Crétien van Campen and Clara Froger*
Fig. 1.Picture taken during color:odor experiment in an art studio. Participating synesthetes (on the left) smell odors with their eyes shut and choose corresponding colors from the selection of color chips on the table. The assistants (on the right) note the numbers (on the back of the color chips) that contain NCS information on hue, chroma and blackness.
The authors describe a practical method for assessing personal profiles of color:word, color:taste, color:music and color:odor synesthesia. The Netherlands Color Synesthesia (NeCoSyn) method is based on the Swedish Natural Color System and the test of genuineness for colored-word synesthesia developed by Baron-Cohen et al. The NeCoSyn method has been tested scientifically and shown to reliably distinguish different types of color synesthesia. It provides individual profiles of color synesthesia in the dimensions of hue, chroma and blackness. This article describes the method and discusses possible applications of NeCoSyn profiles in different fields of the arts and sciences.
Synesthesia is the phenomenon in which the stimulation of one sense modality gives rise to a sensation in another sense modality. The term "synesthesia" originates from the Greek syn (together) and aisthesis (perceive). The most prevalent form of synesthesia is "hearing" music or vowels in color. Sean Day has stressed the multiple forms of synesthesia as those of a related set of various cognitive states having in common that the stimulation of one sense, such as smell, is involuntarily simultaneously perceived by one or more other senses, such as sight and/or hearing . Color synesthesia, as one branch within this family tree of perceptual phenomena, refers to a person's experience of color as a result of the stimulation of a nonvisual sense modality. From subjective reports, we know that this color experience may range from internal feelings to external experiences (called photisms). Several researchers have stressed the neurological nature of the phenomenon and distinguished the phenomenon from mental construction . Normally, persons with the same type of synesthesia, e.g. color:word synesthesia, have differing experiences: the same word or letter will evoke different colors in each person, as was found in several studies. Even scholars as ancient as Aristotle and Pythagoras studied the correspondences of musical intervals and shades of gray . Artists have explored the phenomenon of color-music and synesthesia since the 17th century; scientific study started with a medical case study followed by psychological experimentation with groups of subjects in the 19th century. A revival of the study of synesthesia started with neurological research in the late 1980s . The study of synesthesia is characterized by multidisciplinarity in the sciences and the arts .
Diagnosing synesthesia is a complex matter, because the condition is not observable from
the outside. Diagnosis has to rely on self-reports and psychological testing. In
the last few decades, the following methods have been developed to determine,
diagnose, assess or distinguish synesthetes and synesthetic experiences:
Self-report is the most often-used method. Synesthetic experiences are described to a person and the person is asked if he or she has experienced this phenomenon. Self‑reports are not always valid or reliable. Some independent measure or standard should be used to supplement self‑reports.
Diagnostic criteria for synesthetic experiences have been proposed by Cytowic . Synesthetic experiences are: involuntary (but elicited), projected, durable, memorable and emotional. This method is more objective (i.e. more independent of subjective feeling) than self-report. To state the diagnosis, however, the clinician still must depend on self-reports of subjects. This makes the method less reliable; the diagnosis also depends to a great extent on the expertise of the clinician .
Brain imaging. In the late 1980s, Cytowic began recording the cerebral blood flow of a synesthete during his experiences of intense synesthesia, revealing an “abnormal" pattern of brain activity . Studies of blood flow among synesthetes, using PET scans and fMRI, are being continued by Paulesu et al., Aleman et al. and Ramachandran and Hubbard . These methods may be the most advanced brain tests available, but they have some disadvantages: (1) The studies have not yet resulted in clear criteria, scales or critical values for synesthetic brain activity and (2) the research is very expensive, time consuming and difficult for the participants.
