- A condition in which one type of stimulation evokes the sensation of another, as when the hearing of a sound produces the visualization of a color.
- A sensation felt in one part of the body as a result of stimulus applied to another, as in referred pain.
- The description of one kind of sense impression by using words that normally describe another.
synesthesia
Dictionary:
syn·es·the·sia syn·aes·the·sia (sĭn'ĭs-thē'zhə)  |
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Synaesthesia literally, ‘joining the senses’. People who experience synaesthesia (synaesthetes) inhabit a world slightly, but magically different from that of most people — a world of extra colours, shapes, and sensations. ‘Mine is a universe of black “Is” and pink “Wednesdays”, numbers that climb skywards and a roller-coaster shaped year’ is one description, reported by Motluk (1997). For synaesthetes, the experience of a single sense is accompanied by sensations in other sensory modalities.
Coloured-hearing is the most common form of synaesthesia, in which hearing a word elicits the perception of colour. The colour sensation elicited by a word is often determined by the letters in the word, with the first letter being the most influential. ‘For me “run”, “right”, and “religion” are all black … because the letter R is so strikingly black. … Even the word “red” … is a black word, while the “black” is, because of its B, blue’, said one synaesthete. The experience that words have particular colours can be helpful. Miss Stone, reported by Francis Galton in 1883, said ‘I have always associated the same colours with the same letters, and no effort will change the colour of one letter … Occasionally, when uncertain how a word should be spelt, I have considered what colour it ought to be, and have decided in that way. I believe this has often been a great help to me in spelling, both in English and foreign languages.’ Some composers report experiencing colours in response to chords or notes. For example, Olivier Messiaen stated; ‘I see colours which move with the music, and I sense these colours in an extremely vivid manner.’ Other forms of synaesthesia combine many of the senses. An extreme example was experienced by the patient ‘S’ who was intensively studied by the Russian neuropsychologist, Alexander Luria. Presented with a tone of 2000 Hz at 113 decibels, S said, ‘It looks something like fireworks tinged with a pink-red hue. The strip of colour feels rough and unpleasant and it has an ugly taste — rather like that of a briny pickle.’ In this example a sound is eliciting experiences of colour, touch, and taste.
Synaesthetes are not simply using metaphorical language to describe sensations that are, in reality, no different from those of other people, nor have they simply learned peculiar associations between different senses. The synaesthetic experience is an automatic and involuntary response to certain stimuli. The experience is vivid and consistent: true synaesthetes give precisely the same descriptions of their experiences even when these are separated by months or years. In support of an organic basis, synaesthetes seem to have had their experiences from earliest childhood and certainly before the age of four, and the syndrome seems to run in families. A transient experience of synaesthesia can be induced in non-synaesthetes by drugs such as hashish and mescaline. All these observations suggest that an explanation of synaesthesia needs to be sought at the level of brain function.
The techniques of functional brain imaging (positron emission tomography and functional magnetic resonance imaging) have been used to observe brain activity associated with a synaesthetic experience. As yet, only one fully-controlled study has been reported, by Frith and Paulesu (1997). Volunteers were scanned who experienced colours when they heard words. In comparison to people who did not have such experiences, extra areas of brain activity were identified in the synaesthetes when they were hearing words. This extra activity occurred in regions of the brain normally activated when naming the colours of objects, e.g. reporting ‘yellow’ in response to ‘banana’. Activity was not detected in regions of the visual cortex concerned with earlier stages of colour processing. This study confirms that the experiences reported by synaesthetes are associated with characteristic patterns of brain activity. The same regions are activated in non-synaesthetes when they are having experiences which are, to some extent, qualitatively similar. We remain, however, far from an understanding of the physiological basis of synaesthesia.
The problem is to explain how activity occurs in brain regions concerned with aspects of one kind of sense when the incoming stimulation derives from some other sense. There are essentially two possibilities (though very speculative), both of which involve some kind of ‘miswiring’ in the brain. The crosstalk theory suggests that information within the processing stream of one sensation crosses to another stream, leading to anomalous sensations. The feedback theory proposes that information from one sensory stream reaches a central region (e.g. a region concerned with object identity) and is then fed back towards the periphery, activating regions concerned with another sensory modality. Both ideas imply that, for a synaesthetic experience to occur, neural connections exist, that are not present, or not activated, in the more usual, non-synaesthetic individual. One suggestion is that the brain of an infant is naturally synaesthetic, such that information from any modality activates all sensory regions; activity in the cerebral cortex simply reflecting the amount of sensation, whatever its source. During maturation, responses to different modalities become localized in distinct brain regions. This differentiation may be achieved by the selective death of nerve cells, which is known to occur during infancy. Synaesthesia lasting into adulthood could be the consequence of partial failure of this mechanism.
Although synaesthesia is a relatively rare phenomenon (estimated to be 1 in 2000), understanding its physiological basis is of considerable importance to neuroscience. If we can understand synaesthesia then we might also understand the general mechanism by which neural activity is translated into conscious sensory experience. The main philosophical interest of synaesthesia, however, is the vivid example that it provides of how subjective our perceptions really are.
— Chris Frith
Bibliography
- Baron-Cohen, S. and Harrison, J. E. (1997). Synaesthesia: classic and contemporary readings. Blackwell, Oxford
See also perception; sensation; sensory integration.
| Literary Dictionary: synaesthesia |
synaesthesia
| Philosophy Dictionary: synaesthesia |
Confusion between the senses, as when musical notes are experienced as coloured.
| World of the Mind: synaesthesia |
In the 19th century Francis Galton, a cousin of Charles Darwin, noticed something peculiar. He found that a certain proportion of the general population — who were otherwise completely normal — tended to get their senses mixed up. For example, he (or she) might experience the colour red every time he hears the note C sharp played on the piano or the colour blue for F sharp. Or any time he sees the Hindu/Arabic numeral 5 on a sheet of paper he sees it tinged red, whereas a different number might evoke a different colour. The particular colour evoked by a given tone or number is not the same for all synaesthetes but within a given synaesthete the particular associations remain remarkably stable over time (Baron-Cohen et al. 1996).
Several facts about synaesthesia have been known for a long time.
1. As Galton noted, synaesthesia tends to run in families and probably has a genetic basis.
2. It appears to be much more common among drug users, especially those who have used LSD.
3. If you have one type of synaesthesia (e.g. tone–colour) you are also more likely to have another (e.g. number–colour).
4. There is some evidence that it is seven times more common among artists, poets, and novelists than in the general population.
5. Synaesthesia can sometimes be acquired rather than inherited. A patient who became completely blind by the age of 40 suddenly started experiencing both unformed photisms (phosphenes) and clearly formed visual images of simple shapes he palpated — presumably because his tactile sensory input had now 'invaded' (or was indirectly activating) his visual cortex (Armell and Ramachandran 1999).
6. In addition to the common types — number (grapheme)–colour and tone–colour — some exotic variants have also been described, such as a man who tasted shapes (Cytowic 2002) and who palpated tastes (Ramachandran and Hubbard 2002)! We have also encountered synaesthetes who automatically classify all numbers and letters as 'good or bad' and 'masculine or feminine' (as the French do for objects). Perhaps this is a quirky manifestation of the normal human brain's tendency to binarize the world into polar opposites. If so (see below) synaesthesia, far from being bizarre, may represent an extreme version of tendencies that exist in all brains. Perhaps Aristotle's notion of a 'sensus communis' — a common sense — was not a mere metaphor!
7. Synaesthesia is almost always unidirectional; numbers and letters evoke colours but colours evoking graphemes is very rare (although it does happen).
8. Synaesthesia used to be considered rare (estimates varying from 1 in 10,000 to 1 in 1,000) but we and others have found that it is actually quite common (1 in 200).
This list of observations seems so bewildering that it is hardly surprising that the phenomenon never won general acceptance in mainstream neuroscience; indeed it was sometimes dismissed as confabulatory.
There have been four styles of explanation put forward in the past to account for this curious phenomenon.
(1) These people are just crazy or trying to draw attention to themselves. This of course is a common reaction in science towards 'anomalies' — they tend to get brushed under the carpet if they do not fit the picture, the received wisdom.
(2) They are on drugs. This is a reasonable criticism except that it makes the phenomenon more interesting — not less. Why should some chemicals produce this effect — if they do?
(3) They are just remembering childhood memory associations, e.g. from having played with coloured refrigerator magnets. But if this is true why is the condition inherited?
(4) Maybe they are just being metaphorical. After all ordinary language is replete with sensory metaphors — 'loud shirt', 'sharp cheese' — and maybe they are just more gifted in this regard when they say C sharp is red. This explanation is inadequate because it merely substitutes one mystery (metaphor) for another (synaesthesia) but, as we shall see, it probably has more merit than the three preceding explanations.
These explanations have been largely unsatisfactory but the picture has now changed. The combined use of detailed psychophysics and brain-imaging experiments initiated around the turn of the 21st century has allowed the study of this intriguing phenomenon to make the transition from the era of vague phenomenology to the era of systematic empirical research. In particular, four things have happened (Ramachandran and Hubbard 2001a). First, it is clear that synaesthesia is a genuine sensory phenomenon: the subject literally experiences the 'quale' of the evoked sensation. Second, we now have clearly formulated, testable hypotheses about what the underlying neural basis might be and what parts of the brain might be involved. Third, brain-imaging studies by Nunn et al. (2002) and by our group have provided strong hints that our hypotheses about the brain mechanisms involved are correct at least for some synaesthetes. And fourth, it seems likely that far from being an oddity, synaesthesia might help us understand many enigmatic aspects of the mind such as our capacity for metaphor, aspects of language, and even abstract thought. We will also propose a theory to account for why the apparently useless synaesthesia gene(s) (if there is one) might confer a hidden evolutionary advantage.
