This oxford handbook was edited by Julia Simner and Edward J. Hubbard, with the contribution of many leading scientists in the field of synesthesia. It is a compelling overview of what we know about synesthesia so far and in which directions and branches the research is evolving. This book is recommended to people that want to go deeper in their understanding and can handle the dense information found in this book.
To determine if somebody has been a “genuine” synesthete post mortum is very difficult if not possible. Synesthetic expression through art or lyrics give insight about the multisensory perception of somebody, but may not scientifically be accurate. Therefore it makes more sense to ask those who are alive. For example Collin Pharell, musician and outspoken synesthete. Here a few insights in his synesthetic everyday life.