Larry Marks ñïåöèàëüíî äëÿ


1. When you first addressed the issue of synaesthesia back in the early 1970s, it was a relatively minor topic in psychology and neuroscience, besides, a rather disreputable one. What initially drew you to the phenomenon?

From the time of my graduate studies in the early 1960s, I’ve been interested in the ways that information from different senses combines and interacts, and in processes that are common to different sense modalities. Until recently, not only synesthesia but most of what we now call multisensory processing was considered well outside the mainstream of sensory and perceptual science. For generations, scientists tacitly assumed that every sense modality operates largely or independently of the others and by its own principles. But in graduate school, I was fortunate to have in my department two eminent and heterodox scientists – S. S. Stevens, the founder of modern psychophysics, and Georg von Békésy, Nobel laureate in medicine for his research on mechanisms of hearing. Both Stevens and Békésy were convinced that there are important principles common to most or all of the senses. Although neither of them ever mentioned synesthesia, not in my presence anyway, nevertheless, synesthesia struck me as fitting well within the framework of the “multisensory.” as being one manifestation of a “unity of the senses” (to borrow that expression from Erich von Hornbostel).

A few years later, in the early 1970s, I began to examine synesthesia, especially auditory-visual synesthesia, and discovered that some of the principles underlying the relations between the inducing stimuli and the synesthetically induced sensations, or inductants (to use Flournoy's term) are not unique to synesthesia, but are widespread, if not quite universal. For example, most sound-color synesthetes report that the brightness of the induced color increases as the pitch of the inducing sound increases. Exactly the same relation appears in a variety of perceptual responses of most non-synesthetic perceivers (Aristotle and Arcimboldo notwithstanding; see my response to question 4 below). Non-synesthetes, by definition, do not “see” colors when they hear sounds, but nevertheless they recognize and broadly agree on certain cross-sensory similarities. I suggested many years ago that synesthesia capitalizes on broad sensory and multisensory mechanisms found in non-synesthetes too. My initial interest in synesthesia came largely from my hope that studying it would shed light on general principles of multisensory processing.

2. According to your position regarding synaesthesia, as stated elsewhere, its "fundamental questions remain unanswered." Why is synaesthesia such a hard nut to crack? What remains to be discovered, you think, to reveal the essence of the phenomenon we refer to as synaesthesia?

A full answer probably warrants a full-length chapter, even a book. But let me try to respond as succinctly as I can, starting with the second part of the question: What do we still need to learn about the “essence” of synesthesia? This question presumes, of course, that synesthesia has an essence, that synesthesia is, or can be reduced to, a single common characteristic or conjunction of characteristics. Assuming that synesthesia does have an essence, What is it that makes all of the variants of synesthesia be synesthesia, and differentiates synesthesia from other phenomena with which it may share some characteristics (for instance, imagery, including memory imagery; lucid dreaming; hallucination; etc)?

First we need to decide what is and what is not synesthesia: Consider, as one example, the condition in which people report tactile sensations on a region of the body when they see another person being touched at an analogous location – what has been called “mirror-touch synesthesia.” Certainly mirror-touch synesthesia has several of the characteristics found in other forms of synesthesia – an anomalous sensation (touch) induced by a stimulus to a different modality (vision). What is peculiar to mirror-touch synesthesia, relative to other kinds of synesthesia, is the fact that the what is felt is so closely connected to the content of what is seen, in both cases, someone being touched. In most forms of synesthesia, the relation between inducer and inductant seems abstract, and not particularly "ecological." Unlike most other forms of synesthesia, in mirror-touch synesthesia inducer and inductant actually share a common referent – a tactile sensation.

The mirror-touch phenomenon, to dub it more neutrally, seems closely tied to empathy, as closely as to synesthesia. So if mirror-touch is synesthesia, then perhaps so too are other sensory forms of empathy, such as empathic pain, maybe even the couvade syndrome. In the couvade syndrome, the partners of pregnant women report symptoms, including sensory experiences such as nausea, that are often associated with pregnancy itself. An important finding about mirror-touch synesthesia is that it is often found in association with other forms of synesthesia. This finding is taken by some as evidence that mirror-touch should itself be considered a variant of synesthesia. To the best of my knowledge, nothing is known about a possible association between the couvade syndrome and other forms of synesthesia. In any case, such associations are at best only suggestive. Just because other forms of synesthesia are associated with mirror-touch does not make mirror-touch a form of synesthesia. Synesthesia may also be associated with creative cognition, as Catherine Mulvenna has suggested, but this would not mean that creative cognition is a variant of synesthesia.

