Variation in the oral and nasal sound pressure level of vowels in changing phonetic contexts

This research has used the oral and nasal sound pressure levels as an index of nasality and measurements were made on a series of vowels in the /hVN/ and /NV/ frames. Subjects were recorded on instrumentation which separated the oral and nasal components of speech and a computer was used to analyse the sound pressure level components of the oral and nasal channels for all of the vowels. Statistical analysis of the data revealed that the oral and nasal sound pressure ratio tended to break the vowels into three basic groups and the variable appeared to be the tongue position for the vowel. The nasal component was greatest in high vowels and front vowels. The results also indicated that the nasal component was greater on vowels preceding the nasal consonant and that the nasal component was significantly lower in vowels produced with /m/ than those vowels produced with /n/ and /η/. These findings appear to indicate that the changes in the oral and nasal sound pressure levels are anatomically determined and the articulatory activity involved in protruding and elevating the tongue is transmitted to the nasopharyngeal sphincter.