According to Flege, MacKay and Meador (1999), early exposure to L2 results in better perception and production of L2 sounds. Flege et al (1999) investigated the categorical discrimination of English and Italian vowels in three different sets as follows: English vowel pairs: /i/-/ɪ/, /u/-/ʊ/, /æ/-/ʌ/, and /ɒ/-/ʌ/; one English and one Italian in vowel pairs: /æ/-/a/, /ʌ/-/a/, /u/-/o/ and /e/-/e/; Italian vowel pairs /u/-/o/, /e/-/a/ and /u/-/i/). Their participants were highly experienced Italian-English bilinguals and they were divided into four groups based on their Age of Arrival (AoA) in Canada. Their results showed that native Italian speakers who started to learn English early discriminated English vowels
134
better than late learners, “early bilinguals who are highly experienced in their L2 may perceive L2 vowels in a nativelike fashion” (Flege et al., 1999:2981). These findings led them to conclude that early bilinguals might have established phonetic categories (Flege, 1995) for English vowels /ɪ/ and /ʊ/ which do not occur in Italian. Hence the discrimination patterns for English /i/-/ɪ/ and /u/-/ʊ/ were different between early/mid (AoA) bilinguals and late bilinguals. From the production experiment, Flege et al. (1999) found that late Italian learners of English neutralised the differences between low and mid-central English vowels such as /æ/, /ɒ/ and /ʌ/. Hence the categorical discrimination task for vowel contrasts /æ/-/a/, /ʌ/-/a/, /ʌ/-ɒ/ and /ʌ/-/æ/, the late bilingual group scored less than native speakers of English. Overall, this study supported two SLM hypotheses, i.e. category formation by early learners of L2, and accurate production of L2 depends on the accurate perception of L2. However, later studies (Flege and MacKay, 2004) have shown that native-like perception does not guarantee native-like production of L2 segments.
In an earlier study, Flege et al. (1998) found that three-year exposure to native English input affected the perception of English consonants by native Japanese speakers. Experienced Japanese speakers performed better than inexperienced speakers for the discrimination of consonant contrasts: /ɹ/-/l/, /s/-/θ/, /b/-/v/, and /ɹ/-/w/; however, there was no difference in their performance for the identification of vowel contrasts: /u/-/ʊ/, /ɑ/-/ʌ/, /eɪ/-/ɛ/, and /i/-/ɪ/. This suggests that perceived relations between English and Japanese consonants may change with experience and exposure, but perceived relations between English and Japanese vowels remains unaffected.
Previous studies have supported SLM hypothesis that children are good at category establishment, since they can detect the phonetic and acoustic differences between L1 and L2. Baker et al. (2002) investigated the identification of eight English vowels, /i/- /ɪ/, /u/-
135
/ʊ/, /æ/-/ɛ/, and /ɑ/-ʌ/ by Korean speakers. According to Flege, Bohn and Jang (1997 cited in Baker et al., 2002:3), these pairs of vowels are considered to be difficult to discriminate and easily confused by Korean speakers in perception and production. Cross-language identification tests were carried out with adults (22-23 years old) and children (7-9 years old), all monolingual Korean speakers who have been living in the US for a year or less. The English vowels were embedded in three different contexts: /bVt/, /nVt/ and /hVd/. The listeners had to pick one of the 10 standard Korean vowels and rate on a 7-point scale how similar that sound was to a given Korean vowel. The results showed that assimilation patterns for English vowels were similar for both adults and children. For example: English /i/-/ɪ/ were matched to Korean vowel /i/; English /u/-/ʊ/ were matched to Korean /u/; English /æ/-/ɛ/ were matched to Korean /ɛ/ and /e/ (these were the most confusing vowels for them); and English /ɑ/-/ʌ/ were matched to two separate Korean vowels /a/ and /ʌ/ respectively. The only difference in perception between the two age groups (i.e. adults and children) was the goodness rating, where children’s goodness rating was lower than adults, which suggests that they did not consider English vowels good examples of native Korean vowels. This finding supports the SLM hypothesis that children are good at category establishment, since they can detect the phonetic and acoustic differences between L1 and L2, and as a result perform better (more native-like) in perception and production of L2 vowels. Overall, this study suggests that adult/late learners are unlikely to establish new categories for L2 once their L1 phonological system is fully developed. Further, their results showed that L2 exposure and input improves an adult learner’s perception and production of only those vowels that are non-confusing and similar to L1 vowels.
