The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

5. Although synesthesia often involves adjacent brain areas (an example is grapheme-color synesthesia in the fusiform), it doesn’t have to. Even far-flung brain regions, after all, may have preexisting connections that could be amplified (through disinhibition, say). Statistically speaking, however, adjacent brain areas tend to be more “cross-wired” to begin with, so synesthesia is likely to involve those more often.

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.