Nasal vowels are not [+NASAL] oral vowels
The assumption of minimal articulatory difference between members of nasal–oral vowel pairs deserves greater scrutiny. This study tests the hypothesis that members of nasal–oral vowel pairs share a common vocal tract configuration. Electromagnetic articulography is used to study the vertical position of the tongue and the labial aperture of nasal–oral vowel pairs produced by four speakers of Brazilian Portuguese. Significant differences were found for each vowel pair for at least one speaker, though considerable inter-speaker variation was evident. The most robust differences were tongue-body raising during the nasal vowels /ã/ and /ũ/. Because heavy nasalization tends to raise the perceived quality of low vowels, the lingual raising of /ã/ probably reinforces its nasality and contributes to the description of this vowel as [ɐ]. Because nasalization tends to lower the perceived quality of high vowels, the nasality of /ũ/ may be counteracted by the lingual raising gesture.