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| − | '''Synesthesia''' (also spelled '''synæsthesia''' or '''synaesthesia''') - from the Greek ''syn''- meaning ''union'' and ''aesthesis'' meaning ''sensation'', is a neurological condition in which two or more bodily [[sense]]s are coupled. For example, in a form of synaesthesia known as |
+ | '''Synesthesia''' (also spelled '''synæsthesia''' or '''synaesthesia''') - from the Greek ''syn''- meaning ''union'' and ''aesthesis'' meaning ''sensation'', is a neurological condition in which two or more bodily [[sense]]s are coupled. For example, in a form of synaesthesia known as grapheme-color synaesthesia, letters or numbers may be perceived as inherently colored. In other forms of synesthesia, musical and other sounds may be perceived as colored or having particular shapes. While cross-sensory [[metaphor]]s are sometimes described as "synesthetic", true neurological synesthesia is involuntary and occurrs in about four percent of the population (1 in 23 persons) across its range of variants (see Simner et al., in press). It runs strongly in families, possibly inherited as an X-linked dominant trait. |
Markus Zedler describes in [http://synesthesia.info/abstracts.html a brief article] synesthesia as "a perceptual condition in which the stimulation in one sensory modality elicits a concurrent sensation in another, a perception which is perceived as real." |
Markus Zedler describes in [http://synesthesia.info/abstracts.html a brief article] synesthesia as "a perceptual condition in which the stimulation in one sensory modality elicits a concurrent sensation in another, a perception which is perceived as real." |
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There are many varieties of synesthesia. While almost any sensory pairing is logically possible, certain combinations are much more common than others. In one of the most common forms of synesthesia, grapheme->color synaesthesia, individual letters of the alphabet, as well as numbers, are "shaded" or "tinged" with a color. While no two synesthetes will report the same colors for all letters and numbers, studies of large numbers of synesthetes find that there are some commonalities across letters (e.g., A is likely to be red) (Day, 2005; Simner et al., 2005). |
There are many varieties of synesthesia. While almost any sensory pairing is logically possible, certain combinations are much more common than others. In one of the most common forms of synesthesia, grapheme->color synaesthesia, individual letters of the alphabet, as well as numbers, are "shaded" or "tinged" with a color. While no two synesthetes will report the same colors for all letters and numbers, studies of large numbers of synesthetes find that there are some commonalities across letters (e.g., A is likely to be red) (Day, 2005; Simner et al., 2005). |
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| − | Synaesthetes often report that they were unaware their experiences were unusual until they realized other people did not have them, while others report feeling as if they had been keeping a secret their entire lives. Writer and synaesthete |
+ | Synaesthetes often report that they were unaware their experiences were unusual until they realized other people did not have them, while others report feeling as if they had been keeping a secret their entire lives. Writer and synaesthete Patricia Lynne Duffy remembers one early experience: "'One day,' I said to my father, 'I realized that to make an 'R' all I had to do was first write a 'P' and then draw a line down from its loop. And I was so surprised that I could turn a yellow letter into an orange letter just by adding a line.'"<sup>[http://www.bluecatsandchartreusekittens.com/Blue_Cats_and_Chartreuse_Kittens_Ex.html]</sup> |
Another grapheme -> color synesthete reports: "I often associate letters and numbers with colors. Every digit and every letter has a color associated with it in my head. Sometimes, when letters are written boldly on a piece of paper, they will briefly appear to be that color if I'm not focusing on it. Some examples: "S" is red, "H" is orange, "C" is yellow, "J" is yellow-green, "G" is green, "E" is blue, "X" is purple, "I" is pale yellow, "2" is tan, "1" is white. If I write SHCJGEX it registers as a rainbow when I read over it, as does ABCPDEF." (From a [http://slashdot.org/comments.pl?sid=140022&cid=11726211 slashdot discussion]) |
Another grapheme -> color synesthete reports: "I often associate letters and numbers with colors. Every digit and every letter has a color associated with it in my head. Sometimes, when letters are written boldly on a piece of paper, they will briefly appear to be that color if I'm not focusing on it. Some examples: "S" is red, "H" is orange, "C" is yellow, "J" is yellow-green, "G" is green, "E" is blue, "X" is purple, "I" is pale yellow, "2" is tan, "1" is white. If I write SHCJGEX it registers as a rainbow when I read over it, as does ABCPDEF." (From a [http://slashdot.org/comments.pl?sid=140022&cid=11726211 slashdot discussion]) |
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Other synesthetes report that days of the week, months of the year, and numbers have specific spatial locations, or that numbers will have specific genders and personalities. |
Other synesthetes report that days of the week, months of the year, and numbers have specific spatial locations, or that numbers will have specific genders and personalities. |
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| − | + | James Wannerton, a lexical-gustatory synaesthete reports: "Whenever I hear, read, or articulate (inner speech) words or word sounds, I experience an immediate and involuntary taste sensation on my tongue. These very specific taste associations never change and have remained the same for as long as I can remember". "<sup>[http://www.wannerton.net/]</sup> |
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== Notation == |
== Notation == |
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Given the wide variety of forms of synesthesia, researchers have adopted a convention of indicating the type of synesthesia by using the following notation x -> y, where x is the "inducer" or trigger, and y is the "concurrent" or additional, extra experience. So, for example, seeing letters and numbers (collectively called graphemes) as colored would be indicated as grapheme -> color synesthesia. Similarly, when synesthetes see colors and movement as a result of hearing musical tones, it would be indicated by tone -> (color, movement) synesthesia. |
