Phonetic Sources of Sound Change: the Influence of Thai on Nasality

The phonetic realization of nasal vowels produced by Pwo speakers of different ages can vary. The present study investigated mid and low nasal vowels of Pwo speakers from Mae Hong Son province, Thailand. Due to the higher tendency of language contact with Thai, the younger group’s nasal vowels were expected to lose more nasality than the older group. The emergence of final nasal consonants was also expected in the younger group. The nasalization duration and consonant duration of both groups were analyzed. The results showed that, regardless of age, mid nasal vowels of some speakers had final nasal consonants, while low nasal vowels of all speakers did not. Furthermore, the older group had both longer nasalization duration and consonant duration than the younger group, suggesting their higher tendency to preserve nasality. The younger group had shorter nasalization duration and consonant duration, indicating the loss of nasality in vowels without compensatory final nasal consonants. The change might be due to the vowel quality. High vowels were fully denasalized with no compensatory final nasal consonants. Mid vowels were nasalized with the emergence of final nasal consonants. Low vowels remained nasalized without final nasal consonants. We could not confirm that the emergence of final nasal consonants was induced by Thai because it occurred in both groups. The existence of final nasal consonants in the younger group could not be used as evidence of an effect of contact.