The consistency test is the method most often used by scientists . The Test of Genuineness for Colored-Word Synesthesia was developed by Baron-Cohen et al. in the 1980s . The color:word test is based on the observation that in synesthetes the type of imagery evoked by specific sensations in another modality is stable over time. The results of the studies showed that subjects who reported synesthesia gave exactly the same color correspondences 93% of the time, in spite of being tested over 1.5 years later. Subjects without synesthesia were only 38% accurate, despite being asked only 1 week later to try and remember the colors they had associated with the words. The scope of the test was limited to color:word synesthesia.
from these assessment methods, we set the following scientific and artistic
requirements for the development of the Netherlands Color Synesthesia (NeCoSyn)
From a scientific point of view, our method should be reliable (depending as little as possible on subjective reporting); valid for different types of synesthesia; exact (able to quantify synesthetic experiences on a scale); useful for the assessment of several types of color synesthesia and for differentiating dimensions of color; and feasible (easy and cost-effective to apply in testing individuals and groups). From an artistic point of view, the method should be practical (i.e. usable by scientifically untrained artists), should be comprehensible (providing information that is intelligible) and should yield insight into one person’s synesthesia in relation to other synesthetes. The overall object was to make personal synesthesia comprehensible by means of graphic profiles, differentiating color dimensions and types of color synesthesia.
Below we describe how we developed the NeCoSyn method on the basis of the consistency test of Baron-Cohen et al. and the Swedish Natural Color System (NCS). First we will introduce the NCS and explain why it best fitted our purposes.
The NCS is a logical system built on how humans see color . With the NCS, all imaginable surface colors can be described and given unambiguous notations on the basis of six elementary colors: white, black, yellow, red, blue and green. The NCS color space consists of three dimensions:
indicates the percentage resemblance of a color to two chromatic elementary
colors. For example, the NCS notation Y10R means 90% yellow with 10% redness;
B50G means 50% blue with 50% green. The hue dimension is represented on a color
circle composed of yellow, red, blue and green.
2. Chroma is measured as a percentage of pure hue of a given color. For instance, cherry red has a high degree of chroma and pastel red, often called pink, has a lower degree.
3. Blackness is the degree of resemblance to black. It is the equivalent of a gray scale with white and black at the ends.
The NCS was chosen because it has several advantages over other color systems. First, the NCS uses a notation of colors that is simple to read and understand, even for laypeople. The code for hue indicates what type of color it is: for instance, Y50R indicates that a hue is mid-way between yellow and red. The user understands immediately that this must indicate a kind of orange. The code for blackness shows the percentage of blackness in the color and the code for chroma, the percentage of "pure" hue in a color. Second, the differences between two colors are immediately visible on the basis of their NCS code, even for non-experts. These two advantages go with the advantages of color systems in general: the codes are numeric and the colors can be reproduced, stored in databases and analyzed statistically .
developed the NeCoSyn method in three stages.
1. Validity and reliability. We started with a test to see if the Dutch translation of the English-language consistency test showed the test to be valid and reliable in a non-English language . Nine self-reported synesthetes responded to a call for study participants in the journal of the Dutch Color Society (Nederlandse Vereniging voor Kleurenstudie). The test we used was based on the test of genuineness for color:word synesthesia . For our test, we translated and shortened the English version . Four independent raters compared the participants' responses in the first and second tests. The agreement between raters was very high .
2. Feasibility. In the second stage, an improved version of the test was applied to 223 art students. The subjects were chosen at random out of all students in one class of an art-and-design college. On the basis of the results of the first test stage with nine subjects, the test was adapted into a more sensitive and shorter list of 20 abstract words, i.e. words not referring to a physical object, e.g. the word “government” . The participants used paper and pencil to note the colors they experienced. After a two-week interval the test was repeated. Because the interrater reliability was very high in the first stage, only one rater was used in this stage.
