Transthesia: Comparing the Prevalence of Synesthesia in Transgender and Cisgender Individuals

Abstract Purpose: To evaluate the prevalence of synesthesia in transgender versus cisgender individuals. Methods: A 10-question, self-administered written survey, developed to assess the prevalence of synesthesia, was distributed to transgender individuals (n=96) attending support groups as well as to cisgender participants (n=103) identified among individuals accompanying transgender attendees. Demographic data and prevalence of synesthesia were analyzed using descriptive statistics. Differences between groups were analyzed using a chi-square test. Results: Forty-two percent of transgender participants endorsed synesthesia compared with 16% of cisgender participants. These findings persisted when analyzed by specific gender identity (i.e., male, female, and nonbinary). Conclusion: This study suggests a correlation between synesthesia and transgender identity that may indicate a common biological cause. Limitations of this study include use of a survey that has not yet been validated. Initial findings may justify further research.


Synesthesia
Synesthesia is a neurological condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary sensations in a second sensory or cognitive pathway. Synesthetes may experience colors when they hear sounds, see colors when they hear letters or words, visualize numbers as points in space or geometric shapes, ''feel'' sounds as a tapping on the shoulder, attach scents or tastes to human personalities, and many more. 1,2 Once believed to be extremely rare, recent estimates suggest a prevalence of 4.4%. 3 Synesthesia can be detected by testing the consistency of these sensations over long time intervals. 3 The online Synesthesia Battery, which assesses consistency within a single test session, is also a valid method for assessing synesthesia. 4 Synesthetes can be identified as early as age six. 5 Autism Autism appears to have a biological component. 6,7 Research is proceeding to develop a diagnostic test (examining brain waves, blood, or urine) for autism spectrum disorders. 8,9 Transgenderism Research suggests biological factors in transgenderism. [10][11][12] However, research into objective methodology for assessing transgenderism, especially in children, is still preliminary. 13 Correlations among synesthesia, autism, and transgenderism Synesthesia is more common in individuals with autism. 1,14 Individuals with autism are also more likely to be transgender or gender variant. [15][16][17] No studies could be found discussing whether synesthesia and transgenderism are correlated. Correlation of transgenderism to syndromes with publically accepted biological causes might increase societal acceptance of transgender individuals. Correlation also might assist in developing valid methods for earlier, accurate identification of transgender children, possibly improving these individuals' access to appropriate medical treatment and providing their parents with a longer period of time to access information to support their children. The aim of this study was therefore to identify whether synesthesia and transgenderism are correlated.

Participants and procedures
A 10-question survey was distributed to 199 transgender and cisgender attendees at 8 transgender support groups in King and Pierce Counties in Washington State during January and February 2018. Cisgender participants were generally parents and friends of transgender participants. Participant demographics are summarized in Table 1. The majority of transgen-der participants were age 11-30 years (65, 68%), while the majority of cisgender participants were age 31-50 years (65, 66%).
The Institutional Review Board for the Washington State Science and Engineering Fair approved the survey and the research plan, including the use of human participants. Written informed consent was obtained from all participants. Written parental consent was also obtained for minor participants.

Measures
A self-administered, 10-question survey was developed for the purpose of this study (Table 2). Question 2 (What is your current gender [male, female, nonbinary, other]?) was used to identify participants' gender identity. Question 8 (Do you consider yourself transgender? Yes/No) was used to identify participants who were transgender. Question 5 (Do you perceive things to have additional sensations, such as letters having colors, or sounds having smells? Yes/No) was intended to identify participants who were synesthetes. Question 3 (Do you consider yourself to have a sweet tooth? Yes/ No) and Question 9 (Are you color-blind? Yes/No) were included as red herrings to disguise the researcher's hypothesis (i.e., that synesthesia and transgenderism are correlated) from participants.

Data analysis
The survey was distributed to transgender individuals (n = 96) attending support groups as well as   to cisgender participants (n = 103) identified among individuals accompanying transgender attendees. A chisquare test was performed using a significance level of 0.05.

Discussion
This study suggests an overall prevalence of synesthesia of 28% (42% in transgender and 16% in cisgender participants). This is a higher prevalence than that found by other studies (i.e., 4.4% in the general population). 3 This study asked participants, ''Do you consider yourself transgender?'' Other researchers suggest asking two separate questions (i.e., one for current gender identity and another for birth-assigned gender). 18 This study asked participants whether they had cross-sensory experiences indicative of synesthesia.

Conclusion
This study's results suggest a correlation between transgenderism and synesthesia. The researcher encourages larger scale replication of this study.
Possible practical applications of this area of research include earlier identification of transgender children, which could provide families additional time to support children's gender transitions and make available a greater range of medical treatments to genderquestioning youth. 19

Acknowledgments
The researcher thanks Dr. Jenn Pang (Bellevue College, Bellevue, WA) for assisting in completion of required science fair forms. He thanks Gil Rich (Gender Diversity, Seattle, WA) for aiding in survey revision. He also thanks the following groups for allowing distribution of surveys: Gender Alliance of the South Sound, Gender Diversity, Ingersoll Gender Center, Seattle Counseling Services, Tacoma T-Men, and Tranz group at Lambert House. Each provides a valuable sanctuary for transgender people. Finally, the researcher thanks his mom for her constant support.