Université  Paul  Sabatier  TOULOUSE  III  

 

M2R  NEUROSCIENCES,  COMPORTEMENT,  COGNITION    

                 

GATES, Charlotte

   

Creativity, Personality, and Cognition in Synesthetes

ACKNOWLEDGEMENTS

I would like to thank my lab mentor, Dr. Jean-Michel Hupé, for the constant motivation and the amount of time he

spent teaching me, discussing ideas, and helping to ensure the eventual success of this project.

Many thanks as well to the entire Centre de Recherche Cerveau et Cognition lab team.

And especially thank you to all the participants who dedicated their time to come to the lab.

ABSTRACT

Synesthesia is a subjective phenomenon in which individuals experience a linkage of two

or more senses and/or cognitive concepts in the brain, such as grapheme-color

synesthesia, in which letters or numbers evoke a color association. Little is known about

whether synesthesia is related to other neurological phenomena, such as mirror-touch

(tactile sensations on one's own body when others are being touched) or ticker tape

perceptions (visualization of spoken words, such as a teleprompter). The total synesthesia

prevalence is revisited and novel mirror-touch and ticker tape prevalence estimates are

made with a systematically recruited group (n=1305) from universities and the general

public in southern France.

The current study also compares preliminary data from verified groups of synesthetes

(n=10) and controls (n=10) on culturally relevant measures of four creativity domains

(visual, verbal, convergent, and divergent), controlling for important factors such as

personality and cognition, to examine whether certain individual differences may be the

expression of core synesthetic attributes. Results are discussed considering the current

literature and the potential origins of synesthesia.

INTRODUCTION

Synesthesia is a subjective phenomenon in which individuals experience a linkage of two or more senses and/or

cognitive concepts in the brain (Simner 2010, In Press); for example, grapheme-color synesthesia, in which letters

or numbers evoke a color association. There are approximately sixty different types of genuine synesthesia (Day

2005). Standard criteria for authentic (also referred to as 'idiopathic'; Dann 1998) synesthesia include that it is non-

pathological, involuntary, begins in childhood and tends to remain stable throughout a person’s lifetimea, is difficult

to describe, is personally meaningful and linked with emotion, and is sometimes associated with certain advantages

(such as superior memory due to distinctiveness of information) or disadvantages (such as interference with

cognitive reasoning) (Cytowic 1982; Baron-Cohen, Goldstein & Wyke 1993; Ward 2008a).

Synesthesia runs in families, and has both environmental (Ward, Simner, & Auyeung 2005; Barnett &

Newell 2008) and genetic influences (Barnett & Newell 2008; Ward 2008a). Although previously believed to be

more common in women (Baron–Cohen, et al. 1993), modern evidence suggests that the supposed disparity is

actually due to self-disclosure differences (Ward, et al. 2005). Though prevalence estimates have varied throughout

the years, the modernly accepted prevalence rate of synesthesia ranges between 1 and 5%, according to a recent

study’s approximation of 4.4% (Simner, Mulvenna, Sagiv, Tsakanikos, Witherby, Fraser, Scott, & Ward 2006).

This 'University Study,' to which we will compare our observed prevalence estimates, examined the rates of

synesthesia in 500 participants recruited from two universities. To our knowledge, it was the first study to

systematically verify the number of synesthetes in a large group, unbiased by self-report. Little is known, however,

about the prevalence of similar neurological phenomena that are potentially linked with synesthesia, such as mirror-

touch (the experience of tactile sensation on one's own body when others are being touched; Blakemore 2005) and

ticker tape perceptions (the automatic visualization of words as they are being thought or spoken, often seen such as

static subtitles or a dynamic teleprompter; Day 2005). For continuing clarification, the prevalence of synesthesia and

other neurological phenomena should be systematically examined in as many diverse populations as possible.

There have been many theories concerning the origins of synesthesia; some think it is an atavistic remnant

of our primitive development, while others view it as a new evolutionary adaptation (Dann 1998). Synesthesia has

also been cited as the basis for cross-modal sensations (Hartshorne 1934), language and metaphor (Ramachandran

& Hubbard 2001b), memory (Ward 2008a), creativity (Ramachandran & Hubbard 2001b), and the construction of

meaning (Wheeler & Cutsforth 1922). One commonly accepted theory for the neurological mechanism of

synesthesia is that genetic differences cause either cross-activation or inability to inhibit connections between

different sensory regions in the brain. The “adjacency principle” states that closer proximity in the brain leads to a

greater occurrence of synesthesia between senses (Ramachandran & Hubbard 2001a). Several studies claim fMRI

results of synesthesia-induced BOLD activation for achromatic graphemes, in which both real and synesthetic

colors activated the V4 region (Nunn, et al. 2002; Hubbard et al. 2005). However, recent findings from our lab

suggest otherwise (Hupé, Bordier & Dojat, Submitted for Publication): stricter statistical and methodological criteria

not employed in previous studies (such as accounting for individual functional variability) revealed no fMRI a There are various literature accounts of people gaining/enhancing or losing certain synesthetic abilities (for further detail, refer to Ward 2008a). We had several unverified reports from our survey of people who claimed to gain or lose synesthesia and ticker tape perceptions.

activation for synesthetic colors in the V4 region or elsewhere, regardless of strength of synesthetic associations.

These results are supported in other studies (i.e., Rouw & Scholte 2010), and provide evidence against the theory of

localized coding of synesthetic color perception. The fundamental concepts and neural processes of synesthesia are

still being researched, but a topic of equal interest is whether this neurological anomaly affects other aspects of

synesthetes' cognition and personality.

It has been suggested that synesthesia developed to promote creativity (Ramachandran & Hubbard

2001b); although there is little conclusive research to date, this view is strengthened by the fact that many famous

artists, musicians, and authors are synesthetes (Dann 1998; Mulvenna & Walsh 2005). Synesthetes were also found

to be more likely than controls to have an artistic occupation and to engage in artistic hobbies (Rich, Bradshaw &

Mattingley 2005; Ward, Thompson-Lake, Ely & Kalinski 2008b). Most previous studies that have found

synesthetes to be more creative than controls (Domino 1989; Sitton & Pierce 2004) did not employ any objective

measure to test for authenticity of synesthesia.

A more recent study (Ward, et al. 2008b) validly examined creativity in synesthetes by comparing their

performance to controls on the RAT (Mednick 1967) and the Alternative Uses Test (ALT; Guilford, Christensen,

Merrifield & Wilson 1978), as well as examining artistic engagement. The RAT is a test of convergent thinking (the

ability to focus and link unconnected ideas) in which subjects try to find the connecting concept among three

'unrelated' words, which was revised for their study to accommodate modern culture in the UK. The ALT is a

measure of divergent thinking (the ability to solve problems by generating useful, original ideas) in which subjects

are asked to come up with 6 alternative uses for 6 common objects. Participants also reported their occupation and

how often they create visual art, play an instrument, and look at visual art. Synesthetes' perceptions were confirmed

to be consistent using a test-retest delay of two months. Synesthetes were more likely to be professional artists and

spent more time creating and looking at art, even when statistically matched for occupation. Synesthetes performed

better on the RAT for convergent thinking, but there were no group differences on the ALT for divergent thinking.

No differences were found among the different sub-types of synesthesia, but the number of types made a significant

difference. Ward concluded that synesthetes may be superior at linking unrelated concepts, but not necessarily at the

traditional view of creativity as the ability to come up with helpful, novel ideas; this may reflect the inflexible nature

of their synesthetic perceptions. They also found that synesthetes who had music as an inducer were more likely to

play an instrument and create visual art. The authors suggest that synesthetic experiences may serve as an

inspiration, but not necessarily an evolutionary adaptation, for art and creativity. A potential limitation of the

conclusions of the study is the common recruitment bias of using volunteered, self-reported synesthetes, in addition

to the non-systematic recruitment of acquaintances for the control group. The RAT and ALT measure verbal

creativity only, although conclusions were drawn for visual synesthetes in particular. The current study expands

upon the previous work and tries to ameliorate these potential limitations by eliminating recruitment bias and by

examining convergent and divergent thinking in both verbal and visual domains.