1. Synaesthesia is a genuine sensory effect
2. The neural mechanism of synaesthesia
3. Different types of synaesthesia
The saturation of the synaesthetic colour also diminishes as the contrast of the number (or letter) is reduced, and below 8 per cent contrast the colour vanishes even though the number is still clearly visible. Alternating two spatially superposed graphemes at higher than 7 Hz also abolishes the colour. Such dependence on elementary physical parameters also suggests an early sensory process.
For example, in many synaesthetes the Hindu/Arabic number (e.g. 5 or 6) evokes colour but not the corresponding Roman number (V or VI), and this is true whether you are Roman or Hindu. This implies that it is not the high-level numerical concept or sequence or ordinality that evokes colour, but the visual appearance. This is consistent with the cross-activation theory since the fusiform represents appearance not concept.
In certain other synaesthetes, however, even days of the week and months of the year evoke colour, not just number (e.g. Wednesday is pink, Friday is yellow; or December is red and January is green, etc.). In these 'higher synaesthetes' it is the high-level abstract concept of ordinality that seems to drive the colour. Since the next stage in the colour-processing hierarchy is near the temporo-parieto-occipital (TPO) junction and that is where abstract number sequences are represented, it seems plausible that in these people the cross-activation occurs in the vicinity of the angular gyrus/TPO junction.
Analogously, 'lower synaesthetes' tend to see colours evoked by visually presented alphabets (represented in the fusiform), whereas in higher synaesthetes it is the heard phoneme (represented near the angular gyrus) that evokes the colour.
We postulate a gene mutation that causes cross-activation between these sensory maps encoding different dimensions. If the gene is selectively expressed in the fusiform you get lower synaesthesia; if expressed near the TPO junction you get higher synaesthesia. If expressed in the vicinity of the insular cortex you may get touch–taste or taste–touch synaesthesia given the proximity of taste maps (in the insula) and the hand/touch region of S1 in the Penfield map. Spatially adjacent maps are more likely to be linked than widely separated maps even in normal brains, and so if the mutations were to strengthen these connections synaesthesia is most likely to involve adjacent brain regions. (But it does not always have to, because sometimes even regions far apart might become abnormally connected.) Even foot fetishes could be regarded as a form of synaesthesia that arises because of the anatomical adjacency of the foot and genitals in the Penfield map.
Although number–colour synaesthesia is probably caused by early sensory cross-activation it can be modulated by top-down influences. If a large 5 is composed of a 'texture' of little 2s the synaesthete can alternatively either pay attention to the global 5 or zoom in on the little 2s, and the colour of the display changes accordingly even though the physical image is constant.
We have even come across a colour-anomalous synaesthete who could see only a limited range of colours in the world because of deficient cone pigments. Yet when he looked at numbers he saw 'Martian colours' that he could not see in the real world. This effect occurs because even though his colour receptors in the eye are deficient he presumably has a normal colour area V4 in the fusiform (specified genetically) that can be indirectly stimulated through cross-activation by numbers! The effect also rules out the memory association hypothesis of synaesthesia; how can you 'remember' colours you have never seen?
Some other facts about synaesthesia that have not been previously noticed include:
1. Letter precedence effect: sometimes the whole word takes on the colour of the first letter. This is true even if the first letter is silent (at least in lower synaesthetes).
2. Font: upper case usually evokes more vivid colour. For lower-case letters the same colour is evoked but it is less saturated, more 'patchy' and 'shiny' — colour 'paraesthesiae', one is tempted to call them.
3. In a rare form of synaesthesia the subject classifies all graphemes (sometimes even objects) as being male or female or good or bad — a quirky manifestation of the universal human tendency to binarize entities in the world into polar opposites (hot/cold; good/evil; big/small; yin/yang, etc.). It is hard to explain this in terms of anatomy.
4. Galton noted that in some synaesthetes each number not only has a colour but occupies a particular location in space with the linear sequence of numbers arranged sequentially in space — a 'number line'. Often the subject claims the number line is convoluted — even doubling back on itself — so that 9 might be (say) nearer to 3 in Cartesian space than to 8. In normal individuals the reaction time for judging which of two numbers is bigger varies inversely with the numerical distance between them, as if they are laid out on a perfectly straight imaginary line in the brain, making it harder to discriminate numerically adjacent numbers. We have found this is not true for synaesthetes with convoluted number lines; their reaction times were some messy compromise between Cartesian distance and numerical distance.
5. When asked to 'imagine' or visualize a number, most lower synaesthetes report, paradoxically, that the colour evoked by the visualized number is actually more vivid than one evoked by a real black or white one. This is because top-down imagery activates the same sensory number areas in the fusiform as real images do — thereby evoking the colours — but in the case of a real number there is contradictory bottom-up information partially vetoing the synaesthetic colours. In the absence of such vetoing the colours are more vivid.
Why is synaesthesia much more common among artists, poets, and novelists? One thing they all have in common is a facility with metaphor, a propensity to link seemingly unrelated concepts (e.g. 'Juliet is the Sun', 'he has a sharp mind'). If the 'hyperconnectivity' gene is expressed more diffusely throughout the brain rather than locally, and if we assume that high-level concepts are also represented in brain maps, then the result would be a greater propensity for metaphor. This would explain the higher incidence of synaesthesia in arty types. This is a speculative idea that is not easy to test. But if correct it would explain why the apparently useless synaesthesia gene (if there is such a thing) has survived; it might confer creativity in some outliers.
Synaesthetic propensities might therefore exist in all of us. Consider the two abstract shapes in Fig. 1. If you ask people which one is 'Bouba' and which one 'Kiki'; more than 95 per cent pick the bulbous amoeboid shape as Bouba and the jagged shape as Kiki. (This is not because the jagged shape resembles K; even Tamil speakers make the same choice.) The effect suggests that we are all closet synaesthetes; the sharp inflections of the sound 'ki ki' mimic the sharp inflections of the jagged visual shapes, and the gentle undulation of contours in the amoeboid shapes corresponds to the sound 'bouba'. Since the subjects have never seen these shapes, or heard the sounds, before, there must be a pre-existing non-arbitrary cross-activation between visual shapes represented in the fusiform and sounds represented in the auditory cortex. Such cross-modal transl ation probably requires the mediation of the angular gyrus given its strategic anatomical location at the TPO junction — at the crossroads between visual (occiptal), auditory (temporal), and parietal (touch) areas of the brain.
Since the visual shape Kiki is composed of photons hitting the eyes in parallel whereas the sound kiki is delivered by sequential stimulation of hair cells of the inner ear, the two have nothing in common except the abstract property of jaggedness in Fourier space. What this ability represents, then, is a primitive form of the process of abstraction that humans excel in (e.g. when we say five rabbits, five tones, five unicorns, they have nothing common except fiveness). There are hints that the Bouba/Kiki effect is compromised when the angular gyrus is damaged.
The angular gyrus became progressively larger in primates, and is disproportionately large in the great apes and humans. Perhaps it was originally an adaptation for arboreal living, allowing the primate brain to match the seen visual orientation of a branch with its position felt through proprioception as the hand rotated to grab it. But once in place it could have been adapted for other more sophisticated types of abstraction of the kind that humans excel at.
Metaphors, too, incorporate synaesthetic elements, as when we say 'loud shirt'. Also, we use the word 'disgusting' and scrunch up our nose when confronting a bad taste or smell, but why do we also use the same word and expression for moral disgust? This may occur because olfactory and gustatory disgust are mapped in the orbitofrontal cortex which later became usurped in humans for representing morality and disgust. As Freud said, anatomy is destiny.
Thus synaesthesia, far from being a mere curiosity can provide key insights into some of the most elusive aspects of our mind, such as the emergence of metaphor and abstraction. Once the gene(s) is cloned we can go from the gene to anatomy (fusiform gyrus; angular gyrus) to psychophysics and phenomenology, perhaps all the way to the emergence of metaphor and abstract thought.
Fig. 1.
(Published 1987)
Several facts about synaesthesia have been known for a long time.
1. As Galton noted, synaesthesia tends to run in families and probably has a genetic basis.
2. It appears to be much more common among drug users, especially those who have used LSD.
3. If you have one type of synaesthesia (e.g. tone–colour) you are also more likely to have another (e.g. number–colour).
4. There is some evidence that it is seven times more common among artists, poets, and novelists than in the general population.
5. Synaesthesia can sometimes be acquired rather than inherited. A patient who became completely blind by the age of 40 suddenly started experiencing both unformed photisms (phosphenes) and clearly formed visual images of simple shapes he palpated — presumably because his tactile sensory input had now 'invaded' (or was indirectly activating) his visual cortex (Armell and Ramachandran 1999).
