Edited by: Michael Banissy, Goldsmiths University of London, UK
Reviewed by: Henning Holle, University of Hull, UK; Monika Sobczak-Edmans, Brunel University, UK
*Correspondence: Charlotte A. Chun, Department of Psychology, University of North Carolina-Greensboro, Eberhart Building, PO Box 26170, Greensboro, NC 27402-6170, USA e-mail:
This article was submitted to Cognitive Science, a section of the journal Frontiers in Psychology.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
A fundamental question in the field of synesthesia is whether it is associated with other cognitive phenomena. The current study examined synesthesia's connections with phenomenal traits of mirror-touch and ticker tape experiences, as well as the representation of the three phenomena in the population, across gender and domain of work/study. Mirror-touch is the automatic, involuntary experience of tactile sensation on one's own body when others are being touched. For example, seeing another person's arm being stroked can evoke physical touch sensation on one's own arm. Ticker tape is the automatic visualization of spoken words or thoughts, such as a teleprompter. For example, when spoken to, a ticker taper might see mentally the spoken words displayed in front of his face or as coming out of the speaker's mouth. To explore synesthesia's associations with these phenomena, a diverse group (
When probing atypical subjective experiences, for example when asking people questions such as, “Do numbers have colors?” the most typical reaction from people who do not have such experience is puzzlement. Those who do may also be puzzled, either by the idea that not everyone shares this experience or, on the contrary, by the discovery that they are not unique. The more we ask questions about the intimacy of subjective experience, the greater diversity of responses we seem to get. Is there any “normal” or at least common subjective experience? Synesthesia, which at first seemed a very rare and extraordinary condition, now seems to be shared by a large fraction of the population. As soon as researchers started considering so-called atypical subjective experiences, the social demand for numbers has been high, and quite legitimately: people suddenly either discover that they are “different” or may take comfort from not being that “weird.” So the first question is how normative this experience is. Only a few large-scale, systematic studies have been able to provide prevalence estimates so far. The present study aims to contribute to this endeavor by including many subtypes of synesthesia as well as two other, possibly related, subjective phenomena: mirror-touch and ticker tape.
We consider synesthesia as the subjective phenomenon of additional experiences that sometimes, but not always, involves mixing sensory modalities: perceptual, emotional, or imaginary stimulation evokes sensory, representational, cognitive, or affective “synesthetic” experiences. These associations are supplementary, automatic, idiosyncratic, arbitrary, and involuntary (Hupé et al.,
Synesthesia runs in families (e.g., Barnett et al.,
Estimates of the prevalence of synesthesia vary depending on the methodology and criteria employed. A large-scale, systematic study including letter-color, number-color, month-color, day-color, word-color, person-color, person-smell, taste-shape, and music-color indicated a prevalence of 4.4% in the Scottish population (
Mirror-touch is the automatic, involuntary experience of tactile sensation on one's own body when others are being touched (Blakemore et al.,
About 10.8% of an undergraduate British sample (
Ticker tape experiences are the automatic visualization of words as they are thought or spoken, often seen in the mind's eye as static subtitles or a dynamic teleprompter (Galton,
Mirror-touch and ticker tape experiences share some commonalities with synesthesia, and could therefore be considered as subtypes of synesthesia (e.g., Serino et al.,
Knowledge of the co-occurrences of mirror-touch and ticker tape with synesthesia could suggest whether these phenomena have similar genetic or neurological underpinnings. As an example, Gregersen et al. (
Possible co-occurrence of mirror-touch and ticker tape with synesthesia may, however, be expressed in a complex or subtle manner. Indeed, the very large-scale study by Novich et al. (
The current study had five main goals (1) to examine whether mirror-touch and ticker tape associations are more prevalent in synesthetes than non-synesthetes, (2) to examine whether mirror-touch and ticker tape are associated with specific subtypes of synesthesia, (3) to examine gender differences in the proportions of synesthesia, mirror-touch, and ticker tape experiences, (4) to determine whether proportions of synesthesia, mirror-touch, and ticker tape experiences differ across domain of career and education, and (5) to provide prevalence estimates of phenomenal traits in the French population.
A focal point of this project was its ambition to employ methods for participant recruitment unbiased by self-referral. An effort was made to systematically recruit participants from a large and diverse group. Presentations were given to individuals at eight universities and one museum in Toulouse, southern France, in which a short description of the project was provided (a 5-minute oral presentation in the classroom or a quick explanation of the flyer for the museum). Flyers were then distributed with the internet address for a short online survey, “Interior Experiences.”
