Decades of work on speech variability by linguists and speech scientists has shed much light on its structure and sources, but has largely consisted of fine-grained studies of a handful of phonetic cues and languages (e.g. VOT, English), whose scope is limited by the fact that collecting and annotating speech data is time-consuming and expensive. This talk describes two studies of sound systems in large cross-linguistic corpora of read speech, which scale up relative to previous work, in terms of cross-linguistic coverage, sample size, and acoustic cues considered. We are able to scale up in part by using innovative speech analysis software enabling “large-scale studies” of sound systems, a direction also being pursued in a new Digging Into Data project on variation in English sounds across three countries which I briefly describe.
Study 1 : How stop consonants are realized in terms of acoustic cues—including VOT and closure voicing—differs greatly between languages, and by position within a language. This variability in phonetic realization of the “same” phonological contrasts — laryngeal contrasts, e.g. “voicing contrasts” — has long been of interest for reasoning about phonological representation, especially feature specification. For example, « laryngeal realism” theories hypothesize a close tie between phonological features and phonetic realization cross-linguistically, based on several phonetic criteria, such as speech rate correlations with VOT. These criteria have mostly been tested in isolation, on 1-2 languages. Using data from seven languages, we test whether these criteria hold and give convergent evidence. We find that they broadly do, supporting a close relationship between feature specification and phonetic realization, but with interesting exceptions.
Study 2 : Sound change commonly arises from « phonetic precursors » : small phonetic effects assumed to hold across languages and individuals, which evolve into full-blown contrasts over time. Relatively little is known about the robustness of most phonetic precursors : variability in their effect size across languages and speakers, which matters for establishing which precursors are robust enough to plausibly lead to change. Two widely-studied precursors, which also form a good test case for an automated analysis, are the effect of vowel height and preceding consonant voicing on F0 (VF0 and CF0). We assess the degree of cross-linguistic and interspeaker variability in VF0 and CF0 effects across 14 languages. We find that the existence of VF0 and CF0 effects are relatively robust across languages, confirming that they are possible phonetic precursors to sound changes, but their robustness across speakers is less clear, possibly helping explain why they rarely do lead to sound change. A methodological finding is that VF0 and CF0 effects can be detected in non-laboratory speech with minimal statistical controls, despite not accounting for many factors greatly affecting F0 (e.g. intonation).
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