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upcoming conference abstracts
4th Annual Conference Presenters and Abstracts
Greta Berman, The Juilliard School
Synesthesia among contemporary composers and performing artists
One day, Carol Steen and I had lunch together and ran into Ben Wolfe, a bass player, composer, and jazz music faculty member at Juilliard. Spontaneously, she asked him if he was a synesthete. He had no idea what that meant, but, when further queried as to whether he saw music in color, he responded, "Of course!"
I propose to interview Ben Wolfe and see how and if he is a synesthete, and in any case, how he uses synesthesia to compose.
A while back, I had a similar experience with the well-known composer, Libby Larsen (b. 1950). Meeting her at a social event, I noticed she had titled some works as Black Birds, Red Hills; Blue Third Pieces; Deep Purple; and the like. I asked her if she was a synesthete, and she replied, “Probably,” as I recall.
Over the course of twenty-five years of teaching at Juilliard, I have encountered numbers of student composers, dancers, and choreographers who have acknowledged that they possessed synesthetic capabilities.
For my paper, I will present views and insights from interviews, perceptions, etc., of these and possibly other contemporary artists.
Alicia Callejas, University of Granada, Spain
A. Callejas1, 2, D. Smilek1, M. Dixon1, and P. Merikle1
1. Synaesthesia Research Centre, University of Waterloo, Canada
2. University of Granada, Spain
A web-based descriptive study of grapheme-colour synaesthesia
We report on a web-based study (http://www.synaesthesia.uwaterloo.ca/) of grapheme-colour synaesthesia in which we interviewed about 300 synaesthetes. The study consisted of both a subjective and an objective measure of synaesthesia. For the subjective measure, synaesthetes completed a structured survey about their synaesthetic experiences. The survey required synaesthetes to report on qualitative aspects of their synaesthetic colour experiences, such as whether they were perceived “out there in space” or “in the mind’s eye” and whether their experiences changed over time. In addition we asked synaesthetes to report on other aspects of their synaesthesia, such as the age and circumstance in which they first realized that their experiences differed from those of others. For the objective measure, synaesthetes matched colours to digits (0 to 9) and to capital letters (A to Z) two times in immediate succession. We used the distance (in CIE Lab space) between the two colour matches for each grapheme as a measure of the consistency of each grapheme-colour match. Based on the subjective reports and the consistency of the colour matches, we highlight both general trends and individual differences within this group of graphemic-colour synaesthetes. For example, in terms of general trends, the majority of the sample was female (4.3:1 female to male ratio), and synaesthetic colours were experienced for both letters and digits – only 15.7% experienced colours for a single class of stimuli. In terms of individual differences, associator synaesthetes outnumbered projector synaesthetes by a ratio of 7.1:1, but these two subgroups showed equivalent consistency in their grapheme-colour matches.
Richard E. Cytowic, MD, Washington, D.C.
Synesthesia: transition from implicit to explicit
Cognitive development throughout the life-span is making implicit knowledge explicit, and emotional intelligence is bringing automatic schematic responses more under our deliberate control.
Furthering his early conjecture that synesthesia is a normal process in everyone’s brain, Dr. Cytowic shares ongoing thoughts regarding why only a minority of individuals are explicitly conscious of it. Examples based on fragrance and aroma are drawn from his recent lectures in Japan (http://cytowic.net/ “upcoming lectures”).
Sean A. Day, Trident Technical College
How many types of synesthesia are there? Working Lunch
Well before 1694, when John Locke alluded to blind mathematician Nicholas Saunderson's mention that the color red must be like the sound of a trumpet, the concept of synesthesia was around in poetry and imagination. However, as a medical phenomenon, the types of synesthesia conceived of were basically restricted to just 'sound -> color' and 'touch -> color'. In the mid 1800's, we may find reference to composers Franz Liszt and Joachim Raff, for example, having 'sound -> color' types of synesthesia. By the 1880's, more than a few researchers were also mentioning colored letter and numbers. And, by 1903, debate was emerging as to whether there should be separate classifications for colored words (morphemes) as opposed to colored speech sounds (phonemes) as opposed to colored letters (graphemes). More recently, in 1989, Cytowic's book titled "Synesthesia" numbered the different types of actual recorded cases of synesthesiae as being in the teens.
