum of Brandy Gale |url=http://library.fora.tv/2013/04/19/The_Wondrous_Sensory_Spectrum_of_Brandy_Gale |url-status=usurped |archive-url=https://web.archive.org/web/20150202210315/http://library.fora.tv/2013/04/19/The_Wondrous_Sensory_Spectrum_of_Brandy_Gale |archive-date=2 February 2015 |access-date=2 February 2015 |work=FORA.tv}}</ref><ref>{{Cite web | title=Brandy Gale Fine Art | url=https://www.brandygalestudio.com/ | archive-url=https://web.archive.org/web/20170426120839/http://brandygalestudio.com/ | access-date=2025-06-02 | archive-date=2017-04-26}}</ref> David Hockney perceives music as color, shape, and configuration and uses these perceptions when painting opera stage sets (though not while creating his other artworks). Kandinsky combined four senses: color, hearing, touch, and smell.<ref name="isbn0-262-03296-1" /><ref name="Cytowic_Eagleman2009" />
==== Composers ==== [[File:Mikalojus Konstantinas Ciurlionis - FINALE (I) - 1908.jpg|thumb|''Sonata of the Sea. "Finale"'' (1908) by synesthete Mikalojus Konstantinas Čiurlionis, accompanying his symphonic poem ''The Sea'']]
Several composers had experienced synesthesia.
Mikalojus Konstantinas Čiurlionis, a Lithuanian painter, composer, and writer, perceived colors and music simultaneously. Many of his paintings bear the names of matching musical pieces: sonatas, fugues, and preludes.{{Citation needed|date=January 2026}}
Alexander Scriabin composed colored music that was deliberately contrived and based on the circle of fifths, whereas Olivier Messiaen invented a new method of composition (the modes of limited transposition) specifically to render his bi-directional sound–color synesthesia.<ref name="Cytowic_Eagleman2009" /><ref>{{cite book |title=Olivier Messiaen: Music and Color. Conversations with Claude Samuel. |vauthors=Samuel C |date=1994 |publisher=Amadeus Press |location=Portland, Oregon |translator=Glasow ET |author-link1=Claude Samuel |orig-date=1986}}</ref> For example, the red rocks of Bryce Canyon are depicted in his symphony ''Des canyons aux étoiles...'' ("From the Canyons to the Stars"). New art movements such as literary symbolism, non-figurative art, and visual music have profited from experiments with synesthetic perception and contributed to the public awareness of synesthetic and multi-sensory ways of perceiving.<ref name="campen2007" /> Other composers who reported synesthesia include Duke Ellington,<ref>Duke Ellington as quoted in {{cite book |title=Sweet man: The real Duke Ellington. |vauthors=George D |date=1981 |publisher=G.P. Putnam's Sons |location=New York |page=226}}</ref> Nikolai Rimsky-Korsakov,<ref>{{cite journal |vauthors=Yastrebtsev V |date=1908 |title=On N.A.Rimsky-Korsakov's color sound- contemplation. |journal=Russkaya Muzykalnaya Gazeta |language=Russian |issue=39–40 |pages=842–845}} cited by Bulat Galeyev (1999).</ref> and Jean Sibelius.<ref name="berman1999" />
Several contemporary composers with synesthesia are Michael Torke,<ref name="berman1999" /> and Ramin Djawadi, best known for his work on composing the theme songs and scores for such TV series as ''Game of Thrones'', ''Westworld'' and for the ''Iron Man'' movie. He says he tends to "associate colors with music, or music with colors".<ref>{{Cite news |title=Meet the musical genius behind the ''Game of Thrones'' soundtrack who watches each season before anyone else|work=Business Insider|url=http://www.businessinsider.com/game-of-thrones-music-composer-ramin-djawadi-interview-2016-7 |access-date=2018-01-11}}</ref>
