Spontaneous nasalization after glottal consonants in Thai: An rt-MRI investigation of rhinoglottophilia

Abstract

The affinity between glottal and nasal articulations (“rhinoglottophilia”) facilitates spontaneous nasalization. In Thai, low vowels nasalize after /h/ and to a lesser degree after glottal stop. Nasalization after /h/ may occur because breathiness and nasalization share high energy at low frequencies and a raised first harmonic. Glottal consonants generally may cause nasalization because aerodynamically they do not require a closed velopharyngeal port. We investigated whether Thai vowels after /h/ and glottal stop exhibit similar degrees of velopharyngeal opening (VPO) and compared these results with acoustic measures of nasalization / breathiness. We calculated nasalization / breathiness by the energy ratio of low and high harmonics; we measured VPO by processing oblique real-time magnetic resonance images of the velopharyngeal port. Four Thai speakers (two females, two males) produced relatively large VPO and high acoustic nasalization / breathiness after /h/. Female speakers nasalized vowels after glottal stop, though they produced overall less VPO and lower acoustic nasalization / breathiness when compared to vowels after /h/. In Thai, vowels after /h/ exhibit more physiological nasalization than vowels after glottal stop; furthermore, low VPO is associated with low acoustic nasalization / breathiness. We conclude VPO is primarily responsible for impressions of nasalization in this context.