Given the wide variety of forms of synesthesia, researchers have adopted a convention of indicating the type of synesthesia by using the following notation x -> y, where x is the "inducer" or trigger, and y is the "concurrent" or additional, extra experience. So, for example, seeing letters and numbers (collectively called graphemes) as colored would be indicated as grapheme -> color synesthesia. Similarly, when synesthetes see colors and movement as a result of hearing musical tones, it would be indicated by tone -> (color, movement) synesthesia. |
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| ⚫ | Estimates of the prevelance of synesthesia have varied widely (from 1 in 20 to 1 in 20000). However, these previous studies all suffered from the methodological shortcoming of relying on [[Self-selection|self-selected]] samples. That is, the only people included in those earlier studies were those who reported their experiences to the experimenter. Simner et al., (in press) conducted the first random population study, arriving at a prevalence of 1 on 23. Recent data (Day, 2005; Simner et al., in press) suggests that grapheme -> color, and days of the week -> color variants are most common. |
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| − | Almost every study that has investigated the topic has suggested that synesthesia clusters within families, consistent with a genetic origin for the condition. The earliest references to the familial component of synesthesia date to the 1880s, when Francis Galton first described the condition in the pages of Nature. Since then, other studies have supported this conclusion. However, early studies (Baron-Cohen et al., 1993; 1996) which claimed a much higher prevalence in women than in men (up to 6:1) most likely suffered from a [[Sampling_bias|sampling bias]] due to the fact that women are more likely to self-disclose than men. More recent studies, using random samples find a sex ratio of approximately 1:1 (Simner et al., in press). |
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| − | The observed patterns of inheritance have suggested an [[X-linked|x-linked]] mode of inheritance, although research into the genetics of synesthesia is still very preliminary. For example, father-to-son transmission is rare, while mother-to-son and mother-to-daughter transmission are quite common. Pairs of identical twins have been identified where only one member of the pair experiences synesthesia (Smilek et al., 2002; 2005) and it has been noted that synesthesia can skip generations within a family (Hubbard and Ramachandran, 2003), consistent with models of [[Penetrance|incomplete penetrance]]. Additionally, Simner et al. (in press) note that it is quite common for synesthetes within a family to experience different types of synesthesia, suggesting that the gene or genes involved in synesthesia do not lead to specific types of synesthesia. Rather developmental factors such as [[Gene_expression|gene-expresssion]] and environment must also play a role in determining which types of synesthesia an indivudal synesthete will experience. |
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== Demonstrating the Reality of Synesthesia == |
== Demonstrating the Reality of Synesthesia == |
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Finally, studies of grapheme-color synesthesia have demonstrated that synesthetic colors can improve performance on certain visual tasks, at least for some synesthetes. Inspired by tests for [[Color_blindness|color blindness]], Ramachandran and Hubbard (2001) presented synesthetes and non-synesthetes with displays composed of a number of 5s, with some 2s embedded among the 5s. These 2s could make up one of four different shapes; square, diamond, triangle or diamond. For a synesthete who sees 2s as red and 5s as green, their synesthetic colors would be expected to help them to find the "embedded figure". This is indeed what was found. Subsequent studies have explored these effects more carefully, and have found that 1) there is substantial variability among synesthetes and 2) while synesthesia is evoked early in perceptual processing, it does not occur prior to attention. |
Finally, studies of grapheme-color synesthesia have demonstrated that synesthetic colors can improve performance on certain visual tasks, at least for some synesthetes. Inspired by tests for [[Color_blindness|color blindness]], Ramachandran and Hubbard (2001) presented synesthetes and non-synesthetes with displays composed of a number of 5s, with some 2s embedded among the 5s. These 2s could make up one of four different shapes; square, diamond, triangle or diamond. For a synesthete who sees 2s as red and 5s as green, their synesthetic colors would be expected to help them to find the "embedded figure". This is indeed what was found. Subsequent studies have explored these effects more carefully, and have found that 1) there is substantial variability among synesthetes and 2) while synesthesia is evoked early in perceptual processing, it does not occur prior to attention. |
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| + | ==Case studies== |
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| + | Over the last 100 years there have been a number of case studies reported in the scientific literature and there have been references in the biographies of notable artists indicating that they experienced the condition. |
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| − | [[Image:synaesthesiabrain.jpg|thumb|right|300px|Regions thought to be cross-activated in grapheme-color synesthesia (from Ramachandran and Hubbard, 2001).]] |
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| − | There are two major classes of theories concerning the neural basis of synesthesia. |
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| + | {{Main| Case studies in synesthesia}} |
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| − | Both theories start from the observation that there are dedicated regions of the brain that are specialized for certain functions. For example, the part of the human brain involved in processing visual input, called the [[Visual_cortex|visual cortex]] can be further subdivided into regions that are preferentially involved in color processing (the fourth visual area, [[Visual_cortex#V4|V4]]) or with motion processing, called [[Visual_cortex#V5|V5]] or MT. Based on this notion of specialized regions, some researchers have suggested that increased cross-talk between different regions specialized for different functions may account for different types of synesthesia. |
