Synaesthesia is where a percept or concept (such as words, sounds or touch) automatically triggers an experience in another modality (such as colour, space or taste). The triggering experience is called the inducer, and the triggered experience is known as the concurrent. For someone who experiences colours when reading letters, the letters would be the inducer and the colours the concurrent. Most types of synaesthesia are named using the format “inducer” – “concurrent”, such as grapheme-colour synesthesia (Grossenbacher & Lovelace, 2001). The inducer and concurrent are often in different modalities (for example vision-sound synaesthesia) though they can be in the same modality (for example grapheme-colour where both the inducer and concurrent are visual).
Synaesthesia is linked to all the senses; audition (sound), gustation (taste), olfaction (smell), somatosensation (skin sensation, internal organs and proprioception), and vision (sight). It is also linked to some skills or concepts (such as time, words, location and personalities). Certain types are more common than others. More frequent types are time-colour, grapheme-colour (Simner et al., 2006) and sequence-space (Rothen, Jünemann, Mealor, Burckhardt, & Ward, 2015). A list of reported synaesthesia types can be found on Sean Day’s website http://www.daysyn.com/Types-of-Syn.html.
Synaesthetes quite often have more than one type of synaesthesia. Synaesthetes with multiple types are more likely to experience additional forms which are within a cluster of types (Novich, Cheng, & Eagleman, 2011). For example, if someone has months-colour synaesthesia, they are more likely to also experience grapheme-colour synaesthesia than to have sound-smell.
The overall rate of having any form of synaesthesia is about 4% (Simner et al, 2006). Some forms of synaesthesia are more common than others. Seventy-three types of synaesthesia have been self-reported so far (http://www.daysyn.com/Types-of-Syn.html), however not all of these have been researched. Most research is conducted on more prevalent types or ones which are easier to research. The most heavily researched type is grapheme-colour.
Synaesthesia prevalence is higher in first degree relatives of synaesthetes suggesting a genetic component. Though two relatives may both have synaesthesia, if they have the same type their specific associations may differ, or the type of synaesthesia they experience may be different (Barnett et al., 2008). Preliminary genetics studies have been conducted however these are not conclusive and only conducted on specific types of synaesthesia (Asher et al., 2008; Tomson et al., 2011). It used to be thought that females were more likely to have synaesthesia than males, however prevalence studies have shown that there is equal likelihood between the sexes (Simner et al., 2006). Research has shown that learning and childhood experience also has a strong influence on synaesthetic experiences (Witthoft, Winawer, & Eagleman, 2015). Synaesthesia is therefore likely due to an interaction of genetic predisposition and learning during childhood.
When someone has had synaesthesia since childhood or “as long as they can remember” (Rich, Bradshaw, & Mattingley, 2005), it is described as developmental synaesthesia.
Research has shown that for some children who have synaesthesia like experiences, their experiences strengthen and consolidate during childhood. For other children with synaesthesia like experiences, these will weaken as they get older (Simner & Bain, 2013). We don’t currently know why some children will develop stable synaesthesia that remains into adulthood and others lose it, or what is likely to cause either outcome.
Learning during childhood appears to influence the experiences of some synaesthetes. For example, the specific letter-colour pairings found in alphabet sets used as a toy/ learning aid during childhood are found in a larger proportion of adult grapheme-colour synaesthetes than expected by chance (Witthoft, Winawer, & Eagleman, 2015).
If someone develops synaesthesia or synaesthesia like experiences later in life, it is described as acquired synaesthesia. There have been several training grapheme-colour synaesthesia studies, some of which have created synaesthesia like phenomenology (Bor, Rothen, Schwartzman, Clayton, & Seth, 2014; Colizoli et al., 2016; Colizoli, Murre, & Rouw, 2012; Meier & Rothen, 2009) though the experiences generally stop soon after training ends. There have been several reports of acquired synaesthesia after brain damage or sensory deprivation (Afra, 2009; Nair & Brang, 2019) however their phenomenology is generally not as rich as developmental synaesthetes. Temporary synaesthesia like experience can also be created using hypnosis (Anderson, Seth, Dienes, & Ward, 2014; Cohen Kadosh, Henik, Catena, Walsh, & Fuentes, 2009; Kallio, Koivisto & Kaakinen, 2017; Terhune, Luke, & Kadosh, 2017). This stops after the hypnosis ends and there is debate whether the behaviour matches that of developmental synaesthetes. Certain hallucinogenic drugs are reported to create temporary synaesthesia like experiences (Luke & Terhune, 2013), though these are less likely to follow the same inducer-concurrent pattern which characterises synaesthesia. (We recommend not taking hallucinogenic drugs to try and induce synaesthesia unless as part of an ethically approved and carefully controlled research study!). Synaesthesia like experiences can also be acquired through the use of sensory substitution devices (Ward & Wright, 2014). Sensory substitution devices allow people without access to a particular type of information to receive it through a different sense (for example devices that convert images into sounds for people who are blind; https://www.seeingwithsound.com/). The key to research in acquired synaesthesia is whether it matches developmental synaesthesia both phenomenologically and behaviourally and remains over time after the intervention.
