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.
REFERENCES Baron-Cohen, S., Wyke, M.A. & Binnie, C. (1987). Hearing words and seeing coulours: An experimental investigation of a case of synaesthesia. Perception, 16, 761-767. Baron-Cohen, J.H., Goldstein, L.H. & Wyke M. (1993). Colored speech perception: Is synaesthesia what happens when modularity breaks down? Perception, 22, 419-426. Barnett, K. & Newell, F. (2008). Synaesthesia is associated with enhanced, self-rated visual imagery. Consciousness and Cognition, 17(3), 1032-1039. Bayes, T. & Price, R. (1763). "An Essay towards solving a Problem in the Doctrine of Chance. By the late Rev. Mr. Bayes, communicated by Mr. Price, in a letter to John Canton, M. A. and F. R. S.". Philosophical Transactions of the Royal Society of London, 53(0), 370–418. Blakemore, S.J., Bristow, D., Bird, G., Frith, C. & Ward, J. (2005). Somatosensory activations during the observation of touch and a case of vision–touch synaesthesia. Brain, 128(7), 1571–1583. Cytowic, R.E. & Wood, F.B. (1982). Synesthesia: I. A review of major theories and their brain basis. Brain and Cognition, 1, 23-35. Dann, K.T. 1998(1956). Bright Colors Falsely Seen: Synaesthesia and the Search for Transcendental Knowledge. New Haven: Yale University Press. Day, S. (2005). Some demographic and socio-cultural aspects of synesthesia. In L.C. Robertson & N. Sagiv (Eds.), Synesthesia: Perspectives from cognitive neuroscience. Oxford: Oxford University Press. Domino, G. (1989). Synaesthesia and creativity in fine arts students: An empirical look. Creativity Research Journal, 2, 17-29. Eckblad M.L. & Chapman L.J. (1983). Magical ideation as an indicator of schizotypy. Journal of Consultational Clinical Psychology, 51, 215–225. Feist, G. J. (1998). A meta-analysis of the impact of personality on scientific and artistic creativity. Personality and Social Psychological Review, 2, 290–309. Furnham, A. & Bachtiar, V. (2008). Personality and intelligence as predictors of creativity. Personality and Individual Differences, 45, 613-617. Gibson, K. L., McKelvie, S. J. & De Man, A. F. (2008). Personality and culture: A comparison of Francophones and Anglophones in Quebec. The Journal of Social Psychology, 148(2), 133-65. Goldberg, L.R. (1999). A broad-bandwith, public domain, personality inventory measuring the lower-level facets of several five-factor models. In I Mervielde, I. Deary, F. De Fruyt, & F. Ostendorf (Eds.), Personality psychology in Europe 7, 7-28. Tilburg, The Netherlands: Tilburg University Press. Grégoire, J. (2004). Factor structure of the French adaptation of the Wechsler Adult Intelligence Scale—3rd Version. Educational and Psychological Measurement, 64, 463–474. Guilford, J. P., Christensen, P. R., Merrifield, P. R. & Wilson, R. C. 1978. Alternate uses: Manual of instructions and interpretation. Orange, CA: Sheridan psychological Services. Hartshorne, C. 1934. The philosophy and psychology of personality. New York: Basic Books. Hubbard, E. M., Arman, A.C. Ramachandran, V.S. & Boynton, G.M. (2005). Individual differences among grapheme-color synesthetes: brain-behavior correlations. Neuron, 45(6), 975-85. Hupé, Bordier & Dojat. Submitted for Publication. The neural bases of grapheme-color synesthesia are not localized in real color sensitive areas. Maddux, W. & Galinsky, A. (2009). Cultural borders and mental barriers: The relationship between living abroad and creativity. Journal of Personality and Social Psychology, 96(5), 1047-106 McCrae, R.R. & Costa, P. C., Jr. (1987). Validation of the five-factor model across instruments and observers. Journal of Personality and Social Psychology, 52, 81–90. Meehl, P. (1962). Schizotaxia, schizotypy, schizophrenia. American Psychologist, 17(12), 827-838. Mednick, S.A. 1967. The Remote Associates Test. Boston: Houghton Mifflin Company. Mulvenna, C. & Walsh, V. (2005). Synaesthesia. Current Biology, 15, 399-400. Nettle, D. & Clegg, H. (2006). Scizotypy, creativity and mating success in humans. Proceedings of the Royal Society of London B, 273, 611–615. Nunn, J.A., Gregory, L.J., Brammer, M., Williams, S.C.R., Parslow, D.M., Morgan, M.J., Morris, R.G., Bullmore, E.T., Baron-Cohen, S. & Gray, J.A. (2002). Functional magnetic resonance imaging of synesthesia: Activation of V4/V8 by spoken words. Nature Neuroscience, 5, 371-175. Rader, C.M. & Tellegen, A. (1987). An investigation of synesthesia. Journal of Personality and Social Psychology 52, 981-987.