This study was conducted across 2 years. The first year involved recruitment at both universities and a museum; due to administrative restraints, recruitment presentations were different for universities and for the general public. In the first year of the study, university presentations included a definition and specific example of synesthesia as one of many different kinds of thought and perception. Flyers given to the general public explained that everyone has a different way of thinking, yet without any reference to synesthesia (note that in France, synesthesia is still unknown by the vast majority of the population, unlike in the United States and the United Kingdom). The proportion of respondents who reported synesthesia was very similar (less than 1% difference) between university and general public samples, so the explicit reference to synesthesia in the first case did not seem to induce more synesthetes to complete the survey. In the second year of the study, only university students were recruited and no reference to synesthesia was made in the presentation. A unique code was given to each person, allowing us to evaluate the response rate for every class and museum group, but the respondents could remain anonymous if desired. Students were recruited from the domains of economics, political science, law, engineering, agronomy, applied science, veterinary, medicine, psychology, and biology. Members of the general public were systematically recruited from conferences at the local Natural History Museum and during city-wide “Brain Week” events. We distributed a total of 3743 flyers.
This 5-minute online survey (whose translation is provided in the Appendix) involved questions concerning general demographic information, career and education, and the following types of synesthesia: grapheme-color (letters and/or numbers evoking colors/forms), temporal-color (numbers and/or time sequences: days, months, centuries,
To assess mirror-touch, participants were asked “When you observe a person being touched on a place on his/her body by someone or something, do you feel the sensation on your own body on the place where the person was touched?” Unlike a previous study that asked participants to rate the degree to which they experience mirror-touch on a five-point scale (Banissy et al.,
Consistent with the criteria of synesthesia being arbitrary and idiosyncratic, participants were counted as non-synesthetes if they marked “yes” to questions about synesthesia yet gave only common examples in the audition-color/form, “other,” or final comment box, such as smells triggering tastes or stimulation eliciting emotions and memories: for example, a taste or odor bringing to mind a precise visual memory. Participants were also counted as non-synesthetes if their only descriptions were clearly cultural or metaphorical associations; for example, spring associated with a floral ambiance or red, green, and yellow associated with reggae music. Individuals who gave these types of examples in addition to other valid synesthetic examples were still counted as synesthetes for their other subtypes. Participants were counted as non-mirror-touch if their descriptions only mentioned empathy or emotion without physical experience. Because no specific comment box was provided for ticker tape or other subtypes of synesthesia, anyone who answered “yes” to these questions was counted as a synesthete; furthermore, individuals were classified as ticker tapers whether their visual experiences occurred for words that were heard, spoken/thought verbally, or both.
Individuals' career or education domain was classified into three different groups, according to the French education system: (1) Scientific (S), (2) Economic and Social (ES), and (3) Literary (L). The following career and education areas were coded as Scientific: medicine, veterinary, biology, agronomy, applied science, and engineering. The following areas were coded as Economic and Social: political science, economics, and law. The following areas were coded as Literary: psychology, literature, and language.
Response rates from students and the general population were ~30 and 16%, respectively. Forty-two individuals who began but did not finish the survey and 38 individuals whose maternal language was not French were removed (i.e., not used in the study), providing usable data from a total of 1017 respondents (university:
Of these respondents, ~70% reported at least one type of synesthetic association. Such a high proportion indicates an obvious response bias, as well as potential false-positive reports. We decided to hypothesize a very strong response bias, assuming that those who did not complete the survey had neither synesthesia nor other phenomenal traits. In other words, we considered that all people who thought that their inner experience may be special had the motivation to check the online questionnaire and complete the full survey. Such an assumption is of course very conservative. But without verification using consistency tests, we had no way to detect potential false-reports so our initial criteria were certainly too liberal. We hoped that our conservative assumption would balance our liberal criteria. The comparison of our prevalence estimates with those from the few other studies available (see the Discussion section) indicates that these assumptions put us in the right ballpark.
