The Midland
The region of the Midwestern United States west of the Appalachian Mountains begins the broad zone of what is generally called "Midland" speech. In older and traditional dialectological research, this is divided into two discrete subdivisions: the "North Midland" that begins north of the Ohio River valley area and the "South Midland" dialect area. In more recent work such as the Atlas of North American English, the former is designated simply "Midland" and the latter is reckoned as part of the South. The (North) Midland is arguably the major region whose dialect most closely approximates "General American".
The North Midland and South Midland are both characterized by having a distinctly fronter realization of the /oʊ/ phoneme (as in boat) than many other American accents, particularly those of the North; the phoneme is frequently realized with a central nucleus, approximating . Likewise, /aʊ/ has a fronter nucleus than /aɪ/, approaching . Another feature distinguishing the Midland from the North is that the word on contains the phoneme /ɔ/ (as in caught) rather than /ɑ/ (as in cot). (Obviously this only applies to Midland speakers not subject to the cot–caught merger, on which see below.) For this reason, one of the names for the North-Midland boundary is the "'On' line".
In some areas of the Midland, words like "roof" and "root" (which in many other dialects have the vowel uː) are pronounced with the vowel of "book" and "hoof" ʊ.
A common non-phonological feature of the greater Midland area is so-called positive anymore: it has become possible to use the word anymore with the meaning 'nowadays' in sentences without negative polarity, such as Air travel is inconvenient anymore.
Read more about this topic: North American English Regional Phonology