In order to answer the question of whether early L2 learners can perceive L2 vowels like native speakers of that L2, Flege and MacKay (2004) investigated the perception of six English vowels /ɒ/-/ʌ/, /ɛ/-æ/ and /i/-/ɪ/ by native speakers of Italian, grouped by: early
136
(child) vs. late (adult) learners, age of arrival in Canada (AoA), length of residence (LoR) in Canada, and regular use of L1 (Italian). Their findings showed that though early learners were better in their discrimination and perception, some adult learners also perceived the contrasts accurately. Despite this, their findings broadly supported the SLM hypothesis that late learners’ perception of L2 vowels is not as accurate as early learners. They showed that experience and exposure to L2 can help to establish new categories for L2 vowels, as this ability remains intact throughout life (Flege, 1995). Interestingly, some of their findings from early learners of L2, who used L1 more often than L2, were not as predicted and they concluded that learning an L2 at a young age does not guarantee native-like competence in L2. Similar to previous studies, this study did not answer why age (child vs adult) and experience (exposure to L2) affect some learners’ perception of L2 vowels but not others.
Contrary to the above-mentioned studies, Jia et al. (2006) reported that experienced adult L2 learners perform better than young L2 learners. They reported that the amount of L2 exposure and age (young vs. adult learners) has a strong effect on the perception and production of L2 vowels. In particular, their findings suggested that in a non-native context with non-native input of L2, adult learners have an advantage in accurately perceiving and producing L2 sounds. In China, participants’ lack of exposure to native input “…an older chronological age predicted a significantly higher discrimination accuracy of all vowel contrasts and higher production accuracy of two difficult vowels” (Jia et al., 2006:127). This contradicts the SLM hypothesis that children are better at perceiving and producing L2 vowels because their L1 phonetic system is not fully developed (Baker et al., 2002).
Individual differences in vowel perception were highlighted by Wang (2006) who investigated the perceptual assimilation patterns of Mandarin speakers living in Canada
137
for six English vowels, /i/-/ɪ/, /u/-/ʊ/ and /æ/-/ɛ/, with temporal and spectral variations by synthetic manipulation. The results showed that Mandarin speakers used duration cues more so than spectral cues for the English vowel pair /i/-/ɪ/. Hence their assimilation patterns were not native-like. In addition, the results from individual listeners showed different strategies for discrimination/identification, and that most of the listeners did not manage to identify English vowels /æ/-/ɛ/ and /u/-/ʊ/ as two distinct categories. This is somewhat similar to how native speakers of American English integrated both spectral and duration cues to identify French /ɔ/-/o/ in synthetic stimuli, whereas native speakers of French used only spectral cues to identify these two vowels (Gottfried and Beddor, 1988).
Gottfried and Beddor, (1988) investigated the perception of French /o/-/ɔ/ vowels in /kot/- /kɔt/, with temporal and spectral variations using synthetic manipulation. Participants consisted of a group of native French speakers and two groups of American English speakers, one that studied French and another that did not study French. Their results showed that French native speakers did not pay attention to the temporal cues in both categorisation and category rating tasks. However native speakers of American English integrated spectral and temporal information in order to categorise the two vowels. This led them to conclude that
“[P]erceptual integration of the acoustic properties relevant to a given vowel contrast does not simply follow from experience with that contrast. Rather, perceptual integration depends on the extent to which the acoustic properties correlate within the broader context of a phonological system” (Gottfried and Beddor, 1988:63).
Although experience and exposure to L2 (early versus late) is considered an important factor in the perception of L2, the relationship between temporal and spectral cues and
138
the phonological system of L1 also plays a significant role in the perception of L2 sounds. This could explain why experience does not affect the perception of certain L2 sounds (Flege and MacKay, 2004).
All the above studies are based on monolingual L2 learners who receive native input at some point in their life. None of these studies considered L2 learners who start learning English at a very young age, but do not receive native input except for Jia et al. (2006).
In the past three decades, the research on SLM has focussed on the role of L1, experience, exposure to L2, and age of learning. The studies on SLM showed that accurate perception and proficiency do not guarantee accurate production. These studies lack investigation of individual variations in speech perception and production in order to answer why age, experience and exposure to L2 do not affect perception and production in some cases.