UC San Diego

Grapheme-color synesthesia is a neurological phenomenon in which graphemes, such as letters of the alphabet, evoke an additional, automatic, consistent sensation of color (e.g. “R is sky blue”). An as-yet unsolved question in the field of synesthesia research is what causes a particular synesthete to associate a particular grapheme with a particular color. The present work explores how properties of synesthesia and properties of language interact during development to determine which color synesthetes (and even non-synesthetes) will associate with a particular grapheme.

Chapter One demonstrates that hypotheses about color etiology in synesthesia, which have long been confounded, can be disentangled using a multi-language dataset: language can help us understand synesthesia. Chapter Two describes a case study of a Bengali grapheme-color synesthete, the first ever report of synesthetic phenomenology in an abugida writing system. Systematic differences between synesthesia in Bengali and in English suggest ways in which Bengali grapheme representations might be structured: synesthesia can help us understand language. Chapter Three demonstrates that synesthesia research can generalize to the (much larger) non-synesthetic population by engaging with a long-standing debate about the whether synesthesia is "special" or on one end of a continuum of experience. Non-synesthetes are found to have "synesthesia-like" associations for a subset of letters, suggesting that differences between synesthetes and non-synesthetes are differences in degree, not in kind. Chapter Four probes the limits of this generalizability, demonstrating that synesthetic and non-synesthetic associations are sometimes different because synesthetes' associations are "locked in" during childhood, whereas non-synesthetes' associations remain flexible through adulthood. Together, these studies suggest that synesthesia offers a window into the brain, that lets us literally see how we think about letters.