British composer Daniel Liam Glyn created the classical-contemporary music project Changing Stations using grapheme–colour synesthesia. Based on the 11 main lines of the London Underground, the eleven tracks featured on the album represent the eleven main tube line colours.<ref>{{cite web |date=27 April 2017 |title=Sounds of the Underground: Synaesthetic Musician Creates LP Based on Tube Map |url=https://www.bigissue.com/news/sounds-underground-synaesthetic-musician-creates-lp-based-tube-map/ |access-date=15 May 2018 |publisher=The Big Issue}}</ref> Each track focuses heavily on the different speeds, sounds, and mood of each line, and are composed in the key signature synaesthetically assigned by Glyn with reference to the colour of the tube line on the map.<ref>{{cite web |title=Do all London Underground lines have a unique sound? |url=http://pages.cdn.pagesuite.com/7/8/7848c73a-e3c4-4f48-9fd3-18c7ac451991/page.pdf |access-date=3 April 2017 |publisher=Norwegian Air Magazine}}</ref>
==== Musicians ==== The producer, rapper, and fashion designer Kanye West is a prominent interdisciplinary case. In an impromptu speech he gave during an ''Ellen'' interview, he described his condition, saying that he sees sounds and that everything he sonically makes is a painting.<ref>{{Citation |title=Kanye West FULL Banned Ellen Interview HD May 19 2016 | date=7 May 2018 |url=https://www.youtube.com/watch?v=W58_fnZ3oGQ |access-date=2022-08-20}}</ref> Other notable synesthetes include musicians Billy Joel,<ref name="Seaberg2011">{{cite book | vauthors = Seaberg M | year = 2011| title = Tasting the Universe | publisher = New Page Books | isbn = 978-1-60163-159-6}}</ref>{{rp|89, 91}} Andy Partridge,<ref>{{cite web |url=https://tidal.com/magazine/article/inside-synesthesia/1-72048 |title=Chords Become Colors: Inside Synesthesia |work=Tidal |last=Enos |first=Morgan |date=9 April 2020 |access-date=11 May 2023}}</ref> Itzhak Perlman,<ref name="Seaberg2011" />{{rp|53}} Lorde,<ref>{{cite web | vauthors = Trendell A |title=Lorde explains the experience of having synaesthesia |url=https://www.nme.com/news/music/lorde-synaesthesia-explained-2069855 |website=NME |access-date=15 June 2021 |date=2017-05-11}}</ref> Billie Eilish,<ref>{{cite web | vauthors = Nattress K |title=Billie Eilish Explains How Synesthesia Affects Her Music |url=https://www.iheart.com/content/2019-05-29-billie-eilish-explains-how-synesthesia-affects-her-music/ |website=iHeartRadio |access-date=15 June 2021 |language=en}}</ref> Charli xcx,<ref>{{Cite news |date=2013-12-12 |title=Charli XCX: Pop, punk and synaesthesia |url=https://www.bbc.com/news/entertainment-arts-25330600 |access-date=2025-03-18 |work=BBC News |language=en-GB}}</ref> Brendon Urie,<ref>{{Cite magazine|url=https://www.rollingstone.com/music/music-features/panic-at-the-discos-brendon-urie-band-is-outlet-for-nonchalant-chaos-188429/|title=Panic! at the Disco: Band Is 'Outlet for Nonchalant Chaos'| vauthors = Spanos B |date=2016-01-15|magazine=Rolling Stone|language=en-US|access-date=2019-11-13}}</ref><ref>{{Cite web|url=https://culturacolectiva.com/music/singers-with-synesthesia-inspiration-sounds |title= 4 Singers Who Draw Inspiration From Synesthesia To Write Music |website=Cultura Colectiva|date= 23 January 2018 |language=en-US|access-date=2020-04-16}}</ref> Ida Maria,<ref>{{cite news|url=http://entertainment.timesonline.co.uk/tol/arts_and_entertainment/music/article3404605.ece |archive-url=https://web.archive.org/web/20080718210434/http://entertainment.timesonline.co.uk/tol/arts_and_entertainment/music/article3404605.ece |archive-date=18 July 2008 |title=Times Online interview|date=24 February 2008| vauthors = Cairns D |access-date=2008-07-24|location=London|work=The Times}}</ref> Brian Chase,<ref name="guardian-interview">{{cite news|url=https://www.theguardian.com/music/2009/mar/30/pop-music-yeah-yeah-yeahs|title=Emma Forrest meets New York's favourite art-punk rockers Yeah Yeah Yeahs|date=30 March 2009| vauthors = Forrest E |work=guardian.co.uk|publisher=The Guardian|access-date=2009-05-07|location=London}}</ref><ref name="blog">{{cite web|url=http://site.yeahyeahyeahs.com/blog/brian.aspx |title=Brian Chase's blog | vauthors = Chase B |work=yeahyeahyeahs.com |access-date=2009-05-07 |archive-url=https://web.archive.org/web/20090125080016/http://site.yeahyeahyeahs.com/blog/brian.aspx |archive-date=25 January 2009}}</ref> and classical pianist Hélène Grimaud. Musician Kristin Hersh sees music in colors.