During the past ten years of operating The Synesthesia List, I have seen the estimated number of types of synesthesia jump up, such that I now record nearly 40 distinctly different types. But how valid are these categories? How useful? What more is needed? And what can be conflated? Can we now include colored "auras" as a type of synesthesia? Colored genres?
The purpose of this working lunch is to initiate discussion toward an emergent international consensus on classificatory labels for types of synesthesia.
Sabrina DeTurk, La Salle University
Does perception influence reception in the visual arts?
Despite an insistence on the significance of interpretation in understanding the work of art, art historians have a strong bias toward the assumption that viewers do see largely the same thing when encountering an art object. That is, that the basic physical and spatial elements of color, form, line, and so on are largely perceived in the same way by different individuals, across time and space.
The existence of a phenomenon such as synesthesia calls into question that basic assumption about similarity of perception and, perhaps, allows us also to rethink our notions of reception as well. Can recognition and investigation of sensory phenomena such as synesthesia offer the opportunity to reshape the critical framework of art history, just as theories about the reception of works of art have sought to destabilize accepted patterns of meaning in art history, often by inserting ideas of race, class, and gender difference into art historical narratives?
As both an art historian and a synesthete (who sees letters and numbers in color), I feel I can offer an unusual and hopefully provocative approach to this question. As my own work has often engaged with the impact of gender on the reception of works of art, this paper provides an opportunity to engage with a familiar topic on an even more personal level by investigating the ways in which the very process of seeing can deeply impact our interpretations of works of art.
Nina F. Dronkers, VA Northern California Health Care System
Nina F. Dronkers1,2, Rachel Edelson2,3, Jenny Ogar1, David Wilkins1,4, and Joseph T. Elder5
1. VA Northern California Health Care System
2. University of California, Davis
3. Sacramento City College
4. San Francisco State University
5. VA Medical Center, Atlanta and Emory University
“Letteral Invision”: a speech-to-text form of synesthesia
We have recently encountered a novel form of synesthesia in which the sensation of hearing a phrase or clause triggers the perception of seeing the entire utterance in printed form. Here we describe an individual, “Dahlia”, who sees a “tickertape” of words in her mind’s eye, lined up in clauses starting at the left of her field of vision, always in black “comic book-like” font. Stressed words appear in larger font or are italicized. Her synesthetic response to speech never interferes with what she is looking at, nor does it distract her from talking or listening. While there are somewhat vague descriptions of other synesthetes who may picture colorized words that they hear, Dahlia actually visualizes whole phrases with syntactic organization and proper punctuation, written in a consistent, specific black font, never colored. Several structured tasks designed to elicit her particular synesthetic experience under various conditions were administered. These revealed that her synesthetic perception is invoked both when she hears external speech and when she thinks silently. It is modified by contextual changes such as prosody, lexical ambiguity, and conceptual difficulty. This form of synesthesia is unique in that both the stimulus and the triggered perception are fully language- and literacy-dependent, and that it involves envisioning phrases or sentences rather than basic percepts (e.g., colored photisms). As such, this case represents a form of synesthesia that has not yet been reported, but that might inform theories of synesthesia, particularly with regard to the involvement of higher levels of cognitive processing in cross-modal integration.
David Eagleman, University of Texas
David Eagleman1, Edward Hubbard2, Arielle, Kagan1
1. University of Texas, Houston Medical School
2. University of California, San Diego
The genetics of synesthesia: linking genes to perception
Synesthesia is a rare perceptual condition in which stimulation of one sense triggers anomalous sensory experiences in another sense. For example, synesthetes may experience colors in response to letters or digits, tastes in response to words, colors when they hear words, or several other forms. While numerous psychological and neuroimaging studies have explored synesthesia, what remains unknown is the determination of the genetic basis of synesthesia. Synesthesia is an ideal system for ’perceptual genomics’ for 3 reasons: (1) A battery of perceptual tests allows confident phenotyping of synesthetes, (2) synesthesia clusters in families and current data suggests that it is inherited as a dominant X-linked gene, and (3) synesthetic perception may result from over-connectivity between neighboring neural areas, which suggests a set of candidate genes involved in neuronal pruning, arborization or apoptosis. The goal of this study is to perform linkage analysis to map gene(s) that are correlated with synesthesia. We have developed a battery of psychophysical tests to quickly phenotype synesthetes, i.e., to distinguish them from control subjects. Having gathered pedigrees from synesthetes, we are collecting blood samples from all participating family members; these samples will be processed in the Genetics Core laboratory at the University of Texas. A genome wide scan of the family will be completed using 100 highly polymorphic microsatellite markers. The most probable genetic region responsible for synesthesia in these families will be identified. Within the mapped region, candidate genes will be sequenced and screened for a segregating synesthesia-causing variation. When a probable variation is observed, 100 banked controls will be sequenced for the same variation to eliminate the possibility of a general population polymorphism. The objective of this study is to better understand and characterize the genetic basis of synesthesia, an identifiable perceptual variant.
