Fascinating book. Easy to follow. Very informative.

Six-word review: Why some brains multiply sensory experience.

Extended review:

In the decades since I first learned that my somewhat unusual way of perceiving written words had a name, synesthesia has ceased being regarded as a dubious, unprovable claim by oddballs who were probably either blatant attention seekers or deluded hostages to an alphabet of plastic refrigerator magnets remembered from childhood. It is now a field of study in its own right within the respectable discipline of neuroscience. Tools provided by advances in technology have combined with a resurgent interest in the phenomena of consciousness to yield objective evidence of the subjective experiences of synesthetes and begin to explore their implications for further study of the human brain.

Eight well-documented chapters of Cytowic's book describe various manifestations of synesthesia in ample detail. The most common variety, grapheme -> color synesthesia, typically consists in seeing words and letters as if they possessed an attribute of color. Other sensory crossovers include hearing music as if it had color and form, experiencing tastes as if they were variously shaped concrete objects, and seeing numbers as having locations in three-dimensional space. Some people have several types.

The ninth chapter treats possible explanations of how crosstalk might occur between and among areas of the brain: might it actually take place in everyone, but (for most) at a level below conscious experience? or might it be universally present in infancy, but persistent to maturity in relatively few individuals? Research into such questions is in its early stages, so much of the information currently gathered is anecdotal, with several instances of data coming from a single individual's self-reports. Chapter 10 points to areas for further research.

There's an afterword by Dmitri Nabokov, son of the famously synesthetic novelist, and extensive notes, a bibliography, and an index.

I read this book with, let me confess, a slight chip on my shoulder. As someone who thought up until about age eleven that everybody saw letters of the alphabet in color, I was surprised when I first tried to talk about it and found out that it was weird. After that I rarely mentioned it again--unless I met someone else who had the same experience and somehow the subject came up.

The first book I read on the subject, also by Cytowic (The Man Who Tasted Shapes, 1993), seemed off base to me in so many ways that it made me growl out loud. Foremost among the points that raised my hackles was the persistent use of the term "association" to denote the connection between the objective stimulus and the inner perception--a perception that, for example, the letter C is chartreuse and the number 3 is bright red. The suggestion that I might have internalized the colors of plastic refrigerator magnets (which didn't even come on the market until I was in my teens--and besides, my colors include many more hues and shades than you'll find in a standard set) struck me as willfully obtuse. The colors are not an association any more than you see grass as green because of an association. It's a property.

It seemed to me that the author was writing about something of which he had no first-hand experience, and hence choosing language that was simply not quite the right fit for the situation.

Moreover, I was put off by his breathless, self-congratulatory tone, as if he had invented synesthesia all by himself and continued to hold a proprietary claim to it.

Even more exasperating was the simplistic notion that color values might have come about through some lingering reflection of personal history; for instance, that I might have thought J was blue because my mother's name began with J and blue was her favorite color. Certainly that kind of association could happen (and I do think of my mother when I see her favorite color, which wasn't blue). But because the concept of association in this context is in itself so misleading, an explanation that settles for it is no explanation at all; it devalues and dismisses the experience of those doing the reporting.

Thus prepared, I tackled this recent work armed with a pencil. This, I should note, is my usual mode when reading nonfiction, which I invariably regard as a dialogue. My marginal notations give evidence that I did a lot of interacting with the text.

And here are my conclusions, based not on any specialized knowledge but on my own experience, internal logic, and rational consideration:

This 2009 work does show progress. It uses much more temperate language and offers many more examples. It cites actual research such as had not been done at the time of the previous publication. And it presents interesting hypotheses that might lead to explanations for the experience of synesthesia and shed light on other brain functions as well.

However, it falls short of expectation in numerous ways:

• There's a pervasive quality of disingenuousness and gee-whizziness that makes synesthesia sound too little like a subject of scientific study and slightly too much like a parlor trick.
• There's a shortage of alternative explanations. Nobody over about the age of five, for example, actually believes that the voice is coming from the ventriloquist's dummy; that is no kind of evidence for the tight coupling of sight and sound in our perception (page 165). We suspend disbelief and play along for the fun of it, and that's all.
• The authors base too many of their hypotheses on research that's too limited and that also seems to have been designed by non-synesthetes. Testing a subject who attributes gender to letters by using letters to construct male and female stick figures (page 84) disregards the fact that those restroom icons are learned cultural conventions--and outdated ones, too, since women are no longer universally attired in skirts.
• A number of varieties of synesthesia in their typology come from a single source--the same single source--and need much more documentation, in my layperson's opinion, to stand up as generalizable descriptions.

In short, it appears to me that there is on the authors' part a basic failure to comprehend the experience they're writing about.

The authors still, annoyingly, use the term "association," but they own that whatever the connection might be, it isn't a result of idiosyncratic personal history. However, the refrigerator-magnet theory still comes up. And speaking of color "choices" seems to exhibit a persistent noncomprehension.

In sum, the baloney quotient is much lower for this work than it was for its 1993 predecessor, but it's still too high for my comfort.

So why four stars? I'm giving extra points for tackling a squirrelly subject at all and making some sense of it, and the ideas in chapter 9 sound promising; and besides, there are lots of good pictures. It's groundwork. I hope it's solid in enough places that I can look forward to seeing some stable architecture on this spot in another decade or so. ( )

It's now available as an ebook on the MITpress portal http://mitpress-ebooks.mit.edu/product/wednesday-indigo-blue