Roger Lass, the laxing occurred in the 17th century, but other linguists have suggested that it took place potentially much earlier. The short mid vowels have also undergone lowering and so the continuation of Middle English (as in words like dress) now has a quality closer to in most accents. Again, however, it is not clear whether the vowel already had a lower value in Middle English. Pin–pen merger The pin–pen merger is a conditional merger of and before the nasal consonants , , and . The merged vowel is usually closer to than to . Examples of homophones resulting from the merger include pin–pen, kin–ken and him–hem. The merger is widespread in Southern American English and is also found in many speakers in the Midland region immediately north of the South and in areas settled by migrants from Oklahoma and Texas who settled in the Western United States during the Dust Bowl. It is also a characteristic of African-American Vernacular English. The pin–pen merger is one of the most widely recognized features of Southern speech. A study of the written responses of American Civil War veterans from Tennessee, together with data from the Linguistic Atlas of the Gulf States and the Linguistic Atlas of the Middle South Atlantic States, shows that the prevalence of the merger was very low up to 1860 but then rose steeply to 90% in the mid-20th century. There is now very little variation throughout the South in general except that Savannah, Austin, Miami, and New Orleans are excluded from the merger. The area of consistent merger includes southern Virginia and most of the South Midland and extends westward to include much of Texas. The northern limit of the merged area shows a number of irregular curves. Central and southern Indiana is dominated by the merger, but there is very little evidence of it in Ohio, and northern Kentucky shows a solid area of distinction around Louisville. Outside the South, most speakers of North American English maintain a clear distinction in perception and production. However, in the West, there is sporadic representation of merged speakers in Washington, Idaho, Kansas, Nebraska, and Colorado. However, the most striking concentration of merged speakers in the west is around Bakersfield, California, a pattern that may reflect the trajectory of migrant workers from the Ozarks westward. The raising of to was formerly widespread in Irish English and was not limited