The ten people in one million who are synesthetes are born into a world where one sensation (such as sound) conjures up one or more others (such as taste or colour). Although scientists have known about synesthesia for 200 years, until now the condition has remained a mystery. Experiments with more than 40 synesthetes led Richard Cytowic to an explanation of synesthesia - and to conception of the organization of the mind, one that emphasized the primacy...