Acoustic and articulatory modifications of Mandarin vowels in clear and Lombard speech

This study investigated the acoustic modifications of Mandarin vowels /a, i, u/ in clear speech and Lombard speech. Their underlying articulatory movements in the tongue and lips were also examined using ultrasound imaging and lip videos. Plain (i.e., conversational), clear and Lombard speech productions were elicited through a series of map tasks, where participants were prompted by pre-recorded videos to interact with the listener on the screen. Results showed that clear and Lombard speech in Mandarin resulted in longer syllable duration as well as greater vowel RMS intensity than plain speech. Spectrally, not all three vowels were modified to enhance their phonological features in response to clear or Lombard speech conditions. However, the differential F1/F2 modifications did result in an expanded vowel space. Some associations and mismatches between F1/F2 measurements and articulatory movements were observed. Particularly, greater mouth opening and lowering of tongue body in /a/ in clear and Lombard speech could account for the raising of F1. Few modifications in /i/ tongue position and lip configurations also corresponded to no significant F1/F2 change. The acoustic-articulatory relationship for /u/, in contrast, was less straightforward. These observations are discussed in relation to existing clear speech and Lombard speech literature.