Synesthesia is usually inherited (called congenital synesthesia), but exactly how people inherit it is unknown.
Synesthesia is sometimes reported by people using psychedelic drugs, after a stroke, or during an epileptic seizure. It is also reported to be a result of blindness or deafness. Synesthesia that comes from events unrelated to genes is called adventitious synesthesia. This synesthesia results from some drugs or a stroke but not blindness or deafness. It involves sound being linked to vision or touch being linked to hearing.
Some musicians and composers have a form of synesthesia that allows them to "see" music as colors or shapes. This is called chromethesia. Mozart is said to have had this form of synesthesia. He said that the key of D major had a warm "orangey" sound to it, while B-flat minor was blackish. A major was a rainbow of colors to him. This may explain why he wrote some of his music using different colors for different music notes, and why much of his music is in major keys.
Another composer who had color-hearing was the Russian composer Alexander Scriabin. In 1907, he talked with another famous composer, Nikolai Rimsky-Korsakov, who had synesthesia, and they both found that some musical notes made them think of certain colors. Scriabin worked with a man named Alexander Mozer who made a color organ.
The same type of synesthesia may have different effects (pronounced and less pronounced) on different people.
Synesthetes often say that they did not know their experiences were unusual until they found out that other people did not have them. Others report feeling as if they had been keeping a secret their entire lives. Most synesthetes consider their experiences a gift—a "hidden" sense. Most synesthetes find out in their childhood that they have synethesia. Some learn to apply it in daily life and work. For example, they might use their gift to memorize names and telephone numbers or do mental arithmetic. Many people with synesthesia use their experiences to help them be more creative, for example, in making drawings and music.
- Grapheme–color synesthesia: Letters or numbers are seen to have colors of their own.
- Ordinal linguistic personification: Numbers, days of the week, and months of the year are felt to have their own personalities.
- Spatial-sequence: Numbers, months of the year, and/or days of the week are located in specific places in space. For example, 1980 may be "farther away" than 1990. Or a year may be seen three-dimensionally as a map.
- Visual motion → sound synesthesia: Hearing sounds in response to seeing motion.
- "BBC - Science & Nature - Horizon". bbc.co.uk. March 2006. Retrieved 4 March 2011.
- Campen C (1999). "Artistic and psychological experiments with synesthesia". Leonardo. 32 (1): 9–14. doi:10.1162/002409499552948.
- Cytowic, Richard E. 2002. Synesthesia: a union of the senses. 2nd ed, Cambridge, Massachusetts: MIT Press. ISBN 0-262-03296-1
- 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, p. 842-845 (in Russian), cited by Bulat Galeyev (1999).
- Hubbard EM, Arman AC, Ramachandran VS, Boynton GM (March 2005). "Individual differences among grapheme-color synesthetes: brain-behavior correlations". Neuron. 45 (6): 975–85. doi:10.1016/j.neuron.2005.02.008. PMID 15797557.CS1 maint: multiple names: authors list (link)
- van Campen, Cretien (2007). The Hidden Sense: Synesthesia in Art and Science. Cambridge, Massachusetts: MIT Press. ISBN 0-262-22081-4. OCLC 80179991.
- Day, Sean, Types of synesthesia. (2009) Types of synesthesia. Online: http://home.comcast.net/~sean.day/html/types.htm, accessed 18 February 2009.
- Rich AN, Mattingley JB (January 2002). "Anomalous perception in synaesthesia: a cognitive neuroscience perspective". Nature Reviews Neuroscience. 3 (1): 43–52. doi:10.1038/nrn702. PMID 11823804.
- Hubbard EM, Ramachandran VS (November 2005). "Neurocognitive mechanisms of synesthesia". Neuron. 48 (3): 509–20. doi:10.1016/j.neuron.2005.10.012. PMID 16269367.
- Simner J, Holenstein E (April 2007). "Ordinal linguistic personification as a variant of synesthesia". Journal of Cognitive Neuroscience. 19 (4): 694–703. doi:10.1162/jocn.2007.19.4.694. PMID 17381259. Retrieved 2008-12-27.
- Smilek D, Malcolmson KA, Carriere JS, Eller M, Kwan D, Reynolds M (June 2007). "When "3" is a jerk and "E" is a king: personifying inanimate objects in synesthesia". Journal of Cognitive Neuroscience. 19 (6): 981–92. doi:10.1162/jocn.2007.19.6.981. PMID 17536968. Retrieved 2008-12-27.CS1 maint: multiple names: authors list (link)
- Galton F (1880). "Visualized Numerals". Nature. 22: 494–5. doi:10.1038/021494e0.
- Seron X, Pesenti M, Noël MP, Deloche G, Cornet JA (August 1992). "Images of numbers, or "When 98 is upper left and 6 sky blue"". Cognition. 44 (1–2): 159–96. doi:10.1016/0010-0277(92)90053-K. PMID 1511585.CS1 maint: multiple names: authors list (link)
- Sagiv N, Simner J, Collins J, Brian Butterworth, Ward J (August 2006). "What is the relationship between synaesthesia and visuo-spatial number forms?". Cognition. 101 (1): 114–28. doi:10.1016/j.cognition.2005.09.004. PMID 16288733.CS1 maint: multiple names: authors list (link)
- Saenz M, Koch C (August 2008). "The sound of change: visually-induced auditory synesthesia". Current Biology. 18 (15): R650–R651. doi:10.1016/j.cub.2008.06.014. PMID 18682202. Retrieved 2008-12-28.