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| ⚫ | Estimates of the prevelance of synesthesia have varied widely (from 1 in 20 to 1 in 20000). However, these previous studies all suffered from the methodological shortcoming of relying on [[Self-selection|self-selected]] samples. That is, the only people included in those earlier studies were those who reported their experiences to the experimenter. Simner et al., (in press) conducted the first random population study, arriving at a prevalence of 1 on 23. Recent data (Day, 2005; Simner et al., in press) suggests that grapheme -> color, and days of the week -> color variants are most common. |
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| + | ==Genetic basis== |
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| − | For example, Ramachandran and Hubbard (2001) have noted that regions involved in the identification of letters and numbers lie adjacent to V4, which is involved in color processing. They have therefore suggested that the additional experience of seeing colors when looking at graphemes might be due to "cross-activation" of V4. This cross-activation may arise due to a failure of the normal [[Neural_development|developmental process]] of pruning, which is one of the key mechanisms of [[Synaptic_plasticity|synaptic plasticity]], in which connections between brain regions are partially eliminated with development (note this need not be all or none). Similarly, tastes evoked by hearing words (lexical -> gustatory synesthesia) may be due to increased connectivity between adject regions of the [[Insular_cortex|insula]] in the depths of the [[Lateral_sulcus|lateral sulcus]] involved in taste processing that lie adjacent to [[Temporal_lobe|temporal lobe]] regions involved in auditory processing. Similarly, taste -> touch synesthesia may arise from connections between gustatory regions and regions of the [[Somatosensory_system|somatosensory system]] involved in processing touch. Note, however, that not all forms of synesthesia are easily explained by adjacency. |
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| + | Almost every study that has investigated the topic has suggested that synesthesia clusters within families, consistent with a genetic origin for the condition. |
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| + | {{Main| The genetic basis of synasthesia}} |
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| − | Alternatively, synesthesia may arise though "disinhibited feedback" or a reduction in the amount inhibition along feedback pathways (Grossenbacher and Lovelace, 2001). It is well established that information not only travels from the [[Primary_sensory_areas|primary sensory areas]] to [[Cerebral_cortex#Association_areas|association areas]] such as the [[Parietal_lobe|parietal lobe]] or the [[Limbic_system|limbic system]], but also travels back in the opposite diretion, from "higher order" cortical regions to early sensory areas. Normally, the balance of excitation and inhibition are maintained. However, if this feedback were not adequately inhibited, then signals coming from later stages of processing might influence earlier stages of processing, such that tones would activation visual cortical areas in synesthetes more than in non-synesthtes. In this case, it might be possible to temporarily have synesthetic experiences after taking drugs like [[LSD|LSD]] or [[Mescaline|mescaline]]. Indeed, some psychedelic drug users report synesthesia like experiences, although the exact degree of similarity between these drug induced experiences and congenital synesthesia is still unclear. |
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| − | Given that synesthesia is known to run in families, it has been suggested that a genetic difference, or [[Single_nucleotide_polymorphism|single nucleotide polymorphisms]] (SNPs, pronounced "SNiPs") might be responsible for either decreased pruning or decreased inhibition in the synesthete brain, leading to increased activation. Note, too, that these theories are not mutually exclusive. It may be that both mechanisms are possible causes of synesthesia, but that one or the other is present in differing degrees between different synesthetes, or for different sub-types of synesthesia. |
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| − | Neuroimaging studies using [[Positron_emission_tomography|positron emission tomography]] (PET) and [[FMRI|functional magnetic resonance imaging]] (fMRI) have demonstrated significant differences between the brains of synesthetes and non-synesthetes. In the first such study, Paulesu and colleagues (1995) used PET to demonstrate that some regions of the visual cortex (but not V4) were more active when auditory word -> color synesthetes listened to words compared to tones. More recent studies using fMRI have demonstrated that V4 is more active in both word -> color and grapheme -> color synesthetes (Nunn et al., 2002; Hubbard et al., 2005; Sperling et al., 2006). However, these neuroimaging studies do not have the spatial and temporal resolution to distinguish between the pruning and disinhibited feedback theories. Future research will continue to examine these questions using not only fMRI but also [[Diffusion_tensor_imaging|diffusion tensor imaging]] (DTI), which allows researchers to directly investigate neural connectivity in the human brain and [[Magnetic_resonance_imaging#Magnetic_resonance_spectroscopy|magnetic resonance spectroscopy]] (MRS) which allows researchers to measure the amounts of different neurotransmitters in the brain. |
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| + | {{main| The neurological basis of synesthesia}} |
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== Associated Cognitive Traits == |
== Associated Cognitive Traits == |
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In general very little is definitively known about the overall cognitive traits associated with synesthesia (or, indeed if there are any cognitive traits that are consistently associated with synesthesia). Some studies have suggested that synsthetes are unusually sensitive to external stimuli (see, e.g., Cytowic, 2002). Other possible associated cognitive traits include left-right confusion, difficutlies with math, and difficulties with writing (Cytowic, 2002). However, synesthetes may be more likely to participate in creative activities (Rich et al., 2005), and some studies have suggested a correlation between synesthesia and creativity (Domino, 1989; Dailey et al., 1991). Other research has sugggested that synesthesia may contribute to superior memory abilities (Luria, 1968; Smilek et al., 2002). However, it is unclear whether this is a general feature of synesthesia or whether it is true of only a small minority. This is a major topic of current and future research. |
