Synesthesia & metaphor — I’m not feeling it

Wired online carried a story recently on a talk by ‘neuroscientist extraordinaire’ V.S. Ramachandran, one of the folks responsible for a lot of creative thinking in the brain sciences. Brandom Keim writes on a recent talk Ramachandran gave at the World Science Festival in a story, Poetry Comes from Our Tree-Climbing Ancestors, Neuroscientist Says. While I typically find his stuff both fascinating and resonant, this particular piece left me unpersuaded.

Normally, I might take issue with the sloppy logic of the title (‘poetry’ coming from ‘tree-climbing ancestors’ being a dangerous conflation between non-proximate contributing factors and eventual effects — you could just as logically say that ‘poetry comes from spinning disk of post-stellar material in proto-solar system’…), but I’ve got bigger fish to fry: synesthesia.

Rmachandran’s work on synesthesia is excellent; for example, his piece with in Neuron on synesthesia is essential reading, and the piece he co-authored on the condition in Scholarpedia is my source for a fair bit of what I will write. The problem is that I don’t think that synesthesia is a good metaphor for, well, metaphor.

Although there may be some ways that metaphor is like synesthesia, when we add up the pros and cons, synesthesia as a metaphor for metaphor may not help us too much to understand the latter, and I seriously doubt that the two are linked in a more profound causal fashion (like a ‘gene’ for both synesthesia and metaphor). Similarly, attention-based failure to perceive something may be like blindness, but using one to try to explain the other is futile. In other words, not all metaphors are equally useful, and I’m concerned that the synesthesia metaphor for metaphor might do more harm than good.

Synesthesia is a neurological condition in which stimulation in one sensory channel causes involuntary sensations in another. For example, in grapheme, or color synesthesia, letters or numbers are perceived as having inherent colours; in ordinal linguistic personification, numbers, days of the week and months are perceived to have personalities; and in spatial-sequence, or number form synesthesia, numbers, days of the week or months elicit precise locations in space, or are perceived as occurring in topographical relationships (this is closely paraphrased from the Wikipedia article on synesthesia). Although the condition (it’s not really a ‘disorder’) was once thought very rare, but now some sources say that it may occur in around 4% of the population.

Synesthesia has been getting a lot of press of late for reasons that are not entirely clear to me. There’s a small (and probably not terribly lucrative) cottage industry on the boundary zone of social sciences and humanities where ‘synesthesia’ gets a lot of mileage. It appears to me to be part of a rethinking of psychological disorders into analogues for large-scale socio-cultural processes or global ethos, such as looking at Western society as schizophrenic or economics as autistic. While this has the agreeable side effect of pointing out that the gap between ‘disordered’ and ‘ordered’ development is perhaps not so great (and it can be great fun), it’s not clear that it always provides perfect analogues.

Part of the confusion produced by treating synesthesia as a metaphor for metaphor seems to stem from its use by Marshall McLuhan to discuss the effects of media (see James C. Morrison, Hypermedia and Synesthesia). While evocative, it’s not really a fair metaphor, in my opinion, and the farther we follow its implications, the worse it gets.

For example, if I say that many people are ‘paralyzed’ by fears about global climate change, that doesn’t necessarily mean that studying they neurological phenomenon of paralysis will necessarily get me any better understanding of the psychological reaction to fear of the planet warming. That is, a metaphor is a limited cognitive tool, an annalogic lens that highlights certain characteristics, but also with many other non-comparable traits; the metaphoric equation of synesthesia to creative metaphor may be implying many traits that are not equivalent.

In fact, cross-modal sensory associations are pretty damn interesting, and they are robust neurological phenomena; Ramachandran’s work has elsewhere helped to highlight how the human brain might be making this cross modal connections. But synesthesia is a very peculiar cross-modal connection, unlike metaphor in several crucial ways:

First, synesthetic associations are stable: two is always blue to a person, or Monday always has a particular personality, say grumpy.

Second, synesthetic associations are involuntary; there’s no getting around experiencing blue when you count two, and you can’t have a madcap Monday if that’s not your association.

Third, synesthetic associations are cross-modal and unidirectional; my sensory conflating between number and personality does not switch but keeps to a particular pairing of sensory channels, and it only tends to work in one direction. Two is blue, but it doesn’t necessarily suddenly seem to exist in a particular space or develop an impatient personality. And I don’t perceive the reverse: perceiving ‘two’ when I see blue.

Fourth, synesthetic associations are idiosyncratic; even if we’re both color synesthetes, you and I will associate different sensory qualities to letters or words (‘no… “T” is not mauve; it’s lavendar!’).