3. Exactness. In the third stage, the Natural Color System was introduced and our method was refined with respect to accuracy, distinction of types of color synesthesia and distinction of color dimensions. On the basis of the experiences and results from the earlier stages, the use of color names appeared too little refined to assess the color experiences. We therefore decided to use a standard selection of color chips: the subjects had the opportunity to choose up to three color chips to indicate the colors they experienced when exposed to certain tastes, odors or sounds of musical instruments. We asked them to rank the three colors in order of dominance . The taste stimuli were varied on the dimensions saltiness, sweetness, bitterness and sourness. Odors were varied on the same dimensions plus the dimension lightness-heaviness. The musical instruments were chosen from a variety of wind and stringed instruments playing the same note or chord---D major for example . In the taste and the odor sessions the participants kept their eyes shut during stimulus exposure (Fig. 1).
The Natural Color System distinguishes three dimensions of color: hue, chroma and blackness. Can these dimensions also be found in color synesthesia? Our first question was: Do synesthetes' experiences differ in color dimensions? We statistically tested the hypothesis that no differences existed in consistency scores with respect to color dimensions. The hypothesis was rejected in most cases, indicating that color dimensions of synesthesia exist .
The results of the analysis show us some interesting patterns. Comparing the participants' responses on the dimensions of blackness, chroma and hue, it appears that more participants responded more consistently on the blackness dimension than on the hue dimension. This observation relates to the distinction recently made by Martino and Marks between general and particular forms of synesthesia . General synesthesia is experienced by many "normal" people and refers to cross-sensory correspondences (e.g. a high-frequency tone sounds more "white" than a low tone). In particular synesthesia, experienced by far fewer people, a vivid image of a hue is evoked in response to stimulation in a nonvisual sense modality (e.g. a piano tone evokes a blue hue).
Our results suggest that the distinction between general and particular synesthesia might be based in the dimensions of color synesthesia. Particular synesthesia is related to the dimension of hue and general synesthesia is related to the dimension of blackness.
Day and others have suggested that types of synesthesia are distinct and not related . A person is not a synesthete in general but has one (or more) types of synesthesia, e.g. color:word synesthesia or color:taste synesthesia. Statistically, we tested the hypothesis that no differences exist between types of synesthesia . The results show that color:word synesthesia is significantly different from each of the other three types of synesthesia.
The NeCoSyn profile of one synesthete, shown in Fig. 2, is a detailed personal multidimensional representation of color synesthesia. Before she participated in the study, this synesthete reported that she experiences words in color and that she uses her personal colors of tastes while cooking. The NeCoSyn profile provides a detailed insight into her color synesthesia. The consistency of her color:word synesthesia is very strong on all three dimensions. Her color:taste synesthesia is based in the dimensions of chroma and blackness; the hue dimension is weaker. Finally the NeCoSyn profile reveals another perceptual competence that the subject did not report before: She has a moderate to strong ability to perceive the blackness of odors.
In general the NeCoSyn profiles are maps of individuals' color synesthesia. Since they are scaled, the profiles can be compared to profiles of other synesthetes and to group means. In this section we look for possible applications of this new method in the fields of art and science.
Fig 2. NeCoSyn profile of a synesthete.This graphic representation shows a personal profile of four types and three dimensions of synesthetic perceptions in one person. The four types of synesthesia are color:word, color:music, color:taste and color:odor. The dimensions are hue, chroma and blackness. The consistency (or strength) of synesthesia for each type on each dimension is presented in percentages (at left). More than 90% indicates a strong synesthetic perception. This person has strong synesthetic perceptions for the colors of words (on all dimensions) and for the chroma and blackness (but not the hue) of tastes.
In the fields of the arts, the NeCoSyn profiles can be used as an analytic tool by individual artists for understanding and gaining more detailed insight into their personal synesthetic experiences. Compare for instance how visual artists like Carol Steen and David Hockney and musicians like Olivier Messiaen and György Ligeti profited from gaining insight into their synesthetic experiences . The NeCoSyn profiles can be used as an input for the creative process. Fred Collopy has shown how knowledge of synesthetic correspondences is put into musical visualizers and other multimedia instruments . In art schools and art education the NeCoSyn method and profiles can be used to teach students about their personal perceptual functioning and sensibilities. In the process of developing our method we tested a group of art students. The testing revealed synesthesia to some students and stimulated discussion of synesthesia and perception.