The experiences of individual synaesthetes who have the same type of synaesthesia are usually highly variable. Using the example of grapheme-colour synaesthesia (letters or numbers triggering colour experiences), two synaesthetes would likely have very different letter-colour matches. For this reason, synaesthesia is described as idiosyncratic (Grossenbacher & Lovelace, 2001). If the grapheme-colour matches for many synaesthetes are measured, general trends are found. Therefore, although individuals have highly variable experiences, there are certain letter-colour pairs which are more likely to be found (Simner et al., 2005). How similar the experiences of synaesthetes are varies depending on the type of synaesthesia.
There are two general methods of synaesthesia measurement. The first is questionnaires used to measure which percepts or concepts someone reports to have associations between (Eagleman, Kagan, Nelson, Sagaram, & Sarma, 2007). These are often used for people to self-report the types of synaesthesia someone experiences. Individual follow up is required to confirm synaesthesia. Another way of using questionnaires is to record the experience of a particular type of synaesthesia is more detail (Rothen, Tsakanikos, Meier, & Ward, 2013), or identify synaesthesia subtypes, such as whether someone is a project or associator grapheme-colour synaesthete (eg. Anderson & Ward, 2015; Rouw & Scholte, 2007; Skelton, Ludwig, & Mohr, 2009).
The other method is through consistency, considered the gold standard of synaesthesia measurement. One such example is the Synesthesia Battery (Eagleman, Kagan, Nelson, Sagaram, & Sarma, 2007). To measure grapheme-colour consistency, a letter (or number) is shown on the computer monitor. The synaesthete selects the colour that matches it on a colour pallet or indicates that they have no colour association for that letter. This is done for each letter, three times. The similarity level of the colour selected for each letter over the three responses gives a measure of consistency. Synaesthetes are usually more consistent in their responses than non-synaesthetes (Rothen, Seth, Witzel, & Ward, 2013).
It is possible to measure your own associations for certain types of synaesthesia at https://synesthete.org/.
Synaesthesia is not a physical or mental health condition. No negative aspects are included in the definition of synaesthesia. The majority of synaesthesia researchers describe synaesthesia as a difference in perceptual experience. Synaesthesia is generally a very positive experience which has some associated benefits.
As synaesthesia isn’t a medical or mental health condition, most people won’t require professional confirmation that they have it. For those who want confirmation, please visit your general practitioner. Some people don’t realise they have synaesthesia until adulthood. Alternatively, some people who think they have synaesthesia aren’t synaesthetes.
Most scientific investigation into synaesthesia has been conducted by researchers at universities who specialise in psychology, cognitive neuroscience or medicine. There is no specific test used to determine whether someone has synaesthesia. Researchers sometimes use a combination of questionnaires or computer programs that can measure the specific associations someone experiences. These are not available for all types of synaesthesia, some require specific equipment or software, and not all measures are freely available. Researchers also use their knowledge of scientific literature on synaesthesia and information gained through talking to synaesthetes about their experiences when making judgements about whether someone is likely to be a synaesthete or not.
There have been a few publications suggesting a link between synaesthesia and autism spectrum disorder (ASD). Please be aware this is preliminary research and much still has to be learnt and replicated before general statements are made. Two smaller scale studies have suggested higher rates of Autism (Baron-Cohen et al., 2013) or Asperger syndrome (Neufeld et al., 2013) in synaesthetes. A larger scale study didn’t find conclusive support for a link between ASD and grapheme-colour synaesthesia (Carmichael, Smees, Shillcock, & Simner, 2018). ASD is a rare condition and grapheme-colour synaesthesia is a rare experience. Measuring concurrent rates of these therefore requires large samples of people. This difficulty is a limitation in the research suggesting a link between ASD and synaesthesia. Finding a link between ASD and a specific type of synaesthesia also doesn’t necessarily mean that a link would be found between ASD and all types of synaesthesia.
A prevalence study found no link between grapheme-colour synaesthesia and dyslexia (Carmichael, Smees, Shillcock, & Simner, 2018). Other conditions which were not linked to synaesthesia in their investigation were ADD/ADHD, asthma, depression, eczema, hay fever, insomnia, irritable bowel syndrome, migraine, sleep apnoea and stomach ulcers.
There are millions of people on the planet who have synaesthesia, and as such it is expected that there are people who will have synaesthesia and a mental health problem or learning difficulty. As differences in perception can be a part of synaesthesia as well as a range of conditions, it can be difficult for some people to separate synaesthesia from a condition. If you have a concern, please visit your general practitioner.