Fifth, synesthesia, by definition, associates sensations from different sensory channels.

Finally, as Ramachandran himself argues (see Ramachandran & Hubbard 2001a), synesthesia is a perceptual effect, not a memory association, a symbolic link, or an analogy.

Metaphor has none of these traits: it is unstable and varies widely; associations are voluntary, even creative; and metaphor can be crossmodal, but it does not always flow from one channel into a specific other one. Unlike synesthesia, metaphor is typically used in communication and might even be considered ineffective if the association does not successfully communicate to an audience. And metaphors very frequently operate within a single sensory channel, for example, highlighting similarity in visual sensations or sounds. Finally, and perhaps most importantly, metaphor is not perceptual — metaphoric analogy may highlights perceptual qualities, but it is driven by elective choices to highlight qualities that may involve symbolic meanings or create meaningful analogies.

Unlike synesthesia, metaphor is the creative ability to summon up multiple associations to highlight different characteristics; far from being compulsory, many of the most evocative metaphors are novel and unexpected, and they are motivated by some perceived similarity, unlike the arbitrary, compulsory associations made in synesthesia.

Ramachandran himself would no doubt emphasize these differences if asked to contrast synesthesia with metaphor. For example, in their piece on synesthesia in Scholarpedia, Ramachandran and David Brang write:

The link between synesthesia and metaphor (Ramachandran & Hubbard, 2001b) has already been alluded to. The nature of the link remains elusive given that synesthesia involves arbitrarily connecting two unrelated things (e.g. color and number) whereas there is a non-arbitrary conceptual connection between Juliet and the sun. One potential solution to this problem comes from realizing that any given word only has a FINITE set of strong first order associations (sun = warm, nurturing, radiant, bright) surrounded by a penumbra of weaker second order associations (sun = yellow, flowers, beach, etc.) and third and fourth order associations that fade way like an echo. The overlapping region between two halos of associations (e.g. Juliet and the sun; both are radiant, warm and nurturing) – the basis of metaphor- exists in all of us but is larger and stronger in synesthesia as a result of the cross-activation gene. In this formulation synesthesia is not synonymous with metaphor but the gene that produces synesthesia confers a propensity towards metaphor. A side- effect of this may be that associations that are only vaguely felt in all of us (e.g. masculine or feminine letters or good and bad shapes produced by subliminal associations) may become more explicitly manifest in synesthetes, a prediction that can be tested experimentally. For instance most people consider certain female names, e.g. Julie, Cindy, Vanessa, Jennifer, Felicia, etc. to be more “sexy” than others e.g. Martha and Ingrid. Even though we may not be consciously aware of it, this may be because the former involve pouting, tongue, lips etc. with unconscious sexual overtones. The same argument would explain why the French language is often thought of as more sexy than German. It might be interesting to see if these spontaneously emerging tendencies and classifications are more pronounced in synesthetes.

In this passage, I think Ramachandran and Brang recognize differences, highlight some similarities, but then posit an improbable ‘gene the produced synesthesia’ that also ‘confers a propensity towards metaphor.’ Although much of the research leading up to this passage is persuasive, this is where I draw the line.

A more promising approach to thinking about how these intriguing patterns of association (like names being ‘sexy’ or shapes being ‘kiki’ or ‘booba’) arise consistently and remain stable is not so much to look at synesthesia, in my opinion, but to look more closely at the phenomenology of these sensations. For example, Ramachandran and Brang describe how movements of the mouth might make certain names sound ‘sexy’; the easier explanation is to look to these movements, not to point to synesthesia, which typically involves arbitrary, unimodal sensory associations.

In other words, in this case, the explanation might be more phenomenological than neurological, as is the case with much of metaphor. Metaphors are compelling to us, and may successfully communicate, because they usually focus on some sensory or conceptual association, not because, like synesthetes, we invariably and compulsively associate the metaphor with the reference. (And the phenomenological explanation wouldn’t need to ignore the fact that the same names likely aren’t sexy in every language…)

One of the things that makes metaphors work is that, when we share them, they are persuasive to other people because those people, too, can perceive the analogy. Synesthetes don’t associate things because they share some resonant perceptual quality (that is, to anyone BUT the synesthete). In fact, even synesthetes themselves don’t agree on what things are linked when they have the same sort of synesthesia; not all graphemes think three is red. None of this would be news to Ramachandran, who knows far more about synesthesia than I ever will. It’s just that he thinks synesthesia is a useful metaphor for metaphor; like any metaphor, however, we can disagree about whether it’s a good one. The fact that it produced conjectures of a shared metaphor-synesthesia gene suggests to me that it’s not one I want to employ.