6. In addition to the common types — number (grapheme)–colour and tone–colour — some exotic variants have also been described, such as a man who tasted shapes (Cytowic 2002) and who palpated tastes (Ramachandran and Hubbard 2002)! We have also encountered synaesthetes who automatically classify all numbers and letters as 'good or bad' and 'masculine or feminine' (as the French do for objects). Perhaps this is a quirky manifestation of the normal human brain's tendency to binarize the world into polar opposites. If so (see below) synaesthesia, far from being bizarre, may represent an extreme version of tendencies that exist in all brains. Perhaps Aristotle's notion of a 'sensus communis' — a common sense — was not a mere metaphor!
7. Synaesthesia is almost always unidirectional; numbers and letters evoke colours but colours evoking graphemes is very rare (although it does happen).
8. Synaesthesia used to be considered rare (estimates varying from 1 in 10,000 to 1 in 1,000) but we and others have found that it is actually quite common (1 in 200).
This list of observations seems so bewildering that it is hardly surprising that the phenomenon never won general acceptance in mainstream neuroscience; indeed it was sometimes dismissed as confabulatory.
There have been four styles of explanation put forward in the past to account for this curious phenomenon.
(1) These people are just crazy or trying to draw attention to themselves. This of course is a common reaction in science towards 'anomalies' — they tend to get brushed under the carpet if they do not fit the picture, the received wisdom.
(2) They are on drugs. This is a reasonable criticism except that it makes the phenomenon more interesting — not less. Why should some chemicals produce this effect — if they do?
(3) They are just remembering childhood memory associations, e.g. from having played with coloured refrigerator magnets. But if this is true why is the condition inherited?
(4) Maybe they are just being metaphorical. After all ordinary language is replete with sensory metaphors — 'loud shirt', 'sharp cheese' — and maybe they are just more gifted in this regard when they say C sharp is red. This explanation is inadequate because it merely substitutes one mystery (metaphor) for another (synaesthesia) but, as we shall see, it probably has more merit than the three preceding explanations.
These explanations have been largely unsatisfactory but the picture has now changed. The combined use of detailed psychophysics and brain-imaging experiments initiated around the turn of the 21st century has allowed the study of this intriguing phenomenon to make the transition from the era of vague phenomenology to the era of systematic empirical research. In particular, four things have happened (Ramachandran and Hubbard 2001a). First, it is clear that synaesthesia is a genuine sensory phenomenon: the subject literally experiences the 'quale' of the evoked sensation. Second, we now have clearly formulated, testable hypotheses about what the underlying neural basis might be and what parts of the brain might be involved. Third, brain-imaging studies by Nunn et al. (2002) and by our group have provided strong hints that our hypotheses about the brain mechanisms involved are correct at least for some synaesthetes. And fourth, it seems likely that far from being an oddity, synaesthesia might help us understand many enigmatic aspects of the mind such as our capacity for metaphor, aspects of language, and even abstract thought. We will also propose a theory to account for why the apparently useless synaesthesia gene(s) (if there is one) might confer a hidden evolutionary advantage.
1. Synaesthesia is a genuine sensory effect
2. The neural mechanism of synaesthesia
3. Different types of synaesthesia
1. Synaesthesia is a genuine sensory effect
Recent experiments suggest strongly that synaesthesia is a sensory phenomenon, not a high-level memory association. If you have a set of 2s embedded among a matrix of randomly placed 5s, normal non-synaesthetes have great difficulty in discerning the 2s since they are mirror images of each other and share the same constituent features (three horizontal lines and two vertical lines). If the 2s are arranged to form a shape such as a triangle or a square, normal subjects take tens of seconds to report the hidden shape accurately. On the other hand synaesthetes who (say) see the 2s as red and 5s as green see the global 'red' triangle or square 'pop out' much more quickly — their reaction time for correctly reporting the shape is much shorter. (And they report seeing a red triangle against a green background.) Since they are better than normals at this task, synaesthesia cannot be confabulatory and must be a genuine sensory effect rather than a high-level memory association.The saturation of the synaesthetic colour also diminishes as the contrast of the number (or letter) is reduced, and below 8 per cent contrast the colour vanishes even though the number is still clearly visible. Alternating two spatially superposed graphemes at higher than 7 Hz also abolishes the colour. Such dependence on elementary physical parameters also suggests an early sensory process.
2. The neural mechanism of synaesthesia
The cortical colour area V4 in the brain and the area representing visual appearance of Hindu/Arabic numbers and letters (graphemes) happen to be right next to each other in the fusiform gyrus. Given that grapheme–colour synaesthesia is the commonest form we suggested that the phenomenon is caused by an abnormal cross-activation between these two areas resulting from a gene mutation(s) that results in defective 'pruning' between brain modules, disinhibition between them, or hyperactivation of ordinarily silent back projections (Armell and Ramachandran 1999; Ramachandran and Hubbard 2002). Preliminary evidence from brain-imaging studies (Nunn et al. 2002) has provided strong hints that this idea might be right.3. Different types of synaesthesia
There are at least two types of synaesthesia and possibly many 'in-between' categories. We call these 'higher' and 'lower' synaesthesia, depending on the presumed anatomical stage at which the cross-activation occurs.For example, in many synaesthetes the Hindu/Arabic number (e.g. 5 or 6) evokes colour but not the corresponding Roman number (V or VI), and this is true whether you are Roman or Hindu. This implies that it is not the high-level numerical concept or sequence or ordinality that evokes colour, but the visual appearance. This is consistent with the cross-activation theory since the fusiform represents appearance not concept.
In certain other synaesthetes, however, even days of the week and months of the year evoke colour, not just number (e.g. Wednesday is pink, Friday is yellow; or December is red and January is green, etc.). In these 'higher synaesthetes' it is the high-level abstract concept of ordinality that seems to drive the colour. Since the next stage in the colour-processing hierarchy is near the temporo-parieto-occipital (TPO) junction and that is where abstract number sequences are represented, it seems plausible that in these people the cross-activation occurs in the vicinity of the angular gyrus/TPO junction.
Analogously, 'lower synaesthetes' tend to see colours evoked by visually presented alphabets (represented in the fusiform), whereas in higher synaesthetes it is the heard phoneme (represented near the angular gyrus) that evokes the colour.
We postulate a gene mutation that causes cross-activation between these sensory maps encoding different dimensions. If the gene is selectively expressed in the fusiform you get lower synaesthesia; if expressed near the TPO junction you get higher synaesthesia. If expressed in the vicinity of the insular cortex you may get touch–taste or taste–touch synaesthesia given the proximity of taste maps (in the insula) and the hand/touch region of S1 in the Penfield map. Spatially adjacent maps are more likely to be linked than widely separated maps even in normal brains, and so if the mutations were to strengthen these connections synaesthesia is most likely to involve adjacent brain regions. (But it does not always have to, because sometimes even regions far apart might become abnormally connected.) Even foot fetishes could be regarded as a form of synaesthesia that arises because of the anatomical adjacency of the foot and genitals in the Penfield map.
Although number–colour synaesthesia is probably caused by early sensory cross-activation it can be modulated by top-down influences. If a large 5 is composed of a 'texture' of little 2s the synaesthete can alternatively either pay attention to the global 5 or zoom in on the little 2s, and the colour of the display changes accordingly even though the physical image is constant.
We have even come across a colour-anomalous synaesthete who could see only a limited range of colours in the world because of deficient cone pigments. Yet when he looked at numbers he saw 'Martian colours' that he could not see in the real world. This effect occurs because even though his colour receptors in the eye are deficient he presumably has a normal colour area V4 in the fusiform (specified genetically) that can be indirectly stimulated through cross-activation by numbers! The effect also rules out the memory association hypothesis of synaesthesia; how can you 'remember' colours you have never seen?
Some other facts about synaesthesia that have not been previously noticed include:
1. Letter precedence effect: sometimes the whole word takes on the colour of the first letter. This is true even if the first letter is silent (at least in lower synaesthetes).
2. Font: upper case usually evokes more vivid colour. For lower-case letters the same colour is evoked but it is less saturated, more 'patchy' and 'shiny' — colour 'paraesthesiae', one is tempted to call them.
3. In a rare form of synaesthesia the subject classifies all graphemes (sometimes even objects) as being male or female or good or bad — a quirky manifestation of the universal human tendency to binarize entities in the world into polar opposites (hot/cold; good/evil; big/small; yin/yang, etc.). It is hard to explain this in terms of anatomy.
4. Galton noted that in some synaesthetes each number not only has a colour but occupies a particular location in space with the linear sequence of numbers arranged sequentially in space — a 'number line'. Often the subject claims the number line is convoluted — even doubling back on itself — so that 9 might be (say) nearer to 3 in Cartesian space than to 8. In normal individuals the reaction time for judging which of two numbers is bigger varies inversely with the numerical distance between them, as if they are laid out on a perfectly straight imaginary line in the brain, making it harder to discriminate numerically adjacent numbers. We have found this is not true for synaesthetes with convoluted number lines; their reaction times were some messy compromise between Cartesian distance and numerical distance.
5. When asked to 'imagine' or visualize a number, most lower synaesthetes report, paradoxically, that the colour evoked by the visualized number is actually more vivid than one evoked by a real black or white one. This is because top-down imagery activates the same sensory number areas in the fusiform as real images do — thereby evoking the colours — but in the case of a real number there is contradictory bottom-up information partially vetoing the synaesthetic colours. In the absence of such vetoing the colours are more vivid.
