Last semester I became increasingly interested with this condition of sorts, and chose it as my topic of concentration for an essay in a graduate Visual Perception and Cognition course. For anyone interested, below is my essay. As well as my list of resources, which may prove helpful for further information on this topic.
(Not sure if this was the final-final-edited-version, so please excuse any small grammatical/spelling errors)
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Synaesthesia: Current Research and Findings
Kaile Smith
Visual Perception and Cognition
Professor Dr. Arien Mack
New School University
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Abstract
Synaesthesia is a perceptual and cognitive phenomenon “in which an otherwise normal person experiences sensations in one modality when a second modality is stimulated” (E.D. Hubbard, 2005, p.509). One of the most common forms is grapheme-colour synaesthesia, in which when a synaesthete views a particular letter or number, it elicits a specific colour response. In this essay I will summarize and critique current research concentrating on grapheme-colour synaesthesia, as well as other relevant findings regarding synaesthesia in general.
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“When I see the real figure or grapheme as it is represented on whatever medium is right in front of me, or I hear it spoken, I understand it how it exists in reality, but also, a picture develops in my head of a colour and I understand it to be that colour even though I do not directly see it. From that I can remember static numbers and letters as a colour scheme, as well as a larger picture. Not only colour is associated, but also in semi-linear space like an ocean landscape and also in relation to a family structure. Especially with the numbers 1-9, and the alphabet less so. I understand them as personalities and they have a familial relationship. The number 23, is rose and green, 2 is a mom and a 3 is a pet or young baby. 19 is black and then yellow, and has a father and his oldest son relationship.”
-Rebecca O’Brien, age 22, synaesthete
Synaesthesia is a “condition in which an otherwise normal person experiences sensations in one modality when a second modality is stimulated.” Synaesthesia was first researched over one hundred years ago, and remained a popular topic of interest until halfway through the nineteenth century. Within the last ten to fifteen years there has been a revival of interest in the phenomenon due renewed interest in perceptual and cognitive processes added by advances in neurology and technology (E.D. Hubbard, 2005, p.509). While there are many variations of synaesthesia, grapheme-colour synaesthesia is believed to be the most common form, and as a result has been the most heavily studied in recent years. Topics within synaesthesia research varies from identifying processing levels, if some of synaesthetic associations are learned, the role of attention in synaesthetic experience as well as if the phenomenon is unidirectional or bidirectional.
One of the most common questions addressed in current grapheme-colour synaesthesia research is to try to “identify the level of processing involved in the formation of the subjective colours experienced by synaesthetes: are they perceptual phenomena or are they due to memory and association learning” (C. Gheri, S. Chopping, M.J. Morgan, 2008, p.841).
As a result of advances made in synaesthesia research, grapheme-colour synaesthesia is commonly broken into two major categories consisting of lower synaesthetes and higher synaesthetes, or projectors and associators, respectively, as a result of their different stages in processing. It is believed that lower synaesthetes “may have cross-wiring (or cross activation) within the fusiform gyrus.” When projector synaesthetes look at a grapheme, they see a colour projected or overlaid on the physical printed letter, number or symbol, studies have shown that the individual processes these projections as concrete perceptual phenomenon. In contrast, higher synaesthetes, “may have cross-activation in the angular gyrus” as a result of a genetic mutation casing “defective pruning of connections between brain maps,” so when associator synaesthetes look at a grapheme, they see a colour in a more conceptual manner, somewhere in their mind’s eye, or just know that the grapheme is a certain colour (V.S. Ramachandran & E.M. Hubbard, 2001, p4, E.M. Hubbard, 2005, p.509). The pruning theory is a commonly held explanation for all forms of synaesthesia as well because it has “been suggested that infants may be innately synaesthetic with sensory differentiation coming only with development and the gradual pruning of connections (or at least development of inhibition) between sensory areas” (Witthoft & Winawer, p.1).
Grossencacher and Lovelace (2001) came across another important associator synaesthetic finding. They observed “for most synaesthetes font and case have no impact on the colour.” What this argues is that if font and case did have an effect, that would mean that they synaesthetic experience was triggered by specific shape information, but because that is not the case it shows “that the representation that produces the concurrent is more abstract, concerned with the category to which the letter belongs” (Witthoft & Winawer, p.5). This is also supported by findings by Mills et al. (2002) in which a particular synaesthete, AED, was studied in depth to find many similaries between her colour associations in both English and Cyrillic letters that held similar conceptual similarities (Witthoft & Winawer, p.2).
An area of inquiry that is currently being investigated in depth, regards frequency correlates in grapheme-colour synaesthesia. Researchers have been finding important connections that shed light on what may cause certain colour associations to be more common among many grapheme-colour synaesthetes and to what extent these associations are learned. Studies by Rich et al. (2005) have shown “significant prevalences” of certain grapheme-colour associations. For example, common letters tend to be associated with common colours, i.e. in roughly forty percent of participants; A was red (Rich, 2008, p.1). Associations have also been shown to reflect the colours’ name, i.e. B is often blue or brown, and y is often yellow (G. Beeli, Mm. Esslen, L. Jancke, 2007, p.788). However, these are only approximations because each synaesthete sees a very specific hue, saturation, and lightness for each colour, which may be quite different from another synaesthete’s although both are categorized as red, for example.
