Intelligibility of English L2: The Effects of Incorrect Word Stress Placement and Incorrect Vowel Reduction in the Speech of French and Italian Learners of English

There is a debate in the literature on whether the intelligibility of English second language (L2) speech is more affected, among other things, by incorrect vowel reduction or by incorrect word stress placement. Identifying which features interfere most with intelligibility will assist in selecting what to prioritize in teaching pronunciation. The focus of this pilot study was to determine how incorrect vowel reduction or incorrect word stress placement, alone or in combination, impacts the intelligibility of Canadian French (CF) and Italian (I) L2 English. A close shadowing test was administered in which native (L1) English speaker/listeners responded to CF‐ and I‐accented English words containing naturally occurring word stress and vowel reduction errors in various combinations. Correct word identification and reaction time results confirm that both incorrect stress and vowel reduction interfere with L2 intelligibility. Results also suggest that even though misplaced word stress is damaging to intelligibility, incorrect vowel reduction is more detrimental. Andrée Lepage and Maria Grazia Busà 388 Arguably, one of the most pressing issues in L2 pronunciation research is the quest to identify the factors that contribute to an L2 English speaker’s intelligibility, or lack thereof (Chen, 2011; Field, 2005; Jenkins, 2000, 2002; Pickering, 2006; Zielinski, 2008). Intelligibility refers to the listener’s ability to correctly identify or recognize words or utterances (Field, 2005; Hustad, 2012; Jenkins, 2000, 2002; Kent, Weismer, Kent & Rosenbek, 1989; Kirkpatrick, Deterding & Wong, 2008; Smith & Nelson, 1985; Zielinski, 2006). It is influenced by many factors, one of which is the listener’s L1. In fact, it is now well‐known that when L1 listeners listen to L2 speech they apply their L1’s speech processing strategies in order to segment speech and identify words. Thus, when L1 English listeners listen to L2 English speech, some loss of intelligibility may be due to listeners applying their L1 speech processing strategies, to a speech signal that contains features that are non‐standard in terms of English phonology (Cutler, Mehler, Norris & Segui 1986; Cutler & Norris, 1988; Cutler & Van Donselaar, 2001; Field, 2005; Munro, 2008; Otake, Hatano, Cutler & Mehler 1993; Strange, 1995; Tyler & Cutler, 2009; Zielinski, 2008). In English, an important acoustic cue in word recognition and retrieval (i.e., identification) is word stress. This is because word stress (primary stress) in English is not fixed to a given position. In some words the first syllable is stressed, in other words the second syllable is stressed, and so on (e.g. parliament [ˈpɑɹ·lә·mәnt] versus parliamentary [pɑɹ·lә·ˈmɛn·tɹi]). It is a phonological characteristic (saved in the mental dictionary) and can serve a contrastive function to help distinguish between semantically distinct words (Friederici, Friedrich & Christophe, 2007; Honbolygo & Csépe, 2012; Kijak, 2009; Klein, 1984; Tremblay, 2007, 2008a, 2008b, 2009; Weber, Hahne, Friederich & Friederici, 2004). Word stress also gives rise to phonetic/phonological processes that can affect the phonetic quality of segments in the stressed and/or unstressed syllables (MacKay, 1987). For example, in English, stressing one syllable is accompanied by vowel reduction in one or more surrounding syllables (Ladefoged, 1975; Mackay, 1987) (e.g. photograph [ˈfo·tә·gɹæph] vs photographer [fә·ˈtɑ·gɹә·fɚ] vs photographic [fo·tә·ˈgɹæ·fәk]). 1 As argued by Huart (2002, p. 43), “the reduced form of a vowel in English is not a ‘form’ in itself but the consequence of lack of stress” (“les formes faibles ne sont pas à proprement parler des « formes », mais la conséquence de la non‐ accentuation.”) Therefore, instead of vowel reduction being viewed as a 1 A reduced vowel, as used in this paper, refers to the phoneme that is often taken to be a mid‐central vowel and is commonly termed schwa. Intelligibility of English L2 389 segmental phenomenon, it should be viewed as a suprasegmental phenomenon (phonological) which influences not only word identification (Braun, Lemhöfer and Mani, 2011; Flemming, 2009; Huart, 2002; Oostendorp, 1998) but also a language’s rhythmic properties (Capliez, 2011; Huart, 2002; Préfontaine, 2013). In short, in English, word stress and vowel reduction (prosodic features) have been found to help L1 English listeners identify spoken words (Cooper, Cutler & Wales, 2002; Field, 2005; Fear, Cutler & Butterfield, 1995; Munro, 2008; Tremblay, 2009; Trofimovich & Baker, 2006). Several studies have evaluated how word stress and vowel reduction impact L2 speakers’ intelligibility, but opinion is divided as to the relative contribution made by each. Some studies claim that misplacing word stress most compromises the intelligibility of L2 speech (Anderson‐Hsieh, Johnson & Koehler, 1992; Bond, 2005; Bond & Small, 1983; Cutler & Clifton, 1984; Field, 2005; Slowiaczek, 1990; Van Donselaar, Koster & Cutler, 2005; Zielinski, 2008), and that intelligibility is much more impaired when word stress is shifted to the right of its canonical position than when it is shifted to the left (Cutler & Clifton, 1984; Field, 2005). Other studies claim that L2 mis‐stressing has little effect on intelligibility as long as stressed vowels retain their quality and unstressed vowels are reduced (Cooper et al., 2002; Cutler, 1986). Conversely, another study found that changes in vowel quality, when stress is shifted, have no effect on word recognition (Small, Simon, & Goldberg, 1988). Research has yet to tease apart the effect that word stress and vowel reduction have on intelligibility, and precisely to determine if it is the isolated effect of each, or the combination of the two errors that impairs intelligibility. Identifying how intelligibility in English L2 speech is affected by these features fills out a gap in the literature. In addition, from a pedagogical perspective, knowing how these specific features of (mis)pronunciation, alone or in combination, contribute to the intelligibility of English L2 speech can provide valuable information to those testing, learning and teaching second languages (Derwing, Munro, & Wiebe, 1998; Derwing & Munro, 2005). This study sought to determine how incorrect word stress and incorrect vowel reduction, alone or in combination, impact the intelligibility of Canadian French and Italian‐accented English. Notable aspects of French and Italian‐accented English are incorrect word stress and incorrect vowel reduction; both negatively affect the intelligibility of L2 English speech for native English speakers (Busà 1995; Dupoux, Pallier, Sebastián‐Gallés & Mehler, 1997; Dupoux, Pallier, Sebastián‐Gallés, Navarete & Peperkamp, Andrée Lepage and Maria Grazia Busà 39