The multi-dimensional nature of creativity makes it both controversial and difficult to isolate, especially in

laboratory environments. Many creativity theories hold that the production and synthesis of ideas requires a certain

intellectual threshold. A recent study showed that general intelligence was correlated with divergent thinking on the

ALT; this effect declined when the Openness personality factor was controlled for, yet still remained at a medium

effect size (Silva 2008). On the other hand, a meta-analysis of 83 creativity studies found that personality more than

intellect was responsible for heightened creativity, with Openness and Extraversion being the most important factors

(Feist 1998), as confirmed by recent research (Furnham & Bachtiar 2008). Cognition and personality have unclear

roles in the expression of creativity, but are essential factors to consider when measuring creative thinking.

In the history of psychology, there are many models of personality traits, but the most commonly accepted

and reliably confirmed is the Five Factor Model (FFM), a collaborative effort of researchers over many decades.

The five personality factors are Openness (appreciation for a variety of different experiences), Conscientiousness

(self-disciplined, goal-oriented tendencies), Extraversion (seeking the company of others), Agreeableness

(compassionate and easy to get along with), and Neuroticism (emotional instability, negative emotions) (McCrae &

Costa 1987; Goldberg 1999). The International Personality Item Pool (IPIP; Goldberg 1999) was created as a cross-

culturally relevant measure of the big five personality factors. When examining personality traits it is particularly

important to use appropriate recruitment techniques because volunteers are more likely to have high Openness and

Extraversion factor scores, which could significantly alter results.

There is currently little research on synesthesia and personality traits; however, one study examined

synesthete and control group scores on the Multidimensional Personality Questionnaire (MPQ; Tellegen 1982) and

found a positive relationship between synesthesia and the Absorption factor, the participation in and enjoyment of

imaginative activities, although no other significant relationships were found (Rader & Tellegen 1987). However,

upon closer inspection of the MPQ, many of the items on the Absorption scale (Tellegen & Atkinson 1974) are

directly related to or indistinguishable from synesthesia, for example: “Textures, such as wool, sand, wood,

sometimes remind me of colors or music” or “I find that different odors have different colors.” The results are

consequently unsurprising and provide little valid information about synesthetes’ imaginativeness apart from their

natural associations. Therefore the question remains: can certain differences in the synesthetic brain be considered

core attributes of synesthesia, or are they simply the secondary traits of synesthetic expression?

The purpose of Study One was to give a broad look at the prevalence of synesthesia and other

neurological phenomena in a large, systematically recruited group from the general population. The main goal of

Study Two was to explore whether synesthetes have creative thinking abilities that are 1) distinct from those of non-

synesthetes and 2) important enough to persist independently of factors such as personality, creativity, and global

cognition. Before being equipped to answer these questions, we must examine the feasability of such an

undertaking. Important factors to consider are whether non-biased recruitment of participants is possible, whether

our tests are valid and sensitive enough to capture such dynamic and elusive constructs, and whether it is feasible to

test the number of participants necessary to reveal these potential differences. With a sample of 89 synesthetes and

119 controls, Ward et al. (2008b) found a significant difference in RAT scores, with an effect size within the range

of what we would desire to find in order to consider the implications of this creative difference not only statistically

significant, but also behaviorally meaningful. Given the time constraints, a sample size this large was not possible so

we focused our efforts on developping a valid methodology concerning recruitment strategy and testing materials.

We aimed to test at least 10 synesthetes and 10 controls, which we fixed as the minimum sample size needed to

evaluate the feasibility of our overall study. These primary results should provide us with basic information about

potential differences and the resources to evaluate our methodology for future continuation.

STUDY ONE METHODS

Recruitment

One important and distinguishing factor of this project is its ambition to employ non-biased methods for participant

recruitment. The majority of previous studies have recruited volunteered, self-reported synesthetes. This is limiting

as it excludes the population of synesthetes who would be unlikely to spontaneously volunteer for research due to

various reasons, such as potential personality differences or to lack of awareness that their perceptions are any

different from what the majority of people experience. Moreover, to find a comparable control group, it is important

to employ identical recruitment methods (there is no way to recruit a large number of self-reported non-synesthetes).

Therefore an effort was made to systematically recruit participants from a large and diverse group.

Presentations were given to psychology, biology, and medical students at three universities in southern France, in

which a 5-minute description of the project was presented. Papers were then distributed with the internet address of

a short online survey, 'Les Expériences Intérieures' (Interior Experiences) which involved questions concerning

general demographic information, career and education, general artistic and sports activities, verbal/visual

processing, and the neurological phenomena of ticker tape, mirror-touch, and synesthetic perceptions (for a detailed

list of each synesthesia subtype included and how we defined them, refer to the Methods section). A personal code

was given to each student allowing us to evaluate the response rate for every class. Members of the general public

were recruited from conferences at the local Natural History Museum and during city-wide 'Brain Week' events.

Flyers were distributed with a short description of the project, as well as the internet address and a personal code.

STUDY 2 METHODS

Primary Participant Selection

Potential participants for the second part of this study were selected from the basis of our online survey. The

potential experimental group was chosen based on affirmative responses to questions about synesthetic perceptions.

Primary selection criteria for all potential participants included right-handedness, geographic proximity, and being

aged 18-65. Participants were not selected if they marked "yes" to questions about synesthesia yet gave only vague

or common examples of smells triggering tastes, smells or music triggering emotions and memories, etc. They were

also eliminated if their only examples were of common cultural or metaphorical associations, for example: sadness

associated with grey or spring associated with a floral ambiance. This initial exclusion was performed after survey

response collection and before participant selection; likewise, these responses were not used to calculate our

estimated synesthesia prevalence (participants who listed these type of examples in addition to other types of

synesthesia were still included). This was done in order to conform as closely as possible to Simner et al.'s (2006)

'University Study' methodology, in which participants were given a definition and description of synesthesia

beforehand, as well as an explanation of how it differs from metaphorical associations.

Since there were few male respondents, all potential male synesthetes were contacted for further

participation; potential female synesthetes were contacted in the order in which they completed the online survey.

This potential experimental group was invited to complete the Synesthesia Questionnaire, a detailed survey about

synesthetic perceptions, which was adapted from a previous questionnaire used in our lab (Hupé, et al. Submitted for

Publication) and expanded to include questions about a broader range of synesthetic subtypes, as well as in-depth

questions about ticker tape and mirror-touch phenomena. Potential participants were also asked to make a detailed

list of their associations including specific examples (drawings, etc. as applicable), and for color associations were

asked to choose the specific hues using their computer's color palette. Of the eighty potential synesthetes invited to

complete the Synesthesia Questionnaire, we received thirty responses (partial and complete).

Secondary Participant Selection

Secondary selection was based on authenticity, clarity, and specificity of responses. Only synesthetes who had

ample associations that we could verify or re-test in our lab were selected; therefore synesthetes who reported only

unspecified assocations with taste, music, or sexual touch were excluded. Color associations were classified as

either basic (common and monolexemic) or complex (rare, such as "mauve," and/or multi-lexemic, such as "light

green"). To meet selection criteria, synesthetes had to have at least fifteen basic associations or at least nine testable,

complex associations. All participants who met selection criteria and gave adequate examples of testable

associations were invited for further participation. Of the fourteen potential synesthetes invited for further testing,

eleven accepted. Controls were then selected using semi-matching techniques to have similar group mean

characteristics for sex, age, education level, presence/absence of a general artistic activity, presence/absence of

ticker tape perceptions, and presence/absence of mirror-touch perceptions.

Participants from the experimental group were given a re-test of their synesthetic associations at least one

week later. Inclusion criteria mandated a test-retest accuracy of greater than 70%, based on accuracy dispersion data

from Baron-Cohen's Test of Genuineness-Revised (TOGr; Baron-Cohen, Wyke & Binnie 1987). One experimental

participant was excluded based on a test-retest inaccuracy of 50%. The final sample consisted of 10 synesthetes (4

male, 6 female) and 10 non-synesthetes (4 male, 6 female).

Pilot Testing

Since many of the measures used in this experiment were created, translated, and/or culturally adapted for the first

time, a pilot-testing phase was run to verify and improve the validity, clarity, and difficulty level of the tests and

questionnaires. Four non-synesthetes and seven self-reported synesthetes (not included in the present study)

completed the pilot-testing phase, after which tests were modified and improved before official testing began.

