I've been enjoying this book so much over the course of my FMP, and its what drove me to stylise my "Things That are Blue" book. Its section on Synesthesia was, however, not as helpful. It almost seems as if it avoided the topic slightly. I hope achieve a more accurate portrayal of Synesthesia with my own data.
Mendelsund, P. (2014). What we see when we read. New York: Knopf Doubleday Publishing Group.