In this research, I studied grapheme–color synesthesia, a neurological condition in which people associate letters and numbers with colors. To this end, I investigated letter-color associative pairings across English-, Spanish-, and German-speaking populations. Then, I utilized complex circular correlational statistics to determine that the hue associated with a letter is strongly correlated with the frequency of that letter in written language. These correlational analyses were repeated across three languages and three distinct groups of synesthetes. Subsequently, I ruled out other possible influences, such as letter order, color term frequency, and cultural biases, via supplementary studies.
These findings were integrated into current developmental accounts of synesthesia: the findings help to explain the cause of individual grapheme-color associations and suggests that synesthetes’ exposure to written language guides the grapheme–color associations that they form. This bolstered previous neurophysiological data, which suggested the existence of excess neural connections between cortical area V4 and the VWFA (visual word form area) in synesthetes, due to the neuroanatomy of these areas, which are organized by color hue and letter frequency respectively. Additionally, this study provided the first large-scale collection of Spanish-speaking synesthetes’ letter-color associations.