The merger of /u/ and /uw/ before /l/ in full and fool, pull and pool might be expected to be parallel to the merger of /i/ and /iy/ in the same environment. However, the distribution shown in Map 5 is different from that of Map 4 in more than one way. The main concentration of red circles, showing the complete merger in production and perception is not concentrated in the South, but in the North Midland, particularly in Pennsylvania. The most consistent concentration of complete merger is in Western Pennsylvania among speakers in the Pittsburgh area. We also see a moderate representation of such complete merger, along with partial mergers, in Eastern Pennsylvania and in southern Indiana.
The areas of central and western North Carolina which showed a strong tendency to merge /i/ and /iy/ before /l/ do not show many instances of complete merger. However, there are 7 speakers in this area who show in one way or another that the pairs are close, and very little such tendency elsewhere in the South.
The pattern in the West is not dissimilar to that of Map 4, indicating that there may be much more of a parallel movement in the laxing of both vowels before /l/. The acoustic analyses to follow will give a clearer picture on this issue.
The concentration of this merger in Pennsylvania strongly suggests that the merger of /u/ and /uw/ before /l/ is associated with the vocalization of the dark final /l/ in this region. Ash 1982 shows that Pennsylvania, and particularly western Pennsylvania, is the leading area for the vocalization of /l/. The tensing of both vowels before a lax vocalic glide would then show the characteristic tense/lax differentiation of English syllables.
To compare the distributions of the /il/~/iyl/ and /ul/~/uwl/ mergers, see Map 6.