Corpus and acoustic analyses

Corpus analyses, acoustic and articulatory studies are fundamental for the study of phonological variation. They allow researchers better to define the output of the production process. As such, they may also provide useful information on the nature of the mechanisms underlying the production of words with several pronunciation variants. While psycholinguistic issues have long been the prerogative of experimental on-line investigations, recent large-scale corpus studies have also allowed researchers to address important questions related to the representations and mechanisms involved in word production (see for example Bell et al., 2009; Kuperman et al., 2007; Pluymaekers et al., 2005; Raymond, Dautricourt & Hume, 2006).

Large corpora of this kind, unlike controlled experiments, have the advantage of reflecting the natural output of the linguistic system. As such, they provide crucial information on the

44

diverse types of phenomena occurring in connected speech, their frequency and the conditions in which they occur.

The use of corpora for phonetic studies raises a few methodological questions. The first methodological question concerns the criteria/methods used for corpus annotation/alignment.

Until recently, corpora were aligned (i.e., segmented into words and phonemes) manually.

More and more frequently however, automatically aligned corpora are used for phonetic studies. The main advantage of an automatic alignment is to drastically increase the amount of data without requiring additional work. However, depending on the linguistic processes under examination, an automatic alignment may not always be reliable. In Bürki, Gendrot, Gravier, Linares and Fougeron (2008), we investigated the adequacy of different automatic alignment systems for the alignment of French schwa words. This investigation allowed us to document error types (in terms of duration and presence/absence of the schwa vowel) for different alignment systems as well as to examine the variables influencing these errors. Our results show that overall, automatic alignments, be it for duration or the absence/presence of the schwa, are rather imprecise and strongly biased by the surrounding consonantal context.

In addition, they differ depending on the properties of the alignment systems. Hence, automatic alignments do not always provide sufficient precision for the study of phonological variation and may require a manual correction of the segmentation.

Manual alignments, on the other hand, also have their drawbacks. Firstly, a manual alignment is extremely time-consuming. Hence, studies using a manual alignment often use smaller data sets. Secondly, while manual alignments are more precise than automatic alignments, they are also reliant on the criteria used for segmentation. For instance, in Bürki et al. (submitted) we showed that depending on the classification method (perceptual versus acoustic-based), criteria and coding conditions (e.g., isolated words versus sentences), what is considered a schwa or a non-schwa variant in a given corpus can differ drastically. Hence, the influences of these methodological choices on the studies’ outcomes have to be taken into account.

A second methodological issue concerning the use of corpora for the study of phonological variants concerns the generalizability of these studies’ findings. Corpora are often restricted to a given speech style or register. We know that phonological variation is largely influenced by speech style and register. Hence, one must be aware of the fact that results of such analyses cannot always be generalized to other forms of speech.

45

Apart from corpus analyses, the output of the production of phonological variants can also be examined through detailed acoustic and articulatory analyses. According to Baayen (2007), evidence is accumulating that the speech signal itself is a source of information about the architecture of the mental lexicon. Studies investigating the fine phonetic details of realized forms have indeed provided useful information on this issue. For instance, acoustic studies have allowed researchers to suggest that processes that have traditionally been considered to be categorical (with a locus in the lexical or phonological component) show acoustic evidence in favor of a gradual process arising in the phonetic component. This is the case, for instance, with schwa deletion in English (Davidson, 2006).

Acoustic and articulatory studies also raise a few methodological issues. Firstly, we know that many different variables may influence the acoustic realization of words. Acoustic and articulatory studies often rely on the comparison between different words or sequences.

However, it is not always straightforward to disentangle the acoustic cues related to the phenomenon under consideration from acoustic cues that are related to other variables that differ between the words or sequences being compared. For instance, several studies have investigated the acoustic properties of clusters in non-schwa variants (e.g., [pl] in p’louse

‘lawn’). The key questions were whether these clusters show different acoustic properties from identical underlying clusters (e.g., [pl] in plage ‘beach’), and whether acoustic residues attributable to schwa are apparent in the non-schwa variants’ clusters. These studies often found differences between clusters in non-schwa variants and identical clusters in non-schwa words or pseudowords. However, in these studies, many variables differed between the sequences under consideration (e.g., word length, cluster position with regard to word boundaries, etc.). As a consequence, it is not possible to decide whether the observed differences are due to schwa or to these other variables. This issue will be further discussed in Chapter II. We will perform an acoustic analysis of clusters in schwa and non-schwa words with a strict control of possible confounding variables.

A second methodological issue related to the study of phonological variants through acoustic and articulatory studies relates to the phonotactic restrictions of a given language.

Phonological variants may lead to sound sequences which do not obey the phonotactic rules of the language. As a consequence, it is not always possible to find the appropriate stimuli for comparison (i.e., words with the same sound sequences but which are underlying rather than the result of a phonological process). For instance, for most non-schwa variants in French, there is no existing word with an identical underlying cluster in the same position

46

regarding word and syllable boundaries. Thus, the lack of relevant material for comparison makes it difficult to examine whether clusters in non-schwa variants behave similarly to identical underlying clusters. This issue will be further discussed in Chapter II (Phonetic study 1).

As argued above, we believe that corpus, acoustic and articulatory studies are fundamental for the study of phonological variants. We also believe that such studies are by themselves insufficient. In addition to these off-line tasks, on-line experimental data are needed to provide information about the time course of the production process and pinpoint the exact locus of the phenomena under consideration.