Prevalence estimates of phenomenal traits in the population were estimated based on the full recruitment pool receiving flyers (Table
Any synesthesia ( |
19.0 |
Grapheme-color ( |
4.1 |
Temporal-color ( |
7.2 |
Sequence-space ( |
8.8 |
Grapheme-personification ( |
11.9 |
Person-color ( |
6.6 |
Audition-color ( |
4.6 |
Mirror-touch ( |
10.2 |
Ticker tape ( |
6.9 |
To examine whether phenomenal traits are more frequent in synesthetes, we computed Pearson χ2 values to test whether the co-occurrences of phenomenal traits with subtypes of synesthesia were higher than chance (Table
Mirror-touch | – | 3.8 (0.06) | 8.7 (0.09) | |||||
Ticker tape | – | 8.1 (0.09) | 2.4 (0.05) | |||||
Grapheme-color | – | |||||||
Temporal sequence-color | – | |||||||
Sequence-space | – | |||||||
OLP | ||||||||
Person-color | ||||||||
Audition-color | – |
Mirror-touch was associated with all six subtypes of synesthesia (association with temporal sequence-color was marginally significant, depending on the level of statistical correction) and ticker tape was associated with every subtype except temporal sequence-color, and only marginally with grapheme-color. Though these associations were significant, the
The majority of respondents did not indicate whether their mirror-touch experiences were felt in a mirrored fashion. Of those who did provide this information (
We performed similar analyses to evaluate co-occurrences among subtypes of synesthesia (Table
In the first year of the study, we compared ES, S, and L domains. We found no differences among the three domains. In the second year of the study, recruitment was only conducted at S and ES universities. We summed the responses across both years using the common S (
No significant differences were found between men (
Our pattern of results (significant, positive correlations between most items) suggested that some individuals might be more likely to endorse items in general. In order to evaluate possible acquiescence effects, we conducted
Twenty-seven point-biserial correlations were conducted so the family-wise error rate was set to
Few systematic studies exist to date on the prevalence of synesthesia, certain synesthetic subtypes, and mirror-touch; to our knowledge, no previous study has tried to evaluate the prevalence of ticker tape. Knowledge of the frequency of synesthesia and phenomenal traits is important both for informing the general public and to guide future research efforts (e.g., sample size and recruitment requirements). High prevalence rates of certain subtypes may also be a concern for studies not interested in synesthesia a priori but in general cognitive traits, since undisclosed synesthetic experiences may interfere with other measures, as in the example of sequence-space synesthesia (e.g., Price and Mentzoni,
Important limitations of our study are the brevity of the screening questionnaire and the absence of verification using consistency tests, so we had no way to detect potential false-reports. However, the free reports provided in the comment boxes, as well as a follow-up study with a subset of participants recruited from this screening (Chun and Hupé,
Another strong limitation of our study is that less than a third of the people to whom we distributed flyers filled out the online questionnaire. The very high prevalence rate of synesthesia that we measured among those who did respond suggested a strong bias presiding upon the choice to fill out the questionnaire. Our prevalence numbers (Table
Our measures of co-occurrences between subtypes of synesthesia and phenomenal traits could also be contaminated by response bias, if people with some specific traits were for any reason more (or less) motivated to fill out the online questionnaire. Without completely ruling out this possibility, several observations argue for a limited influence of such a bias. First, we measured similar rates of synesthesia and phenomenal traits in men and women. Previous gender differences reported in synesthesia (e.g., Baron-Cohen et al.,
There was considerable variety in individuals' experience of phenomenal traits. Mirror-touch was described for many different sensations, including: pain, general pleasure, sexual pleasure, kissing, temperature, tickling, pinches, etc. We even received reports of mirror-touch experiences in response to observation of very specific activities, such as clipping fingernails or putting on lotion. This is consistent with reports that mere observation or imagination of motor activity can induce synesthetic associations, as seen in swimming-style synesthesia (Nikolic et al.,
Banissy et al. (
Ticker tape experiences also showed a wealth of individual differences, as reported in semi-structured interviews of participants recruited from our sample for another study (Chun and Hupé,
Table
To our knowledge, this is the first study to present systematic data on ticker tape experiences. Prevalence rates are estimated at 7% for ticker tape and 10% for mirror-touch. In a previous mirror-touch study, detailed interview and examination of response to videos of tactile stimuli reduced the number of potential mirror-touch subjects by a factor of over 4 (Banissy et al.,
In contrast with the previously found preponderance of specular mapping in individuals with mirror-touch (
OLP synesthesia may be more prevalent in Francophone (12%) than in Anglophone (1.4%) populations. This would be logical given the masculine-feminine categorization built into the structure of the French language. In French, grammatical gender exists only for words (which we did not specifically inquire about) but personification associations are seen at the level of numbers and letters. It has already been shown that childhood cultural experience can shape the expression of specific associations within synesthesia (Ward and Simner,
