Oral configurations during vowel nasalization in English

Abstract

Speech nasalization is achieved primarily through the opening and closing of the velopharyngeal port. However, the resultant acoustic features can also be influenced by tongue configuration. Although vowel nasalization is not contrastive in English, two previous studies have found possible differences in the oral articulation of nasal and oral vowel productions, albeit with inconsistent results. In an attempt to further understand the conflicting findings, we evaluated the oral kinematics of nasalized and non-nasalized vowels in a cohort of both male and female American English speakers via electromagnetic articulography. Tongue body and lip positions were captured during vowels produced in nasal and oral contexts (e.g., /mɑm/, /bɑb/). Large contrasts were seen in all participants between tongue position of /æ/ in oral and nasal contexts, in which tongue positions were higher and more forward during /mæm/ than /bæb/. Lip aperture was smaller in a nasal context for /æ/. Lip protrusion was not different between vowels in oral and nasal contexts. Smaller contrasts in tongue and lip position were seen for vowels /ɑ, i, u/; this is consistent with biomechanical accounts of vowel production that suggest that /i, u/ are particularly constrained, whereas /æ/ has fewer biomechanical constraints, allowing for more flexibility for articulatory differences in different contexts. Thus we conclude that speakers of American English do indeed use different oral configurations for vowels that are in nasal and oral contexts, despite vowel nasalization being non-contrastive. This effect was consistent across speakers for only one vowel, perhaps accounting for previously-conflicting results.

Keywords: American English; electromagnetic articulography; labial; lingual; oral configuration; vowel nasalization.

Figure 1.

Schematized analysis. The left panel shows tongue and tongue sensor positions during one production by one participant of /bæb/ (blue) and /mæm/ (red). Orientations of x and y dimensions are shown, but note that the origin lies in the midsagittal plane, midway between the back two molars. The center panel shows overlay of tongue positions for three productions each of /bæb/ and /mæm/ by one participant. Average positions are calculated and a vector is plotted from the mean center of oral productions to the mean center of nasal productions. The right panel schematizes the average of vectors across participants shifted to a common origin, with vector lengths still in mm. The dashed circles in the right panel are of radius .88 mm, which is the error inherent in the NDI Wave system (Berry, 2011).

Figure 2.

Tongue position change vectors for vowels / ɑ,æ,i,u/. Each arrow represents data from one participant (P1, P2, P3, etc.). The origin of each arrow represents the participant’s tongue position during vowels in oral contexts; these origins have been aligned to compare across participants. The magnitude (in mm; length of arrow) and direction of the arrow represent the change in tongue position between vowels in oral contexts (origin) and vowels in nasal contexts (end of each arrow). Arrow directions are interpretable as in the schematic in Figure 1; that is, an arrow pointing to the left suggests that tongue positions are more forward during nasal contexts, and an arrow pointing down suggests that tongue positions are lower during nasal contexts. Colors are assigned per participant and are consistent across plots as shown on bottom right.

Figure 3.

Differences in tongue position and lip aperture between vowels in nasal and non-nasal contexts. Each dot represents one participant. The gray box shows the standard deviation and the black line shows the group mean. (A) shows the differences in tongue forwardness, in which negative numbers mean the tongue is more forward in nasals. (B) shows the differences in tongue height, in which positive numbers means the tongue is higher during nasals. (C) shows differences in lip aperture, in which negative numbers mean the lips are closed more during nasals. (D) shows differences in lip protrusion, in which negative numbers mean the lips are more protruded during nasals. Dimensions are in the original mm along the respective axes (e.g., tongue height is a difference in the superior/inferior axis).

Figure 4.

Formant changes per participant. F1 and F2 shown as in a typical acoustic vowel space, with decreasing F2 on the x axis and increasing F1 on the y axis. This mirrors the tongue position changes to modify F1 and F2: raising the tongue lowers F1, and moving the tongue forward raises F2. The common nasal resonance around 1000 Hz is marked in grey.