Testing Methods and Confidentiality

Lab testing was divided into two sessions: Session One included all creativity tests (~1.5 hours) and Session Two

was the WAIS-III (1.5~2 hours). Participants had the option to complete the testing sessions in two separate days, or

to complete both sessions in one day (including a mandatory hour and a half break between sessions). Participants

were assigned a subject code for the WAIS-III and all creativity tests that were not considered personal. The TTCT

drawing production was considered more personal; therefore participants were asked to create a non-identifying

code, composed of three letters and three numbers, that was joined with only their name and final score by a blind

researcher that did not participate in the scoring. To ensure confidentiality, the same system was used for the

personal online questionnaires examining personality traits, experiences, and activities. Informed consent was

obtained before laboratory testing and all participants were compensated for their time.

Materials

Interior Experiences Survey. This was our primary online questionnaire, which took about 5-10 minutes and

included questions about general demographic information, career and education, general artistic and sports

activities, verbal/visual processing, and the neurological phenomena of ticker tape and mirror-touch perceptions.

Participants were also asked whether they experience any of the following types of synesthesias (for which the first

word is the initial sensory 'inducer' and the second word is the evoked synesthetic 'concurrent'): grapheme-color

(letters and/or numbers evoking colors/forms), temporal-color (numbers and/or time sequences--days, months,

centuries, etc.--evoking colors/forms), temporal-spatial (numbers and/or time sequences being organized in space),

grapheme-personification (letters and/or numbers associated with gender/personality), person-color (people

associated with a color), audition-vision (sounds/voices/music evoking colors/forms), lexical-gustatory (words

evoking tastes), or 'other' (other connections between sensory modalities). A space was provided for any

commentary and participants had the option to leave their email address for further participation.

Weschler Adult Intelligence Scale-Third Edition; French version (WAIS-III; Wechsler 1997; Grégoire 2004). The

WAIS-III is a traditional measure of global cognition. It contains thirteen subtests divided between two scales: the

Verbal Scale (Vocabulary, Similarities, Arithmetic, Digit Span, Information, Comprehension, and Letter-Number

Sequencing) and the Performance Scale (Picture Completion, Digit-Symbol Coding, Block Design, Matrix

Reasoning, Picture Arrangement, Symbol Search); four indices (Verbal Comprehension, Perceptual Organization,

Working Memory, and Processing Speed); and an optional subtest (Object Assembly). Subtest raw scores are

converted to standard scores based on age. Standard scores are then used to compute Total, Scale, and Index scores,

which have a median of 100 and a standard deviation of 15 points. Reliability scores range from 0.68 to 0.90 for the

subtests, and from 0.86 to 0.97 for Scale and Index scores. Test-retest reliability scores range from 0.70 to 0.90, with

variance due largely to test and strategy learning.

Remote Associates Test - French Revised version (RAT-FR). The Remote Associates Test (RAT; Mednick 1967)

is a measure of verbal, convergent creativity, which presents three words (often seemingly unrelated) and asks

participants to find the conceptual link among them. The RAT we used was translated and culturally adapted into

French, based primarily on a version created by Maddux (Maddux & Galinsky 2009). However, we found that

some of the originally translated items did not transfer culturally, so several items were removed and several new

items were created for a total 18 items. We eliminated timing strategies by presenting items one-by-one, with thirty

seconds for each item (instead of all at once, with a total time limit). It was also emphasized to participants that we

were looking for a single, specific response that would make sense to everyone and when incorrect answers were

given, participants were asked to continue searching or to specify their answer. After each failed item, participants

were told the correct response; this helped us to verify that participants understood the overall goal of the test,

understood each conceptual connection, and did not lose motivation due to frustration. If a participant did not

understand a cultural reference, the item was removed to compute the score for that subject.

Category Fluency (CF). This study used the Animal Naming Test (ANIMALS; Read 1987) of verbal fluency, in

which participants have one minute to come up with as many different animals as possible. In pilot testing, a second

trial was used, in which participants were asked to name as many fruits and vegetables as possible; however, it was

found that many participants used vivid mental imagery as a potentially confounding strategy. In a semi-directed

post-test interview, several participants reported "mentally zooming-in on a continent" or "taking a tour through a

familiar grocery store" and reporting the animals or the fruits and vegetables they saw. In an attempt to diminish

strategical imagery differences in the actual testing phase, a different second trial of categorical fluency was

employed in which participants were given one minute to come up with as many words that start with the letter C as

possible. Scoring for both trials is based solely on fluency, the number of categorically appropriate responses given.

Alternative Uses Test (ALT; Guilford, Christensen, Merrifield, & Wilson 1960). The ALT assesses verbal,

divergent creativity. We used a format in which participants have one minute to come up with as many different

uses as possible for different common objects. Participants were told to think of unique ideas that other people

would not think of. Five trials were run: a brick, a pencil, a newspaper, a paperclip, and a watering hose. Scoring is

based on Fluency (total number of responses, eliminating those used more than once by the same participant),

Originality (rarity of responses: traditionally one point for unusual responses given by <5% participants and two

points for unique responses given by <1% of participants; yet due to our sample size of n=20, we rounded up and

defined rare responses as those given by only two participants and unique as those thought of by only one person),

Flexibility (number of different categories used; for example, 'folding a newspaper into a hat' and 'using it as a

jacket' would be considered the same category: clothing), and Elaboration (amount of additional detail provided).

Visual Associates Test (VAT). The VAT is a measure of visual, convergent creativity in which participants are

shown three images and asked to find what the three have in common. We created this test based off "threezer"

image cards from "The Best of Tribond" board game (Mattel Inc. 2001). Some original items were used, although

most were modified to ensure that the final test was culturally appropriate. A total of twenty items were used and

were presented one at a time, with thirty seconds for each item. Before timing started, participants confirmed that

they clearly saw and understood each of the three images. It was emphasized that we were looking for a single,

specific response that would make sense for everyone and when incorrect answers were given, participants were

asked to continue searching or to specify their answer. If a participant did not understand a cultural reference, the

item was removed to compute the score for that subject.

Torrance Tests for Creative Thinking; Figural Test (TTCT; Torrance 1966). The TTCT is a measure of visual,

divergent creativity composed of three similar tasks: participants are asked to create and develop complete,

interesting stories from the basis of a dark, rounded form in Activity One; from ten incomplete, irregular figures in

Activity Two; and from thirty pairs of straight lines in Activity Three. They are given ten minutes for each task and

are told to come up with unique and original ideas, including as much detail as possible. Participants create titles for

each drawing to help complete their story. The TTCT comes with a standardized scoring procedure for each activity

to quantify the following factors: Fluency (the number of drawings that meet criteria to be scored), Originality (non-

conventiality based on standardized norms; 0 or 1 point for each item), Elaboration (amount of additional

descriptive detail; elaboration scores fall within a range that translates to a scale from 1-6), Abstractness of Titles (0-

3 points, with a clear definition of what merits each point category) and Resistance to Premature Closure (how

much the picture diverges from the original figure; 0-2 points, with a clear definition of what merits each point

category). The TTCT scoring booklet includes an additional 'Checklist of Creative Strengths' with thirteen

categories that was not used for scoring in this study (see Discussion section).

OCEAN-F. The OCEAN-F is our French translation of the International Personality Item Pool (IPIP; Goldberg

1999), which is based on the Five Factor Model of Personality Traits: Openness to Experiences, Conscientiousness,

Extraversion, Agreeableness, and Neuroticism. We expected to use the French-Revised Version (O.C.E.A.N.Co.-

FR; Gibson, McKelvie & De Man 2008), which contained 60 items, with 10 items for each of the Big Five traits

and an additional "Conservatism" factor. However, the O.C.E.A.N.Co.-FR contained many translational errors and

we found the revised selection of items to be an unrepresentative measure of the Big Five traits. The authors, a

native English speaker and a native French speaker, both fluent in both languages, therefore created our own

translation of the full IPIP, which was then modified and verified during the pilot-testing phase. Our new OCEAN-F

is a culturally relevant translation of all 100 items, with twenty items (ten positively-keyed and ten negatively-

keyed) for each personality trait. The survey was titled 'Your Thoughts, Attitudes, and Behavior' and was presented

on a Likert scale from 1 ('strongly disagree') to 5 ('strongly agree'). In order to ensure honest responses, our

confidentiality procedures were re-iterated and it was emphasized to participants to respond honestly about how

they generally are at this point in their life, and not just how they would like to be.

