Functional Data Analysis
for Speech Research

Abstract: This paper represents a pilot investigation of primed accentuation patterns produced by advanced Dutch speakers of Italian as a second language (L2). Contrastive accent patterns within prepositional phrases were elicited in a semispontaneous dialogue entertained with a confederate native speaker of Italian. The aim of the analysis was to compare learner's contrastive accentual configurations induced by the confederate speaker's prime against those produced by Italian and Dutch natives in the same testing conditions. F0 and speech rate data were analysed by applying powerful data-driven techniques available in the Functional Data Analysis statistical framework. Results reveal different accentual configurations in L1 and L2 Italian in response to the confederate's prime. We conclude that learner's accentual patterns mirror those ones produced by their L1 control group (prosodic-transfer hypothesis) although the hypothesis of a transient priming effect on learners' choice of contrastive patterns cannot be completely ruled out.

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Abstract: A preliminary study on modelling tonal variation as a function of duration is carried out. An experimentally controlled acoustic database was utilized to construct functional linear models. In the construction of the linear models, duration was used as independent variable in predicting disyllabic pitch contours in Taiwan Mandarin, given the target tone sequences. Results showed that by simply adjusting the duration from long to short, tonal curve shapes of disyllables ranging from non-reduced to reduced were approximated with an adequate goodness-of-fit (usually below one semitone RMSE). This study provides a novel approach to examine the relation between duration and F0 realisation of small units such as disyllables and also supports the time pressure account of phonetic reduction in general.

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Abstract: In this study we present a preliminary investigation of the prosodic marking of Verum focus (VF) in Italian, which is said to be realized with a pitch accent on the finite verb (e.g. A: Paul has not eaten the banana - B: (No), Paul HAS eaten the banana!). We tried to discover whether and how Italian speakers prosodically mark VF when producing full-fledged sentences using a semi-spontaneous production experiment on 27 speakers. Speech rate and f0 contours were extracted using automatic data processing tools and were subsequently analysed using Functional Data Analysis (FDA), which allowed for automatic visualization of patterns in the contour shapes. Our results show that the postfocal region of VF sentences exhibit faster speech rate and lower f0 compared to non-VF cases. However, an expected consistent difference of f0 effect on the focal region of the VF sentence was not found in this analysis.

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Abstract: This work introduces Functional Data Analysis (FDA) as a powerful methodology for speech analysis and re-synthesis. FDA allows one to carry out statistical analyses on a set of speech parameter contours in time, like f0, formants, intensity, in isolation or jointly. FDA eliminates the intermediate step of (manual) extraction of shape descriptors, like peak and valley locations, slopes, and so on. All the information contained in the curve shapes is preserved and used in the analysis. A case study illustrates the potential of FDA for phonetics research. The author maintains a website where papers, didactic material and code samples can be freely downloaded.

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Abstract: In this work we propose the use of Functional Data Analysis (FDA) as a powerful methodology to tackle problems where multiple continuous speech parameters have to be analyzed jointly. A production study on contrastive focus placement in Neapolitan Italian is used as illustration. Two features are analyzed, viz. f0 and relative speech rate, both expressed as continuous functions of time. The results show that known facts about the prosody of Neapolitan Italian emerge from the data, but also other interesting local or cross-feature relationships between contour traits appear. Thus, FDA results can be used as guidance in the exploration of speech feature contour shapes, an operation that used to be carried out manually in previous speech research. The capability of jointly analyzing multiple continuous features provides a valuable improvement not only for speech analysis but also for speech re-synthesis.

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Abstract: This study investigates the mechanism of tonal contraction when a disyllabic unit is merged into a monosyllable at fast speech rate in Taiwan Mandarin. Various degrees of contraction of bi-tonal sequences were elicited by manipulating speech rates. Functional Data Analysis was performed to compare trajectories of F0 and velocity in the contracted and non-contracted syllables. Preliminary results show that speakers always make an effort to produce the original tones, even in cases of extreme degrees of reduction. This finding militates against phonology-based accounts like the Edge-in model, according to which contraction is a process of deleting adjacent tonemes while leaving the non-adjacent tonemes intact.

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Abstract: Intonational research is often dependent upon hand-labeling by trained listeners, which can be prone to bias or error. We apply tools from Functional Data Analysis (FDA) to a set of fundamental frequency (F0) data to demonstrate how these tools can provide a less theory-dependent way of investigating F0 contours by allowing statistical analyses of whole contours rather than depending on theoretically-determined “important” parts of the signal. The results of this analysis support the predictions of current intonational phonology while also providing additional information about phonetic variability in the F0 contours that these theories do not currently model.

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Abstract: Creating stimuli for perceptual experiments in intonation research involves manipulation of pitch contours extracted from spoken utterances. Difficulties arise when changes in the contour shape need to be applied globally and smoothly in the whole pitch curve. Moreover, it is hard to relate a gradual modification in some contour trait to its perceptual counterpart. In this paper we propose a novel approach to stimuli manipulation that is based on an extension of Principal Component Analysis (PCA). Starting from a corpus of pitch curves a parametric description of the principal variation in the curve set is obtained. This allows to locate clusters in this parameter space that are related to linguistic categories. The search for pitch curves with desired perceptual characteristics is carried out by choosing convenient point locations with respect to the relevant clusters. We illustrate this approach in a case study on question/ statement opposition in Neapolitan Italian.

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Abstract: In this paper we introduce Functional Data Analysis (FDA) as a tool for analyzing dynamic transitions in speech signals. FDA makes it possible to perform statistical analyses of sets of mathematical functions in the same way as classical multivariate analysis treats scalar measurement data. We illustrate the use of FDA with a reduction phenomenon affecting the French word c’´etait /setE/ ‘it was’, which can be reduced to [stE] in conversational speech. FDA reveals that the dynamics of the transition from [s] to [t] in fully reduced cases may still be different from the dynamics of [s] - [t] transitions in underlying /st/ clusters such as in the word stage.

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