I have suggested elsewhere that the boundaries between synesthesia and other perceptual and cognitive processes may become more clear when synesthesia is better understood, but one might turn this argument around to say that we will not understand synesthesia fully until we can better define it. In this regard, some investigators have come to call constitutional synesthesia (as opposed to synesthesia acquired by injury or illness) as a genetic condition. Certainly there is mounting evidence for a genetic predisposition to synesthesia, and several laboratories are actively seeking specific genes associated with the presence of synesthesia. One might imagine a time in the future when the broadly accepted definition of synesthesia would relate it to the expression of particular genetic alleles. My own suspicion is that the genes involved in synesthesia code for proteins that control some basic neurological processes, and that the alleles associated with the presence of synesthesia are responsible for an ensemble of neurological processes, synesthesia being a manifestation of just one of them. If this scenario is correct, then in the end we may need to continue defining synesthesia in phenomenological, experiential terms – which is, after all, how synesthesia reveals itself. Imagine the following future: We have uncovered all of the genes associated with constitutional synesthesia, but nevertheless find a few people who look talk like synesthetes, act like synesthetes, and perhaps shown evidence (e.g., from neuroimaging) of neural processes like those of synesthetes, but who lack any of the associated genes. From my perspective, these individuals would indeed be synesthetes. A tough nut to crack indeed!

3. Do you think synaesthesia is a phenomenal manifestation restricted to humans only, or can it be experienced by other cognitive forms (in animals)?

It’s funny that you should ask that question, as I used to pose exactly the question to other researchers in synesthesia – often simply by walking up to them at conferences and asking the question directly and without warning, trying to catch their on-the-spot, “gut” responses. Most of the answers that I received were affirmative – but it’s important to keep in mind that I made my inquiries several years ago, before it had become so common to consider synesthesia as much or more in cognitive terms as in purely sensory terms. In the past I too would have answered affirmatively, but now I’m much less certain, especially given all of the recent research implicating not only learning and experience but also language in many instances of synesthesia. Perhaps, however, there are several different forms of synesthesia, akin to the distinction that Vilayanur Ramachandran and Edward Hubbard made between lower and higher synesthesia, and perhaps non-humans and humans share lower forms but not higher one – for instance, pain-color and sound-color, or even mirror-touch, but not word-flavor or number forms. But, then, what would this mean for the definition of synesthesia?

As you can see, I often start answering one question but end up asking another one. My wife thinks this is part of my ethnic upbringing, a style often found in Jewish households of a generation and two ago: Ask “How are you?" and the answer is likely to be something like: "So, how should I be?" More seriously, in synesthesia one question does lead to another, in what seems to be an unending chain. My hope is that a couple of good answers will reverberate throughout.

Back to synesthesia in non-humans and humans: To the extent that synesthesia is grounded in genetic mechanisms, and to the extent that both non-humans and humans might experience some kinds of synesthesia, non-humans and humans might share a genetic mechanism. But the expression of this genetic mechanisms could vary across species. We are just beginning to understand epigenetics: the ways that environmental factors can affect genetic expression. In my opinion, the deeper question, propaedeutic to the question of non-humans vs. humans, is: Why does synesthesia exist at all? Is it just some kind of historical (genetic) accident, propagated because it does no harm, even if it may not provide any Darwinian benefit? (This is possible, but personally I doubt it.) Might synesthesia be an example of what Stephen Jay Gould called a “spandrel” – the accidental outcome of a genetic mechanism responsible for something else … perhaps a role in early neural development, maybe related to pruning? (More likely.) Or might synesthesia actually confer a small Darwinian advantage, if it is associated in some (causal) way with cognitive processes that provide a little extra edge to information processing. Perhaps synesthesia is associated with better memory or – and this is a topic of long-standing interest, albeit few data – creativity. I'm reminded of William James's attempt at explaining free will by arguing that free will confers a modest functional advantage; James suggested that free will might operate like a “hair trigger” – playing a small role in decision-making on occasions where a very small “nudge” is sufficient to push a person to decide one way or another. I sometimes think of synesthesia as providing a small adaptive “nudge.” Certainly this last possibility is intriguing – but I’m not sure I believe it so much as wish it.

