Defining synaesthesia: a response to two excellent commentaries

This paper is an author response to two commentaries on 'Defining Synaesthesia' (Simner, 2012) by David M. Eagleman ('Synesthesia in its protean guises', 2012), and Roi Cohen Kadosh and Devin B. Terhune ('Redefining synaesthesia?', 2012). Together with these authors, I seek to more closely examine existing criteria on which definitions of synaesthesia have been based. In particular, I focus on the fact (a) that existing definitions paint synaesthesia as an overly homogenous condition, (b) synaesthesia may have multiple neurological causes, and (c) synaesthetes and non-synaesthetes may lie on a continuum.