In general very little is definitively known about the overall cognitive traits associated with synesthesia (or, indeed if there are any cognitive traits that are consistently associated with synesthesia). Some studies have suggested that synsthetes are unusually sensitive to external stimuli (see, e.g., Cytowic, 2002). Other possible associated cognitive traits include left-right confusion, difficutlies with math, and difficulties with writing (Cytowic, 2002). However, synesthetes may be more likely to participate in creative activities (Rich et al., 2005), and some studies have suggested a correlation between synesthesia and creativity (Domino, 1989; Dailey et al., 1991). Other research has sugggested that synesthesia may contribute to superior memory abilities (Luria, 1968; Smilek et al., 2002). However, it is unclear whether this is a general feature of synesthesia or whether it is true of only a small minority. This is a major topic of current and future research. |
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| − | == Links with Other Areas of Study == |
+ | == Links with Other Areas of Study == |
[[Image:BoobaKiki.png|thumb|right|250px|Booba and Kiki shapes|This picture is used as a test to demonstrate that people may not attach sounds to shapes arbitrarily: A remote tribe calls one of these shapes '''Booba''' and the other '''Kiki.''' Decide which is which and then click the image to check your answer.]] |
[[Image:BoobaKiki.png|thumb|right|250px|Booba and Kiki shapes|This picture is used as a test to demonstrate that people may not attach sounds to shapes arbitrarily: A remote tribe calls one of these shapes '''Booba''' and the other '''Kiki.''' Decide which is which and then click the image to check your answer.]] |
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| − | Researchers study |
+ | Researchers study synaesthesia not only because it is inherently interesting, but also because they hope that studying synaesthesia will offer new insights into other questions, such as how the brain combines information from different sensory modalities, referred to as [[Crossmodal|cross-modal perception]] and [[Multisensory_integration|multisensory integration]]. One example of this is the "kiki/bouba effect" (see image at right). This example was first explored by the [[Gestalt_Psychology|Gestalt psychologist]] [[Wolfgang_Köhler|Wolfgang Kohler]]. With individuals on the island of Tenerife, Kohler showed a similar preference between shapes called "takete" and "maluma". Recent work by Daphne Maurer and colleagues has shown that even children as young as 2.5 (too young to read) show this effect. Ramachandran and Hubbard (2001) have argued that this effect might be the neurological basis for [[sound_symbolism|sound symbolism]], in which sounds are non-arbitrarily mapped to objects and events in the world. |
| − | Similarly, |
+ | Similarly, synaesthesia researchers hope that, because of their unusual conscious experiences, the study of synaesthesia will provide a window into better understanding [[Consciousness|consciousness]] and in particular on the [[Neural_correlate|neural correlates]] of consciousness, or what the brain mechanisms that allow us to be conscious might be. In particular, some researchers have argued that synaesthesia is relevant to the [[philosophy|philosophical]] problem of [[qualia]] (see, e.g., Gray et al., 2002; Gray et al., 1997; Ramachandran & Hubbard, 2001), since synaesthetes experience additional qualia evoked through non-typical routes. |
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| − | == Famous Synesthetes == |
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| − | There is a great deal of debate about whether or not synesthesia can be identified through historical sources. [http://home.comcast.net/~sean.day/Synesthesia.htm Sean A. Day], a synesthete, and the President of the American Synesthesia Association, maintains a list of [[famous synesthetes]], "pseudosynesthetes" and individuals who are most likely not synesthetic, but who used synesthesia in their art or music. |
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| − | Below is a short list of confirmed synesthetes. For further elaboration on these and others, see the separarate [[famous synesthetes]] page. |
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| − | * [[Amy Beach]], American pianist and composer. Musical keys -> color. |
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| − | * [[Duke Ellington]], composer and pianist. Timbre -> color. |
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| − | * [[Richard Feynman]], physicist. Graphemes -> color. |
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| − | * [[David Hockney]], artist. Music -> color. |
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| − | * [[György Ligeti]], composer. Grapheme -> color. |
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| − | * [[Franz Liszt]], composer. Music -> color. |
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| − | * [[Olivier Messiaen]], composer and organist. Chordal structure -> color. |
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| − | * [[Vladimir Nabokov]], author. Grapheme -> color. |
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| − | * [[Nikolai Rimsky-Korsakov]], composer. Musical keys -> color. |
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| − | * [[Jean Sibelius]], composer. Sound -> color. |
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| − | * [[Michael Torke]], composer. Multiple synesthesiae. |
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==See also== |
==See also== |
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*[[Proprioception|Kinesthesia]] |
*[[Proprioception|Kinesthesia]] |
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*[[Parosmia]] |
*[[Parosmia]] |
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*[[Multiple Intelligence]] (Learning using multiple senses) |
*[[Multiple Intelligence]] (Learning using multiple senses) |
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| + | *[[Sensory substitution]] |
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*[[Visual thinking]] |
*[[Visual thinking]] |
