In velar fronting, the closure location for a velar consonant is moved forward along the palate due to vowel context. This study is a replication and extension of a previous study on velar fronting [Wodzinski and Frisch, J. Acoust. Soc. Am. 114, 2395 (2003)]. In this study, ten participants produced sentences containing monosyllabic words with /k/ onsets and nine different American English vowels. Ultrasound was used to make measurements of lingual-palatal constriction location at the midpoint of stop closure. Participants were recorded using a head-stabilizing apparatus and an acoustically transparent standoff was used between the ultrasound probe and the jaw. Velar closure location was quantified by the angle of elevation from the horizontal axis of the ultrasound probe to the center of the velar closure. The articulatory frontness of the following vowel was quantified using the frequency of F2 at the vowel midpoint. A strong negative correlation between velar closure angle and the following vowel F2 was seen for all ten participants. The coarticulatory pattern suggests that each velar-vowel combination results in a distinct closure location for the velar. Implications for models of speech production will be discussed.

The purpose of this study is to (1) evaluate the effectiveness of ultrasound imaging to measure velar consonant closure location, and (2) conduct a thorough study of velar fronting by measuring several productions of velar stops in the context of every English vowel. Word onset velar stops were measured in both words (CV or CVC) and nonwords (VCV) within a carrier phrase. Other coarticulatory influences were minimized by using words with no coda or labial coda consonants (e.g., ‘‘Say a gap again,’’ ‘‘Say /oIkoI/ again’’). Measurements were made at the point of maximal closure. Closure location was measured using the radial angle from the center of the ultrasound probe to the center of the velar closure. Pilot data for one subject has been analyzed to date. Closure location appears consistent across all central and back vowels. For front vowels, the degree of fronting of the velar appears to be correlated with the frontness of the vowel. Measures of closure location for diphthongs followed the back vowel pattern in the word targets. For nonwords, the closure location was influenced by the preceding diphthong offset quality and the following diphthong onset quality. Theoretical implications for the phonetics/phonology interface will be discussed.

Velar-vowel coarticulation in English, resulting in so-called velar fronting in front vowel contexts, was studied using ultrasound imaging of the tongue during /k/ onsets of monosyllabic words with no coda or a labial coda. Ten native English speakers were recorded and analyzed. A variety of coarticulation patterns that often appear to contain small differences in typical closure location for similar vowels was found. An account of the coarticulation pattern is provided using a virtual target model of stop consonant production where there are two /k/ allophones in English, one for front vowels and one for non-front vowels. Small differences in closure location along the palate between productions within each context are the result of the trajectory of movement of the tongue from the vowel to vowel through the virtual target beyond the limit of the palate. The overall pattern is thus seen as a combination of a large planned allophonic difference between consonant closure targets and smaller phonetic differences for each particular vowel quality that are the result of coarticulation.

Previous work has found a strong correlation between the frontness of closure location for velar stops (measured manually from ultrasound images) and the frontness of the following vowel (measured by F2). In this study, semi automatic measures of tongue frontness during a velar closure were made. Tongue edge traces were made using the EDGETRAK software (Li et al., 2005, Clinical Linguistics and Phonetics, 545–554). Frontness was then quantified from these traces using three different measures: Bressman’s anteriority index (Bressman et al., 2005, Clinical Linguistics and Phonetics, 573–588), a modified version of the anteriority index created for this study, and a measure of the center of mass of the tongue created for this study. When compared to the original manual measures, the modified anteriority index correlated most highly with both the manual measurement of the consonant closure location and also with F2 of the following vowel. The modified anteriority index uses an angle based weight in the anteriority calculation (as opposed to the arbitrary weights of Bressman’s anteriority index). The center of mass was the worst performing measure, and it appeared to be overly sensitive to the extreme anterior and posterior portions of the tongue edge trace.

Previous work has found a strong correlation between the frontness of closure location for velar stops (measured manually from ultrasound images by a trained expert) and the frontness of the following vowel (measured by F2). In this study, semiautomatic measures of tongue frontness for vowels were made from ultrasound images of the vowel articulation. However, it was found that the acoustic measure, F2, correlated more closely with the frontness of the preceding consonant than any of the ultrasound based articulatory measures of the vowel. Explanations for why an acoustic measure of coarticulation would be better than an articulatory measure will be discussed. It may be that the ultrasound based measures do not adequately capture retraction of the tongue root, which would influence F2 and presumably affect coarticulation with the consonant. Surprisingly, it was also found that the frontness measures for the consonant were more highly correlated with F2 than the frontness measures for the vowel, suggesting that the tongue frontness measures may be indirectly affected by tongue height in some way. Overall, the manual measures of an expert appear to be superior to semiautomatically generated measures.