Hubbard, Edward, and Vilayanur S. Ramachandran. 2005. Neurocognitive Mechanisms of Synesthesia. Neuron 48 (3): 509-520.

Ramachandran, Vilayanur S., and Edward M. Hubbard. 2001a. Neural cross wiring and synesthesia. Journal of Vision 1(3):67 doi:10.1167/1.3.67

Ramachandran, Vilayanur S., and Edward M. Hubbard. 2001b. Synaesthesia: A window into perception, thought and language. Journal of Consciousness Studies 12(1): 3-34.

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Trained as a cultural anthropologist at the University of Chicago, I have gone on to do fieldwork in Brazil and the United States. I have written one book, Learning Capoeira: Lessons in Cunning from an Afro-Brazilian Art (Oxford, 2005). I have also co-authored and co-edited several, including, with Dr. Daniel Lende, The Encultured Brain: An Introduction to Neuroanthropology (MIT, 2012), and with Dr. Melissa Fisher, Frontiers of Capital: Ethnographic Reflections on the New Economy (Duke, 2006). My research interests include neuroanthropology, psychological anthropology, sport, dance, human rights, neuroscience, phenomenology, economic anthropology, and just about anything else that catches my attention.

23 thoughts on “Synesthesia & metaphor — I’m not feeling it

  1. Excellent post. I fully agree that ‘metaphor’ is quite a strange term to use in this context. But that may be the way the reporter phrased it. The kiki and booba forms by the way come from early Gestalt/sound symbolism experiments by Köhler.

    I do have a slight issue with your #4, “synesthetic associations are idiosyncratic”. It is a common claim, yet at the same time there are some broad tendencies that do turn up time and again. For example, in tone>colour synesthetic associations, low tones tend to correlate with dark hues and high tones with lighter hues, even though the exact qualities of the hues may be unique for each synesthete. Likewise in the classic audition colorée, back vowels (/a/) tend to correlate with dark colours and high vowels (/i/) with light colours.

    So what does that imply for the idiosyncrasy point? Synesthesia is idiosyncratic, but only to some extent?

  2. Yeah, Mark, that’s a good point. Maybe I need to be more specific about ‘idiosyncratic.’ Perhaps I could say something that even though synesthesia is ‘typical’ (with many people perceiving colors for numbers or smells for certain colours), the specific associations within this type-association are ‘arbitrary’ (color synesthetes associating different colours with the same number). I’d have to look at more of Ramachandran’s work to get a real sense of the variety; my understanding is that there’s a much greater proliferation of forms than previously realized. Perhaps this is why Ramachandran is inclined to see the phenomenon as much broader than I might perceive it to be.

    To me, the ‘typicality’ of synesthesia — that there are lots of color synesthetes but not so many haptic-sound synesthetes — has to be linked to neuro-architecture. I can come up with no plausible developmental story where the modes or sensations associated by synesthetes are actually linked through experience, so there must be some sort of non-experiential association. But my impression is that the modes that are typically associated are not proximate in the sensory cortex, so I just can’t even suggest how these patterns of cross-stimulation are built up.

    So I agree with Ramachandran that synesthesia is a fascinating question (that’s not even getting into the phenomenological ‘what are they feeling when they perceive five-purple?). It’s just that I don’t think these questions get us closer to metaphor.

  3. Nice article. The only objection I have is that, like virtually every article on synaesthesia (including the scientific literature), you give it a definition and then contradict this definition in the very next sentence.

    Synaesthesia is NOT necessarily a condition in which stimulation in one sensory channel causes activity in another. In grapheme-color synaesthesia, for example, letters are typically SEEN on the page, and then colours are experienced (in a variety of different ways, but at least sometimes in a straightforwardly visual sense). There is no cross-modal activity going on here, it is visual in and visual out. The vast majority of synaesthesias, it turns out, involve automatic and involuntary associations between particular kinds of categories (such as letters and numbers) and various seemingly arbitrary characteristics. These characteristics are often sensory, but often not – for example, many grapheme-colour synaesthetes describe numbers and letters as having specific personalities and genders. Furthermore, something like grapheme-colour syn can often be triggered by seeing the letter, by hearing its name pronounced out loud, by thinking about it (“what is the letter that comes after c?”), etc.