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* Duffy, Patricia Lynne, 2001. Blue Cats and Charteuse Kittens. New York: Henry Holt & Company. |
* Duffy, Patricia Lynne, 2001. Blue Cats and Charteuse Kittens. New York: Henry Holt & Company. |
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* Gray, J. A., Chopping, S., Nunn, J., Parslow, D., Gregory, L., Williams, S., et al. (2002). "Implications of synaesthesia for functionalism: Theory and experiments." Journal of Consciousness Studies, 9(12), 5-31. |
* Gray, J. A., Chopping, S., Nunn, J., Parslow, D., Gregory, L., Williams, S., et al. (2002). "Implications of synaesthesia for functionalism: Theory and experiments." Journal of Consciousness Studies, 9(12), 5-31. |
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| − | * Gray, J. A., Williams, S. C. R., Nunn, J., & Baron-Cohen, S. (1997). "Possible implications of synaesthesia for the hard question of consciousness." In S. Baron-Cohen & J. E. Harrison (Eds.), Synaesthesia: Classic and contemporary readings. (pp. 173-181). Malden, MA: Blackwell. |
+ | * Gray, J. A., Williams, S. C. R., Nunn, J., & Baron-Cohen, S. (1997). "Possible implications of synaesthesia for the hard question of consciousness." In S. Baron-Cohen & J. E. Harrison (Eds.), Synaesthesia: Classic and contemporary readings. (pp. 173-181). Malden, MA: Blackwell.[http://psy.ucsd.edu/~edhubbard/papers/JCS.pdf pdf] |
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| − | * Grossenbacher, Peter G., and Christopher T. Lovelace, 2001. "Mechanisms of synesthesia: cognitive and physiological constraints." Trends in Cognitive Sciences; volume 5:1: 36-41. |
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| − | * Hubbard, E.M., Arman, A.C., Ramachandran, V.S. and Boynton, G.M., 2005. [http://psy.ucsd.edu/~edhubbard/papers/Hubbard_Neuron05.pdf "Individual differences among grapheme-color synesthetes: Brain-behavior correlations"] Neuron, 45(6): 975-985. |
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| − | * Nunn, J.A., L.J. Gregory, M. Brammer, S.C.R. Williams, D.M. Parslow, M.J. Morgan, R.G. Morris, E.T. Bullmore, S. Baron-Cohen, and J.A. Gray, 2002. "Functional magnetic resonance imaging of synesthesia: activation of V4/V8 by spoken words." Nature Neuroscience ; volume 5, 371 - 375. |
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| − | * Robertson, Lynn C., Sagiv, Noam, eds., 2005. Synesthesia: Perspectives from Cognitive Neuroscience. Oxford, UK: Oxford University Press. |
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* Smilek, Daniel, B.A. Moffatt, J. Pasternak, B.N. White, M.J. Dixon, and P.M. Merikle, 2002. "Synaesthesia: a case study of discordant monozygotic twins." Neurocase; vol. 8: 338-342. |
* Smilek, Daniel, B.A. Moffatt, J. Pasternak, B.N. White, M.J. Dixon, and P.M. Merikle, 2002. "Synaesthesia: a case study of discordant monozygotic twins." Neurocase; vol. 8: 338-342. |
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* Steen, Carol J., 2001. "Visions Shared: A Firsthand Look into Synesthesia and Art." Boston: Leonardo, The MIT Press: Vol 34, No. 3. |
* Steen, Carol J., 2001. "Visions Shared: A Firsthand Look into Synesthesia and Art." Boston: Leonardo, The MIT Press: Vol 34, No. 3. |
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| + | *Wheeler, RH. and Cutsforth, T.D. (1925) Synaesthesia in the development of the concept, Journal of Experimental Psychology 8: 149-52. |
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| − | ==Novels Featuring Synaesthetic Characters== |
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| − | * Nabokov, Vladimir. 1991/1938. [[The Gift (Nabokov book)|The Gift]]. New York: Vintage. |
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| − | * Kernan, Brent M. 2002. The Synesthete. Lincoln, NE: Writer's Showcase. |
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| − | * Mass, Wendy. 2003. A Mango-Shaped Space. London: Little Brown and Co. |
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| − | * Yardley, Jane. 2003. Painting Ruby Tuesday. London: Doubleday. |
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| − | * Moore, Jeffrey. 2004. The Memory Artists. Toronto: Penguin. |
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| − | * Berry, Michelle. 2005. Blind Crescent. Toronto: Penguin. |
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| − | * Parker, T. Jefferson. 2006. The Fallen. New York: William Morrow. |
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==External links== |
==External links== |
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*[http://www.mixsig.net/nexus A forum with discussions concerning many different types of synesthesia] |
*[http://www.mixsig.net/nexus A forum with discussions concerning many different types of synesthesia] |
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*[http://community.livejournal.com/synaesthesis/ A community of synesthetes on livejournal.com, for discussion and sharing of personal experiences and theories] |
*[http://community.livejournal.com/synaesthesis/ A community of synesthetes on livejournal.com, for discussion and sharing of personal experiences and theories] |
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| − | *[http://www.bluecatsandchartreusekittens.com/ Blue Cats and Chartreuse Kittens] by |
+ | *[http://www.bluecatsandchartreusekittens.com/ Blue Cats and Chartreuse Kittens] by Patricia Lynne Duffy |
=== Scientific resources === |
=== Scientific resources === |
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| − | *[http://www.synesthete.org/ The Synesthesia Battery:] take the tests to discover if you are synesthetic. Developed by |
+ | *[http://www.synesthete.org/ The Synesthesia Battery:] take the tests to discover if you are synesthetic. Developed by David Eagleman, PhD. |
*[http://Cytowic.net/ Richard E. Cytowic, MD] Downloads and information. |
*[http://Cytowic.net/ Richard E. Cytowic, MD] Downloads and information. |
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*[http://psy.ucsd.edu/~edhubbard Edward M. Hubbard, PhD] Synesthesia research including pdf versions of scientific articles. |
*[http://psy.ucsd.edu/~edhubbard Edward M. Hubbard, PhD] Synesthesia research including pdf versions of scientific articles. |
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*[http://home-1.tiscali.nl/~cretien/pub/syneng.htm Crétien van Campen] 'Artistic and psychological experiments with synesthesia' gives the historical background. |
*[http://home-1.tiscali.nl/~cretien/pub/syneng.htm Crétien van Campen] 'Artistic and psychological experiments with synesthesia' gives the historical background. |