Why is synaesthesia much more common among artists, poets, and novelists? One thing they all have in common is a facility with metaphor, a propensity to link seemingly unrelated concepts (e.g. 'Juliet is the Sun', 'he has a sharp mind'). If the 'hyperconnectivity' gene is expressed more diffusely throughout the brain rather than locally, and if we assume that high-level concepts are also represented in brain maps, then the result would be a greater propensity for metaphor. This would explain the higher incidence of synaesthesia in arty types. This is a speculative idea that is not easy to test. But if correct it would explain why the apparently useless synaesthesia gene (if there is such a thing) has survived; it might confer creativity in some outliers.
Synaesthetic propensities might therefore exist in all of us. Consider the two abstract shapes in Fig. 1. If you ask people which one is 'Bouba' and which one 'Kiki'; more than 95 per cent pick the bulbous amoeboid shape as Bouba and the jagged shape as Kiki. (This is not because the jagged shape resembles K; even Tamil speakers make the same choice.) The effect suggests that we are all closet synaesthetes; the sharp inflections of the sound 'ki ki' mimic the sharp inflections of the jagged visual shapes, and the gentle undulation of contours in the amoeboid shapes corresponds to the sound 'bouba'. Since the subjects have never seen these shapes, or heard the sounds, before, there must be a pre-existing non-arbitrary cross-activation between visual shapes represented in the fusiform and sounds represented in the auditory cortex. Such cross-modal transl ation probably requires the mediation of the angular gyrus given its strategic anatomical location at the TPO junction — at the crossroads between visual (occiptal), auditory (temporal), and parietal (touch) areas of the brain.
Since the visual shape Kiki is composed of photons hitting the eyes in parallel whereas the sound kiki is delivered by sequential stimulation of hair cells of the inner ear, the two have nothing in common except the abstract property of jaggedness in Fourier space. What this ability represents, then, is a primitive form of the process of abstraction that humans excel in (e.g. when we say five rabbits, five tones, five unicorns, they have nothing common except fiveness). There are hints that the Bouba/Kiki effect is compromised when the angular gyrus is damaged.
The angular gyrus became progressively larger in primates, and is disproportionately large in the great apes and humans. Perhaps it was originally an adaptation for arboreal living, allowing the primate brain to match the seen visual orientation of a branch with its position felt through proprioception as the hand rotated to grab it. But once in place it could have been adapted for other more sophisticated types of abstraction of the kind that humans excel at.
Metaphors, too, incorporate synaesthetic elements, as when we say 'loud shirt'. Also, we use the word 'disgusting' and scrunch up our nose when confronting a bad taste or smell, but why do we also use the same word and expression for moral disgust? This may occur because olfactory and gustatory disgust are mapped in the orbitofrontal cortex which later became usurped in humans for representing morality and disgust. As Freud said, anatomy is destiny.
Thus synaesthesia, far from being a mere curiosity can provide key insights into some of the most elusive aspects of our mind, such as the emergence of metaphor and abstraction. Once the gene(s) is cloned we can go from the gene to anatomy (fusiform gyrus; angular gyrus) to psychophysics and phenomenology, perhaps all the way to the emergence of metaphor and abstract thought.
Fig. 1.
(Published 1987)
— V. S. Ramachandran/Richard L. Gregory
- Bibliography
- Armel, K. C., and Ramachandran, V. S. (1999). 'Acquired synesthesia in retinitis pigmentosa'. Neurocase, 5/4.
- Baron-Cohen, S., Burt, L., Smith-Laittan, F., Harrison, J., and Bolton, P. (1996). 'Synaesthesia: prevalence and familiarity'. Perception, 25/9.
- Cytowic, R. E. (2002). Synaesthesia: A Union of the Senses. (2nd edn.).
- Dehaene, S. (1997). The Number Sense: How the Mind Creates Mathematics.
- Domino, G. (1989). 'Synesthesia and creativity in fine arts students: an empirical look'. Creativity Research Journal, 2/1–2.
- Galton, F. (1997). 'Colour associations'. In Baron-Cohen, S., and Harrison, J. E. (eds.), Synaesthesia: Classic and Contemporary Readings.
- Merikle, P., Dixon, M. J., and Smilek, D. (2002). 'The role of synaesthetic photisms on perception, conception and memory'. Talk presented at the 12th Annual Meeting of the Cognitive Neuroscience Society, San Francisco, 14–16 Apr.
- Nunn, J. A., Gregory, L. J., Brammer, M., et al. (2002). 'Functional magnetic resonance imaging of synesthesia: activation of V4/V8 by spoken words'. Nature Neuroscience, 5/4.
- Ramachandran, V. S., and Hubbard, E. M. (2001a). 'Psychophysical investigations into the neural basis of synaesthesia'. Proceedings of the Royal Society of London, Series B, 268.
- — — (2001b) 'Synaesthesia: a window into perception, thought and language?' Journal of Consciousness Studies, 8/12.
- — — (2002). 'Synesthetic colors support symmetry perception, apparent motion, and ambiguous crowding'. Talk presented at the 43 Annual Meeting of the Psychonomics Society, 21–24 Nov.
- Zeki, S., and Marini, L. (1998). 'Three cortical stages of colour processing in the human brain'. Brain, 121.
| Poetry Glossary: Synesthesia or Synæsthesia |
The perception or description of one kind of sense impression in words normally used to describe a different sense, like a "sweet voice" or a "velvety smile." It can be very effective for creating vivid imagery.
| Wikipedia: Synesthesia |
For other uses, see Synesthesia (disambiguation).
Synesthesia (also spelled synæsthesia or synaesthesia, plural synesthesiae or synaesthesiae)—from the Ancient Greek σύν (syn), "together," and αἴσθησις (aisthēsis), "sensation"—is a neurologically based phenomenon in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. [1][2][3][4] People who report such experiences are known as synesthetes. In one common form of synesthesia, known as grapheme → color synesthesia or color-graphemic synesthesia, letters or numbers are perceived as inherently colored,[5][6] while in ordinal linguistic personification, numbers, days of the week and months of the year evoke personalities.[7][8] In spatial-sequence, or number form synesthesia, numbers, months of the year, and/or days of the week elicit precise locations in space (for example, 1980 may be "farther away" than 1990), or may have a (three-dimensional) view of a year as a map (clockwise or counterclockwise).[9][10][11] Yet another recently identified type, visual motion → sound synesthesia, involves hearing sounds in response to visual motion and flicker.[12] Over 60 types of synesthesia have been reported by people,[13] but only a fraction have been evaluated by scientific research.[14] Even within one type, synesthetic perceptions vary in intensity [15] and people vary in awareness of their synesthetic perceptions.[16]
While cross-sensory metaphors (e.g., "loud shirt," "bitter wind" or "prickly laugh") are sometimes described as "synesthetic," true neurological synesthesia is involuntary. It is estimated that synesthesia could possibly be as prevalent as 1 in 23 persons across its range of variants.[17] Synesthesia runs strongly in families, but the precise mode of inheritance has yet to be ascertained. Synesthesia is also sometimes reported by individuals under the influence of psychedelic drugs, after a stroke, during a temporal lobe epilepsy seizure, or as a result of blindness or deafness. Synesthesia that arises from such non-genetic events is referred to as "adventitious synesthesia" to distinguish it from the more common congenital forms of synesthesia. Adventitious synesthesia involving drugs or stroke (but not blindness or deafness) apparently only involves sensory linkings such as sound → vision or touch → hearing; there are few, if any, reported cases involving culture-based, learned sets such as graphemes, lexemes, days of the week, or months of the year.
Although synesthesia was the topic of intensive scientific investigation in the late 1800s and early 1900s, it was largely abandoned by scientific research in the mid-20th century, and has only recently been rediscovered by modern researchers.[18] Psychological research has demonstrated that synesthetic experiences can have measurable behavioral consequences, while functional neuroimaging studies have identified differences in patterns of brain activation.[6] Many people with synesthesia use their experiences to aid in their creative process, and many non-synesthetes have attempted to create works of art that may capture what it is like to experience synesthesia. Psychologists and neuroscientists study synesthesia not only for its inherent interest, but also for the insights it may give into cognitive and perceptual processes that occur in synesthetes and non-synesthetes alike.
Definitional criteria
Although sometimes spoken of as a "neurological condition," synesthesia is not listed in either the DSM-IV or the ICD classifications, since it most often does not interfere with normal daily functioning. It has, however, appeared for many years in both Dorland's and Steadman's medical dictionaries. Indeed most synesthetes report that their experiences are neutral, or even pleasant.[19] Rather, like color blindness or perfect pitch, synesthesia is a difference in perceptual experience and the term "neurological" simply reflects the brain basis of this perceptual difference. To date, no research has demonstrated a consistent association between synesthetic experience and other neurological or psychiatric conditions, although this is an active area of research (see below for associated cognitive traits).
It was once assumed that synesthetic experiences were entirely different from synesthete to synesthete, but recent research has shown that there are underlying similarities that can be observed when large numbers of synesthetes are examined together. For example, sound-color synesthetes, as a group, tend to see lighter colors for higher sounds[20] and grapheme-color synesthetes, as a group, share significant preferences for the color of each letter (e.g., A tends to be red; O tends to be white or black; S tends to be yellow etc.,[19][21][22]). Nonetheless, there are a great number of types of synesthesia, and within each type, individuals can report differing triggers for their sensations, and differing intensities of experiences. This variety means that defining synesthesia in an individual is difficult, and indeed, the majority of synesthetes are completely unaware that their experiences have a name.[19] However, despite the differences between individuals, there are a few common elements that define a true synesthetic experience.
