Perceptual constraints and phonological change: a study of nasal vowel height

To address the claim that listener misperceptions are a source of phonological shifts in nasal vowel height, the phonological, acoustic and perceptual effects of nasalisation on vowel height were examined. We show that the acoustic consequences of nasal coupling, while consistent with phonological patterns of nasal vowel raising and lowering, do not always influence perceived vowel height. The perceptual data suggest that nasalisation affects perceived vowel height only when nasalisation is phonetically inappropriate (e.g. insufficient or excessive nasal coupling) or phonologically inappropriate (e.g. no conditioning environment in a language without distinctive nasal vowels). It is argued that these conditions, rather than the inherent inability of the listener to distinguish the spectral effects of velic and tongue body gestures, lead to perceptual misinterpretations and potentially to sound change.