4. In Cretien van Campen's book on synaesthesia, he points out that Arcimboldo's and Aristotle's were reverse correspondences of musical tones and colours (i.e. high-pitch tones to a darker palette) relative to our current habitual associations (high-pitch to lighter colours). Besides, there are other sensorial relationships recorded both in and outside western culture strikingly different from those of ours. How do you explain such possible mismatches in terms of synaesthetic mechanisms?

From Crétien’s account, Arcimboldo may have come up with his scheme based on a formal conception rather than perception. Perhaps Aristotle did too.

But let me start with another example. Many years ago, I was studying cross-modal correspondences in preschool-aged and school-aged children. One set of correspondences of interest comprised the associations of color with temperature – the well-known “warm” and “cool” colors. When we began to test children in the age range 6-10 years, we discovered that very few showed the normative (adult-like) associations of reds and oranges as warm colors, blues and greens as cool colors. Most of the children seemed to respond randomly, although a few did not. When we inquired further of those children who responses did show the normative pattern, all of them mentioned that in school they had been explicitly taught the correspondences. We soon discontinued the study, but other investigators have reported that color-temperature associations become stable developmentally only around the time of adolescence. It has long been argued that these associations are universal because they are based on physical regularities in the world – for example, because bodies of water feel cool to the touch and are generally seen as blue. But the correspondences aren’t perfectly universal. On several occasions, I’ve observed scientists use red colors in their graphs to represent lower temperatures and blue colors to represent higher ones, reversing the normative direction. I’ve also occasionally stayed in hotels in which the warm faucet was labeled with blue and the cold faucet with red, to my great displeasure. If some people don’t learn the normative associations (assuming they are learned), then these individual may use other criteria besides the physical correlation to form their cross-sensory representations.

But what of pitch and lightness? I’ve found, in children as young as 4 years, who hadn’t yet learned the words for low and high pitch, a near universal correspondence between higher pitch and greater lightness, just as I find in synesthetic and non-synesthetic adults. Catherine Mulvenna found the same correspondence amongst the Himba tribes-people of Namibia, who have virtually no contact with Western culture. If, as I proposed many years ago, the synesthetic correspondence between the pitch of sounds and the lightness of colors is hard-wired, deriving from basic neural mechanisms of sensory coding in hearing and vision, then why would it not be absolutely universal? I can only suggest a couple of possible explanations, which I freely admit are pure guesses. One possibility, suggested earlier, is that a given individual may bypass perceptual similarity by using a formal or theoretical scheme to construe or construct cross-sensory correspondences. Another possibility is that a given individual may experience incidental associations of sound and color that go in the opposite direction to the norm, and this individual may then “imprint on” her or his idiosyncratic experiences.

In many, perhaps most, forms of synesthesia, learning plays a critical role – obviously, one must learn letters, numbers, and words, before one has, for instance, grapheme-color or word-flavor synesthesia. In non-synesthetes, learning appears critical to the development of some sensory correspondences (as in color-temperature). How do cultures come to adopt novel sensory correspondences? Anthropology provides possible explanations within several theoretical frameworks: functionalist, structuralist, etc. From a structuralist perspective, variations in patterns of sensory correspondence might represent differences only in surface structures, but not necessarily in deep structures. But these considerations take us too far afield. In any case, even if pitch-brightness correspondences are in some sense hard-wired, this does not mean that heredity is always destiny.

As I've said, I believe that the pitch-lightness correspondence in synesthetes and in non-synesthetes comes from a common source – an idea first expounded by Theodore Karwoski and his colleagues more than 75 years ago, which I endorsed in my writings in the 1970s, and which has been picked up more recently by Jamie Ward. Nevertheless, we still don’t fully understand the relationship between pitch-lightness similarity in non-synesthetes and pitch-lightness correspondence in synesthetes. That they are related I have no doubt; how they are related is less clear, and understanding how they are related is critical to explaining “mismatches.” "Mismatches" could have different sources in synesthetes and non-synesthetes. A non-synesthete may, for instance, construe cross-sensory correspondences based on a logical or mathematical or conceptual framework that simply bypasses perceptual similarity. As Crétien also points out in his book, Newton did something like this when he proposed 7 primary colors for the spectrum, thereby matching the number of colors to the number of notes of the musical scale. The ability to transcend or transform either neurophysiologically or environmentally engendered correspondences is a hallmark of originality and creativity.