Neurologist Richard Cytowic identifies the following diagnostic criteria of synesthesia:[1][2][3]
- Synesthesia is involuntary and automatic.
- Synesthetic perceptions are spatially extended, meaning they often have a sense of "location." For example, synesthetes speak of "looking at" or "going to" a particular place to attend to the experience.
- Synesthetic percepts are consistent and generic (i.e., simple rather than pictorial).
- Synesthesia is highly memorable.
- Synesthesia is laden with affect.
Cytowic's early cases included individuals whose synesthesia was frankly projected outside the body (e.g., on a "screen" in front of one's face). Later research showed that such stark externalization occurs in a minority of synesthetes. Refining this concept, Cytowic and Eagleman[3] differentiate between "localizers" and "non-localizers" to distinguish those synesthetes whose perceptions have a definite sense of spatial quality.
Experiences
Synesthetes 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, as has been documented in interviews with synesthetes on how they discovered synesthesia in their childhood.[14] The automatic and ineffable nature of a synesthetic experience means that the pairing may not seem out of the ordinary. This involuntary and consistent nature helps define synesthesia as a real experience. Most synesthetes report that their experiences are pleasant or neutral, although, in rare cases, synesthetes report that their experiences can lead to a degree of sensory overload.[19]
Though often stereotyped in the popular media as a medical condition or neurological aberration, synesthetes themselves do not experience their synesthetic perceptions as a handicap. To the contrary, most report it as a gift—an additional "hidden" sense—something they would not want to miss. Most synesthetes have become aware of their "hidden" and different way of perceiving in their childhood. Some have learned how to apply this gift in daily life and work. Synesthetes have used their gift in memorizing names and telephone numbers, mental arithmetic, but also in more complex creative activities like producing visual art, music, and theater.[14]
Despite the commonalities which permit definition of the broad phenomenon of synesthesia, individual experiences vary in numerous ways. This variability was first noticed early on in synesthesia research[23] but has only recently come to be re-appreciated by modern researchers. Some grapheme → color synesthetes report that the colors seem to be "projected" out into the world (called "projectors"), while most report that the colors are experienced in their "mind's eye" (called "associators").[24] It is estimated that approximately one or two per hundred grapheme-color synesthetes are projectors; the rest are associators.[24]
Additionally, some grapheme → color synesthetes report that they experience their colors strongly, and show perceptual enhancement on the perceptual tasks described below, while others (perhaps the majority) do not,[15] perhaps due to differences in the stage at which colors are evoked. Some synesthetes report that vowels are more strongly colored, while for others consonants are more strongly colored.[19] In summary, self reports, autobiographical notes by synesthetes and interviews show a large variety in types of synesthesia, intensity of the synesthetic perceptions, awareness of the difference in perceiving the physical world from other people, the way they creatively use their synesthesia in work and daily life.[14][25] The descriptions below give some examples of synesthetes' experiences, which have been experimentally tested, but do not exhaust their rich variety.
Various forms
Synesthesia can occur between nearly any two senses or perceptual modes. Given the large number 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 experience, and y is the "concurrent" or additional experience. For example, perceiving 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 as tone → (color, movement) synesthesia.
While nearly every logically possible combination of experiences can occur, several types are more common than others.
Grapheme → color synesthesia
In one of the most common forms of synesthesia, grapheme → color synesthesia, individual letters of the alphabet and numbers (collectively referred to as graphemes), are "shaded" or "tinged" with a color. While different individuals usually do not report the same colors for all letters and numbers, studies with large numbers of synesthetes find some commonalities across letters (e.g., A is likely to be red).[19][21]
As a child, Pat Duffy told her Dad, "I realized that to make an R all I had to do was first write a P and 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." Another grapheme synesthete says, "When I read, about five words around the exact one I'm reading are in color. It's also the only way I can spell. In elementary school I remember knowing how to spell the word 'priority' [with an "i" rather than an "e"] because ... an 'e' was out of place in that word because e's were yellow and didn't fit."[26]
Sound → color synesthesia
Cytowic calls sound → color synesthesia "something like fireworks": voice, music, and assorted environmental sounds such as clattering dishes or dog barks trigger color and simple shapes that arise, move around, and then fade when the sound stimulus ends.[3] For some, the stimulus type is limited (e.g., music only, or even just a specific musical key); for others, a wide variety of sounds triggers synesthesia.
Sound often changes the perceived hue, brightness, scintillation, and directional movement. Some individuals see music on a "screen" in front of their face. Deni Simon, for whom music produces waving lines "like oscilloscope configurations—lines moving in color, often metallic with height, width and, most importantly, depth. My favorite music has lines that extend horizontally beyond the 'screen' area."[3]
Though individuals hardly ever agree on what color a given sound is (composers Liszt and Rimsky-Korsakov famously disagreed on the colors of music keys), synesthetes show the same trends as non-synesthetes do. For example, both groups say that louder tones are brighter than soft tones, higher ones are smaller and brighter than low ones, and low tones are both larger and darker than high ones.
Number form synesthesia
A number form is a mental map of numbers, which automatically and involuntarily appears whenever someone who experiences number-forms thinks of numbers. Number forms were first documented and named by Francis Galton in "The Visions of Sane Persons".[27] Later research has identified them as a type of synesthesia.[10][11] In particular, it has been suggested that number-forms are a result of "cross-activation" between regions of the parietal lobe that are involved in numerical cognition and spatial cognition.[28][29] In addition to its interest as a form of synesthesia, researchers in numerical cognition have begun to explore this form of synesthesia for the insights that it may provide into the neural mechanisms of numerical-spatial associations present unconsciously in everyone.
Personification
Ordinal-linguistic personification (OLP, or personification for short) is a form of synesthesia in which ordered sequences, such as ordinal numbers, days, months and letters are associated with personalities.[7][30] Although this form of synesthesia was documented as early as the 1890s[23][31] modern research has, until recently,[1] paid little attention to this form.
For example, one synesthete says, "T’s are generally crabbed, ungenerous creatures. U is a soulless sort of thing. 4 is honest, but… 3 I cannot trust… 9 is dark, a gentleman, tall and graceful, but politic under his suavity." [31] Likewise, Cytowic's subject MT says, "I [is] a bit of a worrier at times, although easy-going; J [is] male; appearing jocular, but with strength of character; K [is] female; quiet, responsible...."[1]
For some people in addition to numbers and other ordinal sequences, objects are sometimes imbued with a sense of personality. Recent research has begun to show that alphanumeric personification co-varies with other forms of synesthesia, and is consistent and automatic, as required to be considered a form of synesthesia.[7]
Lexical → gustatory synesthesia
In the rare lexical → gustatory synesthesia, individual words and the phonemes of spoken language evoke taste sensations in the mouth. According to James Wannerton, "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."
Jamie Ward and Julia Simner have extensively studied this form of synesthesia, and have found that the synesthetic associations are constrained by early food experiences.[32][33] For example, James Wannerton has no synesthetic experiences of coffee or curry, even though he consumes them regularly as an adult. Conversely, he tastes certain breakfast cereals and candies that are no longer sold.
Additionally, these early food experiences are often paired with tastes based on the phonemes in the name of the word (e.g., /I/, /n/ and /s/ trigger James Wannerton’s taste of mince) although others have less obvious roots (e.g., /f/ triggers sherbet). To show that phonemes, rather than graphemes are the critical triggers of tastes, Ward and Simner showed that, for James Wannerton, the taste of egg is associated to the phoneme /k/, whether spelled with a "c" (e.g., accept), "k" (e.g., York), "ck" (e.g., chuck) or "x" (e.g., fax). Another source of tastes comes from semantic influences, so that food names tend to taste of the food they match, and the word "blue" tastes "inky."
Research history
The interest in colored hearing dates back to Greek antiquity, when philosophers asked if the color (chroia, what we now call timbre) of music was a quantifiable quality.[34] Isaac Newton proposed that musical tones and color tones shared common frequencies, as did Goethe in his book, "Theory of Color." Despite this idea being false, there is a long history of building color organs such as the clavier à lumières on which to perform colored music in concert halls[35][36][37]
The first medical description of colored hearing is in a German 1812 thesis.[38] The father of psychophysics, Gustav Fechner reported the first empirical survey of colored letter photisms among 73 synesthetes in 1871,[39][40] followed in the 1880s by Francis Galton.[9][41][42] Research into synesthesia proceeded briskly in several countries, but due to the difficulties in measuring subjective experiences and the rise of behaviorism, which made the study of any subjective experience taboo, synesthesia faded into scientific oblivion between 1930 and 1980.
As the 1980s cognitive revolution began to make inquiry into internal subjective states respectable again, scientists once again looked to synesthesia. Led in the United States by Larry Marks and Richard Cytowic, and later in England by Simon Baron-Cohen and Jeffrey Gray, research explored the reality, consistency, and frequency of synesthetic experiences. In the late 1990s, the focus settled on grapheme → color synesthesia, one of the most common[19][22] and easily studied types. Synesthesia is now the topic of scientific books and papers, Ph.D. theses, documentary films, and even novels.