The potential role of culture and maternal language on the development and expression of synesthesia remains speculative for several reasons: (1) the current study lacked verification of associations, (2) Simner and Holenstein's (
One possible cause of the discrepancy in observed prevalence rates for person-color associations (6.6% in our study vs. 2% by Simner et al.,
Table
Sagiv et al. (
Novich et al. (
Novich and colleagues emphasized the relative independence between subtypes of synesthesia, showing, for example that the proportion of people having each type of synesthesia was very similar for synesthetes with or without sequence-space synesthesia. Our results do not contradict this observation: sequence-space synesthesia was significantly correlated with every other subtype, not any subtype in particular (all small effect sizes,
Our results therefore show that, even if synesthetic subtypes cluster in different groups, as shown by Novich et al. (
Our study had five main goals. First, to examine whether mirror-touch and ticker tape associations are more prevalent in synesthetes than non-synesthetes. The answer is yes (which may indicate common genetic or neural mechanisms), though only to a weak degree in our study, and we cannot exclude that the elevated frequency of these phenomenal traits in synesthetes resulted from our recruitment bias. Our second goal was to examine whether mirror-touch and ticker tape are associated with specific subtypes of synesthesia. The answer is no: co-occurrences, if real, were distributed across all subtypes. Our third aim was to examine gender differences in proportions of synesthesia, mirror-touch, and ticker tape experiences; no differences were found. The fourth goal was to determine whether proportions of synesthesia, mirror-touch, and ticker tape experiences differ across domain of career and education; no differences were found. Finally, we aimed to provide prevalence estimates of phenomenal traits in the French population. We estimated ticker tape at 7% and mirror-touch at 10%. These numbers place the prevalence of these phenomena within the range of those of grapheme-color (4%) and sequence-space (9%), the most studied subtypes of synesthesia. We observed frequent associations of people with colors (7%) and graphemes with gender or personality (12%). These proportions are higher than previously presumed, based indirectly on sampling of Anglo-Saxon populations. We suggest that grapheme-personifications may be more frequent in the French population. If confirmed, this cultural difference would show that culture and maternal language play an important role in the development and/or expression of synesthesia.
The main strength of this study was its systematic recruitment, though the sample was still biased toward scholarly individuals. The use of a brief online questionnaire yielded a sizeable sample but introduced greater ambiguity than face-to-face studies. The study's main limitation was our inability to test the authenticity and consistency of participants' perceptions. For example, report of synesthetic-like experiences resulting from drug use or neurological conditions reflect possible sources of error. In light of these limitations, the authors made every effort to provide conservative estimates of synesthesia and phenomenal traits. However, without verification of the consistency and number of synesthetic associations, the group of synesthetes may be better described as “individuals with synesthetic-like experiences.” Considering these shortcomings, evidence of a higher prevalence of mirror-touch and ticker tape associations in the synesthetic population is tentative.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Research funded by Agence Nationale de Recherche ANR-11-BSH2-010. Charlotte Chun was sponsored by a Fulbright fellowship.
Thank you very much for accepting to participate in this study, led by the Brain and Cognition Research Center, laboratory of the University of Toulouse and of CNRS (
Know that your responses and personal information—if you provide us with them—will be kept confidential and evidently won't be distributed to exterior parties. You will have the possibility to give us your email address at the end of the questionnaire. In this case, we will be able to ask you to participate in the next step of our study. We will select a varied sample, representative from this questionnaire if possible. So it is important that you complete it carefully even if you do not wish to participate in the next step of the study.
If you are willing and selected, we will later ask you to respond to other questions (via internet), then to come in to the laboratory to take several playful tests, using your creative and imaginative capacities. We will then explain in more detail what that consists of and of course you will always have the choice to continue or stop your participation at any moment. You will be compensated for the time spent at the lab.
If you have questions, do not hesitate to contact us.
1. What is the code indicated on the piece of paper we distributed to you?
2. First and last name (or your initials if you do not want to participate in the rest of the study—see below).
3. Birthday
4. Where do you live? (city and department)
5. Maternal language
6. Are you multilingual? (considered as any language in which you think—habitually or in certain contexts)
Yes/No
If yes, indicate which languages you learned before starting school
7. Gender
Male/Female
8. Handedness
Left/Right/Ambidextrous
9. Main professional activity (student is a possible answer)
10. Highest level of education or diploma obtained to date
11. Main specialization of your studies
1. Do you have a regular artistic activity?
(We consider all types of artistic practices—whether in fine arts, photography, music, dance, theatre, writing, etc.—from the moment that you produce a “piece or work,” whether in an institutional or private setting).