5. In your paper "Synesthesia across the Spectrum" you ponder that the way one interprets synaesthesia is per se indicative of the interpreting researcher's mind and method. In your view, have there been similar correspondences throughout the history of synaesthesia research? Specifically, how the attitudes to and understandings of synaesthesia as a phenomenon of the human mind can characterise the state of cognitive and psychological sciences as such?

Scientists all have their own metaphors for understanding the world, especially those parts of the world that they study. Many of these metaphors are shared, and tend to come from physical science and, especially, from technology – in brain/behavioral science, an important shared metaphor of a century ago was the brain-as-a-telephone-switchboard, a guiding metaphor in the hay-day of associationistic thinking. With the development of computers in the middle of the last century, brain and mind came to be conceptualized within the language of computer science. It’s hard to avoid uses certain locutions, such as how such-and-such a circuit in the brain "computes" this or that – even though I still often cringe when I hear it. After all, computers “compute” because of the way we interpret the binary outputs. Of course, when we talk about computers we're generally talking about one specific kind of computer, namely, digital computers. Early in my career, I had the opportunity to work with analog computers, which are quite wonderful devices for modeling much of the world. There are a few neuroscientists and others who recognize the potential significance of analog processes – which were championed by the Gestalt psychologists. Wolfgang Köhler relied on analog processing in his theory of the isomorphism between the brain and perception/behavior. This may seem a digression from your question, but it’s isn’t – at least, not completely. I’ve always thought of synesthesia as an implicit system of analogies, although I never tried to develop a formal model.

This leads me to your next question.

6. Taking advantage of my initiative to interview you, I can't help asking you about my own model of the neurophysiologic basis of synaesthesia that I first advanced at the 2009 Granada conference to which you had been invited as the key speaker. How viable you think might be a vision that theorises wide-scale oscillation across multiple frequency bands as the integrative neuronal foundation of synaesthetic coherences?

Absolutely: There are long-standing hypotheses regarding the ways that coherence in temporal frequency of oscillation could provide a basis to perceptual binding (in non-synesthetic perception), and these accounts could readily extend to synesthesia too. Coherence in multiple frequency bands seems to me essential. In fact, this might provide a relatively simple account of synesthetic correspondences.

7. By this point, it will have become clear to the reader that you are not a synaesthete (the question that haunts most synaesthetes when running into an inquisitive neuroscientist). Have you ever regretted not being one? Would it give you a competitive edge in your research?

Of course I'd love to be a synesthete! There are several reasons for this. One is pure curiosity: What is it like to experience synesthesia in the first person? I'm not sure how much of a competitive edge being a synesthete would give to my scientific work, but to the extent that I'd be satisfied with experiments using a single subject, I'd have one constantly available. On the other side of this coin, there's the risk that my synesthesia might mislead me to believing that my own phenomenal experiences necessarily characterize synesthesia in general. And as to regretting not being a synesthete, no, I don't regret it, no more than I don't regret not looking like Paul Newman. Oh. Um. Wait a moment: I take this back.

8. Almost all the dominant theories consider the phenomenon of synaesthesia strictly in terms of “involuntary reactions.” It is only recently that some researchers and theorists have started integrating the semantic correlations and agency into their perspectives. What is your take on the relations between synaesthesia and human creativity in general?

A traditional view of synesthesia sees it as consisting of involuntary, automatic responses to inducing stimuli. A prototypical example of synesthesia is colored hearing – the arousal by an acoustic stimulus of color sensations (synesthetic) as well as the usual auditory sensations of pitch, loudness, and so on (non-synesthetic). This view fits comfortably within the (also traditional) stimulus-response physiologies that developed from the seventeenth century into the psychologies that emerged in the late nineteenth and early twentieth centuries. In applying this scheme to colored-hearing synesthesia, an acoustic stimulus would be an inducer, which automatically leads to both non-synesthetic auditory sensations and concurrent synesthetic color sensations. By this account, synesthesia is involuntary, and doesn't require intent on the part of the individual.