Michael Esterman, University of California Berkeley
Michael Esterman_, Timothy Verstynen_, Richard Ivry_, and Lynn Roberston_,_
_ Department of Psychology, Helen Wills Neuroscience Institute, University of California,
_ Medical Research, Veterans Administration, Martinez, California
Attenuating the synesthetic experience with rTMS
Despite a recent explosion of behavioral and brain imaging studies, little is known about the causal roles of brain regions implicated in the synesthetic experience. In a recent fMRI study, Rich et al. (2003) identified a superior occipital region, near the parietal lobe junction, that was correlated with color-grapheme synesthetic experiences as well as color imagery. We used transcranial magnetic stimulation (rTMS) which briefly disrupts the function of a stimulated brain area through a pulse delivered over the scalp, and targeted this area to evaluate the necessity of this region for synesthetic color-grapheme binding. We found that stimulation of this area did in fact disrupt the binding process in the two synesthetes we tested. Both were female and right handed, and we objectively verified the change in their synesthesia with a color-naming Stroop task in which letters were presented in a color either congruent or incongruent with their normal synesthetic experience. Before rTMS, both participants showed facilitation in response times when letters were presented in their synesthetic color (Congruent condition) and interference when colors were incongruent with their synesthesia (Incongruent condition). Following 1Hz rTMS to the right dorsal parieto-occipital junction, the interference observed in the Incongruent condition was significantly attenuated. This effect disappeared approximately 6 minutes after cessation of the stimulation. In contrast, the facilitation during Congruent trials was unaffected by rTMS. These results implicate the dorsal parieto-occipital junction as playing a causal role in one aspect of the synesthetic experience.
Veronica Gross, Boston University
Melissa Mercado, Veronica Gross, Sandra Neargarder, Alice Cronin-Golomb
Significance of letter arrangement in the color-graphemic synesthetic experience
Color-graphemic synesthesia is a phenomenon in which visually presented letters, numbers, words or shapes elicit a stable color photism either in the field of vision or in the internally represented field of vision ("mind's eye"). One of the reported features of color-graphemic synesthesia is that the color of a word is dominated by the color of the first letter. For example, if the letter "t" were blue, the entire word "turtle" would be perceived as that same shade of blue. However, anecdotal evidence has suggested that the letters in the interior of the word may also contribute to the overall color of the word. We designed a word-matching task to assess the importance of non-primary letters in the overall word color. Six synesthetes (5 women, 1 man) and six control participants (all women) were presented with 120 word pairs (100 ms first word, 300 ms mask, 100 ms second word) and asked whether the words were the same or different, either as a nonsense word or anagram. Both nonsense words and anagrams could begin with either the same letter as or a different letter from the target word. Synesthetes performed significantly better (20% on average) than the control group in determining whether a word was the same as or different from a second, different, word spelled with the same first letter. This result, coupled with the self-reports of the synesthetes during the administration of the exam, suggests that color-graphemic synesthetes perceive colors for interior letters and that such perception improves performance on this task. Recent imaging studies suggest that the neuroanatomical substrate for color-graphemic synesthesia includes the left fusiform gyrus.
Peter Grossenbacher, Naropa University
Peter G. Grossenbacher, Christian J. De Ocejo, Nadine P. Hassemer
Consciousness Laboratory, Naropa University, Boulder, Colorado
Meaning, Artistic Creativity, and Synesthetic Conception
This talk presents new data on synesthesia, artistic training, and artistic creativity. In an interview study of over 100 persons with synesthesia, we found statistically strong relations between participantsÍ synesthesia and their engagement with artistic creativity that differed markedly from relations between synesthesia and artistic training. The observed pattern opposed our initial expectations, and has spurred two competing theoretical accounts relating artistic creation with synesthetic conception. Synesthetic conception encompasses those forms of synesthesia in which ideas or concepts are experienced as having one or more sensory attributes (Grossenbacher & Lovelace, 2001). For example, in a relatively common form of synesthetic conception, numeric values (e.g., fiveness or fifty-threeeness) are experienced as having location in space. The importance of meaning in both synesthetic experience and artistic creation is discussed.