Tellegen Absorption Scale-French Revised version (TAS-FR). The Tellegen Absorption Scale (TAS; Tellegen &

Atkinson 1974) is a measure of "the openness to absorbing and self-altering experiences." The original version was

made up of thirty-four items, all positively-keyed and divided into six factors: Responsiveness to Engaging Stimuli

(seven items), Synesthesia (six items), Enhanced Cognition (seven items), Oblivious or Dissociative Involvement

(seven items), Vivid Reminiscence (three items), and Enhanced Awareness (four items). Our TAS-FR is a French

translation with the Synesthesia factor items removed. The survey was titled 'Your Experiences' and responses were

presented on a Likert scale from 1 ('strongly disagree') to 5 ('strongly agree'). In order to ensure honest responses,

our confidentiality procedures were re-iterated and it was emphasized to participants to evaluate each item based on

their natural experiences only, and not those under the influence of alcohol or other drugs.

Artistic and Cultural Activities. Participants were also asked about their creation and appreciation of different artistic

and cultural activities. The questionnaire was presented online and involved questions about the 'production' or

'consumption' of visual arts, music, dance, theater, film, writing, and meditative/martial arts. Participants were asked

how often they engaged in each artistic activity on a three-point scale: Never, Sometimes, or Often (a five-point

scale was used for the question "Do you consider yourself a "music-lover?"). If they indicated participating

"Sometimes" or "Often," they were asked to specify the frequency of the activity, the type or genre within the

activity, and (for production) whether or not they made public presentations or exhibits.

Proposed Study One Analyses

For Study One, we first tested statistical differences between two proportions from groups within our popoulation of

survey respondents: 1) We calculated p-values for differences in ticker tape and mirror-touch proportions between

self-reported groups of synesthetes and non-synesthetes. 2) We calculated p-values for differences between males

and females in proportions of self-reported perceptions of ticker tape, mirror-touch, and synesthesia: total

synesthesia (having at least one type of synesthesia), grapheme-color, temporal-color, temporal-spatial, grapheme-

personification, person-color, audition-vision, and lexical-gustatory. 3) Next, we used simple calculations and

probability from Bayes' Theorem (Bayes & Price 1763) to find correction factors between this study and Simner et

al. 'University Study' (2006). 4) We used these correction factors to calclate prevalence estimates of neurological

phenomena. 5) Finally, we tested statistical differences between prevalence estimates from this study and Simner's

study.

Proposed Study Two Analyses

Considering the small sample sizes during this phase of our study, it was not possible to determine accurate

normality of the distribution of our data. In this case, it is more conservative to run non-parametric tests; however

for each of our analyses, we also report parametric p-values and corresponding effect sizes (“partial eta-squared”,

pη2, a normalized measure of effect size that varies between 0 and 1, that is equivalent to the Pearson correlation

coefficient R (= r2) and can be interpreted in the same way).

Analyses were conducted in ten parts, with α = 0.05 used for all tests: 1) We compared synesthetes to non-

synesthetes on demographic and general information using Student's t-tests and Mann-Whitney U tests. 2) To

identify potential co-factors, we used correlation analyses to determine whether education, global cognition,

category fluency, or personality factors were related to creativity test scores. We hypothesized that Openness and

Extraversion would be positively related to creativity. We also examined correlations among personality factors and

artistic/cultural activities to identify any co-variables to be controlled for during further analyses. We hypothesized

that Absorption would be correlated with Openness, Art Production, Art Consumption, and the practice of

yoga/meditative activities. Significant co-variables were controlled for during further analyses using ANCOVA

tests. Since the valid use of an ANCOVA depends on the hypothesis that the two factors are correlated

independently of group, we verified that there was no difference in correlation slopes between synesthete and

control groups for each factor before running the ANCOVA 3) We compared synesthetes to non-synesthetes on

verbal fluency and four measures of creativity using Student's t-tests and Mann-Whitney U tests. We hypothesized

that synesthetes would score higher on the RAT, VAT, and TTCT, but that there would be no group differences for

the ALT. 4) We examined group differences in cognition on WAIS Total, Scale, and Index scores, using Student's t-

tests and Mann-Whitney U tests. We expected synesthetes to use their associations as a mnemonic advantage and to

therefore exhibit higher Working Memory Index scores. 5) We compared synesthetes with non-synesthetes on

personality measures, using Student's t-tests and Mann-Whitney U tests. We hypothesized that synesthetes would

score higher on the Openness factor of the OCEAN, and show higher Absorption scores on the TAS. 6) We

compared group differences in the production and consumption of artistic/cultural activities, using Student's t-tests

and Mann-Whitney U tests. We expected synesthetes to have more frequent production and consumption of art and

culture, even with the two groups being matched for the presence/absence of a general artistic activity. 7) To

measure whether it would be possible to observe an adequately powered effect for each of our tests during the future

continuation of this study, we used our observed means and variance to calculate the sample size per group that

would be required for our observed difference between controls and synesthetes to be significant with a power of

0.9. 8) For N=45 (based off results from the sample size calculations stated above), we calculated the difference

between means of synesthete and non-synesthete groups that would be possible to detect at a statistical threshold of

p=0.05, with a power of 0.9. This possible difference of means was used to determine the hypothetical effect sizes

that would be possible to obtain. Feasability is discussed for each test.

STUDY ONE RESULTS

Recruitment presentations were given to seventeen different university classes; flyers were distributed at various

Brain Week events and Natural History Museum conferences.

Table 1. Recruitment Results: Number of people reached with presentations/flyers

Group N (potential population) # Respondents Response Rate % Resp. agreed to

further participation University 578 228 39.50% 72.80% Gen. Public 727 117 16.10% 81.20%

TOTAL 1305 345 26.44% 75.70%

Mirror-touch and ticker tape perceptions were found in a significantly larger percentage of synesthetes than of non-

synesthetes. No significant gender differences were found (all perceptions were based on self-report from our

population of survey respondents; see Table 2).

Table 2. Differences in proportions of self-reported neurological phenomena between groups:

a) Self-reported Synesthetes vs. Non-synesthetes; b) Males vs. Females

Proportion Category Synesthetes (N=199) Non-Synesthetes (N=146) p-value

Ticker Tape 0.2965 0.1301 0.0003 Mirror Touch 0.4975 0.2055 <1E-4

Proportion Category Males (N=75) Females (N=270) p-value

Ticker Tape 0.2133 0.2296 0.7653 Mirror Touch 0.3333 0.3852 0.4116

TOTAL SYN. 0.6133 0.5667 0.4693 Grapheme-Color 0.1733 0.1037 0.0993 Temporal-Color 0.2267 0.1963 0.5629 Temporal-Spatial 0.2133 0.2815 0.2377

Grapheme-Personif. 0.2667 0.3037 0.5341 Person-Color 0.1733 0.2074 0.514

Audition-Vision 0.2267 0.1444 0.0876 Lexical-gustatory 0.0000 0.0074 0.4547

Since we were unable to verify the authenticity of all potential synesthetes, we will estimate the true prevalence of

synesthesia by calculating a correction ratio between our study and the systematically conducted 'University Study'

(Simner, et al. 2006). This will be done using two plausible methods: 1) comparing total self-report of synesthesia in

both studies (similar primary exclusion criteria had already been applied, but no test-retest verification) and 2)

comparing our grapheme-color estimate (corrected using our falsification factor from Study Two's test-retest

verifications) to Simner's grapheme-color estimate (test-retest verified). Examining grapheme-color synesthesia is a

theoretically appropriate comparison method because of the precise nature of grapheme-color associations,

rendering the chance of false reports relatively low compared to many other sub-types. Additionally, this provides a

common basis between the two studies, as not all subtypes of synesthesia examined in our survey were represented

in the selection of synesthetes in the 'University Study'. We will use data from both studies under the definition of

grapheme-color synesthesia as the experience of color with letters and/or numbers. Calculations from these methods

rely on the hypotheses that our total and grapheme-color synesthesia populations are comparable. Bearing in mind

potential differences between the studies (refer to Discussion), we will do a crude 'validity test' of comparability by

using Simner's data to calculate our response bias with probability equations from Bayes’ Theorem (Table 3). If the

response bias we calculate seems possible, it will validate the plausibility of the hypotheses that our populations are

comparable.