    So the standard definition of synaesthesia is simply incoherent as soon as one considers a few basic examples. Synaesthesia does not necessarily involve two consistently-paired sensory modalities, the inducing stimuli can often come through a variety of different sensory channels, and the synaesthetic concurrent (the unusual “additional” experience that synaesthetes have) need not be sensory at all.

    Unfortunately, I don’t have a terribly good alternative definition for you. If anyone does, let me know :).

    And yeah, I’m pretty suspicious of the synaesthesia as metaphor thing. But with further elucidation, it might make more sense.

  4. hi, i am not here to argue whether synesthesia can be called a metaphor. i was wondering if syn can be a very big distraction in learning?! becoz, when we are supposed to add up 2 + 3 in the classroom and if we start perceiving red and blue colours for the numbers, would we be able to complete the sum??

    very interesting phenomenon! but it could be stressful to those who experience it.

  5. Two flutes playing a major third is a bite of cold, juicy watermelon.

    Metaphor works for me -as long as the sensory aspect is actually concrete. -and metaphors are generally meant to be…well, metaphors. I guess my statement about my synesthetic experience would appear to be a metaphor to everyone else but for me it lies somewhere between a metaphor in the cognitive sense and a reality in the sensory.

    Synethesia is the thought of an ocean that is actually wet.

    -My attempt at a metaphor for synesthesia.

  6. I agree quite strongly with Marcus that there have been inconsistent definitions of synaesthesia, but I believe that metaphor still has a close relationship with synaesthesia, depending of course on how you define the word. A lot of the miscomprehension results from the fact that neuroscientists have eluded to metaphor in many different ways when studying synaesthesia. When studying the clincal involuntary form of the condition, where for example synaesthetes cannot help but see colours when listening to music, or smell words on a page, neuroscientists play down metaphor to show how the condition is perceptual and it is not the result of simply ‘metaphorical thought’ or hallucinations. The second form is perhaps what we can call ‘pseudo-synaesthesia,’ which is the unconscious form we all have to a certain extent, as evidenced by the bouba-kiki effect. When describing this form neurologists like V.S. Ramachandran have liked to play up its link to metaphor, in showing how it shares certain characteristics. This particular form is perhaps voluntary and more ‘conceptual’ with links to non-sensory linguistic domains of thought e.g. advanced metaphors such as LOVE IS A JOURNEY, etc (e.g. ‘I went all the way with her!’). I am attracted to the work of the scientist Daphne Maurer who has suggested infants are conscious synaesthetes for the first few months of life when their brains have not yet fully modularised. Later, when their brains develop, these transient connections are pruned and infants learn to abstract between differentiated sensory modalities. They no longer appear to perceive conscious synaesthesia, except in the case of ‘clinical synaesthetes’ who go on to continue perceiving synaesthesia consciously for the rest of their lives. This period of conceptual reorganisation in infants corresponds to the ‘babbling’ stage of language acquisition. Perhaps their growing brains allow them to abstract between more than just the senses? The relationship between synaesthesia and metaphor does exist, but of course this relationship is the domain of unconscious synaesthesia which, although might not equal metaphor in its own right, could form the underlying neurological basis for it. I am particularly attracted to Richard Cytowic’s statement that ‘synaesthesia is a condition prematurely displayed to consciousness in a minority of individuals.’ (He is of course referring to the clinical form of the condition).

  7. Hi All,

    I am a student researcher who will be conducting a study this summer at City College New York on the neural mechanisms underlying Tone-Color Synesthesia under the tutelage of Prof. John Foxe, Director of the Cognitive Neuroscience Program in Psychology.

    Study participation will include the non-invasive electrical recording of your neural activity via electrodes placed on the scalp as you are presented various auditory and/or visual stimuli from a computer monitor. Recording will take a total of 2.5 to 3.5 hours and preliminary behavioral testing, including synesthesia confirmation and documentation of your synesthetic associations will take a total of 4 to 5 hours.

    To qualify for study participation: You must be 18 or older; you must not have color-blindness; and you must not have any prior history with neurological conditions such as clinical depression, ADHD, anxiety disorders, Asperger’s Syndrome, Autism, Dyslexia, etc. Subject Compensation will be $12/hr. If you think you may have Colored-Hearing Synesthesia or for more information about this study, please contact Cordelia Sendax at or at 1-646-872-8346.

    Cordelia Sendax

  8. Sorry, to clarify. The study is still being conducting into the fall and probably throughout the winter and spring as well.

  9. It seems the unidirectionality thing has been contested as well:

    Kadosh, C. (2007) “The Neuronal Correlate of Bidirectional Synesthesia: A Combined Event-related Potential and Functional Magnetic Resonance Imaging Study” Journal of Cognitive Neuroscience, 19 (12).

