Is Acquisition of L2 Phonemes Difficult? Production of English Stress by Japanese Speakers

This study examined the production of English lexical stress by Japanese speakers to determine which acoustic features associated with English lexical stress are difficult for Japanese speakers to acquire. Realization of lexical accent differs between languages. English is a stress-accent language where the accent is expressed by a combination of pitch, duration, intensity and vowel quality (Fry 1955, Gay 1978, Kochanski et al. 2005 & Kochanski and Orphanidou, 2008). In contrast, Japanese is a pitch-accent language where the accent is dominantly realized by a fall in the fundamental frequency (F0) from an accented high pitched mora to the following mora, and there is very little use of intensity to mark accent (Fujisaki et al. 1986). Studies on non-native English learners have shown that problems on acquiring English stress vary depending on their first language (L1). For example, Arabic speakers show different use of F0 and formant frequencies in stressed and unstressed vowels compared with native English speakers (Zuraiq & Soreno 2007). Lee et al (2006) also reported that Japanese speakers found it difficult to achieve vowel centralization of English unstressed vowels. This study investigated the effect of Japanese (L1) prosody on English (L2). In particular, the study focused on how Japanese speakers who speak fluent English still show the influence of Japanese phonology, and also examined whether there are any characteristics notably different from native English speakers’ utterances. Different factors influence L2 speech rhythm. For example, different languages use different phonological units to keep speech rhythm. Japanese uses the mora as the fundamental unit for its speech rhythm and many studies have reported mora-based timing control for Japanese. The duration of each mora is not necessarily equal, but the duration of a word or phrase is determined by the number of morae in it (Port et al., 1987). There is mora-based segmental elasticity and durational compensation between CV which constitutes a mora rather than between V-C across a mora boundary (Campbell and Sagisaka, 1991; Sato, 1993). The effect of the mora on L2 has been reported in English (Mochizuki-Sudo & Kiritani 1991) and in French (Kondo & Shinohara, 2003 & 2006). Vowel quality is also an important cue for stress in English. Everything being equal, vowels in unstressed syllables are shorter and have centralized quality. Although the order of importance among these acoustic cues of English stress varies from study to study, all these are important cues to differentiate stressed and unstressed syllables in English (Fear et al., 1995). Considering the prosodic differences between English and Japanese, various factors affect L2 speech rhythm. An earlier study (Kondo, 2007) found an L1 influence in English speakers’ Japanese utterances. English speakers showed strong influence of lexical accent on vowel duration in their Japanese utterances. They showed two patterns: (i) large F0 increase but little durational increase, and (ii) durational increase instead of any F0 increase. In the present study most of the Japanese subjects spent some years in English speaking environments and spoke relatively good English. However, they still showed some influence of their L1, Japanese, in their English utterances. Among these acoustic features, i.e. vowel duration, F0, intensity and quality, some features are easier to acquire than others and some take longer to acquire during the process of L2 sound acquisition.