I. Comparison of Total Synesthesia: 199/345 = 57.68% of our respondents thought they were synesthetes 120/500 = 24% of Simner's population thought they were synesthetes 0.58/0.24 = 2.4 correction factor between our populations

Table 3. Plausibility of Comparison I: Calculation of our survey Response Bias using Bayes’ Theorem

Term Definition Explanation Formula Calc.

P(S) Probability of thinking you’re a synesthete

Simner’s # who initially thought they were synesthetes 120 / 500 0.24

P(F) Probability of filling out survey # of our respondents out of total flyers distributed 345 / 1305 0.26

P(S|F) Probability of thinking you’re a synesthete when filling out survey

# of our respondents who affirmed at least one type of synesthesia 199 / 345 0.58

P(F|S) Probability of filling out survey if you think you’re a synesthete

Bayes’ theorem : P(F|S) = P(S|F) * P(F) / P(S)

(0.58*0.26) / 0.24 0.63

Conclusion People who think they’re synesthetes had a 63% chance of filling out our questionnaire.

P(N) Probability of thinking you’re not a synesthete

Simner’s # who initially thought they were not synesthetes 380 / 500 0.76

P(F) Probability of filling out survey # of our respondents out of total flyers distributed 345 / 1305 0.26

P(N|F) Probability of thinking you’re not synesthete when filling out survey

# of our respondents who didn't affirm any types of synesthesia 146 / 345 0.42

P(F|N) Probability of filling out survey if you think you’re not a synesthete

Bayes’ theorem : P(F|N) = P(N|F) * P(F) / P(N)

(0.42*0.26) / 0.76 0.14

Conclusion People who think they’re not synesthetes had a 14% chance of filling out our questionnaire.

Response Bias

[Probability of filling out survey if you think you’re a synesthete] / [Probability of filling out survey if you think you’re not a synesthete] 0.63 / 0.14 4.5

General Conclusion People who think they’re synesthetes are 4.5 times more likely to fill out our questionnaire than people who think

they're not synesthetes

4.5 is a reasonable response bias. Since responding required participants to go online and fill out the survey, it is

logical that people who were more interested would be more likely to make the required effort. Due to the

information presented to interest potential subjects during recruitment, it is reasonable to believe that people who

think they are synesthetes would be more interested than those who do not (though as we will examine later, this

effect is arguably generalized to anyone who believes they may have an exceptional way of thinking). Since the

response bias calculated using Simner's data is plausible, our total synesthesia populations are roughly comparable

and we will therefore accept the 2.4 correction factor for prevalence estimates.

II. Comparison of Grapheme-Color Synesthesia: 41/345 = 11.88% of our respondents said they were grapheme-color synesthetes *1/11 = 9.1% falsification rate of self-reported grapheme-color synesthetes [11.88% - (11.88% * 0.091)] = 10.80% corrected grapheme-color prevalence in our population 10/500 = 2% verified grapheme-color synesthetes in Simner's population 0.108/0.2 = 5.4 correction factor between our populations

Plausibility of Comparison II:

Even without calculating the Bayes’ Theorem probability, we can figure that this correction factor is not plausible.

The most conservative hypothesis possible is that every grapheme-color synesthete in our population (n=1305)

filled out the survey. The estimate of true grapheme-color synesthetes in our population, when corrected using our

9.1% falsification factor is 37. Therefore 37/1305 = 2.84% is the minimum grapheme-color prevalence possible in

our population. Since it cannot be as low as Simner’s 2%, the 5.4 correction factor is not validly applicable.

However, to approach Simner's data as closely as possible and to provide a minimum prevalence estimate, we can

use this conservative hypothesis (that 100% of grapheme-color synesthetes filled out our questionnaire) to calculate

a conservative correction factor using the minimum.

III. Alternate correction factor calculation from Grapheme-Color Synesthesia 37/345 = 10.8% observed (corrected) grapheme-color 37/1305 = 2.8% minimum grapheme-color 0.108/0.28 = 3.8 correction factor

IV. Application of correction factors

We have calculated two possible correction factors: one likely factor based on Simner’s verified data and one very

conservative factr that will define our minimum. We can now apply these correction factors to give us an estimate

range for each neurological phenomenon examined (Table 4)

Table 4. Prevalence estimate ranges of neurological phenomena

Obs. [uncorrected] Corrected 3.8 → Min Corrected 2.4 → Estimate

Grapheme-Color 11.88% 3.13% 4.95%

Total Synesthesia 57.68% 15.18% 24.30%

Mirror-Touch 37.97% 9.99% 15.82%

Ticker Tape 22.60% 5.95% 9.42%

Plausibility of Application IV:

To accept these estimate ranges, we must verify that the same correction factor is applicable for all neurological

phenomena. Did our recruitment presentation increase the response rate of (self-professed) synesthetes only or of

anyone who believes they have a different thinking style; that is to say, is our response bias general or specific?

H0: People who believe they have phenomenally different thoughts/perception have an increased--yet equal--

likelihood of responding, regardless of whether the phenomenon is synesthesia.

H1: People who have synesthesia in particular are more likely to respond because they feel more implicated in our

research due to the specific examples we presented.

Due to certain timing and administrative restraints, recruitment presentations were different for

universities and for the general public. University presentations included a definition and specific example of

synesthesia as one of many different ways of thinking. Flyers given to the general public explained that everyone

has a different way of thinking, yet without any reference to synesthesia. If the proportion of respondents who think

they are synesthetes is equal in both university and general public populations, we cannot reject the null hypothesis

and can induce with relative confidence that the response bias is not specific to synesthesia:

Percentage of University respondents who think they are synesthetes: 131/228 = 57.5% Percentage of General Public respondents who think they are synesthetes = 68/117 = 58.1%

Conclusion: People are equally likely to respond if they believe they think differently in general, and not only

because they feel specifically implicated in our research. We will assume that people who experience mirror-

touch and ticker tape have an equal response rate to synesthetes. We therefore accept the application of our

calculated correction factors to estimate the prevalence of synesthesia, mirror-touch, and ticker tape phenomena.

Next, we can statistically compare proportion differences between studies. Our estimated proportions of total and

grapheme-color synesthesia in the general population are significantly higher than Simner's. Our minimum total

synesthesia prevalence is significantly larger in comparison, though our minimum grapheme-color prevalence is not

statistically different from Simner's estimate (Table 5).

Table 5. Statistical difference between studies in estimated prevalences of synesthesia

Category Our Minimum (N=345)

Simner (N=500) p-value Our Estimate

(N=345) Simner (N=500) p-value

Total Syn. 0.1518 0.044 <1E-4 0.243 0.044 <1E-4 Graph.-Color 0.0313 0.02 0.2974 0.0495 0.02 0.0167

STUDY TWO RESULTS

Demographic and General Information

There were no significant differences between synesthetes (n=10) and non-synesthetes (n=10) in Age (p=0.809),

Education (p=0.613), General Art (p=0.661) Verbal Thinking (p=0.189), Visual Thinking (p=0.744), Ticker Tape

(p=0.615), or Mirror-Touch (p=1). These results are not representative comparisons of the populations as a whole,

but instead reflect the controlled matching of our groups.