In scientific disciplines such as the medical and social sciences, the NeCoSyn method provides an addition to existing consistency methods. It provides the opportunity to differentiate types of sensory domain synesthesia and dimensions of color synesthesia. In comparison with the method of self-report, we can report from our interviews with participants that the profiles provide additional objective information . Another point is that the subjective intuition of participants was objectified and specified in numbers by the NeCoSyn assessment method. In particular, the extra information on color dimensions of synesthetic experiences was new to participants. In comparison to the clinical method of diagnosis on the basis of criteria, the NeCoSyn offers more standardized results, independent of the rater's individual judgment. The instrument is robust and less prone to different interpretations.
The main advantages over the test of genuineness for color:word synesthesia are the assessment of color dimensions and the extensions to other types of color synesthesia.
In comparison with brain imaging, the NeCoSyn is far cheaper to administer, is less burdensome to participants and can therefore be used in larger testing populations. One of our subjects was tested in the medical lab of Utrecht University . Comparing the results of brain imaging and the NeCoSyn profile, the latter provided more specific results on the contents of her synesthesia.
This means that the NeCoSyn method is not limited to its current uses. The artistic and scientific studies of synesthesia have grown along separate lines, more by tradition than by logic. The example of NeCoSyn shows that the critical interaction of both disciplines results in new insights in multisensory sensibility in general and color synesthesia in particular.
The development of the NeCoSyn method has been ongoing for more than 5 years at the time of this writing, and we would like to thank all the people who were so generous in helping us: the participating synesthetes, Florence Husen and the students of the Lucas College, Elbert, Rosa and Fenna, and NCS Sweden.
References and Notes
* Crétien van Campen is a
psychological researcher and editor of the Leonardo On-Line bibliography
"Synesthesia in Art and Science." Rubicondreef 20, 3561 JC
Utrecht, the Netherlands. E-mail:
webmaster Web site:
Clara Froger is a visual artist, color consultant and synesthete. In her work as an artist she tries to capture her colorful experiences in paintings and sculpture. Lisbloemstraat 4, Rotterdam, 3051 TR, the Netherlands. E-mail: firstname.lastname@example.org.
1. Sean A. Day, "Types of Synesthesia," <http://www.users.muohio.edu/daysa/synesthesia.html>.
2. R.E. Cytowic, Synesthesia: A Union of the Senses (New York: MIT, 2002); J. Harrison, Synaesthesia: The Strangest Thing (New York: Oxford Univ. Press, 2001); V.S. Ramachandran and E.M. Hubbard, "Synaesthesia: A Window into Perception, Thought and Language," Journal of Consciousness Studies 8, No. 12, 3--34 (2001).
3. J. Gage, Colour and Culture: Practice and Meaning from Antiquity to Abstraction (London: Thames & Hudson, 1993); R. Ferwerda and P. Struycken, "Aristoteles" Over kleuren ("Aristotle" on Colors) (Budel, Netherlands: Damon, 2001).
4. Crétien van Campen, "Artistic and Psychological Experiments with Synesthesia," Leonardo 32, No. 1, 9--14 (1999).
5. See the Leonardo On-Line bibliography by Crétien Van Campen, Greta Berman and Bulat Galeyev, "Synesthesia in Art and Science" <http://mitpress2.mit.edu/e-journals/Leonardo/isast/spec.projects/synesthesiabib.html> (2001) for citations in the fields of perceptual psychology, psychology of consciousness, neonatal studies, creativity and cognitive science, neurology and brain imaging, genetics, psychopharmacology, art history and musicology. In the arts, studies of synesthesia can found in multimedia and Internet studies, linguistics, literature and visual music.