  10. Also, if it helps, Rich et al. describe its idiosyncratic nature as “idiosyncratic in the sense that the same inducer will elicit a different concurrent for different people (e.g. Galton, 1880). For example, the letter ‘A’ might elicit dark red for one synaesthete and lime green for another.”

    A.N. Rich et al., A systematic, large-scale study of synaesthesia: implications for the role of early experience in lexical colour associations, Cognition 98 (2005), pp. 53–84.

    I’m doing a 20p lit review on synesthesia tonight for class. If Marcus has a good reference disproving the cross-modal association outside of his own speculation, that would be useful for me. 🙂 I’m not finding it.

    The idiosyncratic question is actually very interesting. With grapheme-color synth. there’s some widespread consistency with which colors match which letters, which has led some researchers to attribute standard children’s books or even refrigerator alphabet magnets toward some sort of environmentally learned early imprint. However, this doesn’t gel very well with the evidence toward a hereditary connection. Perhaps its one of those conditions like my ankylosing spondylitis where the gene/capacity is passed on, but only manifests by a particular environmental stimulus.

    I’m just a librarian, so don’t ask me. 🙂

  11. Ahh – Rich & Mattingly, 2002, talk about synth perceptions occuring in the same modality, like Marcus mentioned. I’ll stop talking to myself here now. (Sorry – If there was an edit button, I would have just changed my initial comment.)

  12. Hello again. I don’t agree with Greg’s statement that ‘metaphor can be crossmodal, but it does not always flow from one channel into a specific other one’. Perhaps I’ve misunderstood this statement but the overwhelming weight of evidence shows that metaphor IS unidirectional, in that a particular specific source domain is used to provide meaning or analogy for a second particular target domain, and not the other way round. The source domain is usually based on physical sensory experience and natural phenomena, like simply moving around and walking for instance, whereas the target domain is usually more abstract, like ‘love.’ You’d describe love as being like a journey for instance, because a journey is based on real-word experiences of travelling, but you wouldn’t really describe a journey as love. Moreover the connections made my synaesthesia aren’t arbitrary, they are systematic and usually occur along similar dimensions (and even the same dimension, such as vision in coloured-letter synaesthesia), although the exact nature of the concurrents might vary from person to person. The angular gyrus of the brain has been identified by fMRI scans as being involved in the integration of info from different sensory channels in both synaesthetes and non-synaesthetes and abstracting similarities between them, which is why the bouba-kiki effect seems to ‘work’. So to a certain extent synaesthesia does seem to be based on the idea of the fundamental similarity of information from different sensory channels.

  13. Hi to everybody,
    I’m working on synesthesia with a research group in this too-much-broad field which is cognitive science. More precisely, our inquiry is on coloured hearing synaesthesia, and includes neural network simulations.
    One of the feature of synesthesia that discouraged us was the idiosyncracy. We focused the research on a possible objective mapping between colors and music, and at the beginning we thought that as they both are defined by three variables (hue, saturation and value for color; pitch, duration, intensity for music)we could try to match these three variables to observe the underlying law of music-color correspondance.
    We also found that somebody before us created a particular device for blind people that was based on this variables matching (you can read about this project here!OpenDocument)
    Despite this, going deeper into the literature about synesthesia, it seems that we’re dealing with such a arbitrary phaenomenon that it’s not possible to find a law explaining the senses switch. Can anybody suggest me references about the non-idiosyncracy of synaesthesia? (i.e. some evidence that the perception of the “Do” results in the perception of red for almost all synaesthetes?)
    Moreover at the moment I’m attending corses at Aarhus Center for semiotics, and here metaphor is one of the principal topic of interest. It would be interesting to discover a link between synaesthesia and metaphor, though I agree we still have no evidence to claim it.

  14. Dr. Julia Simner has done work on non-idiosyncrasy of synaesthesia:
    Simner, J., Ward, J., Lanz, M., Jansari, A., Noonan, K., Glover, L., & Oakley, D. (2005). Non-Random Associations of Graphemes to Colours in Synaesthetic and Normal Populations. Cognitive Neuropsychology, 22(8), 1069-1085.


  15. The point seems continually to be missed in this discussion that there is no such thing as any conscious “thought” which is NOT “metaphorical” in that, in order for thoughts to be “reflected” upon (that is,”known” in conscious awareness),they must be “reflections of something ELSE. (What, if not “metaphor” is THIS process?)

    Barbara Ritchie

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