Nasals are the colour of the morning sky: a pilot study on distinctive features' sensory correlates in phoneme-colour synaesthetes

This study explores the possibility of using phonemic synaesthesia as a source of evidence in phonology: if synaesthesia is sensitive to phonological units, it can serve as a diagnostic tool for phonological phenomena. Synaesthesia has been shown to be able to refer to acoustic properties and morphological units, which entails it has access to linguistic information. However, there is no similar research on the interaction of synaesthesia and phonology. The literature mentions the existence of phonemic (as opposed to graphemic) synaesthetes, which suggests that synaesthesia can make reference to phonemes: if /f/ is blue, that will be the colour for the coda segment of LAUGH /lɑ:f/, even though isn’t in the spelling. It is therefore not unreasonable to suggest that it may also be influenced by smaller phonological units such as distinctive features, which might trigger colour percepts corresponding to feature-based natural classes in phonemic synaesthetes. 
The study has mapped the synaesthetic colour correlates of 3 phonemic synaesthetes for items in their phonological systems and concludes that phonological synaesthesia seems to be influenced by phonological features. These results are of relevance for certain larger debates in phonology, such as whether features are innate or emergent, whether they are devoid of phonetic content or not, whether features or rather gestures are the building blocks of phonemes.