Avishai Henik, Ben-Gurion University of the Negev, Israel
Avishai Henik, Roi Cohen-Kadosh, & Maya Tadir
Department of Behavioral Sciences and Zlotowski Center for Neuroscience,
Ben-Gurion University of the Negev, Israel
Colors affect numerical processing in synesthesia
Much research on synesthesia has examined the perceptual nature of the phenomenon. Recently, several studies have examined the effect of synesthesia on higher cognitive operations, studying conceptual levels of information processing. In several experiments, we examined effects of synesthesia on numerical processing. We employed a Stroop-like paradigm and presented synesthetes with digits in colors and asked them to compare the numerical values of the digits and ignore their colors. Displayed colors were either congruent or incongruent with experienced colors. One digit-color synesthete showed the classical congruity effect. Namely, she was slower to identify numerically larger numbers when they deviated from her experience than when they matched her experience. In addition, the effect of color on her comparative judgments was modulated by numerical distance. In contrast, performance by non-synesthetes was not affected by colors. Moreover, in another experiment with two synesthetes, we found that irrelevant color distance facilitated numerical processing. That is, participants were faster to compare two digits when the colors indicated a larger distance than the relevant numerical values (e.g., the digits 4 and 5 printed in the colors that induced 2 and 7, respectively). This suggests that colors can evoke magnitudes in some synesthetes. We propose that effects of colors on numerical processing may be mediated by connections between brain areas involved in magnitude processing (e.g., the intraparietal sulcus [IPS]) and areas involved in color processing. Furthermore, by using the current paradigm it is possible to infer the stage at which color-digit binding in synesthesia occurs.
Daphne Maurer, McMaster University, Keynote Speaker
The infant as synesthete?
In The World of the Newborn (1988), Charles Maurer and I proposed that newborns have a form of synesthesia. We wrote that “the newborn does not keep … sensations separate from one another,” but rather “mixes sights, sounds, feelings, and smells into a sensual bouillabaisse” in which “sights have sounds, feelings have tastes”, and smells can make the baby feel dizzy. In this talk, I will re-evaluate the hypothesis in light of recent evidence on the way the brain changes during development, on how infants react when objects are presented to more than one sense, and on apparent remnants of the early synesthesia in adulthood.
Kevin J. Mitchell, Trinity College Dublin, Ireland
Kevin J. Mitchell1, Ciara Finucane2, Aiden P. Corvin1,3 and Fiona N. Newell2
1. Dept. of Genetics,
2. Dept. of Psychology,
3. Dept. of Psychiatry and Institute of Neuroscience, Trinity College Dublin, Ireland.
A systematic study in the Irish population of the phenotypic characteristics and familiality of synaesthesia
A number of models have been proposed to explain the phenomenon of synaesthesia, a condition of involuntary sensory cross-activation presumably resulting from functional overlap between normally separate cortical areas. One problem, however, in trying to develop a single explanation for synaesthesia is that it is quite heterogeneous at the psychological level in terms of the modalities involved, the direction of synaesthesia, the nature of the inducing stimulus, attentional control and the subjective experience of the concurrent percept. A developmental genetic perspective, combined with detailed physiological characterization, may help to provide a unifying model of the emergence of synaesthesia.
Synaesthesia shows a high degree of familiality but it is not known whether different forms of synaesthesia result from heterogeneity at a genetic level or from a common genetic mechanism modified by developmental variability and experience. To address these questions, we have formed a multidisciplinary team to systematically study this phenomenon in the Irish population. To date, we have identified over 75 probands, and 20 families with multiple affected individuals. We propose to characterize in detail the phenotypes of individual synaesthetes, combining psychophysical tests with neuroimaging to determine the cortical location and time course of cross-activation. A comparison of these phenotypic characteristics within and across families should reveal which aspects of synaesthesia are determined genetically and which can vary due to other factors. This detailed phenotyping will also form the basis for a full-scale genetic mapping study aimed at identifying the affected gene(s) and underlying developmental mechanisms and explaining the concomitant perceptual experiences.
