As is customary for urban varieties, the varieties of Vienna are predominantly social varieties. Education and social background form the primary factors which define the language behaviour of the speakers.
The Viennese dialect belongs to the Middle Bavarian dialect group. Around the turn of the century, a sound change arose which monophthongized the diphthongs /aɛ/ and /ɑɔ/ to /æ:/ and /ɒ:/ repectively. This sound change was accomplished around 1950. As a result of the Viennese monophthongization, the palatal constriction location became overloaded. As early as the thirties, Kranzmayer observed what he called the "e-confusion", i.e., people stopped to discern the /e/-vowels, "Segen" (blessing) and "sehen" (to see) became homophones: [se:ŋ].
5 female and 5 male speakers of the Viennese dialect were asked to name pictures, to read sentences, and to speak spontaneously.
As a consequence of the Viennese monophthongization and the consecutive overcrowding of the palatal constriction location, speakers of the Viennese dialect developed two strategies. One group, in the sense Kranzmayer observed, neutralized /e/ and /ɛ/ to /e/. This neutralization made room for the new palatal vowel /æ/.
The other group, however, preserved /e/ and /ɛ/, but sometimes applied the two vowels incorrectly, i.e., produced /ɛ/ instead of /e/ and the other way round. However, since no neutralization took place, the vowel /i/ is shifted to the pre-palatal constriction location. By this shift, room is created on the palatal bar for the new vowel /æ/.
Group II discerns the vowels as follows:
Lip rounding and duration is distinctive for each vowel system.
Paper by Sylvia Moosmüller about the front vowels in the Viennese dialect (in German), May 2009: moosmuller_final_2009may11_mit_diagramm.pdf