Correlation analyses between tests (Table 6, all subjects, N = 20)

‘O.C.E.A.N’ Personality dimensions, Absorption (total TAS score) and global cognition (total WAIS score) were

not significantly correlated with creativity scores of either convergent thinking (RAT and VAT) or divergent

thinking (ALT and TTCT), whether the task was verbal (RAT and ALT) or visual (VAT and TTCT). Category

Fluency (CF) was significantly correlated with VAT scores (and with ALT scores; however this is to be expected

since Fluency is an ALT sub-category). Education was significantly correlated with ALT scores. Not shown: TAS

scores were positively correlated with Openness (r2=0.35) and Art Production (r2=0.31), and negatively correlated

with Conscientiousness (r2=-0.35; ANCOVA-corrected r2 (pη2) = (-)0.45, see below). No significant relationship

was found between TAS scores and participation in yoga, meditative, or martial arts activities.

Table 6. Correlation analyses with Creativity tests: r2 values

r2 Educ. WAIS Total Fluency O C E A N TAS RAT 0.12 0.03 0.03 0.01 0.03 -0.05 -0.07 0.12 0.00 ALT *0.22 0.12 *0.45 -0.01 0.12 0.18 0.05 -0.02 0.00 VAT 0.01 0.08 *0.31 0.04 0.13 0.18 0.00 -0.05 0.01

TTCT 0.11 0.05 0.01 0.03 0.03 0.01 0.16 -0.04 0.00 *p<0.05

Comparison of Creativity tests between synesthetes (N=10) and non-synesthetes (N = 10 ; Table 7)

No significant differences were found between synesthetes and non-synesthetes for RAT score (Table 2) or reaction

time (Not shown). No significant group differences were found for Verbal Category Fluency. Synesthetes scored

significantly higher than non-synesthetes on the ALT Fluency category (p=0.041), but no ALT Total or other ALT

category score differences were found. Since Education was significantly correlated with ALT scores, we ran an

ANCOVA to verify that Education did not affect ALT score comparisons between synesthetes and controls. ALT

score group differences remained insignificant (p=0.201) when considering Education as a co-variable. There was a

non-significant trend for synesthetes to perform better than non-synesthetes on the VAT, with no reaction time

differences found (Not shown). Since Fluency was significantly correlated with VAT scores, we ran an ANCOVA

to verify that Fluency did not affect VAT score comparisons between synesthetes and controls. Parametric

groupdifferences on VAT scores remained borderline significant (p=0.064) considering Fluency as a co-variable.

No group differences were found for TTCT Total or TTCT categorical scores.

Table 7. Creativity test results: Synesthetes vs. Controls

TEST parametric p-value (non-parametric) Effect Size RAT Total 0.921 (0.701) 0.001 ALT Total 0.373 (0.364) 0.044 VAT Total 0.099 (0.052) 0.144

TTCT Total 0.914 (1.00) 0.001 CF Total 0.882 (1.00) 0.013

Figure 1. Creativity test results: Synesthetes vs. Controls.

Cumulative histograms of individual scores on each of the four creativity measures:

Top left: RAT Score = # of correct associations / # understood (max = 18).

Top right: ALT Score = sum of all factor scores: Fluency, Flexibility, Elaboration, Originality (no max).

Bottom left: VAT Score = # of correct associations / # understood (max = 20).

Bottom right: TTCT Score = sum of all factor scores: Fluency, Elaboration, Originality, Abstractness of Titles,

Resistance to Premature Closure (no max).

Comparison of Cognitive tests between synesthetes (N=10) and non-synesthetes (N = 10; Table 8)

No differences were found between synesthetes and non-synesthetes in global cognition on WAIS Total or Verbal

Scale scores. Non-synesthetes had marginally significant higher Performance Scale scores and Perceptual

Reasoning Index scores than synesthetes but no other index or subtest score differences reached significance.

Table 8. Cognition Tests: Synesthetes vs. Controls

TEST parametric p-value (non-parametric) Effect Size WAIS-III Total 0.237 (0.495) 0.077

Verbal Scale 0.817 (0.940) 0.003 Performance Scale 0.035 (0.089) 0.225

Verbal Comprehension Index 0.706 (0.939) 0.008 Perceptual Reasoning Index 0.030 (0.040) 0.235

Working Memory Index 0.946 (1.000) 0.0002 Processing Speed Index 0.120 (0.103) 0.129

Comparison of Personality between synesthetes (N=10) and non-synesthetes (N = 10; Table 9)

Responses were gathered from online questionnaires for which, to retain complete confidentiality, participants

created a personal code that they sent to a blind researcher (who did not participate in scoring). Personally created

codes were linked to official subject codes by a blind researcher only after final scoring was completed. It was

explained to participants that in this way, their specific responses would remain completely confidential from all

researchers, in order that they would respond as honestly as possible.

Synesthetes scored significantly higher on the 'O.C.E.A.N.' Conscientiousness factor than non-synesthetes,

but no other personality differences were revealed. No group differences were found for TAS total or factor scores.

The average overall TAS score was around 90, across 28 questions. This gives an average of 3.2 points per

question, which relates to just over neutral on a scale of 1 to 5, meaning there were no ceiling or floor effects. No

group differences were found in the 'production' or 'consumption' of Artistic and Cultural Activities. TAS scores

were significantly correlated with Openness, Art Production, and (-) Conscientiousness, we ran an ANCOVA to

verify that these factors did not affect TAS score comparisons between synesthetes and controls. Group differences

on TAS scores were significant when considering personality and art production as co-variables (p<0.01).

Table 9. Personality and Activity Results: Synesthetes vs. Controls

MEASURE parametric p-value (non-parametric) Effect Size

OCEAN: Openness 0.859 (0.850) 0.002

OCEAN: Conscientiousness 0.009 (0.006) 0.326

OCEAN: Extraversion 0.331 (0.198) 0.053

OCEAN: Agreeableness 0.615 (0.545) 0.014

OCEAN: Neuroticism 0.102 (0.273) 0.142

TAS: Absorption [uncorrected] 0.694 (0.623) 0.009

TAS: Absorption [corrected] 0.008 0.383

Artistic/Cultural Production 0.313 (0.133) 0.057

Artistic/Cultural Consumption 1.00 (1.00) 0.000

Sample Size Calculations

Ward et al. 2008b found synesthetes to have higher scores than non-synesthetes on the RAT. We did not reproduce

this result but our sample size (N = 10 / 10) was much smaller than Ward’s (N = 89 / 119). The score difference

between group means measured by Ward = 1.8 (18 total items). Using our observed score variability (specific to our

test), we did a power analysis. We found that to observe a similar effect for α = 0.05 and power = 0.9, we would

need two groups of at least 45 subjects. With N=45/group, we would also be adequately powered to observe

potential group differences, if they exist, for the ALT, WAIS Performance Scale, WAIS PRI, WAIS PSI, OCEAN

C, and OCEAN N. For all hypothetical N-values and required mean differences, see Appendices B & C.

DISCUSSION

In Study One, we used data collected from a relatively large group to revisit the prevalence of synesthesia compared

with a well-founded prevalence study, and to provide novel estimates of mirror-touch and ticker tape perceptions.

We found no difference between males and females in the number of people who thought they were synesthetes, or

for any subtype of synesthesia, adding further evidence towards a gender-equivalent prevalence rate (Ward, et al.

2005). Using correction factors calculated from Simner's 'University Study' and from the absolute minimum (pre-

adjusted for potential falsification), we were able to create an estimate range of sysnesthesia in the French

population. We estimate a general synesthesia prevalence of 1 in every 4 to 6 people. It is neither surprising nor

indicative of flawed methodology that our total [corrected] estimate is drastically larger than Simner's estimate of

about 1 in 22 (p<1E-4): our survey questioned participants about 'grapheme-personification' synesthesia, in which

letters or numbers are automatically associated with a gender or a particular personality (Smilek, Malcohnson,

Carriere, Eller, Kwan & Reynolds 2007)b. Grapheme-personification was not evaluated in the 'University Study' but

was our most common subtype, found in over 7-12% [corrected] of our general population; in addition, over half of

reported synesthetes had this subtype (either exclusively, or in addition to other synesthesias)! It is important to keep

in mind that differences in subtypes of synesthesia examined, survey format (online vs. in-person), and culture could

all potentially affect the comparability of our studies. Although we were not able to use Simner's grapheme-color

estimate for calculations because it was below our minimum, their estimate of a 2% grapheme-color prevalence is

within the same order of our 2.8%-4.95% range, lending further validity to the general comparability of our studies.