<ref>{{cite web|url=https://thequietus.com/articles/29947-seeing-sideways-kristin-hersh-interview|title=Strange Angels: Kristin Hersh On Music & Motherhood| vauthors = Seaman D |date=May 8, 2021|website=The Quietus|access-date=November 8, 2021}}</ref> Drummer Mickey Hart of the Grateful Dead wrote about his experiences with synaesthesia in his autobiography ''Drumming at the Edge of Magic''.<ref>{{cite book | vauthors = Hart M, Stevens J, Lieberman F | date = 1990 | title = Drumming at the edge of magic: a journey into the spirit of percussion | location = San Francisco, CA | publisher = Harper |page = 133}}</ref> John Frusciante, guitarist of the Red Hot Chili Peppers, talks about his experiences with synesthesia in a podcast with Rick Rubin.<ref>{{Citation |title=John Frusciante of the Red Hot Chili Peppers Returns, Part 1 {{!}} Broken Record (Hosted by Rick Rubin) | date=14 October 2022 |url=https://www.youtube.com/watch?v=hXFlTdM3UDc |access-date=2023-05-20 |language=en}}</ref> Pharrell Williams, of the groups The Neptunes and N.E.R.D., also experiences synesthesia<ref>{{unreliable source?|date=January 2014}} It just always stuck out in my mind, and I could always see it. I don't know if that makes sense, but I could always visualize what I was hearing... Yeah, it was always like weird colors." From a Nightline interview with Pharrell</ref><ref>{{cite web|url = http://www.psychologytoday.com/blog/tasting-the-universe/201203/synesthetes-people-the-future|title = Synesthetes: "People of the Future"|date = 3 March 2012|access-date = 15 May 2014|website = Psychology Today}}</ref> and used it as the basis of the album ''Seeing Sounds''. Singer/songwriter Marina and the Diamonds experiences music → color synesthesia and reports colored days of the week.<ref>{{cite web | url = http://www.itv.com/lifestyle/loosewomen/videos/m/celebrityguests/marinaandthediamonds/ | title = Loose Women: Marina and the Diamonds | work = ITV Lifestyle | publisher = ITV Network | date = 27 April 2010 | access-date = 28 April 2010}}</ref> Awsten Knight from Waterparks has chromesthesia, which influences many of the band's artistic choices.<ref>{{Citation |title=Waterparks' Awsten Can 'See' Music, So We Had Him Paint His Songs 🎨 Seeing Sounds {{!}} MTV | date=14 March 2020 |url=https://www.youtube.com/watch?v=LM1Cotbi-3Q |language=en |access-date=2023-02-14}}</ref>
==== Artists without synesthesia ==== Some artists frequently mentioned as synesthetes did not, in fact, have the neurological condition. Scriabin's 1911 ''Prometheus: The Poem of Fire'', for example, is a deliberate contrivance whose color choices are based on the circle of fifths and appear to have been taken from Madame Blavatsky.<ref name="Cytowic_Eagleman2009" /><ref name="Dann">{{page needed|date=January 2014}} {{cite book |title=Bright colors falsely seen: synaesthesia and the search for transcendental knowledge |vauthors=Dann KT |publisher=Yale University Press |year=1998 |isbn=978-0-300-06619-7 |location=New Haven, Connecticut}}</ref> The musical score has a separate staff marked ''luce'' whose "notes" are played on a color organ. Technical reviews appear in period volumes of ''Scientific American''.<ref name="Cytowic_Eagleman2009" /> On the other hand, his older colleague Rimsky-Korsakov (who was perceived as a fairly conservative composer) was, in fact, a synesthete.<ref>This is according to an article in the Russian press, Yastrebtsev V. "On N.A.Rimsky-Korsakov's color sound- contemplation". ''Russkaya muzykalnaya gazeta'', 1908, N 39–40, pp. 842–845 (in Russian), cited by Bulat Galeyev (1999).</ref>
