6. The link between synesthesia and metaphor has already been alluded to. The nature of the link remains elusive given that synesthesia involves arbitrarily connecting two unrelated things (such as color and number), whereas in metaphor there is a nonarbitrary conceptual connection between two things (for example, Juliet and the sun).
One potential solution to this problem emerged from a conversation I had with the eminent polymath Jaron Lanier: We realized that any given word has only 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) and third-and fourth-order associations that fade way like an echo. It is the overlapping region between two halos of associations that forms the basis of metaphor. (In our example of Juliet and the sun, this overlap derives from observations that both are radiant, warm, and nurturing). Such overlap in halos of associations exists in all of us, but the overlaps are larger and stronger in synesthetes because their the cross-activation gene produces larger penumbras of associations.
In this formulation, synesthesia is not synonymous with metaphor, but the gene that produces synesthesia confers a propensity toward metaphor. A side effect of this may be that associations that are only vaguely felt in all of us (for example, masculine or feminine letters, or good and bad shapes produced by subliminal associations) become more explicitly manifest in synesthetes, a prediction that can be tested experimentally. For instance, most people consider certain female names (Julie, Cindy, Vanessa, Jennifer, Felicia, and so on) to be “sexier” than others (such as Martha and Ingrid). Even though we may not be consciously aware of it, this may be because saying the former involves pouting and other tongue and lip movements with unconscious sexual overtones. The same argument would explain why the French language is often thought of as being more sexy than German. (Compare Busten-halten with brassière.) It might be interesting to see if these spontaneously emerging tendencies and classifications are more pronounced in synesthetes.
Finally, my student David Brang and I showed that completely new associations between arbitrary new shapes and colors are also learned more readily by synesthetes.
Taken collectively, these results show that the different forms of synesthesia span the whole spectrum from sensation to cognition, and indeed this is precisely why synesthesia is so interesting to study.
Another familiar yet intriguing kind of visual metaphor, where meaning resonates with form, is the use (in advertising, for example) of type that mirrors the meaning of the word; for example, using tilted letters to print “tilt,” and wiggly lines to print “fear,” “cold,” or “shiver.” This form of metaphor hasn’t yet been studied experimentally.
7. Effects similar to this were originally studied by Heinz Werner, although he didn’t put it in the broader context of language evolution.
8. We have observed that chains of associations, which would normally evoke only memories in normal individuals, would sometimes seem to evoke qualia-laden sense impressions in some higher synesthetes. So the merely metaphorical can become quite literal. For example, R is red and red is hot so R is hot, and so forth. One wonders whether the hyperconnectivity (either the sprouting or disinhibition) has affected back projections between different areas in the neural hierarchy in these subjects. This would also explain an observation David Brang and I made—that eidetic imagery (photographic memory) is more common in synesthetes. (Back projections are thought to be involved in visual imagery.)
9. The introspections of some higher synesthetes are truly bewildering in their complexity; as they go completely “open loop.” Here is a quotation from one of them: “Most men are shades of blue. Women are more colorful. Because people and names both have color associations, the two don’t necessarily match.” Such remarks imply that any simple phrenological model of synesthesia is bound to be incomplete, although it is not a bad place to start.
In doing science one is often forced to choose between providing precise answers to boring (or trivial) questions such as, How many cones are there in the human eye? or vague answers to big questions such as, What is consciousness? or, What is a metaphor? Fortunately, every now and then we get a precise answer to a big question and hit the jackpot (like DNA being the answer to the riddle of heredity). So far, synesthesia seems to lie halfway between those two extremes.
10. For up-to-date information, see the entry “Synesthesia,” by David Brang and me, at Scholarpedia (www.scholarpedia.org/article/Synesthesia). Scholarpedia is an open-access online encyclopedia written and peer-reviewed by scholars from around the world.
CHAPTER 4 THE NEURONS THAT SHAPED CIVILIZATION
1. A young orangutan in the London zoo once watched Darwin play a harmonica, grabbed it from him, and started to mime him; Darwin had already been thinking of the imitative capacities of apes in the nineteenth century.
2. Since their original discovery, the concept of mirror neurons has been confirmed repeatedly in experiments and has had tremendous heuristic value in our understanding the interface between structure and function in the brain. But it has also been challenged on various grounds. I will list the objections and reply to each.
(a) “Mirroritis”: There is a great deal of media hype surrounding the mirror-neuron system (MNS), with anything and everything being attributed to them. This is true, but the existence of hype doesn’t by itself negate the value of a discovery.
(b) The evidence for their existence in humans is unconvincing. This criticism seems odd to me given that we are closely related to monkeys; the default assumption should be that human mirror neurons do exist. Furthermore, Marco Iacoboni has shown their presence by directly recording from nerve cells in human patients (Iacoboni & Dapretto, 2006).
(c) If such a system exists, why isn’t there a neurological syndrome in which damage to a small region leads to difficulty in BOTH performing and miming skilled or semiskilled actions (such as combing your hair or hammering a nail) AND recognizing the same action performed by someone else? Answer: Such a syndrome does exist, although most psychologists are unaware of it. It is called ideational apraxia and it’s seen after damage to the left supramarginal gyrus. Mirror neurons have been shown to exist in this region.
(d) The antireductionist stance: “Mirror neurons” is just a sexy phrase synonymous with what psychologists have long called “theory of mind.” There’s nothing new about them. This argument confounds metaphor with mechanism: It’s like saying that, since we know what the phrase “passage of time” means, there is no need to understand how clocks work. Or that, since we already knew Mendel’s laws of heredity during the first half of the twentieth century, understanding DNA structure and function would have been superfluous. Analogously, the idea of mirror neurons doesn’t negate the concept of theory of mind. On the contrary, the two concepts complement each other and allow us to home in on the underlying neural circuitry.
This power of having a mechanism to work with can be illustrated with many examples; here are three: In the 1960s, John Pettigrew, Peter Bishop, Colin Blakemore, Horace Barlow, David Hubel, and Torsten Wiesel discovered disparity-detecting neurons in the visual cortex; this finding alone provides an explanation for stereoscopic vision. Second, the discovery that the hippocampus is involved in memory allowed Eric Kandel to discover long-term potentiation (LTP), one of the key mechanisms of memory storage. And finally, one could argue that more was learned about memory in five years of research by Brenda Milner on the single patient “HM,” who had hippocampal damage, than in the previous hundred years of purely psychological approaches to memory. The falsely constructed antithesis between reductionist and holistic views of brain function is detrimental to science, something I discuss at length in Note 16 of Chapter 9.