Raaikmakers and Shiffrin (1992) did a test with a group of nineteen “colour-hearing” synaesthetes to prove this. “Each letter or digit was spoken aloud by the experimenter,” and all of the participants reported perceiving “the induced colour automatically and immediately after hearing the inducing letter or digital stimulus.” The participants were then asked to reproduce their synaesthetic colour via Adobe Photoshop 7.0 on a HSL scale (RGB hue, saturation, and lightness). This allowed them “to choose from 16,777,216(256^3) colours.” The participants were then asked to repeat the task 57 days later, “all of them demonstrated consistency.” The results found eighteen of the nineteen synaesthetes experiences the digit 0 as uncoloured (saturation =0). For letters, “there was a high incidence of white and yellow colours for I, j, and s (G. Beeli, Mm. Esslen, L. Jancke, 2007, p.789). The reported colours for 1 and I were highly similar in about half the subjects.” Letters and digits were also compared to “the seminal publication of Benford (1938); for letter frequency,” and “recommendations of Larch and Myers (1990);” for number frequency (G. Beeli, Mm. Esslen, L. Jancke, 2007, p.790). The test showed no relation between digit frequency and hue, although there was a slightly positive correlation between increasing digit frequency and increasing luminance. For letters there was a postitive correlation observed for letter frequency and saturation, so if a letter was more frequent, it had a higher saturation. Due to other strong evidence that synaesthesia has a genetic origin (Baron-Cohen, Burt, Smith-Laittan, Harrison, & Bolton, 1996), but is believed to be “not entirely genetically determined” (Smilek, Dixon, & Merikle, 2005) as proven through twin studies (G. Beeli, Mm. Esslen, L. Jancke, 2007, p.790), this holds consistent to Raaikmakers and Shiffrin’s results. They concluded that synaesthesia is modified by experience, i.e. increased or decrease exposure to different letters and numbers based on their frequency.
Another result of this investigation in frequency findings, was the prevalence of the digits 1 and 0, and letters i and o as commonly being associated as being colourless or white. This is believed to be a result of the characters being made up of natural shapes, a line and a circle, “that we learn to recognize before mastering the alphabet or learning to count,” thus overriding typical alpha-numerical associations (New Scientist, 2007, Vol. 196, Issue 2630). This might imply that “synaethetic linkage [takes] place very early in development, when children have typically not yet learned the digit 0 and its concept” (G. Beeli, Mm. Esslen, L. Jancke, 2007, p.791).
Another test that is commonly done to research the effects of synaesthesia, as well as identify the level of processing in which the phenomenon occurs is by using modified Stroop interference paradigms. This research has proven shown that “synaesthesia is automatic and perhaps obligatory” (Hubbard & Ramachandran, 2005, p.509). Stroop interference paradigms were tested between a group of synaesthetes, projector and associator, as well as a group of otherwise similar control subjects. Traditional Stroop paradigms were given to the controls, while modified version were given to the synaesthetes to be either purposefully congruent or incongruent to each particular synaesthete’s colour associations. For example, “for a synaesthete who sees 7 as yellow, a 7 presented in yellow would be congruent, and a 7 presented in any other colour would be incongruent.” Results showed that in the incongruent condition, for projector synaesthetes, their responses were typically much slower than in congruent conditions. In contrast, incongruent and congruent conditions did not prove to have any corollary results for associator synaesthetes in comparison to the controls taking the Stroop interference paradigms (Hubbard & Ramachandran, 2005, p.509). This reveals the differing levels of processing of synaesthesia between projector and associator synaesthetes.
These Stroop interference paradigm results have been similar to findings reported using search-related paradigms. In a study done by Hubbard and Ramachandran (2001), they “adapted a texture segregation test to subjects with displays in which one of four shapes (4-AFC) composed of a target grapheme was embedded in a background of distracter graphemes. Synaesthetes were significantly more accurate than control subjects in identifying which of the target shapes was presented.” This is congruent to a study by Palmeri et al. (2002) in which search-related tasks were given to synaesthetes in which target and distracter colours were either similar or contrasting. In cases where the target and distracters were similar, synaethete’s were much less efficient than control subjects, and more efficient than controls when the target and distracters were contrasting. These results are consistent with the idea commonly held that synaesthesia is evoked early in perceptual processing. It should be noted however that both of these tests were done with projector grapheme-colour synaesthetes, and evidence has not proven the same results for associator synaesthetes (Hubbard & Ramachandran, 2005, p510).