Supported by the Irish Health Research Board
Alva Noe, University of California Berkeley
Alva Noe, University of California Berkeley; Susan Hurley, University of Warwick
Gray (2003) argues that colored-hearing synaesthesia provides decisive evidence against an enactive (dynamic sensorimotor) approach to perceptual experience. Further, he argues that any functionalist (neobehaviorist) account of perceptual consciousness will be unable to account for the phenomena of synaesthesia. We investigate synaesthesia as a phenomen of neural plasticity and treat it, in particular, as exemplifying of 'cortical dominance' (Hurley and Noe 2003). In responding to Gray's argument, we address a related question: why do not synaesthetic colors adapt away?
Noam Sagiv, University College London, U.K.
Noam Sagiv1, Elias Tsakanikos1,2, Athene Witherby1,3, James Collins1, Julia Simner4, and Jamie
1. Department of Psychology, University College London, U.K.
2. Institute of Psychiatry, King's College, London, U.K.
3. UK Synaesthesia Association, U.K.
4. Department of Psychology, University of Edinburgh, U.K.
Prevalence of synesthesia and number forms
It is widely accepted that synesthesia is at least as common as 1 in 2000. These numbers are based on a newspaper ad placed by Baron-Cohen et al (1996) in a Cambridge newspaper. Many researchers suspect that the phenomenon is more common than previously reported; however, typically these observations have been based on relatively small samples. Here we report prevalence data obtained from over 1000 naive volunteers recruited among visitors in the London Science Museum (tested on site as part of the 'Live Science' public research initiative). We tested the consistency of color-grapheme correspondences followed by a short questionnaire explicitly asking about synesthetic experiences. In a second study, we assessed the prevalence of number forms (consistent and concrete experience of numbers as spatially organized) in three groups: Chromatic-graphemic synesthetes, synesthetes experiencing taste, and non-synesthetes. We found that synesthesia is at least an order of magnitude more common than previously reported. However, we found no evidence for a higher prevalence in school-aged children relative to adults. Data from the second study suggest that number forms are much more common in chromatic-graphemic synesthetes than non-synesthetes or taste synesthetes. We will discuss the implications of these findings for possible modes of inheritance and neurobiological mechanisms underlying synesthesia and number forms.
Marcia Smilack, Photographer, Martha's Vineyard, MA
The art presentation I wish to give at the Fourth American Synesthesia Association Conference is titled: Singing Arches. I intend to share a small collection of images which, like my usual work, are photographs I take of reflections on water. My images are not only inspired by my synesthetic responses to what I see, hear and feel; they are, in fact, the direct result of those responses. The pictures I wish to share in my lecture are from a recent trip I took to Italy where, much to my surprise, the dominating synesthetic response I experienced was not of the color-sound, texture, or motion variety I feel when I shoot images off the coast of Massachusetts. In Italy, I was most influenced by my response to shapes and geometry contained in the architecture, particularly arches which elicited, among other synesthetic responses, sound; the arches of Italy sang to me on a regular basis. I often remarked that I should have brought a tape recorder, not a camera, on my trip, for it was the sounds of Italy, not the sights, that affected me most strongly. As a synesthete, of course, my camera IS a kind of tape recorder, so it is those sounds, as they are captured in my pictures, that I wish to share with the audience.
Christine Söffing, Synaesthesiewerkstatt, Bibertal, Germany
Will your child sing the smell of tomatoes? - Using synaesthesia in workshops for art
Listen to the music and close your eyes. What will happen in your body, when you listen to the music? Can you smell the sound? Are there some colours or shapes? Can you feel the music somewhere? Would you like to dance or to write a poem?
In the last 12 years, my experiments with children between 4 and 12 years show me lots of synaesthetic answers. After a half year being at school, the synaesthetic answers are dwindling away. Five year old children play red sounds in a special kind of way, and blue sounds different, next week the same. They explain the colours of the letters, but are not able to paint them; they first have to learn how to mix the colour.
So we use synaesthesia to know exactly which colour we like to mix, or we build sculptures that show the sound of our self made music; we paint pictures about the taste of lemon, then we sing somebody else’s picture. In this kind of way, everyone is allowed to try out his or her special ideas and, by the way, to use different materials (colour, wood, tone, metal, sound recording technology, video, …).
I will talk about the experiments, about the answers of the children, and I will show some pictures of their works and themselves working.