This poses the interesting question of whether subtype (and perhaps even total) prevalences of synesthesia are

culturally dependent. Synesthetic associations, especially those connected with graphemes, are fixed during

childhood around the age of language development (Simner, Harrold, Creed, Monro & Foulkes 2009). The French

language provides synesthetes and non-synesthetes alike with an adaptive mechanism for learning the gender of

words; personal accounts from native French speakers suggest that many can intuitively tell the correct gender of a

word when learning it for the first time. It is a reasonable hypothesis that this innate tendency toward personification

could be related to an elevated proportion of grapheme-personification synesthesia in the French population, as

compared to a previous estimate of about 4.4%, made with "insufficient data" (Day 2005). For further evidence,

grapheme-personification prevalence should be investigated in cultures with other languages; for example, German,

which contains three genders. Our methodology was not designed specifically for prevalence estimates, since that

was not the main purpose of this study. It did provide a wealth of interesting secondary information worth reporting;

however potential limitations of our study should be taken into careful consideration. Despite our best recruitment

efforts, our population may still not have been diverse enough so future recruitment should be even more varied,

such as including more technical or engineering schools with a 'classically' higher proportion of males (we had to

use unequal numbers of males and females due to limited selection). Future attempts should be make to homogenize

recruitment strategies for students and the general public, although these differences serendipitously revealed

important information about our response bias. Another simple methodological step that we neglected during

recruitment would be to differentiate how many flyers were originally distributed to males vs. to female, in order to

calculate response rates separetely for each group.

It is important to keep a big perspective in mind when interpreting the results of Study Two as well: our

primary goal was to measure creativity across different modalities while controlling for important factors such as

b We even had one account similar to that of Smilek's synesthete T.E. (Smilek, et al. 2007), in which inanimate objects were automatically personified: the association of complex personalities, including a hierarchy system, to silverware.

recruitment method, personality, cognition, and artisticness. Knowing that we would be generally underpowered

due to our sample size, we did not expect to find definitive results but expected instead that any important

differences would be brought to light. Rader & Tellegen (1987) found synesthetes more likely to be absorbed in

imaginative activities, yet it was unknown whether this effect existed independently of their synesthetic associations.

We were able to replicate and legitimize the effect by examining a more valid Absorption factor (one with

synesthesia removed from the core definition) in isolation of important covariables. It is reasonable to believe that

synesthete's associations could cause them to be easily absorbed in their vivid sensory experiences. Larger sample

sizes would allow us to examine whether number of subtypes within synesthesia might have an affect on TAS

scores.

No differences were found between synesthetes and non-synesthetes for divergent thinking tasks in the

verbal or visual modality. Synesthetes did score higher in the fluency sub-category of verbal divergent thinking,

though this seems largely due to the variance from two of the four male synesthetes, who employed a different

strategy than other participants. They produced very high fluency by coming up with things you can do to a brick,

(for example: crush it, bury it, heat it), instead of what a brick can be used for. This was not the purpose of the task

according to the instructions, but was not explicitly prohibited. Increasing your score by finding a way around the

instructions with a useful idea can be an expression of everyday creativity in itself. Moreover, the TTCT gives extra

points for certain creative expressions that are not explicitly referenced in the instructions but show clear

insightfulness. Therefore the mentioned ALT items were counted and affected group fluency means, but there was

still no difference in total scores. This is consistent with our hypothesis based onWard's 2008 results. We did

hypothesize TTCT score differences because we expected synesthetes to have an advantage in the visual modality,

due to the dominantly visual nature of most associations. This modality hypothesis was not supported for divergent

thinking, though it deserves to be mentioned that insightfulness and originality were very difficult to capture on both

tests of divergent thinking, even with scoring guidelines. The TTCT has a "checklist of creative strengths" that we

did not use because it seemed vaguely defined and quite subjective. Future examination could increase test

sensitivity by including important categories from the checklist, such as humor and unusual visualization (drawing

an objective from unique angles or a bird's-eye perspective, for example), yet employing a rigid scoring scale and

multiple evaluators with verified inter-rater reliability.

Modality did make a potential difference in convergent thinking, however: no group differences were

found on verbal, convergent thinking tests but moderate differences were found in visual, convergent thinking. This

was on the level of a rather small effect size, yet is a promising candidate for future study. We need to understand

the potential reasons, other than lack of power, that we did not replicate the RAT effect. There are several

possibilities that could explain our null findings as compared to Ward's on the verbal, convergent thinking task:

group differences in our systematically-recruited synesthetes from their recruitment of acquaintances, differences in

French compared to British populations, or lack of sensitivity of the French-translated RAT. Additionally, we used a

different testing method than Ward and, in an attempt to eliminate strategical time-management differences,

presented items one at a time. It is unlikely that synesthetes have enhanced planning/executive abilities that allowed

them to manage Ward's RAT presentation more efficiently, since executive functioning is broadly tapped in several

WAIS subtests, in particular ones in which synesthetes performed worse. We also allowed participants to continue

searching during the 30-second time limit and did not score items with cultural references that a participant did not

understand. An alternative possibility is that there is a large aspect of convergent thinking that involves inhibition of

all ideas except the correct one; we may have diminished this aspect by allowing participants to continue searching

after providing a wrong answer. An interesting follow-up experiment would be to compare groups of synesthetes

and controls using both RAT strategies. Perhaps synesthetes are not just better at associating unrelated ideas, but

also at inhibiting unassociated ideas. Perceiving the number five as red typically happens to the exclusion of other

colors. Although a number can sometimes be associated with two colors, or fluctuate between them (Simner 2010),

the colors that are not associated feel instinctively "wrong" to the synesthete and are inhibited. The opposite of this

exclusion ability is Resistance to Premature Closure, a sub-category examined physically on the TTCT drawing

production by whether or not the artist resists the natural Gestaltian instinct to close off an incomplete figure with a

quick line (no difference was found between synesthetes and controls, p=0.34).

Both inhibition and resistance to premature closure, contradictory as they may seem, are skills that proved

to be essential to all four creativity tests, as confirmed by semi-directed interviews following the testing session. The

RAT and VAT were designed to measure convergent thinking, yet many subjects reported getting blocked on one

idea and having difficulty remaining open to other possibilities. Likewise, participants who scored well were often

those who, after giving a wrong answer along one train of thought, were flexible enough to search in a different

direction. One of the greatest difficulties of the convergent thinking tests is that answers are sometimes concrete and

other times quite abstract; it is necessary to remain open to both possibilities. A typical example is an image with the

Parthenon, a graph, and a newspaper (see Appendix A): many subjects get fixated on the concept of finance or the

economy, and fail to see the visual link that they all have columns. Semi-directed interviews following divergent

thinking tasks revealed an equally unexpected struggle: the obvious task is to create ideas but many participants

reported trouble focusing their ideas, particularly during the TTCT Figural Test. There are an infinite number of

things you could draw, so part of the task is excluding other ideas to decide what to draw.

Convergent thinking is the inhibitive focalization of ideas while divergent thinking is their open creation;

yet results and metacognitive accounts suggest the relationship may not be so distinctive. To ensure that lack of

effect was not due solely to formatting differences, I suggest the RAT (and VAT) be presented in a way that retains

the traditional inhibititory factor of giving one answer only, yet also eliminates differences due to time-management

strategy, frustration, and lack of cultural knowledge. It is also possible that both inhibitive and productive factors are

inextricable from all types of creativity. Are we making an evaluative error by trying to separate creative thinking

into two broad domains? Or, on the other hand, are we lacking in sensitivity because we have not differentiated

creative thinking abilities enough? I propose, in addition to better isolation of convergent and divergent thinking,

that concrete vs abstract creative thinking be explored in the continuation of this study. This would allow us to

examine creativity in a more controlled, quantitave fashion using convergent vs. divergent, verbal vs. visual, and

concrete vs. abstract domains.

