Fronting of /u/, /ʊ/ , and /o/

The back vowels /u/, /ʊ/ , and /o/ are commonly fronted to a central or nearly front position in vowel space resulting in variants whose nuclei might be transcribed as [ʉ] ~ [y], ~ [Y] and [Ɵ] ~ [ø] . Like the low back merger, this is a feature that was identified by earlier dialectological research. The linguistic atlas records show fronted variants of /u/ and /ʊ/ to be fairly common in the South and South Midland while fronting of /o/ appeared to be more geographically restricted and was common in northeastern North Carolina and the Delaware River valley including Philadelphia. Fronting of both /u/ and /o/ was also shown as characteristic on western Pennsylvania (Kurath and McDavid 1961).

More recent evidence suggests that fronting of these back vowels has become very widespread geographically. For example, Lusk (1976) found fronting of all three of the vowels among her Kansas City speakers, and Luthin (1987) reports on similar developments in the speech of Californians. Thomas (2001) provides acoustic evidence of fronting of the vowels in several speakers from central and southern Ohio. The Telsur project has examined the position of /u/ and /o/ on a national level and uses acoustic measurements to distinguish various degrees of fronting (Labov 2001: 479; Labov, Ash, and Boberg fc.). For /u/, the most extreme fronting outside of the South is recorded in St. Louis though the rest of the Midland and West also show significant fronting. For /o/, Labov and his colleagues found extreme fronting in Pittsburgh and across central sections of Ohio, Indiana, and Illinois as well as in various locations in Missouri and Kansas. Less extreme fronting was recorded across most of the West including in Denver, Portland, Fresno, and Tucson. The backest (least fronted) variants of both /u/ and /o/ were generally dominant only in extreme northern areas including Montana, the Dakotas, and Minnesota (as well as in the Inland North and New England).

Fronting of these vowels is not normally found in the context of following liquids (i.e., /l/ and /ɹ/). Thomas (2001) plotted separate means for pre-/l/ tokens such as pool, pull, and pole, and his acoustic portraits show that these means generally remain along the back wall of vowel space even in the case of speakers with extreme fronting of the vowels in other contexts. In terms of their relative progression, /u/ fronting seems generally to lead fronting of /ʊ/ and /o/ (Labov 1994: 208; Thomas 2001: 33).