Since the rise of the Internet in the 1990, synesthetes began contacting one another and creating Web sites devoted to the condition. These early grew into international organizations such as the American Synesthesia Association, the UK Synaesthesia Association, the Belgian Synaesthesia Association, the German Synesthesia Association and the Netherlands Synesthesia Web Community.
Prevalence and genetic basis
Early estimates of prevalence varied widely (from 1 in 20 to 1 in 20,000). These studies all had the methodological shortcoming of relying on self-selection, meaning individuals reporting their experience to investigators. Random population studies later determined that 1 in 23 individuals have some kind of synesthesia, while 1 in 90 have colored graphemes.[17] Colored days of the week and colored graphemes are the most common types.[17][19]
Many studies noted that synesthesia runs in families, consistent with a genetic origin for the condition. Francis Galton's 1880 report noted a familial component. Studies from the 1990s[43][44] that noted a much higher prevalence in women than men (up to 6:1) most likely suffered from a sampling bias due to the fact that women are more likely to self-disclose than men. More recent random samples find an equal sex ratio of 1.1:1.[17]
At first, the observed patterns of inheritance were consistent with an X-linked mode of inheritance because there had been no verified reports of father-to-son transmission, whereas father-to-daughter, mother-to-son and mother-to-daughter transmission were readily observed[1][44][45] However, the first genome-wide association study failed to find X-linkage,[46] and furthermore verified two cases of father-to-son transmission.
Suggestive of incomplete gene penetrance is the situation of identical twins in which only one member of the pair is synesthetic,[47][48] and the observation that synesthesia can skip generations within a family.[49]. It is furthmore common for family members to experience different types of synesthesia, suggesting that the gene(s) involved do not lead to invariably specific types of synesthesia.[45] Developmental factors such as gene expression and environment must also play a role in determining which types of synesthesia an individual has (for example, children must interact with culturally-learned artifacts such as alphabets and food names).
Objective verification
Synesthesia is hard to fake, and easy to prove as a genuine perception. The simplest approach is test-retest reliability over long periods of time, where synesthetes consistently score much higher—around 90% after years, compared to 30-40% after just a month in non-synesthetes even when they are warned they will be retested—using stimuli of color names, color chips, or a computer-screen color picker providing 16.7 million choices.[1][44]
Modified versions of the Stroop effect are popular. In the standard paradigm, it is harder to name the ink color of the word "red," for example, when it is printed in blue ink than when the ink is red. Similarly, if a grapheme → color synesthete is shown the digit 4 (which he sees as red, say) in blue ink, he is slower to name the ink color than when it is printed in red. He sees the blue ink, but the same sort of conflict responsible for the standard Stroop effect occurs between the ink color and the automatic synesthetic color of the grapheme. The conflict is strongest when the ink color is the opponent color to the synesthetic one (e.g., red vs. green), indicating that synesthetic color perception uses the same mechanism as the perception of real colors.[50]
Cross-sensory Stroop tests are possible: for example, a music → color synesthete must name a red swatch while listening to a sound that produces a blue sensation,[51] or a musical key → taste synesthete must identify a bitter taste while hearing a musical interval that tastes sweet .[52] Likewise, Stroop tests work even in those for whom merely thinking about a numeral elicits color. Take a person who sees 7 as yellow and 9 as blue, and make the task one of having to say a math solution out loud followed by naming a color square. In the illustration, having to answer “7” and then “yellow” is congruent with the subject’s synesthesia, which unconsciously primes him to respond faster than controls. The automatic blueness of 9, however, interferes with naming the green square, slowing him down compared to controls.
Synesthetic colors can also improve performance for some synesthetes. Inspired by tests for color blindness, Ramachandran and Hubbard presented synesthetes and non-synesthetes with a matrix of 5s in which embedded 2s formed a hidden pattern such as a square, diamond, rectangle or triangle.[28]. For someone who sees 2s as red and 5s as green, for example, synesthetic colors help zero in on the embedded figure. Subsequent careful studies have found substantial variability among synesthetes in their ability to do this.[15][24] It certainly does not happen instantaneously; while synesthesia is evoked very early in perceptual processing, it does not occur prior to attention.[53][54]
Possible neural basis
Dedicated regions of the brain are specialized for given functions. Increased cross-talk between regions specialized for different functions may account for the many types of synesthesia. For example, the additive experience of seeing color when looking at graphemes might be due to cross-activation of the grapheme-recognition area and the color area called V4 (see figure).[28] One line of thinking is that a failure to prune synapses that are normally formed in great excess during the first few years of life may cause such cross-activation.
An alternate possibility is disinhibited feedback, or a reduction in the amount of inhibition along normally existing feedback pathways.[55] Normally, excitation and inhibition are balanced. However, if normal feedback were not inhibited as usual, then signals feeding back from late stages of multi-sensory processing might influence earlier stages such that tones could activate vision. Cytowic & Eagleman find support for the disinhibition idea in the so-called acquired forms[3] of synesthesia that occur in non-synesthetes under certain conditions: Temporal lobe epilepsy, head trauma, stroke, and brain tumors. It can likewise occur during stages of meditation, deep concentration, sensory deprivation, or with use of psychedelics such as LSD or mescaline, and certain prescription medications.
Functional neuroimaging studies using PET and fMRI demonstrate significant differences between the brains of synesthetes and non-synesthetes. fMRI shows V4 activation in both word → color and grapheme → color synesthetes.[15][56][57] Diffusion tensor imaging allows visualization of white matter fiber pathways in the intact brain. This method demonstrates increased connectivity in fusiform gyrus, intraparietal sulcus and frontal cortex in grapheme-color synesthetes.[58] The degree of white matter connectivity in the fusiform gyrus correlates with the intensity of the synesthetic experience.
Associated cognitive traits
Little is known about what, if any, cognitive traits might be associated with synesthesia. As early as 1980, Richard Cytowic first noted mild difficulties in left-right confusion, arithmetic, and sense of direction.[1] These observations await large-scale confirmation. What has been confirmed is elevated, sometimes photographic, memory.[59] When asked, "What good is it?" synesthetes say, "It helps me remember." Indeed, it was reading Alexander Luria's 1968 book The Mind of a Mnemonist that alerted Cytowic to the link between synesthesia and elevated memory: Luria's subject had a 5-fold synesthesia that gave him extra hooks on which to hang and remember numerous facts.
Autism and epilepsy occur with synesthesia more often than chance predicts. Daniel Tammet, the savant who set a European record for reciting the digits of pi, has all three conditions indicating that they might share an underlying genetic cause. Synesthesia has so far been linked to a region on chromosome 2 that is associated with autism and epilepsy.[46]
Synesthetes are likely to participate in creative activities.[22][60][61] Individual development of perceptual and cognitive skills, and one's cultural environment likely determine the variety in awareness and practical use of synesthetic skills[25][16] These are major topics of ongoing research.
Links with other areas of study
Researchers study synesthesia not only because it is inherently interesting, but also because studying it can offer insights into other questions, such as how the brain combines information from different sensory modalities, referred to as crossmodal perception and multisensory integration.
An example of this is the bouba/kiki effect. In an experiment first designed by Wolfgang Köhler, people are asked to choose which of two shapes is named bouba and which kiki. 95% to 98% of people choose kiki for the angular shape and bouba for the rounded one. Individuals on the island of Tenerife showed a similar preference between shapes called takete and maluma. Even 2.5 year-old children (too young to read) show this effect.[62]
Ramachandran and Hubbard suggest the kiki/bouba effect has implications for the evolution of language, because the naming of objects is not completely arbitrary.[28] The rounded shape may intuitively be named bouba because the mouth makes a more rounded shape to produce that sound, while a more taut, angular mouth shape is needed to articulate kiki. The sound of K is also harder and more forceful than that of B. Such "synesthesia-like mappings" suggest that this effect might be the neurological basis for sound symbolism, in which sounds are non-arbitrarily mapped to objects and actions in the world.
Given synesthetes' extraordinary conscious experiences, researchers hope that their study will provide better understanding of consciousness and its neural correlates, meaning what the brain mechanisms that make us conscious might be. In particular, synesthesia might be relevant to the philosophical problem of qualia,[4][28][63] given that synesthetes experience extra qualia (e.g., a colored sound).
Artistic investigations
The word "synesthesia" has been used for 300 years to describe very different things, from poetry and metaphor to deliberately contrived mixed-media applications such as son et lumière shows or odorama. It is crucial to separate artists using synesthesia as an intellectual idea—pseudo-synesthetes such as Georgia O'Keeffe who used such titles as "Music-Pink and Blue"—from those who had the genuine perceptual variety, such as Wassily Kandinsky or Olivier Messiaen.
Synesthetic art historically refers to multi-sensory experiments in the genres of visual music, music visualization, audiovisual art, abstract film, and intermedia.[14][18][64][65][66][67] Distinct from neuroscience, the concept of synesthesia in the arts is regarded as the simultaneous perception of multiple stimuli in one gestalt experience.[68] Only recently can science verify and study synesthesia in artists; for deceased artists, one must interpret (auto)biographical information.
Synesthetic art can refer to either art created by synesthetes or art that attempts to convey the synesthetic experience. It is an attempt to understand the relation between the experiences of born synesthetes, non-synesthetes, and an appreciation of such art by both groups. These distinctions are not mutually exclusive given that art by a synesthete might also evoke synesthesia-like experiences in the viewer.
