A Multi-Talker Dialect Corpus of Spoken American English: An Initial Report on Development 1

Abstract

A multi-talker multi-dialect corpus of spoken American English has been designed to provide researchers who are interested in variation and variability with a large number of speech samples from twenty talkers in each of four cities located in phonologically distinct dialect regions of the United States: West (Los Angeles), South (Atlanta), Midland (Indianapolis), and Northern Cities (Chicago). The speech samples to be collected include word-length, sentence-length, and paragraph-length utterances, and have been designed to elicit phonological forms that differentiate the four regions. Once collected, these materials can be used for a range of perceptual and acoustic studies investigating the perception and production of dialect variation in the United States. Objectives of the Corpus The purpose of this project is to create a speech corpus containing recordings from a large number of talkers from phonologically distinct dialect regions in the United States for use in a range of perceptual studies and acoustic analyses. Dialect variation, both regional and social in origin, has been an important topic of research in American English since the 1930’s when plans for a “Linguistic Atlas of North America” were first discussed (Cassidy, 1993). The first studies were primarily concerned with regional variation, focusing on differences in lexical items produced by older males from rural areas (Chambers, 1993). More recently, dialect research has been extended to include studies on social and ethnic variation, such as African American Vernacular English and Appalachian English (Wolfram & Schilling-Estes, 1998). Recent research has also begun to focus on phonological variation, particularly on variation and changes in progress that have been documented in the vowel systems of several American English dialects. For example, vowel shifts such as the Northern Cities Vowel Shift found in urban areas surrounding the Great Lakes and the Southern Vowel Shift found in rural areas of the Southern United States have been described in some detail (Wolfram & Schilling-Estes, 1998). While such phonological variation has been studied via field recordings and transcription, relatively little work has been done to document the acoustic properties of these phenomena or to study their perceptual correlates via playback experiments. While acoustic analysis is a commonly accepted technique for comparing and differentiating the vowel systems of different languages, it is not commonly employed in sociolinguistic research due to Labov’s “observer’s paradox” (Wolfram & Schilling-Estes, 1998). Simply put, the paradox refers to the effect of the observer’s presence (the observer being an experimenter, recording equipment, or any other tool of measurement) on the acoustic properties of speech produced by members of a dialect community of interest. The dialect variation that sociolinguists seek to document is almost always found in forms that appear in speech styles used more frequently in casual conversation, in specific pragmatic or situational contexts, or only with other members of the same dialect community. The intrusion of an experimenter from outside the dialect community and the effect of recording equipment on the formality of the conversational setting are perceived as barriers to the elicitation of the “deepest” form of the dialect in question (Wolfram & Schilling-Estes, 1998). Thus, the most commonly used method to investigate the properties of American English and other dialects involves making audio recordings of spontaneous speech and then phonetically transcribing those interviews. MULTI-TALKER DIALECT CORPUS 411 While such methods are useful in describing relatively gross differences between dialects, they suffer from a number of limitations for researchers interested in the acoustic-phonetic properties of phonological forms of a dialect, and for researchers developing controlled stimulus materials varying in dialect for use in perception experiments. First, the use of spontaneous speech entails a lack of control over the particular stimulus materials elicited. For the experimenter hoping to collect numerous tokens of a particular vowel or word in a common phonetic and prosodic context, it is very difficult to elicit such materials in a natural, spontaneous speech style (cf. Harnsberger & Pisoni, 1999). While certain tasks, such as topically-guided conversations or map tasks, can be used to elicit particular words or prosodic phrases, strict control over the phonetic context of these forms cannot be achieved. Control of phonetic context is crucial for any acoustic analysis, as well as in constructing stimulus materials for use in perception tests. Given these constraints, and given the purposes of this corpus, we have chosen to elicit speech materials in a read speech style, enabling control over the materials elicited. For the purposes of comparison only, we will also elicit a spontaneous sample from each talker, taking the form of a conversation with the experimenter administering the tests. While eliciting read speech undoubtedly limits the range of phonological variability we will observe between the dialects, we hope to ameliorate this problem by selecting American English dialects that have been shown in prior research to differ robustly from one another in terms of phonological patterns. We are also interested in documenting American English dialects that constitute relatively large communities within the United States. We believe that this will make the corpus as a whole more representative of American English dialectal variation than a corpus that is focused on much smaller dialect communities. We have therefore decided to record twenty talkers from each of four cities, representing four phonologically distinct regions: Atlanta (South), Indianapolis (Midland), Chicago (Northern Cities), and Los Angeles (West). For summary descriptions of each of the regional dialects, and for the rationale behind the selection of the boundaries defining these regions, see Wolfram and Schilling-Estes (1998) and Labov, Ash, and Boberg (1997). While we recognize that these four cities are not representative of all dialects of American English, we expect that they will provide us with some degree of phonological variation that is both acoustically and perceptually prominent, from a relatively large sample of talkers. The nature of the controlled stimulus materials, the focus on dialect variation, and the large number of talkers we plan to record are the three main features that set this corpus apart from other existing corpora. There are at least three existing spoken language corpora that include speech samples from a large number of talkers from a variety of American English dialects: the Santa Barbara Corpus of Spoken American English (LDC Catalog, 2001c), the CALLFRIEND project (LDC Catalog, 2001a; LDC Catalog, 2001b), and the TIMIT Acoustic-Phonetic Continuous Speech Corpus (Zue, Seneff, & Glass, 1990). The Santa Barbara corpus contains spontaneous speech samples from talkers from a wide range of geographic and socioeconomic backgrounds. The CALLFRIEND project contains recordings of telephone conversations between talkers which are grouped into two broad dialect categories: Southern and Non-Southern. The TIMIT Corpus contains ten read sentences from each of 630 talkers who come from eight defined dialect regions of the United States. The usefulness of the first two corpora in perceptual studies is limited by the lack of common stimulus materials for all talkers. The usefulness of the TIMIT corpus is also limited because of the ten sentences read by each talker, only two of those sentences were read by all 630 talkers. Spoken language corpora that control for stimulus materials also exist. However, they do not necessarily vary the dialect of the talkers in a systematic fashion. For example, corpora used in our lab such as the “Easy-Hard” Word Multi-Talker Speech Database (Torretta, 1995) and the Talker Variability Sentence Database (Karl & Pisoni, 1994) contain fixed sets of stimuli spoken by 10-20 talkers, but no effort was made to identify or control for dialectal variation in the talkers. The new corpus will combine CLOPPER, CARTER, DILLON, HARNSBERGER, HERMAN, CLARKE, PISONI AND HERNANDEZ 412 the systematic variation in dialect found in the TIMIT corpus with the control over a range of stimulus materials found in the “Easy-Hard” and Talker Variability databases. Once the corpus has been collected, we plan to use it in our lab for perceptual studies involving dialect identification, categorization, and discrimination by non-native listeners, lexical decision tasks, and voice quality judgement tasks involving dialect manipulations. This corpus will also be used in a series of perceptual learning tasks on dialect intelligibility after laboratory training and dialect manipulations in voice learning. Finally, the corpus will enable us to conduct acoustic-phonetic studies including descriptions of the vowel systems, analyses of diphthongal differences, and investigations into the acoustic correlates of stress across dialects. Organization of the Corpus

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