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*[http://www.educ.cam.ac.uk/synaesthesia Synaesthesia and Education:] a research project at the University of Cambridge investigating the effects of grapheme-colour synaesthesia on numerical processing in children. |
*[http://www.educ.cam.ac.uk/synaesthesia Synaesthesia and Education:] a research project at the University of Cambridge investigating the effects of grapheme-colour synaesthesia on numerical processing in children. |
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| − | *[http://www.doctorhugo.org/synaesthesia/index.htm Museums of the Mind], a synesthesia portal by |
+ | *[http://www.doctorhugo.org/synaesthesia/index.htm Museums of the Mind], a synesthesia portal by Dr. Hugo Heyrman, more specific on the interaction between art and synesthesia. |
=== Synesthesia articles on the web === |
=== Synesthesia articles on the web === |
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*''[[Scientific American]]'' article [http://www.sciam.com/print_version.cfm?articleID=0003014B-9D06-1E8F-8EA5809EC5880000 Hearing Colors, Tasting Shapes] ([http://psy.ucsd.edu/chip/pdf/SciAm_2003.pdf PDF version]) by [[Vilayanur S. Ramachandran]] and Edward M. Hubbard, May 2003. |
*''[[Scientific American]]'' article [http://www.sciam.com/print_version.cfm?articleID=0003014B-9D06-1E8F-8EA5809EC5880000 Hearing Colors, Tasting Shapes] ([http://psy.ucsd.edu/chip/pdf/SciAm_2003.pdf PDF version]) by [[Vilayanur S. Ramachandran]] and Edward M. Hubbard, May 2003. |
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*[http://www.cortex-online.org/cortex.asp?action=toArticles&folderID=176 Cortex: Special Issue on Cognitive Neuroscience Perspectives on Synesthesia] The neuroscience journal Cortex presents a special issue focusing on modern scientific research of synesthesia. |
*[http://www.cortex-online.org/cortex.asp?action=toArticles&folderID=176 Cortex: Special Issue on Cognitive Neuroscience Perspectives on Synesthesia] The neuroscience journal Cortex presents a special issue focusing on modern scientific research of synesthesia. |
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| − | === Popular press === |
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| − | *[http://news.bbc.co.uk/1/hi/health/4375977.stm Why some see colours in numbers] at [[BBC News]], [[24 March]], [[2005]] |
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| − | *[http://livescience.com/humanbiology/050222_synesthesia.html People who feel color gets scientific acceptance] |
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| − | *[http://www.kuro5hin.org/story/2003/2/21/144256/437 Synaesthesia - union of the senses] (from [[Kuro5hin]]) Note, this article is excellent for the time, but the research has moved forward in the intervening years. |
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| − | *[http://www.freeinfosociety.com/site.php?postnum=693 Interview with a Synesthete] |
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| − | *[http://www.news-medical.net/?id=5619 synesthesia and psychic auras] |
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| − | *[http://develintel.blogspot.com/2005/12/tuned-and-pruned-synaesthesia_22.html Infantile synaesthesia] |
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| − | *[http://www.abc.net.au/science/news/stories/s1119739.htm Mirror Writing could be linked to Synaesthesia] |
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| − | *[http://www.migraine-aura.org/EN/Synaesthesia.html Synaesthesia and Migraine]Synaesthesia may occur as a visual migraine aura. |
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| − | *[http://www.thereminvox.com/story/28/ A Brief History of Synaesthesia and Music] |
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| − | *[http://www.wendymass.com/ A Mango-Shaped Space, a novel about a 13-year-old with synesthesia by Wendy Mass] |
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=== Artificial synesthesia === |
=== Artificial synesthesia === |
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Cognitive Psychology: Attention · Decision making · Learning · Judgement · Memory · Motivation · Perception · Reasoning · Thinking - Cognitive processes Cognition - Outline Index
Synesthesia (also spelled synæsthesia or synaesthesia) - from the Greek syn- meaning union and aesthesis meaning sensation, is a neurological condition in which two or more bodily senses are coupled. For example, in a form of synaesthesia known as grapheme-color synaesthesia, letters or numbers may be perceived as inherently colored. In other forms of synesthesia, musical and other sounds may be perceived as colored or having particular shapes. While cross-sensory metaphors are sometimes described as "synesthetic", true neurological synesthesia is involuntary and occurrs in about four percent of the population (1 in 23 persons) across its range of variants (see Simner et al., in press). It runs strongly in families, possibly inherited as an X-linked dominant trait.
Markus Zedler describes in a brief article synesthesia as "a perceptual condition in which the stimulation in one sensory modality elicits a concurrent sensation in another, a perception which is perceived as real."
Neurologist Richard Cytowic (2003: 76-77; 2002:67-69) identifies the following 'diagnostic' criteria of synesthesia:
- Synesthesia is involuntary and automatic
- Synesthetic images are spatially extended, meaning they often having a definite 'location'
- Synesthetic percepts are consistent and generic (i.e. simple rather than imagistic).
- Synesthesia is highly memorable.
- Synesthesia is laden with affect
Dann (1998: 6-7) adds two more:
- Synesthesia is nonlinguistic and somewhat ineffable.
- Synesthesia occurs in people with normal, noninjured, nondiseased brains.
Synesthetic Experiences
How someone with synaesthesia might perceive (n.b., not 'see') certain letters and numbers.
There are many varieties of synesthesia. While almost any sensory pairing is logically possible, certain combinations are much more common than others. In one of the most common forms of synesthesia, grapheme->color synaesthesia, individual letters of the alphabet, as well as numbers, are "shaded" or "tinged" with a color. While no two synesthetes will report the same colors for all letters and numbers, studies of large numbers of synesthetes find that there are some commonalities across letters (e.g., A is likely to be red) (Day, 2005; Simner et al., 2005).
