Spontaneous nasalization is the emergence of distinctive nasalization in contexts lacking an historical etymological nasal. In Thai, low and mid-low vowels nasalize after /h/ and to a lesser degree after /ʔ/. It has been reasoned that nasalization after /h/ may occur because breathiness and nasalization are acoustically similar; both introduce higher energy at low frequencies and increase spectral tilt. Glottal consonants may generally facilitate nasalization because aerodynamically they do not require velopharyngeal closure. We investigated velopharyngeal opening (VPO) during vowels after /h/ and/ ʔ/ and measured spectral tilt (H1–H2). We measured VPO by processing oblique ultra-fast magnetic resonance images of the velopharyngeal port. Four Thai speakers exhibited a complex system of VPO that varied based on vowel height and preceding consonant. Low vowels after /h/ manifested more physiological nasalization than low vowels after /ʔ/, while the former were often produced with higher spectral tilt, which may be indicative of either increased breathiness or nasalization. While VPO is likely responsible for impressions of greater nasalization after /h/, our findings suggest that breathiness and VPO may interact in the spontaneously nasalized vowels of Thai.

自发性鼻腔化是在缺乏历史词源性鼻腔的情况下独特鼻腔化的出现。在泰语中，在/ h /之后，低和中低元音会鼻音化，在/ʔ/之后会降低鼻音的程度。有理由认为，/ h /之后可能会发生鼻腔化，因为呼吸和鼻腔化在声学上是相似的。两者都会在低频引入更高的能量并增加频谱倾斜。声门辅音通常可以促进鼻腔化，因为在空气动力学上它们不需要关闭咽喉。我们研究了/ h /和/ʔ/之后的元音期间的咽咽口（VPO），并测量了频谱倾斜度（H1-H2）。我们通过处理咽咽口的倾斜超快磁共振图像来测量VPO。四个泰语发言人展示了一个复杂的VPO系统，该系统根据元音高度和前置辅音而变化。/ h /之后的低元音比/ʔ/之后的低元音表现出更多的生理性鼻腔化，而前者通常以更高的频谱倾斜度产生，这可能表示呼吸增加或鼻腔化。虽然VPO可能造成/ h /之后鼻腔增大的印象，但我们的发现表明，呼吸和VPO可能会在泰国的自然鼻腔元音中相互作用。