The question of unidirectional or bidirectional effect is also currently being explored in regards to synaesthesia, among both lowers and higher synaesthetes. Studies seem to lean towards unidirectional effect, as “an object of some sort is required to bind the synaesthetic experiences. For example, when a synaesthete views a letter, it evokes a colour, so there is a visual image that the colour is being ascribed to, be it as a projection, or in the “mind’s eye.” So far there is little evidence to show the reverse of this in which a colour evokes a number because “the number may not be able to be represented as a stimulus with physical properties of size, distance, and the like.” However, there have been arguments made for a bidirectional effect, stating, “the connections leading to synaestetic experience are of the appropriate strength or form to reach conscious awareness, whereas the connections that support bidirectional effects are not” (Hubbard & Ramachandran, 2005, p516). The exactly reasons for this difference however, is still being explored.
Yet another topic of interest among researchers is the relationship between attention and synaesthesia. Similar search-related paradigm tests by Laeng et al. (2004) have suggested, “that perceptual enhancement might occur only within the ‘functional field of attention.’” Or at least that attention is necessary for synaesthetic projections and associations to enter consciousness (Hubbard & Ramachandran, 2005, p.510).
While there have been huge strides made in the field of research relating to synaesthesia, it is often a particularly difficult field to find substantial findings and thus arguments about. One of the problems is that there remain so many varying forms and degrees of synaesthesia even within the same types. This leads to the inability to draw generalizations regarding levels of processing, innate or learned conclusions, as well as other perceptual versus cognitive arguments (Hubbard & Ramachandran, 2005, p.514). Often times studies are done with only one or a few primary subjects in which they researcher tries to make generalizations for the phenomenon of synaesthesia on a whole, and while interesting; it is hardly substantial enough to make a substantial argument. In contrast, when larger studies are done, because of the inherent variability of synaesthesia, important results are often missed as a result of trying to make generalizations based on highly variable data.
One of the most basic problems current research regarding synaesthesia is experiencing is determining an accurate estimate of the prevalence of synaesthesia within the general population. Estimates have ranged from one in twenty-five thousand, to one in twenty. One reason for large discrepancy is a result relying on most synaesthetes in samples as being self-elected participants. Also, the phenomenon on the whole is not widely known about outside the field, and many people are not even aware that they are synaesthetic. In 2006, the first random population study was done and found synaesthesia prevalence to be one in twenty-three people (J. Simner, C. Mulvenna, N. Sagiv et al., 2006, p.1024-1033). However, this has been met with much resistance claiming that its definition of synaesthesia was too broad and that it is the first study of its kind without other similar results being reported to support this argument.
Another problem that is to be considered is that while grapheme-colour synaesthesia is the most prevalent type of synaesthesia, “only 10% of synaethetes are projector synaesthetes. Past research seems to be heavily dominated by studies concentrating on the results of these projector synaesthetes, but much evidence shows that the ways in which lower synaesthetes process their experiences differs greatly from higher synaesthetes (Hubbard & Ramachandran, 2005, p.512). This fact is commonly disregarded or omitted from results.
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Resources
Baren-Cohen, S., Burt, L., Smith-Laittan, F., Harrison, J., and Bolton, P. (1996). Synaesthestia: Prevealence and familiality. Perception, 25, 1073-1079.
Beeli, G., Esslen, M., and Jancke, L. (2007). Frequency Correlates in Grapheme-Color Synesthesia. Psychological Science. Volume 18, Number 9, 788-792.
Brang, D., Edwards, L., Ramachandran, V.S., Coulson, S. (2008). Is the Sky 2? Contextual Priming in Grapheme-Color Synaesthesia. Psychological Science. Volume 15, Number 5. 421-428.
Date, M. (2008). Colour My World. Sydney Morning Herald, 10.
Galton, F. (1880). Visualised Numerals. Nature 21, 252-256.
Gheri, C., Chopping, S., Morgan, M.J. (2008) Synaesthetic Colours Do Not Camouflage Form in Visual Search. Proceedings: Biological Sciences, Volume 272, Issue 1636, 841-846.
Hubbard, E.M., and Ramachandran, V.S. (2001). Synaesthesia- A Window Into Perception, Thought and Language. Journal of Consciousess Studies, 8, Number 12, 3-34.
Hubbard, E.M., and Ramachandran, V.S. (2005). Neurocognitive
Mechanisms of Synesthesia. Neuron. Volume 48, 509-520.
Lehrer, J. (2007). Blue Monday, Green Thursday. New Scientist. Volume 194, Issue 2604, 48-51.
Simner, J.C., Mulvenna and N. Sagiv et al. (2006), Synaesthesia: The Prevelance of Atypical Cross-modal Experiences. Perception 8, 1-24-1033.
Simner, J., Ward, J. (2007). Synaesthesia, Color Terms, and Color Space. Psychological Science. Volume 19, Number 4, 412-414.
Smilek, D., Dixon, M.J., and Merikle, P.M. (2005) Synaesthesia: Discordant Male Monozygotic Twins. Neurocase, 11, 363-370.
Witthoft, N. and Winawer, J. (2003). Syesthetic Colors Determined by Having Colored Refrigerator Magnets in Childhood. Cortex, 1-9.
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As before, I have pdf's of all the above academic journal/magazine articles, email me if you are interested in reading any.
Also, the 'synaesthete' quoted at the beginning of my essay, just so happens to be my roommate back in NY, so I can put you in touch if you want to study her. ha-ha.
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