Synaesthetes often report that they were unaware their experiences were unusual until they realized other people did not have them, while others report feeling as if they had been keeping a secret their entire lives. Writer and synaesthete Patricia Lynne Duffy remembers one early experience: "'One day,' I said to my father, 'I realized that to make an 'R' all I had to do was first write a 'P' and then draw a line down from its loop. And I was so surprised that I could turn a yellow letter into an orange letter just by adding a line.'"[1]
Another grapheme -> color synesthete reports: "I often associate letters and numbers with colors. Every digit and every letter has a color associated with it in my head. Sometimes, when letters are written boldly on a piece of paper, they will briefly appear to be that color if I'm not focusing on it. Some examples: "S" is red, "H" is orange, "C" is yellow, "J" is yellow-green, "G" is green, "E" is blue, "X" is purple, "I" is pale yellow, "2" is tan, "1" is white. If I write SHCJGEX it registers as a rainbow when I read over it, as does ABCPDEF." (From a slashdot discussion)
Other synesthetes report that days of the week, months of the year, and numbers have specific spatial locations, or that numbers will have specific genders and personalities.
James Wannerton, a lexical-gustatory synaesthete reports: "Whenever I hear, read, or articulate (inner speech) words or word sounds, I experience an immediate and involuntary taste sensation on my tongue. These very specific taste associations never change and have remained the same for as long as I can remember". "[2]
Notation
Given the wide variety of forms of synesthesia, researchers have adopted a convention of indicating the type of synesthesia by using the following notation x -> y, where x is the "inducer" or trigger, and y is the "concurrent" or additional, extra experience. So, for example, seeing letters and numbers (collectively called graphemes) as colored would be indicated as grapheme -> color synesthesia. Similarly, when synesthetes see colors and movement as a result of hearing musical tones, it would be indicated by tone -> (color, movement) synesthesia.
Demonstrating the Reality of Synesthesia
Proof that someone is a synesthete is fairly easy to come by, and hard to "fake". The simplest test involves test-retest reliability over long periods of time, and synesthetes consistently score higher on such tests than non-synesthetes (either with color names, color chips or even a color picker providing 16.7 million color choices). Synesthetes may score as high as 90% consistent over test-retest intervals of up to one year, while non-synesthetes will score 30-40% consistent over test-retest intervals of only one month, even if warned that they are going to be retested (e.g., Baron-Cohen et al., 1996).
More specialized tests include using modified versions of the Stroop effect. In the standard Stroop paradigm, it is harder to name the ink color of the word "red" when it is printed in blue than if the word "blue" was presented in blue. This demonstrates that reading is "automatic". Similarly, if we present a grapheme-color synesthete with a four that they see as red, but present it in blue ink, they are slower to identify the ink color. Note that this is not because they cannot see the blue ink, but rather that the same sort of "response conflict" that is responsible for the standard Stroop effect is also occuring between the color of the ink and the automatically induced color of the grapheme. Similar variants of the Stroop can be devised where, for example, someone is asked to name a red color patch while listening to a tone that produces a blue sensation (Ward et al., 2006), or to identify a bitter taste while hearing a musical interval that induces a sweet taste (Beeli et al., 2005).
An example of a test used to demonstrate the reality of synesthetic experiences (from Ramachandran and Hubbard, 2001).
Finally, studies of grapheme-color synesthesia have demonstrated that synesthetic colors can improve performance on certain visual tasks, at least for some synesthetes. Inspired by tests for color blindness, Ramachandran and Hubbard (2001) presented synesthetes and non-synesthetes with displays composed of a number of 5s, with some 2s embedded among the 5s. These 2s could make up one of four different shapes; square, diamond, triangle or diamond. For a synesthete who sees 2s as red and 5s as green, their synesthetic colors would be expected to help them to find the "embedded figure". This is indeed what was found. Subsequent studies have explored these effects more carefully, and have found that 1) there is substantial variability among synesthetes and 2) while synesthesia is evoked early in perceptual processing, it does not occur prior to attention.
Case studies
Over the last 100 years there have been a number of case studies reported in the scientific literature and there have been references in the biographies of notable artists indicating that they experienced the condition.
- Main article: Case studies in synesthesia
Prevelance
Estimates of the prevelance of synesthesia have varied widely (from 1 in 20 to 1 in 20000). However, these previous studies all suffered from the methodological shortcoming of relying on self-selected samples. That is, the only people included in those earlier studies were those who reported their experiences to the experimenter. Simner et al., (in press) conducted the first random population study, arriving at a prevalence of 1 on 23. Recent data (Day, 2005; Simner et al., in press) suggests that grapheme -> color, and days of the week -> color variants are most common.
Genetic basis
Almost every study that has investigated the topic has suggested that synesthesia clusters within families, consistent with a genetic origin for the condition.
- Main article: The genetic basis of synasthesia
Possible Neural Basis
- Main article: The neurological basis of synesthesia
Associated Cognitive Traits
In general very little is definitively known about the overall cognitive traits associated with synesthesia (or, indeed if there are any cognitive traits that are consistently associated with synesthesia). Some studies have suggested that synsthetes are unusually sensitive to external stimuli (see, e.g., Cytowic, 2002). Other possible associated cognitive traits include left-right confusion, difficutlies with math, and difficulties with writing (Cytowic, 2002). However, synesthetes may be more likely to participate in creative activities (Rich et al., 2005), and some studies have suggested a correlation between synesthesia and creativity (Domino, 1989; Dailey et al., 1991). Other research has sugggested that synesthesia may contribute to superior memory abilities (Luria, 1968; Smilek et al., 2002). However, it is unclear whether this is a general feature of synesthesia or whether it is true of only a small minority. This is a major topic of current and future research.
Links with Other Areas of Study
This picture is used as a test to demonstrate that people may not attach sounds to shapes arbitrarily: A remote tribe calls one of these shapes Booba and the other Kiki. Decide which is which and then click the image to check your answer.