6. R.E. Cytowic, The Man Who Tasted Shapes (New York: Putnam, 1993).
7. K.B. Korb, "Synesthesia and Method," Psyche (on-line journal) 2 (1995) <http://psyche.cs.monash.edu.au/v2/psyche-2-24-korb.html>.
8. Cytowic .
9. Paulesu et al. ; A. Aleman et al., "Activation of Striate Cortex in the Absence of Visual Stimulation: An fMRI Study of Synesthesia," in Neuroreport 12, No. 13, 2827--2830 (17 September 2001); Ramachandran and Hubbard .
10. Harrison ; Ramachandran and Hubbard ; F. Svartdal and T. Iversen, "Consistency in Synesthetic Experience to Vowels and Consonants: Five Case Studies," Scandinavian Journal of Psychology 30 (1989) pp. 220--227.
11. S. Baron-Cohen et al., "Hearing Words and Seeing Colours: An Experimental Investigation of a Case of Synaesthesia," Perception 16 (1987) pp. 761--767; S. Baron-Cohen et al., "Coloured Speech Perception: Is Synaesthesia What Happens When Modularity Breaks Down?" Perception 22 (1993) pp. 419--426; S. Baron-Cohen, et al., "Synaesthesia: Prevalence and Familiarity," Perception 25, No. 9, 1073--1079 (1996).
12. See <http://www.ncscolor.com/>.
13. N. Silvestrini, E.P. Fischer and K. Stromer, Farbsysteme in Kunst und Wissenschaft (Cologne, Germany: Dumont, 2002).
14. A relationship between language and synesthesia is suggested by John Gage, who argues that the Russian language lends itself to color-hearing. Not coincidentally, three well-known (presumed) synesthetes were of Russian origin: Nabokov, Kandinsky and Scriabin. See J. Gage, "Making Sense of Colour: The Synaesthetic Dimension," in J. Gage, Colour and Meaning: Art, Science and Symbolism (Oxford, U.K.: Thames & Hudson, 1999) pp. 261--268.
15. Baron-Cohen et al., "Hearing Words and Seeing Colours" ; Baron-Cohen et al., "Coloured Speech Perception" .
16. The Dutch version consisted of 50 words, containing words from four semantic categories (animals, towns, objects, professions), letters of the alphabet, days of the week, nonsense words and abstract words. The test was repeated with 50 words one year later.
17. See details in the scientific report available on the Internet: <http://synesthesia.wolweb.nl/pub/necosynreport.htm>.
18. See details in the scientific report .
19. Sixteen participants were recruited partly from announcements and partly from earlier experiments, offering us the possibility of comparing their scores on different stages of the NeCoSyn test. The stimuli were chosen to cover a range of well-known dimensions.
20. See scientific report .
21. See details in the scientific report .
22. G. Martino and L.E. Marks, "Synesthesia: Strong and Weak," Current Directions in Psychological Science 10, No. 2, 61‑-65 (2001).
23. Day .
24. See details in scientific report .
25. Carol Steen, "Visions Shared: A Firsthand Look into Synesthesia and Art," Leonardo 34, No. 3, 203--208 (2001); Cytowic ; J. Bernard, "Messiaen's Synaesthesia, The Correspondence between Colour and Sound Structure in His Music," Music Perception 4, No. 1, 41--68 (1986); Constantin Floros, György Ligeti: jenseits von Avantgarde und Postmoderne (Vienna: Lafite, 1996).
26. F. Collopy, "Color, Form, and Motion: Dimensions of a Musical Art of Light," Leonardo 33, No. 5, 355--360 (2000).
27. See D. Smilek and Mike J. Dixon, "Towards a Synergistic Understanding of Synaesthesia Combining Current Experimental Findings with Synaesthetes' Subjective Descriptions," Psyche 8, No. 1 (2002) (on-line), <http://psyche.cs.monash.edu.au/v8/psyche-8-01-smilek.html>.
28. Aleman et al. .