I was very disappointed by this book. I've been intrigued by synaesthesia ever since reading The Man Who Tasted Shapes, and I was hoping for more, to find out what has been discovered in the mean time. But this was not the book I was looking for. For example, I wanted to know why it is such "unnatural" symbolic things (letters, digits, days of the week) that get colours? But this is more anecdotal speculation than technical rigour, presented in a rather rambling style. The anecdotes are (mostly) interesting, but they are not backed up with anything much deeper. For example, the stuff about the Desana, who perceive the world through "colour energy" categories, and so are claimed to live in a colour-synaesthetic world: do they? Where is the evidence that this isn't all just a very deep cultural metaphor, but is in fact "real" synaesthesia? Particularly as these colours seem to be consistent across the Desana, whereas "true" synaesthetic colours vary from individual to individual. In fact, there is a lot of this kind of unsubstantiated assertion, for example, about the way a newborn's senses are undifferentiated: where is the evidence? I can't begin to think how there could be any: if there is, I want to know! (There is a reasonable bibliography, and maybe the evidence is cited somewhere there. But it is not explained in the body of the work.)
So, I learned a little, but probably not enough to justify the time I spent on reading this. Read Cytowic instead.