Ramachandran, V.S. & Hubbard, E.M. (2001a). Psychophysical investigations into the neural basis of synaesthesia. Proceeedings of the Royal Society of London B, 268, 979-983. Ramachandran, V.S. & Hubbard, E.M. (2001b). Synaesthesia - A window into perception, thought and language. Journal of Consciousness Studies, 8, 3-34. Read, D. E. 1987. Neuropsychological assessment of memory in early dementia: Normative data for a new battery of memory tests. Unpublished manuscript, University of Victoria, British Columbia. Rich A.N., Bradshaw J.L., Mattingley .J.B. (2005). A systematic, large-scale study of synaesthesia: implications for the role of early experience in lexical-colour associations. Cognition 98 (1), 53–84. Rouw, R. & Scholte, S. (2010). Neural Basis of Individual Differences in Synesthetic Experiences The Journal of Neuroscience, 30(18), 6205– 6213 Silvia, P.J. (2008). Another look at creativity and intelligence: Exploring higher-order models and probable confounds. Personality and Individual Differences, 44, 1012–1021. Simner, J., Mulvenna, C., Sagiv, N., Tsakanikos, E., Witherby, S.A., Fraser, C., Scott, K., & Ward, J. (2006). Synaesthesia: The prevalence of atypical cross-modal experiences. Perception, 35, 1024-1033. Simner, J., Harrold, J., Creed, H., Monro, L. & Foulkes, L. (2009). Early detection of markers for synaesthesia in childhood populations. Brain, 132(1), 57-64. Simner, J. (2010). Defining synaesthesia. British Journal of Psychology, In Press. Sitton, S. C. & Pierce, E. R. (2004). Synesthesia, creativity and puns. Psychological Reports, 95, 577–580. Smilek, D., Malcohnson, K., Carriere, J., Eller, M., Kwan, D. & Reynolds, M. (2007). When 3 is a Jerk and E is a king: Personifying inanimate objects in synesthesia. Journal of Cognitive Neuroscience, 19(6), 981-992. Tellegen, A. & Atkinson, G. (1974). Openness to absorbing and self-altering experiences ("absorption"), a trait related to hypnotic susceptibility. Journal of Abnormal Psychology, 83, 268-277. Tellegen, A. (1982). Brief manual for the Multidimensional Personality Questionnaire. Unpublished manuscript, University of Minnesota, Minneapolis. Torrance, E. P. 1966. Torrance Tests of Creative Thinking: Norms-Technical Manual (Research Edition). Personnel Press, Lexington, MA. Ward, J., Simner, J. & Auyeung, V. (2005). A comparison of lexical-gustatory and grapheme-coulour synaesthesia. Cognitive Neuropsychology, 22, 28-41. Ward, J. 2008a. The Frog Who Croaked Blue: Synesthesia and the mixing of the senses. New York: Routledge. Ward, J., Thompson-Lake, D., Ely, R. & Kalinski, F. (2008b). Synaesthesia, creativity and art: What is the link? British Journal of Psychology, 99, 127–14. Wechsler, D. (1997). Wechsler Adult Intelligence Scale—3rd Edition (WAIS-3®) San Antonio, TX: Harcourt Assessment. Wheeler, R.H. & T.D. Cutsforth. (1922). Synaesthesia and meaning. American Journal of Psychology, 33, 361-384.
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.