French poets Arthur Rimbaud and Charles Baudelaire wrote of synesthetic experiences, but there is no evidence they were synesthetes themselves. Baudelaire's 1857 ''{{lang|fr|Correspondances}}''<!-- (text available here) --> introduced the notion that the senses can and should intermingle. Baudelaire participated in a hashish experiment by psychiatrist Jacques-Joseph Moreau and became interested in how the senses might affect each other.<ref name="campen2007" /> Rimbaud later wrote ''Voyelles'' (1871)<!-- (text available here) -->, which was perhaps more important than ''{{lang|fr|Correspondances}}'' in popularizing synesthesia. He later boasted ''"J'inventais la couleur des voyelles!"'' (I invented the colors of the vowels!).<ref>{{Cite book |title=Sensory Perception: Mind & Matter |vauthors=Barth F, Giampieri-Deutsch P, Hans-Dieter K |publisher=Springer Vienna |year=2012 |isbn=978-3-211-99750-5 |location=Vienna |page=221 |quote=I invented the colours of the vowels!}}</ref>
=== Science === Some technologists, like inventor Nikola Tesla,<ref>{{cite web |title=The Strange Life of Nikola Tesla |url=http://www.neuronet.pitt.edu/~bogdan/tesla/tesla.pdf |archive-url=https://web.archive.org/web/20120717013939/http://www.neuronet.pitt.edu/~bogdan/tesla/tesla.pdf |archive-date=17 July 2012 |access-date=4 September 2012 |work=pitt.edu |vauthors=Tesla N}}</ref> and scientists also reported being synesthetic. Physicist Richard Feynman describes his colored equations in his autobiography, ''What Do You Care What Other People Think?'':<ref>{{cite book |title=What Do You Care What Other People Think? |vauthors=Feynman R |date=1988 |publisher=Norton |location=New York |page=59}}</ref> "When I see equations, I see the letters in colors. I don't know why. I see vague pictures of Bessel functions with light-tan j's, slightly violet-bluish n's, and dark brown x's flying around."<ref>{{cite web |title=Colourful language: U of T psychologists discover enhanced language learning in synesthetes |url=https://www.utoronto.ca/news/colourful-language-u-t-psychologists-discover-enhanced-language-learning-synesthetes |website=University of Toronto News |access-date=20 March 2023 |language=en}}</ref>
=== Film === In the 2024 Canadian film ''Magnetosphere'', the central character is a 13-year-old girl with synesthesia.<ref>{{Cite web |title=Magnetosphere {{!}} Rotten Tomatoes |url=https://www.rottentomatoes.com/m/magnetosphere |access-date=2026-01-17 |website=www.rottentomatoes.com |language=en}}</ref>
''The Colors Within'', a film released in 2024, centers around a high-school student with person-color synesthesia.<ref>{{Cite web |title=The Colors Within {{!}} Rotten Tomatoes |url=https://www.rottentomatoes.com/m/the_colors_within |access-date=2026-02-24 |website=www.rottentomatoes.com |language=en}}</ref>
=== Literature === {{Main|Synesthesia in literature}}
Synesthesia is sometimes used as a plot device or a way of developing a character's inner life. Author and synesthete Patricia Lynne Duffy describes four ways in which synesthetic characters have been used in modern fiction.<ref>{{cite conference|last=Duffy|first=Patricia Lynne|author-link=Patricia Lynne Duffy|year=2006 |title=Images of Synesthetes and their Perceptions of Language in Fiction |conference=6th Annual Meeting of the American Synesthesia Association |url=https://www.synesthesia.info/florida.html |location=University of South Florida |archive-url=https://web.archive.org/web/20120117030538/http://synesthesia.info/florida.html |archive-date=17 January 2012}}</ref><ref>{{cite journal|last1=Duffy|first1=Patricia Lynne|author1-link=Patricia Lynne Duffy|last2=Simner|first2=Julia| title = Synaesthesia in fiction | journal =Cortex| volume = 46 | issue = 2 | pages = 277–278 | date = February 2010 | pmid = 19081086 | doi = 10.1016/j.cortex.2008.11.003 | s2cid = 11224620}}</ref> * Synesthesia as Romantic ideal: in which the condition illustrates the Romantic ideal of transcending one's experience of the world. Books in this category include ''The Gift'' by Vladimir Nabokov.