Yes/No
If yes, explain which type and an approximate frequency
If yes, do you ever present your pieces in public (or have representations in public)?
It's possible that certain questions are difficult to understand—in this case, there is a chance that it concerns a particularity that you don't have and you should answer “no” to the question. If you have doubts, you can indicate and explain them in the space provided for this later.
1. When you think, would you say that it's in verbal form (with an interior dialog)?
Always/Often/Sometimes/Very rarely or never
2. When you think, would you say that it's in the form of images?
Always/Often/Sometimes/Very rarely or never
If this happens, can you explain the dominant nature of these images? (for example, purely visual, auditory, olfactory, audio-visual, etc.)
B3. Do you remember your dreams?
Always/Often/Sometimes/Very rarely or never
B4. Do you have memories before the age of 5?
Yes/No/I don't know
You may explain your earliest memory, if you would like.
B5. Do you get a song stuck “on repeat” in your head?
Often/Sometimes/Very rarely or never
6. When you listen to someone speaking, do you automatically visualize the words the person is saying (like a “prompter” in a way, that scrolls through your head)?
Yes/No
7. When you speak (or think verbally), do you automatically visualize the words you are saying?
Yes/No
8. When you observe a person who is touched on a place on their body by something or someone, does it happen that you feel the sensation on your own body in the place the person was touched?
Yes/No
If yes, explain whether it is systematic. Indicate whether your sensation is mirrored (for example, if a person across from you is touched on their right arm—that is therefore on your left side—do you feel the sensation in your own right arm or your left arm, therefore mirrored). If your experience is close to this but is different than what is described, please explain as well.
9. Do you associate letters or numbers with specific colors?
Yes/No
10. Do you associate temporal sequences (like days of the week or months of the year) with specific colors?
Yes/No
11. Do numbers or temporal sequences have a particular spatial organization for you?
Yes/No
12. Do letters or numbers have a gender for you: masculine/feminine?
Yes/No
13. Do letters or numbers have a specific personality for you?
Yes/No
14. Do you associate specific colors to people? Yes/No
15. Are there sounds (like voices or music) that systematically evoke colors or specific forms for you?
Yes/No
If yes, please explain (examples are welcome)
A16. Does stimulation in another sensory modality evoke a sensation or strong association in another modality (vision, audition, touch, odor, taste, movement, emotion)? (other associations than those of audiovisual asked in the previous questions)
*B17. Does touch systematically evoke color or forms for you?
Yes/No
If yes, please explain (examples are welcome)
A18. Do you know or think you have other immediate family members (siblings, parents, children, cousins, nieces/nephews, or aunts and uncles) that would have responded yes to one of the questions in this section?
If yes, please explain and tell how many (number of brothers, sisters, etc.)
A19. How many immediate family members do you have?
Explain (number of brothers, sisters, etc.)
B20. Do you have other ways of thinking or perceiving that you find are different from most of your friends and family?
Yes/Not to my knowledge
If yes, please explain (examples are welcome)
If you responded “yes” to at least one of the questions 9–17, you are most likely what we call a “synesthete.” You can find more information at the following internet address:
If you have doubts or explanations to give, please indicate them here, with the number to which they correspond.
21. Are you willing to be recontacted for the next step of this study? (We will explain what that consists of in more detail and then you may decide whether or not to participate).
Yes/No
22. Your email address:
Thank you for your time and participation! You may find the description of our research project et follow its development at:
AOnly asked in year one of the study
BOnly asked in year two of the study
*Touch-color experiences were asked about in the second year of the study as part of a recruitment effort for interview-based research on touch-color and orgasm-color synesthesia. It was not included in the current analyses due to its different sample size, as well as the already large number of variables and time constraints in the current study.
1Galton F. Inquiries into human faculty and its development. London: MacMillan, 1883, p. 67: “Some few persons see mentally in print every word that is uttered; they attend to the visual equivalent and not to the sound of the words, and they read them off usually as from a long imaginary strip of paper, such as is unwound from telegraphic instruments. The experiences differ in detail as to size and kind of type, colour of paper, and so forth, but are always the same in the same person.”
2When combining the results of both studies by Simner and colleagues that reported the proportions for color associations to letters or numbers, the proportion of synesthetes was 18/719 (= 2.5%), which is only marginally different from 4.1% (152 synesthetes among 3473 individuals; χ2 = 3.99,