Impact of prosodic structure and information density on vowel space size

We investigated the influence of prosodic structure and information density on vowel space size. Vowels were measured in five languages from the BonnTempo corpus, French, German, Finnish, Czech, and Polish, each with three female and three male speakers. Speakers read the text at normal, slow, and fast speech rate. The Euclidean distance between vowel space midpoint and formant values for each speaker was used as a measure for vowel distinctiveness. The prosodic model consisted of prominence and boundary. Information density was calculated for each language using the surprisal of the biphone Xn|Xn−1. On average, there is a positive relationship between vowel space expansion and information density. Detailed analysis revealed that this relationship did not hold for Finnish, and was only weak for Polish. When vowel distinctiveness was modeled as a function of prosodic factors and information density in linear mixed effects models (LMM), only prosodic factors were significant in explaining the variance in vowel space expansion. All prosodic factors, except word boundary, showed significant positive results in LMM. Vowels were more distinct in stressed syllables, before a prosodic boundary and at normal and slow speech rate compared to fast speech.