{{citation needed|date=December 2025}} * Synesthesia as pathology: in which the trait is pathological. Books in this category include ''The Whole World Over'' by Julia Glass.{{citation needed|date=December 2025}} * Synesthesia as Romantic pathology: in which synesthesia is pathological but also provides an avenue to the Romantic ideal of transcending quotidian experience. Books in this category include Holly Payne's ''The Sound of Blue'' (2004) and Anna Ferrara's ''The Woman Who Tried to Be Normal'' (2018){{citation needed|date=December 2025}} * Synesthesia as psychological health and balance: ''Painting Ruby Tuesday'' by Jane Yardley, and ''A Mango-Shaped Space'' by Wendy Mass.{{citation needed|date=December 2025}}
Literary depictions of synesthesia are criticized as often being more of a reflection of an author's interpretation of synesthesia than of the phenomenon itself.{{citation needed|date=April 2014}}
== Research == thumb|Tests like this demonstrate that people do not attach sounds to visual shapes arbitrarily. When people are given a choice between the words "Bouba" and "Kiki", the left shape is almost always called "Kiki" while the right is called "Bouba".<ref>{{Cite journal |last1=Chen |first1=Yi-Chuan |last2=Huang |first2=Pi-Chun |last3=Woods |first3=Andy |last4=Spence |first4=Charles |date=2016-05-27 |title=When "Bouba" equals "Kiki": Cultural commonalities and cultural differences in sound-shape correspondences |journal=Scientific Reports |volume=6 |article-number=26681 |doi=10.1038/srep26681 |issn=2045-2322 |pmc=4882484 |pmid=27230754|bibcode=2016NatSR...626681C}}</ref>
Research on synesthesia raises questions about how the brain combines information from different sensory modalities, referred to as crossmodal perception or multisensory integration.<ref>{{Cite journal |last1=van Leeuwen |first1=Tessa M. |last2=Singer |first2=Wolf |last3=Nikolić |first3=Danko |date=2015 |title=The Merit of Synesthesia for Consciousness Research |journal=Frontiers in Psychology|volume=6 |page=1850 |doi=10.3389/fpsyg.2015.01850 |doi-access=free |issn=1664-1078 |pmc=4667101 |pmid=26696921}}</ref><ref>{{Cite journal |last=Harvey |first=Joshua Paul |date=June 2013 |title=Sensory perception: lessons from synesthesia: using synesthesia to inform the understanding of sensory perception |journal=The Yale Journal of Biology and Medicine |volume=86 |issue=2 |pages=203–216 |issn=1551-4056 |pmc=3670440 |pmid=23766741}}</ref>
An example of this is the bouba/kiki effect. In an experiment first designed by Wolfgang Köhler, people are asked to choose which of two shapes is named ''bouba'' and which ''kiki''. The angular shape, ''kiki'', is chosen by 95–98% and ''bouba'' for the rounded one. Individuals on the island of Tenerife showed a similar preference between shapes called ''takete'' and ''maluma''. Even 2.5-year-old children (too young to speak) show this effect.<ref name="pmid16669803">{{primary source inline|date=January 2014}} {{cite journal | vauthors = Maurer D, Pathman T, Mondloch CJ | title = The shape of boubas: sound-shape correspondences in toddlers and adults | journal =Developmental Science| volume = 9 | issue = 3 | pages = 316–322 | date = May 2006 | pmid = 16669803 | doi = 10.1111/j.1467-7687.2006.00495.x | s2cid = 7297731 | doi-access = free}}</ref> Research indicated that in the background of this effect may operate a form of ideasthesia.<ref>{{cite journal | vauthors = Milan E, Iborra O, de Cordoba M, Juárez-Ramos V, Artacho MR, Rubio JL | year = 2013 | title = The Kiki-Bouba effect: A case of personification and ideaesthesia | journal =Journal of Consciousness Studies| volume = 20 | issue = 1–2| pages = 84–102}}</ref>