Since divergent thinking (and, as suggested above, perhaps all creative thinking) requires at least a

minimum certain resistance to premature closure, it is quite surprising that Openness was not even slightly

correlated with any of our creativity measures (r2 values<0.04). We may have had a ceiling effect as the average

factor score for Openness was around 15 for both synesthetes and controls (on a scale from -20 to +20). This could

be due to the potential limitations of our recruitment: although we systematically recruited synesthetes and controls

from a variety of populations, they were all within the context of general scientific interest--students from

psychology, biology, or medical fields, and people coming to museums or conferences to learn new things. By

recruiting participants for our "Interior Experiences" study, we unsurprisingly drew from a population that is

inherently open to different experiences. But how do you get people who are not open to exploration to come in for

a laboratory study? Does the very nature of personality make it impossible to study scientifically?

Synesthetes scored higher in the Conscientiousness personality factor: their average was 19 on a scale

from -20 to +20. I believe this was confounded by the fact that synesthetes had an extra, time-consuming step before

coming to the lab. By choosing synesthetes from those who held on to their initial flyer, took the time to fill out the

first questionnaire, took the time to fill out the longer Synesthesia Questionnaire and send in their associations,

responded to emails about scheduling a testing time and successfully made it to the testing center, our methodology

mandated the selection of a very conscientious population, as was especially true for synesthetes. These recruitment

problems are common to most laboratory experiments, yet particularly detrimental when examining personality and

creativity.

In sum, important future modifications include: recruitment from more diverse populations (to eliminate

the potential Openness ceiling effect), recruitment requiring less pre-selection effort (to eliminate the

Conscientiousnes bias), inclusion of a larger sample size (~N=45), more precise prevalence estimates, further

distinction of creative domains, and the inclusion of mental imagery data (which we are currently collecting

concerning vividness, manipulation, and practical use of mental images).

We reinforce Ward et al.'s conclusion that synesthetes do not appear to have enhanced everyday creativity

and that synesthesia is likely not an evolutionary development for art. A reasonable hypothesis concerning the

origins of synesthesia is that it may have developed to promote memory (Ward 2008a). However, contrary to

hypotheses, there were no group differences on the WAIS Working Memory Index or on subtests dealing with the

memorization of graphemes, even though 7 out of our 10 synesthetes had some type of grapheme association! If not

for apparent artistic or mnemonic advantages, why did synesthesia develop and why does it persist?

We first return to the idea (Ward et al., 2008b) that schizotypy, the personality organization associated

with the risk of developing schizophrenia (Meehl 1962), has been proposed as an origin for the development of

creativity. As for synesthetes, it is unclear whether this claim translates into higher scores on cognitive creativity

tests, and appears to rely largely on an increased artistic involvement. It has been suggested that 'unusual

experiences' may be the underlying factor directly responsible for increased creative expression in schizotypes

(Nettle & Clegg 2006) and in synesthetes. Yet I support that potentially enhanced creativity in both synesthetes

(Wheeler & Cutsforth 1922) and schizotypes is moderated by a different (though perhaps related) underlying factor:

the attribution of meaning. This would be logical, as excess dopamine causes paranoid schizophrenics to attribute

salience to ordinary events, as reflected intermediately in the self-referential thinking identified in

positive/'cognitive-perceptual schizotypes' (Eckblad & Chapman 1983). Though synesthesia is definitively non-

pathological, do we have evidence related to this similar pattern of thinking, in which meaning is subjectively linked

with arbitrary cues?

Recent investigations from our lab conducted to investigate synesthetic color processing revealed

unexpected neuroanatomical results that may provide preliminary insight. Global voxel-based morphology

comparisons showed no structural differences between synesthetes and controls in color-sensitive areas; however,

synesthetes were shown to have a significant, bi-lateral increase in white matter in the retrosplenial cortex (RSC,  

Brodmann areas 29 and 30). This increased white matter suggests enhanced connectivity between other areas of the

brain and the RSC, which is shown to be linked with processing of memory and emotion. Synesthesia involves

forming a mnemonic and emotional connection among typically unlinked domains (Hupé, et al., Submitted for

Publication). For the synesthete, the inducing stimulus is inherently and automatically linked with the concurrent

perception in a meaningful way. If the word 'murmur' is blue for a synesthete, the color is an essential to its meaning

as the definition. These enhancements in the synesthetic brain in the retrosplenial cortex, which could be considered

as a key structure in the process of attribution of meaning, contribute logical evidence towards the theory of

synesthesia as a possible evolutionary development for the construction of meaning (Wheeler & Cutsforth 1922;

Dann 1998; Hupé, et al., Submitted for Publication). Greater cognitive thinking abilities are likely a part of this same

mechanism, involved in attributing meaning to arbitrary experiences. Using our well-matched synesthete and non-

synesthete groups, we can determine whether the structural and functional brain differences found in our lab are

replicated when controlling for factors such as cognition and personality. A correlation between convergent thinking

differences (if they exist) and increased white matter in the RSC would greatly support the hypothesis that

synesthesia developed as a mechanism for meaning. One synesthet participating in our experiments remarked

that "having synesthesia is no different than having blue eyes versus brown" but for the moment, we

continue to examine synesthesia for insight into the perception of human experience.

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APPENDIX A: Creativity Tests (Not representative of presentational format)

APPENDIX B

Table 10. Sample size required for high power: Synesthete vs. Control. N required for our observed means difference and variance to be significant

TEST N/group required for Power=0.9

RAT 9867 ALT 45 VAT 126 TTCT 8252 WAIS Total 74 WAIS Verbal 1810 WAIS Performance 26 WAIS VCI 685 WAIS PRI 11 WAIS WMI 20817 WAIS PSI 44 OCEAN Openness 3064 OCEAN Conscientiousness 18 OCEAN Extraversion 107 OCEAN Agreeableness 387 OCEAN Neuroticism 41 TAS Absorption 630

In blue: tests that would be highly powered for N=45.

APPENDIX C

Table 11. For N=45/group: mean differences required for an effect at p < 0.05, Power > 0.90

TEST Group mean diff req. CONCLUSION

RAT 1.6 Out of 18 items, groups would have to score 1 to 2 pts diff. on average than controls. This is feasibly attainable.

ALT 24.2 Groups would have to score about 6 pts diff. on avg than controls in each of the four categories. This is feasibly attainable but may not be behviorally meaningful.

VAT 1.4 Out of 20 items, groups would have to score 1 to 2 pts diff on avg. This is feasibly attainable. but may not be behviorally meaningful.

TTCT 11 Groups would have to score 2 to 3 pts diff on avg in each of the five categories. This is feasibly attainable but may not be behviorally meaningful.

WAIS Tot 7.9 Groups would have to score about 8 pts diff on avg, in which 15 pts is one SD. This may not

be feasibly attainable. WAIS Verbal 9 Groups would have to score about 9 pts diff on avg, in which 15 pts is one SD. This may not

be feasibly attainable. WAIS Perf. 8.5 Groups would have to score 8 to 9 pts diff on avg, in which 15 pts is one SD. This may not

be feasibly attainable. WAIS VCI 9 Groups would have to score about 9 pts diff on avg, in which 15 pts is one SD. This may not

be feasibly attainable. WAIS PRI 9 Groups would have to score about 9 pts diff on avg, in which 15 pts is one SD. This may not

be feasibly attainable. WAIS WMI 11 Groups would have to score about 11 pts diff on avg, in which 15 pts is one SD. This may

not be feasibly attainable. WAIS

PSI 9.1 Groups would have to score 9 to 10 pts diff on avg, in which 15 pts is one SD. This may not be feasibly attainable.

OCEAN O 5.9 Groups would have to score about 6 pts diff on avg, on a factor ranging from -20 to +20.

This is feasibly attainable. OCEAN

C 8.1 Groups would have to score 8 to 9 pts diff on avg on a factor ranging from -20 to +20. This is feasibly attainable.

OCEAN E 9.5 Groups would have to score 9 to 10 pts diff on avg, on a factor ranging from -20 to +20. This

may not be feasibly attainable. OCEAN

A 6.5 Groups would have to score 6 to 7 pts diff on avg, on a factor ranging from -20 to +20. This may not be feasibly attainable.

OCEAN N 8 Groups would have to score about 8 pts diff on avg, on a factor ranging from -20 to +20.

This is feasibly attainable. TAS

Absorpt. 8 Groups would have to score about 8 pts diff on avg than controls, on a factor ranging from 0 to 140. This is feasibly attainable.