Contemporary synesthetic artists such as Carol Steen[69] and Marcia Smilack[70] have described in detail how they use their synesthesia to create their artworks. They demonstrate the complex interplay between personal experience and artistic creation.
Synesthesia has been a source of inspiration for artists, composers, poets, novelists, and digital artists. Nabokov writes explicitly about synesthesia in several novels. Kandinsky (a synesthete) and Mondrian (not a synesthete) both experimented with image-music correspondences in their paintings. Scriabin composed color music that was deliberately contrived and based on the circle of fifths, whereas Messiaen invented a new method of composition (the modes of limited transposition) to specifically render his bi-directional sound-color synesthesia. For example, the red rocks of Bryce Canyon are depicted in his symphony Des canyons aux étoiles ("From the Canyons to the Stars"). New art movements such as literary symbolism, non-figurative art, and visual music have profited from experiments with synesthetic perception and contributed to the public awareness of synesthetic and multi-sensory ways of perceiving.[14]
Literary depictions
Synesthesia is sometimes used as a plot device or way of developing a character's inner life. Author and synesthete Pat Duffy describes four ways in which synesthetic characters have been used in modern fiction.
- Synesthesia as Romantic ideal: in which the condition illustrates the Romantic ideal of transcending one's experience of the world. Books in this category include The Gift by Vladimir Nabokov.
- Synesthesia as pathology: in which the trait is pathological. Books in this category include The Whole World Over by Julia Glass.
- Synesthesia as Romantic pathology: in which synesthesia is pathological but also provides an avenue to the Romantic ideal of transcending quotidian experience. Books in this category include Holly Payne’s, The Sound of Blue.
- Synesthesia as psychological health and balance: Painting Ruby Tuesday by Jane Yardley, and A Mango-Shaped Space by Wendy Mass.
Many literary depictions of synesthesia are not accurate. Some say more about an author's interpretation of synesthesia than the phenomenon itself.
In Mary Shelley's Frankenstein, the creature describes being in a synesthetic state early in his existence even though the phenomenon was not well documented when the book was written.[71]
People with synesthesia
Determining synesthesia from the historical record is fraught with error unless (auto)biographical sources explicitly give convincing details.
Famous synesthetes include David Hockney, who perceives music as color, shape, and configuration, and who uses these perceptions when painting opera stage sets but not while creating his other artworks.[72] Russian painter Wassily Kandinsky combined four senses: color, hearing, touch, and smell.[3] Vladimir Nabokov describes his grapheme-color synesthesia at length in his autobiography, Speak Memory, and portrays it in some of his characters.[73] Composers include Duke Ellington,[74] Franz Liszt,[75] Nikolai Rimsky-Korsakov,[76] and Olivier Messiaen, whose three types of complex colors are rendered explicitly in musical chord structures that he invented.[3][77] Physicist Richard Feynman describes his colored equations in his autobiography, What Do You Care What Other People Think?[78] Other notable synesthetes include musicians John Mayer and Patrick Stump; actress Stephanie Carswell; electronic musician Aphex Twin (who claims to be inspired by lucid dreams as well as music); and classical pianist Hélène Grimaud. Although it has not been verified, Pharrell Williams of the hip-hop Neptunes and N.E.R.D. claims to experience synesthesia,[79] and to have used it as the basis of the album Seeing Sounds.
Some artists frequently mentioned as synesthetes did not in fact have the condition. Alexander Scriabin's 1911 Prometheus, for example, is a deliberate contrivance whose color choices are based on the circle of fifths and appear to have been taken from Madame Blavatsky.[3][80] The musical score has a separate staff marked luce whose "notes" are played on a color organ. Technical reviews appear in period volumes of Scientific American.[3]
French poets Arthur Rimbaud and Charles Baudelaire wrote of synesthetic experience but there is no evidence they were synesthetes themselves. Baudelaire's 1857 Correspondances (text available here) introduced the notion that the senses can and should intermingle. Baudelaire participated in a hashish experiment by psychiatrist Jacques-Joseph Moreau, and became interested in how the senses might correspond.[14] Rimbaud later wrote Voyelles (1871) (text available here), which was perhaps more important than Correspondances in popularizing synesthesia, although he later boasted "J'inventais la couleur des voyelles!" [I invented the colors of the vowels!].
Sean Day, synesthete and the President of the American Synesthesia Association, maintains a list of famous synesthetes, pseudosynesthetes, and non-synesthetes who used synesthesia in their art or music.
See also
- Audiovisual art
- Ideophone
- Perception
- Parosmia
- Theory of multiple intelligences (using multiple senses)
- Visual music
- The Yellow Sound
References
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- ^ a b c d e f g h i j k l Cytowic, Richard E; Eagelman, David M (2009). Wednesday is Indigo Blue: Discovering the Brain of Synesthesia (with an afterword by Dmitri Nabokov). Cambridge: MIT Press. pp. 309. ISBN 0-262-01279-9.
- ^ a b Harrison, John E.; Simon Baron-Cohen (1996). Synaesthesia: classic and contemporary readings. Oxford: Blackwell Publishing. ISBN 0-631-19764-8. OCLC 59664610.
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- ^ "Slashdot Discussion". 2006-02-19. http://slashdot.org/comments.pl?sid=140022&cid=11726211. Retrieved on 2006-08-14.
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- ^ Gage, J. Colour and Culture. Practice and Meaning from Antiquity to Abstraction. (London:Thames & Hudson, 1993).
- ^ Peacock, Kenneth. "Instruments to Perform Color-Music: Two Centuries of Technological Experimentation," Leonardo 21, No. 4 (1988) 397-406.
- ^ Jewanski, J. & N. Sidler (Eds.). Farbe - Licht - Musik. Synaesthesie und Farblichtmusik. Bern: Peter Lang, 2006.
- ^ Peacock, Kenneth. "Instruments to Perform Color-Music: Two Centuries of Technological Experimentation," Leonardo 21, No. 4 (1988) 397-406.
- ^ Mahling, F. (1926) Das Problem der `audition colorée': Eine historisch-kritische Untersuchung. Archiv für die gesamte Psychologie, 57, 165-301.
- ^ Fechner, Th. (1871) Vorschule der Aesthetik. Leipzig: Breitkopf und Hartel.
- ^ Campen, Cretien van (1996). De verwarring der zintuigen. Artistieke en psychologische experimenten met synesthesie. Psychologie & Maatschappij, vol. 20, nr. 1, pp. 10-26.
- ^ Galton F (1880). "Visualized Numerals". Nature 21: 252–6. doi:.
- ^ Galton F. (1883). Inquiries into Human Faculty and Its Development. Macmillan. http://galton.org/books/human-faculty/. Retrieved on 2008-06-17.
- ^ Baron-Cohen S, Harrison J, Goldstein LH, Wyke M (1993). "Coloured speech perception: is synaesthesia what happens when modularity breaks down?". Perception 22 (4): 419–26. doi:. PMID 8378132.
- ^ a b c Baron-Cohen S, Burt L, Smith-Laittan F, Harrison J, Bolton P (1996). "Synaesthesia: prevalence and familiality". Perception 25 (9): 1073–9. doi:. PMID 8983047.
- ^ a b Ward J, Simner J (2005). "Is synaesthesia an X-linked dominant trait with lethality in males?". Perception 34 (5): 611–23. doi:. PMID 15991697.
- ^ a b Asher, JE, Lamb, JA, Brocklebank, D, et al. (2009). "A whole-genome scan and fine-mapping linkage study of auditory-visual synesthesia reveals evidence of linkage to chromosomes 2q24, 5q33, 6p12, and 12p12". The American Journal of Human Genetics 84: 1–7. doi:.
- ^ Smilek D, Moffatt BA, Pasternak J, White BN, Dixon MJ, Merikle PM (2002). "Synaesthesia: a case study of discordant monozygotic twins". Neurocase 8 (4): 338–42. doi:. PMID 12221147.
- ^ Smilek D, Dixon MJ, Merikle PM (October 2005). "Synaesthesia: discordant male monozygotic twins". Neurocase 11 (5): 363–70. doi:. PMID 16251137. http://www.informaworld.com/openurl?genre=article&doi=10.1080/13554790500205413&magic=pubmed.
- ^ Hubbard EM, Ramachandran VS (2003). "Refining the experimental lever: A reply to Shanon and Pribram" (PDF). Journal of Consciousness Studies 10 (3): 77–84. http://psy.ucsd.edu/~edhubbard/papers/Hubbard_JCS03.pdf.
- ^ Nikolić D, Lichti P, Singer W (June 2007). "Color opponency in synaesthetic experiences". Psychol Sci 18 (6): 481–6. doi:. PMID 17576258. http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=0956-7976&date=2007&volume=18&issue=6&spage=481.
- ^ Ward J, Tsakanikos E, Bray A (February 2006). "Synaesthesia for reading and playing musical notes". Neurocase 12 (1): 27–34. doi:. PMID 16517513. http://www.informaworld.com/openurl?genre=article&doi=10.1080/13554790500473672&magic=pubmed.
- ^ Beeli G, Esslen M, Jäncke L (March 2005). "Synaesthesia: when coloured sounds taste sweet". Nature 434 (7029): 38. doi:. PMID 15744291.
- ^ Edquist J, Rich AN, Brinkman C, Mattingley JB (February 2006). "Do synaesthetic colours act as unique features in visual search?". Cortex 42 (2): 222–31. doi:. PMID 16683496.