Researchers study synaesthesia not only because it is inherently interesting, but also because they hope that studying synaesthesia will offer new insights into other questions, such as how the brain combines information from different sensory modalities, referred to as cross-modal perception and multisensory integration. One example of this is the "kiki/bouba effect" (see image at right). This example was first explored by the Gestalt psychologist Wolfgang Kohler. With individuals on the island of Tenerife, Kohler showed a similar preference between shapes called "takete" and "maluma". Recent work by Daphne Maurer and colleagues has shown that even children as young as 2.5 (too young to read) show this effect. Ramachandran and Hubbard (2001) have argued that this effect might be the neurological basis for sound symbolism, in which sounds are non-arbitrarily mapped to objects and events in the world.
Similarly, synaesthesia researchers hope that, because of their unusual conscious experiences, the study of synaesthesia will provide a window into better understanding consciousness and in particular on the neural correlates of consciousness, or what the brain mechanisms that allow us to be conscious might be. In particular, some researchers have argued that synaesthesia is relevant to the philosophical problem of qualia (see, e.g., Gray et al., 2002; Gray et al., 1997; Ramachandran & Hubbard, 2001), since synaesthetes experience additional qualia evoked through non-typical routes.
See also
- Cognitive neuroscience
- Perception
- Kinesthesia
- Parosmia
- Multiple Intelligence (Learning using multiple senses)
- Sensory substitution
- Visual thinking
References
- Baron-Cohen, Simon, and John E. Harrison, eds., 1997. Synaesthesia: Classic and Contemporary Readings. Oxford, UK: Blackwell.
- Baron-Cohen, Simon, John Harrison, Laura H. Goldstein, and Maria Wyke, 1993. "Coloured Speech Perception: Is Synaesthesia What Happens When Modularity Breaks Down?" Perception; volume 22: 419-426.
- Beeli, Gian, Michaela Esslen, and Lutz Jäncke, 2005. “When coloured sounds taste sweet.” Nature; vol. 434; 3 March: 38.
- Cytowic, Richard E., 2003/1993. The Man Who Tasted Shapes. New York: Tarcher/Putnam.
- Cytowic, Richard E. 2002. Synesthesia: A Union of the Senses, 2nd ed. Cambridge: MIT Press.
- Dann, Kevin T., 1998. Bright Colors Falsely Seen: Synaesthesia and the Search for Transcendent Knowledge. New Haven; London: Yale University Press.
- Day, Sean A., 2005. “Some Demographic and Socio-cultural Aspects of Synesthesia.” In Robertson & Sagiv, eds.; Synesthesia: Perspectives from Cognitive Neuroscience; Oxford: University Press, 11-33.
- Duffy, Patricia Lynne, 2001. Blue Cats and Charteuse Kittens. New York: Henry Holt & Company.
- Gray, J. A., Chopping, S., Nunn, J., Parslow, D., Gregory, L., Williams, S., et al. (2002). "Implications of synaesthesia for functionalism: Theory and experiments." Journal of Consciousness Studies, 9(12), 5-31.
- Gray, J. A., Williams, S. C. R., Nunn, J., & Baron-Cohen, S. (1997). "Possible implications of synaesthesia for the hard question of consciousness." In S. Baron-Cohen & J. E. Harrison (Eds.), Synaesthesia: Classic and contemporary readings. (pp. 173-181). Malden, MA: Blackwell.pdf
- Ramachandran, V.S. & Hubbard, E.M. (2001)."Synaesthesia: A window into perception, thought and language."] Journal of Consciousness Studies, 8(12), 3-34.
- Smilek, Daniel, B.A. Moffatt, J. Pasternak, B.N. White, M.J. Dixon, and P.M. Merikle, 2002. "Synaesthesia: a case study of discordant monozygotic twins." Neurocase; vol. 8: 338-342.
- Steen, Carol J., 2001. "Visions Shared: A Firsthand Look into Synesthesia and Art." Boston: Leonardo, The MIT Press: Vol 34, No. 3.
- Wheeler, RH. and Cutsforth, T.D. (1925) Synaesthesia in the development of the concept, Journal of Experimental Psychology 8: 149-52.
External links
Synesthesia associations
- American Synesthesia Association
- Australian Synaesthesia Association
- Belgian Synesthesia Association
- UK Synaesthesia Association
Synesthesia community sites
- Synesthesia in Chinese
- A forum with discussions concerning many different types of synesthesia
- A community of synesthetes on livejournal.com, for discussion and sharing of personal experiences and theories
- Blue Cats and Chartreuse Kittens by Patricia Lynne Duffy
Scientific resources
- The Synesthesia Battery: take the tests to discover if you are synesthetic. Developed by David Eagleman, PhD.
- Richard E. Cytowic, MD Downloads and information.
- Edward M. Hubbard, PhD Synesthesia research including pdf versions of scientific articles.
- Crétien van Campen 'Artistic and psychological experiments with synesthesia' gives the historical background.
- Synaesthesia and Education: a research project at the University of Cambridge investigating the effects of grapheme-colour synaesthesia on numerical processing in children.
- Museums of the Mind, a synesthesia portal by Dr. Hugo Heyrman, more specific on the interaction between art and synesthesia.
Synesthesia articles on the web
- Scientific American article Hearing Colors, Tasting Shapes (PDF version) by Vilayanur S. Ramachandran and Edward M. Hubbard, May 2003.
- Cortex: Special Issue on Cognitive Neuroscience Perspectives on Synesthesia The neuroscience journal Cortex presents a special issue focusing on modern scientific research of synesthesia.
Artificial synesthesia
- Artificial synesthesia (for the blind)
- The Color of Sound Flash experiment where you can assign colors to sounds and see how other people voted.
- Synesthesia Music Music generated from any pictures in 5 seconds
- Draw your music Software plays what you draw
- Visualising Music Software displays your music to animation
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