Researchers hope that the study of synesthesia will provide a better understanding of consciousness and its neural correlates. In particular, synesthesia might be relevant to the philosophical problem of qualia,<ref name="isbn0-631-19764-8" /><ref>{{cite journal |vauthors=Gray JA, Chopping S, Nunn J, etal |title= Implications of synaesthesia for functionalism: Theory and experiments|journal=Journal of Consciousness |volume=9 |issue=12 |pages=5–31 |year=2002}}</ref> given that synesthetes experience extra qualia (e.g., colored sound). An important insight for qualia research may come from the findings that synesthesia has the properties of ideasthesia,<ref name="ideasthesia" /> which then suggest a crucial role of conceptualization processes in generating qualia.<ref name="MroczkoNikolic2014">{{cite journal | vauthors = Mroczko-Wąsowicz A, Nikolić D | title = Semantic mechanisms may be responsible for developing synesthesia | journal =Frontiers in Human Neuroscience| volume = 8 | page = 509 | year = 2014 | pmid = 25191239 | pmc = 4137691 | doi = 10.3389/fnhum.2014.00509 | doi-access = free}}</ref> Some philosophers argue that synesthesia creates problems for theories that say our conscious experiences are determined by what our minds represent about the world. For example, when both a synesthete and a non-synesthete feel pain in the same way, they might be representing the same bodily damage, but the synesthete also experiences colors while the non-synesthete does not. This suggests that identical mental representations can lead to different conscious experiences.<ref>{{cite web |title=Synesthesia |url=https://iep.utm.edu/synesthe/ |website=Internet Encyclopedia of Philosophy |access-date=9 September 2025}}</ref>
=== Technological applications === Synesthesia also has several practical applications, including 'intentional synesthesia' in technology,<ref>{{cite journal | vauthors = Suslick KS | title = Synesthesia in science and technology: more than making the unseen visible | journal =Current Opinion in Chemical Biology| volume = 16 | issue = 5–6 | pages = 557–563 | date = December 2012 | pmid = 23183411 | pmc = 3606019 | doi = 10.1016/j.cbpa.2012.10.030}}</ref> and sensory prosthetics.<ref>{{Cite journal | vauthors = Scheff CM |date=1986-01-01 |title=Experimental model for the study of changes in the organization of human sensory information processing through the design and testing of non-invasive prosthetic devices for sensory impaired people |journal=ACM SIGCAPH Computers and the Physically Handicapped |issue=36 |pages=3–10 |doi=10.1145/15711.15713 |s2cid=11924232 |issn=0163-5727}}</ref>
==== The Voice (vOICe) ==== Peter Meijer developed a sensory substitution device for the visually impaired called The vOICe (the capital letters "O", "I", and "C" in "vOICe" are intended to evoke the expression "Oh I see"). The vOICe is a privately owned research project, running without venture capital, that was first implemented using low-cost hardware in 1991.<ref>{{cite web| vauthors = Meijer P |title=Augmented Reality for the Totally Blind|url=https://www.seeingwithsound.com/|access-date=4 February 2014}}</ref> The vOICe is a visual-to-auditory sensory substitution device (SSD) preserving visual detail at high resolution (up to 25,344 pixels).<ref>{{cite journal | vauthors = Striem-Amit E, Guendelman M, Amedi A | title = 'Visual' acuity of the congenitally blind using visual-to-auditory sensory substitution | journal =PLOS One| volume = 7 | issue = 3 | article-number = e33136 | date = 16 March 2012 | pmid = 22438894 | pmc = 3306374 | doi = 10.1371/journal.pone.0033136 | doi-access = free | bibcode = 2012PLoSO...733136S}}</ref> The device consists of a laptop, head-mounted camera or computer camera, and headphones. The vOICe converts visual stimuli of the surroundings captured by the camera into corresponding aural representations (soundscapes) delivered to the user through headphones at a default rate of one soundscape per second. Each soundscape is a left-to-right scan, with height represented by pitch, and brightness by loudness.