Vowel density differences among regional dialects of American English.

Over the past decade there has been considerable interest in differences in the size and shape of vowel spaces across different ages and genders of speakers and across different regional dialects of English. Vowel spaces provide information about the distribution of vowels in the F1 by F2 plane in an individual speaker or group of speakers. Recent studies have investigated which vowels should be used to establish the spatial boundaries and what criteria should be used in drawing the boundaries. However, the weakness of all such approaches is that they do not take into account the number of vowels produced in different portions of the vowel space (the occurrence of a single vowel in a peripheral location is sufficient to enlarge the vowel space). This study proposes to expand and refine the concept of vowel space by creating vowel density maps across different regional dialects of American English. These maps represent a three-dimensional overlay of relative vowel frequencies onto the F1 × F2 plane (the borders of which represent the vowel space). Dialectal differences will be described in terms of differences in the intersection of vowel space areas and differences in vowel density within different portions of the intersected spaces.