I see (at least) three important issues raised by this traditional view.

First, there is an implicit sense in this view that the synesthetic and non-synesthetic sensory responses both reflect relatively low-level processes. Contrary to this view is the growing evidence that synesthetic responses often/typically depend on semantic content, on meanings, evidence that is hard to reconcile with the implicit view. All of the terrific work of Julia Simner and others shows a clear role of language and semantic networks in the development of several kinds of synesthesia, especially flavor responses to words (presented either acoustically or optically). To be sure, synesthetic sensations (colors, flavors, or whatever) arise fairly rapidly after presentation of the inducer (although not as rapidly as the primary sensations), but so too do meanings; The meanings of words are processed rapidly, and the neural processing of meaning undoubtedly overlaps in time the processing of low level sensory features. So if linguistic meanings come to be activated quickly and (more or less) automatically, why not also synesthetic sensory qualities? I think there is indeed a great deal of "automaticity" in the arousal of synesthestic perceptions. Note, however, the qualifier: "Great deal" does not mean 100%. This leads to the next issue.

Second, what does it mean to be involuntary? Must involuntary-ness be absolute? Almost certainly, some voluntary control over synesthesia is possible, or more than possible. Once more, let's take a diversion, to the domain of attention to perceptual stimuli, where there is another “traditional” view, namely, that the presentation of a stimulus may briefly direct attention automatically or involuntarily. This exogenous kind of directed attention is commonly contrasted with endogenous attention, which is voluntary and controlled. So, for example, a flash of light initially produces an automatic, exogenous direction of attention to the location of the flash, lasting about a tenth of a second, followed by another perhaps also automatic direction of attention away from the location of the flash (inhibition of return), this lasting a few tenths of a second, after which the person may voluntarily use the location of the light flash to direct attention to that same site or another one.

A very neat story this. It is complicated, however, by evidence that even in the first few tenths of a second, during the period(s) in which attention is driven exogenously, people have some voluntary control over visual spatial attention. So most is not all. Nevertheless, distinctions can be valuable, even when they are not perfect. Synesthetic colors arise much more automatically than do many forms of visual imagery, as imagery can depend to a great extent on voluntary agency.

Let's move away from the example of sound-induced colors to consider other phenomena, such as number forms: Many people have strong spatial representations of numbers, not necessarily linear or even unidimensional represenatations; Francis Galton reported on number forms more than a century ago, and many researchers consider number form to be a variant of synesthesia. Interestingly, the stimuli that induce number forms might be external – hearing or reading the words or numbers themselves – but the inducers may also be internal. If a person with number forms thinks about a sequence of numbers, then the inducers are voluntary, and so too in a sense are the inductants. I may be able to “voluntarily” albeit indirectly affect my blood pressure by thinking about events that lead, themselves automatically, to either vasoconstriction or vasodilatation in peripheral blood vessels. In their wonderful old studies of synesthesia, back in the 1940s, Karwoski, Odbert, and Osgood described what they considered several variants of sound-color and sound-shape synesthesia, noting that some kinds of synesthesia were under much more voluntary control than others. Since then, researchers in synesthesia have become increasingly reluctant to include the voluntary cases as instances of true synesthesia – another example of the problems surrounding definitions. If synesthesia is defined as being primarily or largely automatic, then voluntary synesthesia is impossible. Maybe, however, following Karwoski et al., there are different kinds of synesthesia, some primarily automatic, others much more voluntary.

How might this link to creativity? The notion that synesthesia is somehow connected to creativity has a long history – suggested in large measure by the substantial number of writers, composers, and artists who are, were, or may have been synesthetes. The connections are not well established, however, and there are the well-known pitfalls associated with bias in sampling and reporting. But there is an even deeper issue here that continues to gnaw at me. One of the prime characteristics of synesthesia – often used as a diagnostic criterion in scientific research – is long-term consistency: Synesthetic correspondences tend to be fixed, rigid, invariant, constant over periods of months, years, even decades. How seemingly uncreative!