- ^ Sagiv N, Heer J, Robertson L (February 2006). "Does binding of synesthetic color to the evoking grapheme require attention?". Cortex 42 (2): 232–42. doi:. PMID 16683497.
- ^ Grossenbacher PG, Lovelace CT (January 2001). "Mechanisms of synesthesia: cognitive and physiological constraints". Trends Cogn. Sci. 5 (1): 36–41. doi:. PMID 11164734. http://linkinghub.elsevier.com/retrieve/pii/S1364-6613(00)01571-0.
- ^ Nunn JA, Gregory LJ, Brammer M, et al. (April 2002). "Functional magnetic resonance imaging of synesthesia: activation of V4/V8 by spoken words". Nat. Neurosci. 5 (4): 371–5. doi:. PMID 11914723.
- ^ Sperling JM, Prvulovic D, Linden DE, Singer W, Stirn A (February 2006). "Neuronal correlates of colour-graphemic synaesthesia: a fMRI study". Cortex 42 (2): 295–303. doi:. PMID 16683504.
- ^ Rouw R, Scholte HS (June 2007). "Increased structural connectivity in grapheme-color synesthesia". Nat. Neurosci. 10 (6): 792–7. doi:. PMID 17515901.
- ^ Smilek D, Dixon MJ, Cudahy C, Merikle PM (2002). "Synesthetic color experiences influence memory.". Psychological Science 13 (6): 548–52. doi:.
- ^ Domino G (1989). "Synesthesia and Creativity in Fine Arts Students: An Empirical Look.". Creativity Research Journal 2 (1-2): 17–29.
- ^ Dailey A, Martindale C, Borkum J (1997). "Creativity, synesthesia, and physiognomic perception.". Creativity Research Journal 10 (1): 1–8. doi:.
- ^ Maurer D, Pathman T, Mondloch CJ (May 2006). "The shape of boubas: sound-shape correspondences in toddlers and adults". Dev Sci 9 (3): 316–22. doi:. PMID 16669803. http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=1363-755X&date=2006&volume=9&issue=3&spage=316.
- ^ Gray JA, Chopping S, Nunn J et al. (2002). "Implications of synaesthesia for functionalism: Theory and experiments". Journal of Consciousness 9 (12): 5–31.
- ^ Berman G (1999). "Synesthesia and the Arts". Leonardo 32 (1): 15–22. doi:.
- ^ Maur, Karin von (1999). The Sound of Painting: Music in Modern Art (Pegasus Library). Munich: Prestel. ISBN 3-7913-2082-3.
- ^ Gage, John D. (1993). Colour and culture: practice and meaning from antiquity to abstraction. London: Thames and Hudson. ISBN 0-500-27818-0.
- ^ Gage, John D. (1999). Color and meaning: art, science, and symbolism. Berkeley: University of California Press. ISBN 0-520-22611-9.
- ^ Campen, Cretien van (2009) Visual Music and Musical Paintings. The Quest for Synesthesia in the Arts. In: F. Bacci & D. Melcher. Making Sense of Art, making Art of Sense. Oxford: Oxford University Press.
- ^ Steen, C. (2001). Visions Shared: A Firsthand Look into Synesthesia and Art, Leonardo, Vol. 34, No. 3, Pages 203-208 (doi:10.1162/002409401750286949)
- ^ Marcia Smilack Website Accessed 20 Aug 2006.
- ^ E-text of Mary Shelley's Frankenstein, see p. 86.
- ^ see Cytowic, Richard E. 2002. Synesthesia: a Union of the Senses. Second edition. Cambridge, Massachusetts: MIT Press, and Cytowic, R.E. & Eagleman, D.M. (2009) Wednesday is Indigo Blue." Cambridge: MIT Press
- ^ Nabokov, Vladimir. 1966. Speak, Memory: An Autobiography Revisited. New York: Putnam.
- ^ Ellington, as quoted in George, Don. 1981. Sweet man: The real Duke Ellington. New York: G.P. Putnam’s Sons. Page 226.
- ^ Quoted from an anonymous article in the Neuen Berliner Musikzeitung (29 August, 1895); quoted in Mahling, Friedrich. 1926. "Das Problem der 'Audition colorée: Eine historische-kritische Untersuchung." Archiv für die Gesamte Psychologie; LVII Band. Leipzig: Akademische Verlagsgesellschaft M.B.H. Pp. 165-301. Page 230. Translation by Sean A. Day.
- ^ according to the Russian press: Yastrebtsev V. "On N.A.Rimsky-Korsakov's color sound- contemplation." Russkaya muzykalnaya gazeta, 1908, N 39-40, p. 842-845 (in Russian), cited by Bulat Galeyev (1999).
- ^ see Samuel, Claude. 1994 (1986). Olivier Messiaen: Music and Color. Conversations with Claude Samuel. Translated by E. Thomas Glasow. Portland, Oregon: Amadeus Press.
- ^ Feynman, Richard. 1988. What Do You Care What Other People Think? New York: Norton. P. 59.
- ^ It just always stuck out in my mind, and I could always see it. I don't know if that makes sense, but I could always visualize what I was hearing... Yeah, it was always like weird colors." From a Nightline interview with Pharrell
- ^ Dann, Kevin T. (1998). Bright colors falsely seen: synaesthesia and the search for transcendental knowledge. New Haven, Conn: Yale University Press. ISBN 0-300-06619-8.
Further reading
- Baron-Cohen, S. and Harrison, J. (Eds., 1997). Synaesthesia: Classic and Contemporary Readings. Oxford: Blackwell Publishers. ISBN 0-631-19764-8.
- Bosch, P. (2007) The Name of This Book is Secret Little, Brown Young Readers. ISBN 978-0-31-611366-3.
- Campen, Cretien van. (2007) The Hidden Sense. Synesthesia in Art and Science. Cambridge, MA: MIT Press/Leonardo Books. ISBN 0-262-22081-4
- Cytowic, R.E. (2003)The Man Who Tasted Shapes. Cambridge: MIT Press ISBN 978-0-26-253456-6.
- Cytowic, R.E. (2002) Synesthesia: A Union of The Senses, second edition. Cambridge: MIT Press ISBN 978-0-26-2032964.
- Cytowic, R.E. & Eagleman, D.M. (2009) Wednesday is Indigo Blue: Discovering the Brain of Synesthesia, with an afterword by Dmitri Nabokov. Cambridge: MIT Press ISBN 978-0-26-201279-9.
- Dann, K. (1998). Bright Colors Falsely Seen. Cambridge: Harvard University Press. ISBN 0-300-06619-8.
- Duffy, P. L. (2001). Blue Cats and Chartreuse Kittens: How Synesthetes Color their Worlds. New York: Henry Holt & Company. ISBN 0-7167-4088-5.
- Harrison, J. (2001). Synaesthesia: The Strangest Thing. Oxford: Oxford University Press. ISBN 0-19-263245-0.
- Jay, C. (2009) Breathing in Colour. Little, Brown. ISBN 978-0-74-992978-7.
- Robertson, L. and Sagiv, N. (Eds., 2005). Synesthesia: Perspectives from Cognitive Neuroscience. Oxford: Oxford University Press. ISBN 0-19-516623-X.
- Tammet, D. (2006) Born on a Blue Day: A Memoir of Aspergers and an Extraordinary Mind. Hodder & Stoughton Ltd. ISBN 978-0-34-089974-8.
- Mass, W. (2003) A Mango-Shaped Space. Little, Brown and Company. ISBN 0-316-52388-7
- Ward, J. (2008) The Frog who croaked Blue: Synesthesia and the Mixing of the Senses. Routledge. ISBN 978-0-415-43014-2.
External links
Scientific resources
- Richard E. Cytowic Downloads, videos, and information.
- David Eagleman's Synesthesia Battery: take the test to see if you are synesthetic.
- Edward M. Hubbard Synesthesia research, pdf scientific articles.
- Synesthetics by Cretien van Campen Artistic and scientific experiments, historical background.
- Jamie Ward Information and article links.
Synesthesia associations
- American Synesthesia Association
- Australian Synaesthesia Association
- Belgian Synesthesia Association
- UK Synaesthesia Association
- German Synaesthesia Association | Deutsche Synästhesie-Gesellschaft e.V.
Community sites
- The Synesthesia List Sean Day's moderated e-mail forum for synesthtetes and researchers
- Synaesthete.com A forum, with a section for teenage synesthetes.
- Synesthesia in Art and Science Bibliography compiled by Cretien van Campen for Leonardo/ISAST
- The Nexus discussion forum
- Blue Cats Resource Center by Patricia Lynne Duffy
- A community on livejournal.com
- synaesthesia.com: international synaesthesia community (synaesthesia-tests, workshops, Infos)
On the Web
- TED Blog, including video links to V. S. Ramachandran's TED talk.
- Cytowic's video lecture at the Smithsonian's Hirshhorn Museum Visual Music exhibit. Four-part YouTube version [2].
- Scientific American article Hearing Colors, Tasting Shapes (PDF version) by Ramachandran & Hubbard, May 2003.
- Cortex: Special Issue on Cognitive Neuroscience Perspectives on Synesthesia.
- Campen, Cretien van (2009), The Hidden Sense: On Becoming Aware of Synesthesia, TECCOGS , vol. 1, pp. 1–13.
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