A number of studies have been conducted to investigate the effects of acoustic and perceptual similarities of cross-linguistic phonemes, i.e. vowels and consonants (Elvin et al., 2014; Escudero et al., 2014; Escudero and Williams, 2011; Escudero and Chládková, 2010; Gilichinskaya and Strange, 2010; Escudero, Benders, and Lipski, 2009; Strange et al., 2004; Strange et al., 2005; Escudero and Boersma, 2002). Although, according to Strange et al. (2004), acoustic similarity does not predict perceptual assimilation patterns, these studies suggest that acoustic and phonetic similarities between L1 and L2 can predict the patterns of perceptual assimilation by L2 learners.
In a recent study Elvin et al. (2014) and Escudero et al. (2014) reported that acoustic similarities between L1 and L2 are better predictors of both the assimilation patterns and discrimination difficulties faced by L2 learners. Elvin et al. (2014) investigated if the vowel inventory size and acoustic properties (i.e. similarities and differences) between Australian English (12 monophthongs), Iberian Spanish (5 monophthongs) and Brazilian Portuguese (7 monophthongs) can help to predict the difficulties faced by Australian and Iberian Spanish learners of Brazilian Portuguese. Their results showed that Iberian Spanish learners of Brazilian Portuguese outperformed Australian English learners of Brazilian Portuguese, which suggested that vowel inventory size was non-significant; however, acoustic similarities between Iberian Spanish and Brazilian Portuguese were good predictors.
Escudero et al. (2014) investigated the assimilation patterns of Southern British English (SBE) vowels by 12 male speakers of Salento Italian (SI) who learned English as a foreign language at school. Escudero et al. (2014) compared these assimilation patterns with Peruvian Spanish learners of Southern British English. Despite the fact that both Salento Italian and Peruvian Spanish have a five-vowel system, their assimilation patterns of
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Southern British English vowels were quite different. Therefore, Escudero et al. (2014) concluded that cross-language acoustic similarities between L1 and L2 can predict the assimilation patterns of L2 learners as well the difficulties faced by them. For example, they reported that identical F2 values for SBE /ɪ/ and SI /i/ successfully predicted that SBE /ɪ/ was assimilated to SI /i/, and that similar F1 values for SBE /ɔː/ and SI /o/ predicted that SBE /ɔː/ was assimilated to SI /o/.
Research shows that acoustic similarities between L1 and L2 can help to predict the patterns of assimilation. For instance, Escudero and Williams (2011) investigated the perceptual assimilation patterns of Dutch vowels by naïve Spanish speakers (20 males and 20 females), and they found that there were more single-category (SC) assimilation patterns than two-category (TC). They concluded that the acoustic similarity between Dutch and Spanish vowels helped to predict the possible assimilation patterns. Due to there being far fewer Spanish vowels (5 monophthongs) as compared to Dutch (12 monophthongs) it was predicted that there will be more SC patterns. They did not test the category goodness rating to see if these patterns were representative of good or bad exemplars of L1.
Similarly, in an earlier study, Escudero and Chládková (2010) investigated Spanish listeners’ (20 males and 20 females) perception of American English and Standard Southern British English vowels in a synthetic stimulus of 9 English monophthongs. As they predicted, Spanish listeners showed perceptual assimilation patterns based on the acoustic/spectral similarity between the vowels of Spanish and the particular variety of English, and thus their assimilation patterns for the two varieties of English differed. This study supported L2LP predictions. However, they did not investigate the effects of temporal differences between vowels across languages.
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English tense and lax vowels have proven quite difficult for L2 learners of other languages, as shown in a number of studies (Flege et al., 1998; Flege et al., 1999; Baker et al., 2002; Escudero and Boersma, 2002; Escudero, 2005; Escudero and Chládková, 2010; Escudero et al., 2014). Gilichinskaya and Strange (2010) investigated the perceptual assimilation of 8 American English (AE) vowels /iː/, /ɪ/, /ɛ/, /æː/, /ɑː/, /ʌ/, /ʊ/ and /uː/ in disyllables /Vpə/ by 19 Russian speakers. Their results showed that Russian speakers assimilated AE vowels based on their acoustic similarity with the respective Russian vowels. However, the rest of the vowels were not assimilated consistently. Their findings also showed that /ɪ/-/ɛ/ and /ɑː/-/ʌ/ were the most difficult for Russian speakers. AE /ɑː/-/æː/ were categorised-uncategorised, whereas /iː/-/ɪ/ and /uː/-/ʊ/ showed two- category assimilation patterns. Based on these patterns they predicted that English tense and lax vowels will be easier for Russian speakers to perceive and produce. This shows that L1 plays a significant role in the perception of L2 sounds.
Previous studies have also shown that with regard to the native language, both monolingual and bilingual learners vary in their reliance on spectral and temporal cues for the perception of L2 vowels. For example, Escudero, Benders, and Lipski (2009) investigated the use of spectral and temporal cues for the categorization of the Dutch /ɑ/- /aː/ contrast. The three groups of listeners: monolinguals; L1-Dutch (31), and L1-German (31), bilinguals; L1-Spanish and L2-Dutch (38), were presented with synthetic stimuli of the Dutch vowel contrast in an XAB task. Their findings showed that bilingual (L1- Spanish and L2-Dutch) listeners rely more heavily on temporal than spectral cues. On the other hand, though L1 German listeners showed more reliance on spectral than on temporal cues, L1-German listeners were not accurate in their categorisation of the Dutch contrast. Overall, L1-Spanish and L2-Dutch, with high or intermediate proficiency of Dutch, categorised the vowels correctly as compared to L1 German, who did not have any experience/knowledge of Dutch. Hence experience of L2 affects categorisation; at
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the same time, the role of L1 cannot be neglected since it alters the perception patterns, i.e. paying more attention to temporal (Spanish listeners) or spectral (Dutch and German listeners) cues.