Abstract
Phonetic structures expand temporally and spectrally when they are difficult to predict from their context. To some extent, effects of predictability are modulated by prosodic structure. So far, studies on the impact of contextual predictability and prosody on phonetic structures have neglected the dynamic nature of the speech signal. This study investigates the impact of predictability and prominence on the dynamic structure of the first and second formants of German vowels. We expect to find differences in the formant movements between vowels standing in different predictability contexts and a modulation of this effect by prominence. First and second formant values are extracted from a large German corpus. Formant trajectories of peripheral vowels are modeled using generalized additive mixed models, which estimate nonlinear regressions between a dependent variable and predictors. Contextual predictability is measured as biphone and triphone surprisal based on a statistical German language model. We test for the effects of the information-theoretic measures surprisal and word frequency, as well as prominence, on formant movement, while controlling for vowel phonemes and duration. Primary lexical stress and vowel phonemes are significant predictors of first and second formant trajectory shape. We replicate previous findings that vowels are more dispersed in stressed syllables than in unstressed syllables. The interaction of stress and surprisal explains formant movement: unstressed vowels show more variability in their formant trajectory shape at different surprisal levels than stressed vowels. This work shows that effects of contextual predictability on fine phonetic detail can be observed not only in pointwise measures but also in dynamic features of phonetic segments.
Highlights
Probabilistic reduction of predictable words and subword units has been observed in many languages (e.g., Gahl, 2008; Bell et al, 2009; Bürki et al, 2011; Kuperman et al, 2007; Pellegrino et al, 2011; Pluymaekers et al, 2005a, b)
Following the smooth signal redundancy (SSR) hypothesis (Aylett and Turk, 2004, 2006), we investigate whether the effect of predictability on formant movement is modulated by a word-level effect of prominence, that is, primary lexical stress
The results of the generalized additive mixed models (GAMMs) for F1 and F2 trajectories are presented by the terms in the models, providing a cohesive summary of the effects of surprisal and primary lexical stress and their interaction, word frequency, and the smooth terms on average formant values and the formant trajectory shapes
Summary
Probabilistic reduction of predictable words and subword units has been observed in many languages (e.g., Gahl, 2008; Bell et al, 2009; Bürki et al, 2011; Kuperman et al, 2007; Pellegrino et al, 2011; Pluymaekers et al, 2005a, b). Vowels are more reduced in their spectral distinctiveness when they are difficult to predict from their context compared to predictable vowels (Jurafsky et al, 2001; Wright, 2004; Aylett and Turk, 2006; Clopper and Pierrehumbert, 2008; Scarborough, 2010). This effect of contextual predictability (for brevity—predictability) on segmental properties prevails even after controlling for known prosodic effects on phonetic structures, such as lexical stress (Brandt, 2019). Both perspectives entail that predictability is tightly interwoven with the prosodic structure
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