This book review was completed as a class assignment at Georgia Tech.
Richard Cytowic and David Eagleman's "Wednesday is Indigo Blue: Discovering the Brain of Synesthesia" is a great read for anyone interested in learning about synesthesia and synesthetic experiences. The book is well structured, and filled with examples and testimonials from individuals with various forms of synesthesia. In addition to the entertaining and informative stories, the book also covers the current state of research in the field of synesthesia; from protocols used to tease out the differences between the synesthetic and nonsynesthetic brain to theories of how and why some brains develop synesthesia while others do not.
The book begins with an anecdote to convey the view of synesthesia from the inside perspective and open the reader's mind. There is no way of confirming that the reality you experience is the same as your neighbor's reality. In fact, abnormal experiences, such as those experienced by synesthetes, prove to us that this is not the case. Delving into such extraordinary cases can teach us many things about the brain that we would not otherwise uncover. For this reason, the study of synesthesia is valuable, and will continue to expand as we gain a deeper understanding of how we perceive the world in which we live.
The first chapter of the book explains difficulties with establishing an accurate prevalence of synesthesia. Individuals that have synesthesia have always had synesthesia, and generally assume that everyone else perceives the world in the same way, much as nonsynesthetes do. When they discover that is not the case, they often switch extremes, believing that nobody experiences what they experience. This alone is enough to keep most synesthetes from volunteering information about their internal experiences. Further, due to the extensive diversity of synesthetic cases, it is difficult to define precisely what constitutes synesthesia.
In chapter 2, the authors discuss a few of the forms of synesthesia in detail; from the research data detailing measurable consistencies, to the subjective descriptions of the idiosyncrasies of the synesthetic experience. The chapter begins with more common forms, including number forms, colored graphemes, and tasted words. It continues into descriptions of rarer presentations of synesthesia, such as audio-motor, geometric pain, and sound to touch. Following the examples, the authors question why some kinds of synesthesia are more common than others, and whether there are limits on the variations of synesthesia left to be uncovered.
While much of this book highlights benefits of having the "gift" of synesthesia, such as enhanced memory, in certain cases, the synesthetic experience can be burdensome. An example of this is provided in a synesthete with consistent bidirectional sound-color synesthesia. This synesthete explains that she avoids places with bright lights and loud noises, like the circus, whenever possible because she is unable to distinguish her synesthetic sensations from what is real, and that such an experience can be frightening and exhausting.
This example of such an intense synesthetic experience is in contrast to `milder' forms, such as grapheme-color synesthesia. In grapheme-color synesthesia, letters evoke a sensation of color, but in some individuals, the associations may be weak or even nonpresent for some letters of the alphabet. Such variances in intensity of the experience lead to the question: how much synesthesia is normal? The author proposes a cognitive continuum that ranges from perceptual similarities, to synesthetic equivalences to metaphoric identities to abstract language. The book makes a point to explain that synesthesia is perceptual and not merely metaphoric depictions of normal experience, but suggests that the human capacity to understand metaphor may be linked in some way to the ability for the brain to create synesthetic associations.
The authors describe the landscape of associations in the brain as being similar to a mountainous landscape, in which only some of the peaks break through the cloud cover of consciousness. Further, they claim that, if this were the case, the cross-connections of synesthesia may be present in all brains, but contained below the level of consciousness. Supporting this claim, both synesthetes and nonsynesthetes consistently match higher pitches with brighter colors when asked. Further, the use of phrases of abstract language such as "a loud tie" or "cool jazz" shows that the normal human brain is capable of making and understanding cross-modal associations. However, in most cases, the associations made by synesthesia, such as a pain that feels like the shape of a grid, are foreign to the general population.
The book closes with a description of the current state of synesthesia research and some questions ahead of us on the path to understanding synesthesia. The authors remind us that synesthesia is not localized in one brain region, and that we should be looking throughout distributed networks to understand it. They also suggest that we should be asking not whether cross-talk is present, but to what extent. They claim that both the cross-talk theory and the disinhibited feedback model of synesthesia are incomplete because they do not yet incorporate the role of learning. Depending on both genetics and learning over a ifetime, there are many possible ways in which brain areas may interconnect, leading to different forms of synesthesia. Studies are beginning to explore the individual differences of synesthetes. Finally, they state it is possible for a single gene to underlie all of the different forms of synesthesia, as the condition may be inherited in various forms, but to date, such a gene has not been found.
"Wednesday is Indigo Blue: Discovering the Brain of Synesthesia" was an incredible book, and I would recommend it as both a knowledgeable book for anyone seeking to gain a well rounded understanding of synesthesia and an enjoyable book for a leisure read.