American English schwa characteristics in the context of vowel reduction

Abstract

The mid-central unrounded vowel schwa has been understood as a vocalic produced with a uniform cross-sectional area of the vocal tract that is correlated with formant frequencies occupying the center of the acoustic vowel space. As such, schwas have also been associated with reduced vowels. Vowel reduction occurs in a variety of contexts and factors, and it is commonly described as centralization toward the middle of the vowel space or a migration of formant frequencies toward those associated with a tube of uniform cross-sectional areas. Nonetheless, little is known regarding the extent to which reduced vowels approximate schwa values. The purpose of this study was to establish a within-speaker reference of schwa in the context of vowel reduction. Two questions were addressed. First, do the acoustic characteristics of schwa correspond to the centroid of vowel space? Second, how do schwa values compare to those of reduced vowels? Formant frequencies of vowels in citation and connected speech tasks were compared to schwa productions for the same speaker. It was hypothesized that schwa can be characterized as a centroid region defined within individual speakers’ vowel spaces. It was further hypothesized that reduced vowels in connected speech would closely approximate this centroid region.