Mark Stewart, Willamette University
Photism congruency and false recognitions in grapheme-color synesthetes
Grapheme-color synesthetes report perceiving a specific hue (i.e., photism) upon seeing a particular letter (e.g., the letter 'b' may evoke a photistic experience of red). It is not at all uncommon for these same synesthetes to experience photisms to actual words, with the photisms themselves often being driven by the first letter of the word (e.g., the word 'base' may give rise to a photism of red by virtue of its beginning with the letter 'b'). To date, the vast majority of behavioral and neuroscientific investigations of synesthesia have focused on verifying the perceptual basis of the phenomenon. By comparison, considerably less empirical attention has been paid to exploring issues of potential interest to researchers in memory and/or language.
I shall discuss data from two experiments (synesthetes of 4 and 7, respectively), each of which employed a standard recognition memory paradigm to demonstrate that grapheme-color synesthetes falsely recognized more lure words whose base study words were congruently versus incongruently colored. Results will be discussed in light of the possibility that a differential sensitivity to distinctive perceptual details encountered during study may serve to mediate false alarms occurring at test. Underwood's (1965) implicit associative response theory (IAR), Paivio's (1971) dual-coding hypothesis, and Israel & Schacter's (1997) distinctiveness heuristic will also be discussed.
Diane Swick, Dept. of Neurology; VA Northern California Health Care System
Jenny Ogor1, David Wilkins2, and Nina Dronkers1,3
1. VA Northern California Health Care System
2. Center for Aphasia and Related Disorders and San Francisco State University
3. University of California Davis
Excessive effects of orthography in a text synesthete: results from auditory priming
A previous experiment demonstrated that, even in the absence of printed text, orthography influences the perception of speech in controls making word/nonword decisions about spoken stimuli (Miller & Swick, 2003). The present study applied this paradigm to "Dahlia," who shows a novel form of synesthesia in which the sensation of hearing a word triggers the sensation of seeing that word in printed form. A companion paper by Dronkers describes "text synesthesia." Here, we asked whether Dahlia's synesthesia would lead to exaggerated effects of orthography in the auditory lexical decision task. Stimuli were presented over headphones in prime-target pairs. Subjects were required to make word/nonword discriminations on the second item in each pair. The six conditions were (1) Phonologically Related but orthographically dissimilar to the prime (PR), e.g. drawn-gone; (2) Orthographically Related but phonologically dissimilar (OR), e.g. hood-food; (3) both Orthographically and Phonologically related (OP), e.g.
tell-bell; (4) Unrelated (UN), e.g. jazz-globe; (5) Nonword, Phonologically related (PN), e.g. sort-bort; (6) Nonword, Unrelated (UNN), e.g. filth-gleck. Controls showed rhyme priming (faster RTs) to PR and OP words relative to UN words, with enhanced priming for OP (compared to PR) due to orthographic relatedness. Dahlia showed rhyme priming for OP words that was comparable to controls. However, she demonstrated enhanced sensitivity to conditions of conflict between orthography and phonology. Unlike controls, she was slower in responding to PR and OR words relative to UN (by 35 and 222 ms, respectively). These results provide experimental evidence for the phenomenology experienced by a text synesthete.
Martin van den Berg, University of Virginia
Kathleen A. Spanos, University of Virginia
Michael Kubovy, University of Virginia
The effect of synaesthetically induced colors on perceptual organization
The perceptual reality of synaesthesia is tested in two phases. During the first phase, four color-grapheme synaesthetes report on the synaesthetically induced colors of the letters A-Z and the numbers 0-9 in two sessions. Consistency within and between the two sessions is computed and letters and numbers that have colors that are consistently chosen are identified, taking the strength of the synaesthetic association and the ability of the computer display to represent the synaesthetic color into account.
In the second phase, grouping by proximity is pitted against grouping by similarity, using letters that induced colors either strongly or weakly. The strength of grouping by proximity and grouping by similarity is measured. Synaesthetes are more likely to group a dot pattern according to the similarity of synaesthetic colors, induced by alphanumeric symbols, than by proximity. Moreover, this effect is greater for alphanumeric symbols that induced colors strongly than for alphanumeric symbols that induced colors weakly. This difference is absent in control subjects.
The results show that colors are chosen with very high consistency and that synaesthetically induced colors have an effect on a perceptual organization task. Since these results are based on very precise quantitative methods, they present convincing evidence that synaesthesia is a genuine perceptual phenomenon.