Preliminary research has found a potential link between grapheme-colour synaesthesia and anxiety disorder (Carmichael, Smees, Shillcock, & Simner, 2018) however causation can’t be inferred in this study. Further research into links between synaesthesia and mental health problems or learning difficulties is required.
Occasionally people who have synaesthesia find that their experiences can be distracting or intrusive. There is extensive research showing that synaesthesia is linked to attention (Mattingley, 2009), synaesthetes don’t tend to experience synaesthetic experiences for potentially triggering stimuli that they are not attending to. That being said, the concurrent synaesthetic experience is generally automatic once a synaesthete is attending to an inducing stimulus. We don’t currently know how to stop synaesthesia from occurring or how to reduce distraction in those who have this difficulty.
There are some anecdotal reports of people mixing up information they are trying to remember because they have a shared synaesthetic quality, such as both words being yellow. It’s common for people to mix up information which has a similar quality therefore misremembering information isn’t isolated to synaesthesia.
If you have had similar problems connected to synaesthesia yourself and have advice you are willing to share on what has or hasn’t worked please contact Hazel Anderson at email@example.com.
Some people want to know how to stop synaesthesia. For the large majority of synaesthetes, synaesthesia is a positive experience. For the minority that have negative experiences, we don’t currently know how to stop or reduce synaesthesia. If you have suggestions on solutions that have worked for yourself that you are willing to share, please contact Hazel Anderson at firstname.lastname@example.org.
Benefits of synaesthesia.
Some specific memory advantages have been measured in association with synaesthesia (Rothen & Meier, 2010). These benefits are not necessarily for information linked to their synaesthesia. Memory advantages in synaesthesia may rather reflect differences in brain structure and how perceptual information is processed (Rothen, Meier, & Ward, 2012).
Synaesthetes self reported greater visual imagery ability than the general population (Barnett & Newell, 2008). Further research found that the reported mental imagery benefits were linked to the senses involved in the synaesthetes inducer and concurrent (Spiller, Jonas, Simner & Jansari, 2015). For example, if someone had vision based synaesthesia, they would overall report having better vision based mental imagery than non-synaesthetes, but they wouldn’t generally report having better taste based mental imagery.
Evidence on a relationship between synaesthesia and creativity is mixed. A general creativity advantage has not been measured, rather some specific benefits were found (Ward, Thompson-Lake, Ely, & Kaminski, 2008). There is also preliminary evidence for a higher rate of synaesthesia in art students compared to the general population (Rothen & Meier, 2010). Some synaesthetes use their synaesthesia within their art. Below are links to a few examples.
Melissa McCracken, sound-colour synaesthesia (https://www.melissasmccracken.com/ or
Magazine article on artists with synaesthesia by Jacoba Urist (https://www.thecut.com/2016/07/why-do-so-many-artists-have-synesthesia.html).
Prof Julia Simner (the UKSA Science Officer) and her team at the University of Sussex have been developing supporting information for parents and teachers of children who have synaesthesia. Downloadable information can be found at www.syntoolkit.org. The website is still a work in progress and part of a large project to support child synaesthetes in schools. Prof Julia Simner obtained over a million Euro in funding from the European Research Council for this important and ongoing research.
The UKSA doesn’t currently have a formal membership system. Instead, the UKSA contacts people through two forms of communication. One is a Facebook group and the other a mailing list, both of which we use to connect synaesthetes, synaesthesia researchers and those who are interested in synaesthesia. Through these, information related to synaesthesia is shared. This may be synaesthesia events, interview or media requests, opportunities for synaesthetes to take part in research, and anything else relevant to synaesthesia which we feel may either interest people or which our members may be able to help others with.
The link to our Facebook page is here https://www.facebook.com/groups/128219365930/. To join our mailing list complete the sign up form on our News and Events page.
The UKSA has a history of organising conferences with UK based host institutions which combined scientific research with synaesthesia artistic or creative posters and presentations. These were attended by scientists and synaesthetes amongst others. Future UKSA conferences are planned however there are none currently organised. If your institution is interested in hosting a UKSA conference, please contact James Wannerton at email@example.com.
News and events are shared through our mailing list, on the UKSA Facebook page and other social networking sites (see the Links page).
Sometimes people want to talk to other synaesthetes. Synaesthesia isn’t as rare as originally thought, however some types are not very common. For some synaesthetes, discovering that they experience the world in a slightly different way from most others can be quite surprising. There are synaesthesia groups on social media which some use to connect with other synaesthetes. Links to some of these can be found on our Links page.
There are numerous research groups and projects related to synaesthesia. The UKSA doesn’t conduct research as an organisation, however it sometimes receives information on opportunities for synaesthetes to take part in research which we share with our Facebook group or mailing list. Another option is to complete synaesthesia questionnaires hosted online by individual research groups which they use to contact potential participants. Links to some UK and International research groups are included on our Links page.
The UKSA is run by volunteers and doesn’t have money to support external projects. We wish you the best of luck in obtaining funding!
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