It is not clear to me how synesthesia per itself would contribute to creativity, to creative acts, beyond providing a set of experiences to depict in visual, verbal, or perhaps musical form. But does being synesthetic make one generically more creative? The recognition of synesthesia, the appreciation of the ways that the human mind, through the nervous system, can connect different domains, now that is a mental characteristic that might contribute to creativity – as it is part and parcel of the role of metaphorical thinking, critical to at least certain kinds of creativity. I tentatively explored some of these possible connections more than three decades ago in my book, The Unity of the Senses, and other researchers in synesthesia, such as Richard Cytowic and Vilayanur Ramachandran, have expanded these notions. Of course, in one sense, our lives are filled with creative acts. As the linguist Noam Chomsky pointed out half a century ago, each of us, every day, undoubtedly utters several new sentences, sentences that we have neither heard before nor spoke or wrote before. The use of language is quintessentially creative in this sense, even if most of us speak most of the time in a prose that is inelegant, and often ungrammatical – though creative nonetheless. (Sometimes, to be sure, the ungrammatical may be poetic, and quite lovely, as in Dylan Thomas's "a grief ago," the first line of the poem of the same title.) I’m not sure how much synesthesia itself may add to creativity, but it is plausible that the mechanisms underlying synesthesia – the genetic mechanisms in particular – contribute to creativity, so that synesthesia and creativity are associated although not necessarily causally connected.

9. To your mind, how trustworthy might neuroimaging seem? What are the interpretative and descriptive limits of its reliability in synaesthesia research?

When functional neuroimaging first came on the scene, I was greatly skeptical – in part because many of the early studies struck me as trivial. If you have an essentially materialistic view of the universe, including biology, then you believe, at a minimum, that there are physical bases to all behavioral and mental phenomena. So every mental or behavioral act must be associated with a physical process, especially processes in the brain. Many early studies using functional neuroimaging were of the "gee-whiz-we-can-see-something-different-in-the-brain-when-behavior-changes" sort. Relatively few of the early studies, in my view, actually shed any new light on brain mechanisms or processes. In recent years, the situation has changed for the better, as functional neuroimaging has been wedded to increasingly sophisticated behavioral paradigms. In addition, PET imaging makes it possible, for example, to examine the release of different neurotransmitters, and gives relatively good spatial resolution; magnetic neuroimaging gives better temporal resolution. On the other hand, all of the techniques for neuroimaging remain fundamentally limited. None of them can show the flow of neural information in anything approaching real time, nor can they show the necessary details of neural processing over the complex networks of the brain. This is a real limitation. There are also technical issues having to do with how one calculates the baseline for measuring changes, for example, in the blood flow (BOLD) responses measured in fMRI. Neuroimaging techniques undoubtedly miss lots of important processes, faiing to give information about temporal coding in the nervous system, etc.

But practitioners of neuroimaging understand the limitations. I tend to be more concerned over the way that findings in neuroimaging are often “overbought” by (and sometimes "oversold to") the media and public at large. It is ironic that synesthesia owes its currently improved image in both the scientific community and the broader intellectual community in large measure to neuroimaging, which “proved” to many skeptics that synesthesia is “real.” There really is a lot to the old adage that “seeing is believing.”

10. How have your scientific activity and achievements throughout all your career as a neuroscientist both in the domain of synaesthesia and sensory psychophysics influenced you as a personality and human being?

My scientific activities and achievements are part and parcel of who I am; they express my thinking and my beliefs on a variety of topics: on perception and language, on science and philosophy, on culture (Western, mainly) and its history. The way I approach scientific topics reflects how I think, not just how I think about science. I'm not sure I want to try to figure out whether and how my scientific activities influence my personality, my humanity; whether and how my personality, knowledge, and beliefs influence my scientific activities. The dynamism is understood at least as well from the outside as from the inside, from a third-person rather than first-person perspective. Half of one drawer in my desk at home contains drafts of dozen or so short stories that I have written and rewritten over the last 20 years or so (none being anywhere near “finished”). Often, after drafting a story, I experience an “aha” moment: that, although not aware of this while writing, nevertheless, the story was “really” – symbolically, metaphorically – about some past events, but transformed unconsciously, along lines that Freud would presumably have appreciated. But the “aha” moments and the stories are all constructions all, stories all, “stuff as dreams are made on.” From my inner perspective, what is most important is that the stories satisfy me. And, in the end, what's better than a good story?

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