<ref>{{cite web| vauthors = Carmichael J |title=Device Trains Blind People To 'See' By Listening|date=10 July 2013|url=https://www.popsci.com/science/article/2013-07/synesthesia-blind?dom=PSC&loc=recent&lnk=1&con=read-full-story|access-date=4 February 2014}}</ref> The vOICe compensates for the loss of vision by converting information from the lost sensory modality into stimuli in a remaining modality.<ref>{{cite journal | vauthors = Haigh A, Brown DJ, Meijer P, Proulx MJ | title = How well do you see what you hear? The acuity of visual-to-auditory sensory substitution | journal =Frontiers in Psychology| volume = 4 | page = 330 | year = 2013 | pmid = 23785345 | pmc = 3684791 | doi = 10.3389/fpsyg.2013.00330 | doi-access = free}}</ref>
== See also == * {{annotated link|Allochiria}} * {{annotated link|Apophenia}} * {{annotated link|Exceptional memory}} * {{annotated link|Fantasy-prone personality}} * {{annotated link|Hallucination}} * {{annotated link|Hallucinogen persisting perception disorder}} * {{annotated link|Ideophone}} * {{annotated link|McCollough effect}} * {{annotated link|Parosmia}} * {{annotated link|Psychedelic drug}} * {{annotated link|Smound}} * {{annotated link|The Yellow Sound|''The Yellow Sound''}} * {{annotated link|Theremin}} * {{annotated link|Thought-Forms|''Thought-Forms'' (book)}} * {{annotated link|Vibration theory of olfaction}}
== References == {{reflist}}
== Further reading == {{div col|colwidth=45em}} * {{cite IEP|last1=Allen-Hermanson|first1=Sean|last2=Matey|first2=Jennifer|url-id=synesthe/|title=Synesthesia|ref=none}} * {{cite journal | vauthors = de Broucker T | title = [Synaesthesia, an augmented sensory world: phenomenology and literature review] | language = fr | journal =Revue neurologique| volume = 169 | issue = 4 | pages = 328–334 | date = April 2013 | pmid = 23434143 | doi = 10.1016/j.neurol.2012.09.016 | type = Review|ref=none}} * {{cite journal | vauthors = Cohen Kadosh R, Terhune DB | title = Redefining synaesthesia? | journal =British Journal of Psychology| volume = 103 | issue = 1 | pages = 20–23 | date = February 2012 | pmid = 22229770 | doi = 10.1111/j.2044-8295.2010.02003.x | url = https://research.gold.ac.uk/17077/1/Cohen%20Kadosh%20%26%20Terhune%202010%20BJP.pdf | type = Review|ref=none}} * {{cite book |vauthors=De Cordoba MJ, Riccò D, Day S |url=https://play.google.com/store/books/details/Mar%C3%ADa_José_de_Córdoba_Synaesthesia_Theoretical_art?id=MSREBAAAQBAJ |title=Synaesthesia: Theoretical, artistic and scientific foundations|location=Granada, Spain|publisher=Fundación Internacional artecittà|page=372 |date=July 2014 |isbn=978-84-939054-9-1|ref=none}} * {{cite journal | vauthors = Dael N, Sierro G, Mohr C | title = Affect-related synesthesias: a prospective view on their existence, expression and underlying mechanisms | journal =Frontiers in Psychology| volume = 4 | page = 754 | date = October 2013 | pmid = 24151478 | pmc = 3798864 | doi = 10.3389/fpsyg.2013.00754 | type = Review | doi-access = free|ref=none}} * {{cite web|vauthors=Danis A|title=Grapheme → colour synesthesia|url=https://www.numberphile.com/videos/synesthesia.html|work=Numberphile|publisher=Brady Haran|access-date=6 April 2013|archive-url=https://web.archive.org/web/20150918230906/http://www.numberphile.com/videos/synesthesia.html|archive-date=18 September 2015|ref=none}} * {{cite journal | vauthors = Fitzgibbon BM, Enticott PG, Rich AN, Giummarra MJ, Georgiou-Karistianis N, Bradshaw JL | title = Mirror-sensory synaesthesia: exploring 'shared' sensory experiences as synaesthesia | journal =Neuroscience & Biobehavioral Reviews| volume = 36 | issue = 1 | pages = 645–657 | date = January 2012 | pmid = 21986634 | doi = 10.1016/j.neubiorev.2011.09.006 | type = Review | s2cid = 10536190|ref=none}} * {{cite journal | vauthors = Luke DP, Terhune DB | title = The induction of synaesthesia with chemical agents: a systematic review | journal =Frontiers in Psychology| volume = 4 | page = 753 | date = October 2013 | pmid = 24146659 | pmc = 3797969 | doi = 10.3389/fpsyg.2013.00753 | type = Review | doi-access = free|ref=none}} * {{cite journal | vauthors = Mylopoulos MI, Ro T | title = Synesthesia: a colorful word with a touching sound? | journal =Frontiers in Psychology| volume = 4 | page = 763 | date = October 2013 | pmid = 24155733 | pmc = 3804765 | doi = 10.3389/fpsyg.2013.00763 | type = Review | doi-access = free|ref=none}} * {{cite web |vauthors=Palmer S, Schloss KB |title=What's the Color of Your Favorite Song? – The Crux |url=https://blogs.discovermagazine.com/crux/2015/08/21/color-song/ |work=Discover Magazine Blogs |publisher=Kalmbach Publishing Co. |date=21 August 2015 |access-date=19 April 2016 |archive-date=15 November 2019 |archive-url=https://web.archive.org/web/20191115020132/http://blogs.discovermagazine.com/crux/2015/08/21/color-song/|ref=none}} * {{cite journal | vauthors = Price MC, Mattingley JB | title = Automaticity in sequence-space synaesthesia: a critical appraisal of the evidence | journal =Cortex| volume = 49 | issue = 5 | pages = 1165–1186 | date = May 2013 | pmid = 23237480 | doi = 10.1016/j.cortex.2012.10.013 | type = Review | s2cid = 8151536 | url = https://espace.library.uq.edu.au/view/UQ:292276/UQ292276_fulltext.pdf|ref=none}} * {{cite journal | vauthors = Rothen N, Meier B, Ward J | title = Enhanced memory ability: Insights from synaesthesia | journal =Neuroscience & Biobehavioral Reviews| volume = 36 | issue = 8 | pages = 1952–1963 | date = September 2012 | pmid = 22634573 | doi = 10.1016/j.neubiorev.2012.05.004 | type = Review | s2cid = 9541065|ref=none}} * {{cite journal | vauthors = Sinke C, Halpern JH, Zedler M, Neufeld J, Emrich HM, Passie T | title = Genuine and drug-induced synesthesia: a comparison | journal =Consciousness and Cognition| volume = 21 | issue = 3 | pages = 1419–1434 | date = September 2012 | pmid = 22521474 | doi = 10.1016/j.concog.2012.03.009 | type = Review | s2cid = 15807455|ref=none}} * {{cite journal | vauthors = Simner J | title = Defining synaesthesia | journal =British Journal of Psychology| volume = 103 | issue = 1 | pages = 1–15 | date = February 2012 | pmid = 22229768 | doi = 10.1348/000712610X528305 | s2cid = 9038571 | url = https://www.pure.ed.ac.uk/ws/files/12435588/Defining_synaesthesia.pdf | type = Review|ref=none}} * {{cite journal | vauthors = Suslick KS | title = Synesthesia in science and technology: more than making the unseen visible | journal =Current Opinion in Chemical Biology| volume = 16 | issue = 5–6 | pages = 557–563 | date = December 2012 | pmid = 23183411 | pmc = 3606019 | doi = 10.1016/j.cbpa.2012.10.030 | type = Review|ref=none}} * {{cite journal | vauthors = Ward J | title = Synesthesia | journal =Annual Review of Psychology| volume = 64 | pages = 49–75 | year = 2013 | pmid = 22747246 | doi = 10.1146/annurev-psych-113011-143840 | s2cid = 241155101 | type = Review|ref=none}} {{div col end}}
==External links==
* [https://www.youtube.com/watch?v=nMN22KblIbc The real reason so many great artists experience reality differently], Richard Cytowic * {{cite book | last=Cytowic | first=Richard E. | author-link=Richard Cytowic | title=Synesthesia | date=January 1, 1970 | url=https://cytowic.net/writing/books/synesthesia/ | access-date=April 26, 2026}}
* {{commons category-inline|Synesthesia}} {{Medical resources | ICD11 = {{ICD11|MB27.4}}, {{ICD11|MB27.Y}}, {{ICD11|MB27.Z}} | ICD10 = {{ICD10|R44.8}} | ICD9 = <!-- {{ICD9|782.0}} --> | ICDO = | OMIM = | MedlinePlus = | MeSH = C562460 }}
{{Visual music}} {{Authority control|state=collapsed}}
Category:Synesthesia Category:Visual music Category:Consciousness