Perception of the incoming acoustic signal in bilingual speakers seems to be modulated by the language they believe they are hearing. Second language (L2) learners need to create a second phonetic system for their L2 in order to understand assign meaning to the sounds in that language. Some sounds will be similar to the sounds in their first language (L1), others will differ, and a third group will require a perception readjustment of L1 phonemes. The independence of the L2 system from the L1 system when phonemes are readjusted is unclear.
Previous studies [@Casillas2018; @Gonzales2013; @Gonzales2019] indicate that English-Spanish bilinguals exhibit a double phonemic boundary for the phonemic continuum /b/-/p/ (i.e., a difference between labeling functions obtained when listeners find themselves in Spanish mode and those obtained when they are in English mode). These studies provide evidence supporting the notion that there is some degree of separation between phonetic systems in the bilingual mind even for phonemes belonging to a single continuum when the speakers are both auditorily and conceptually cued and when they are auditorily cued exclusively. The present study intends to replicate previous findings when adult L2 learners at different levels of proficiency are only conceptually cued towards one language or another. This question is central to understand how the bilingual mind adapts perception depending on linguistic context.
Previous studies [@Casillas2018; @Gonzales2013; @Gonzales2019] indicate that bilinguals exhibit a double phonemic boundary, i.e. they adjust their perceptual categorization routines based on the language context. These findings align with language mode theories (@Grosjean1999, @Grosjean2001), according to which speakers move from a language mode to the other depending on the communicative context of an interaction ("Spanish" or "English" mode). Choosing a language mode or another lets speakers shift their mental perception categorization to make sense of the oncoming messages and to produce information with the linguistic properties of the activated language. Bilinguals rely on perceptual cues associated to the language spoken for mode selection [@Grosjean1988; @Molnar2015] but they can also use their own conceptual knowledge of the communicative context [@Grosjean2008; @Tare2010].
Studying interlanguage variation can shed light on how phoneme systems are stored and sounds are rearranged for each language, especially when the categorization of a phoneme continuum needs to be shifted from a first language (L1) to a second language (L2). An example of this shift is the phoneme continuum /b/-/p/, which differs from English to Spanish. In English, utterance-initial /b/ and /p/ are both voiceless, and /p/ is aspirated [@Beckman2013; @Iverson1995; @Lisker1964]. In Spanish, both phonemes are unaspirated, but /b/ is voiced [@Abramson1972; @Kirby2016; @Lisker1964; @Rosner2000]. Thus, aspiration is used to distingish each phoneme in English, while voicing does so in Spanish. These properties make an English speaker perceive an unaspirated, voiceless bilabial stop [p] as /b/, whereas a Spanish speaker will be prone to categorize it as /b/ [@Elman1977; @Garcia_Sierra2009]. In order to accurately categorize the sounds heard, a bilingual speaker will therefore need to shift the phoneme perceptual boundary according to the language she is speaking.
Prior research suggests that perceptual cues [@Gonzales2013] and conceptual cues [@Gonzales2019] can trigger a change in language mode in early bilinguals, and perceptual cues also activate language mode in late bilinguals (@Casillas2018). Thus far, however, no studies have examined whether adult L2 learners can activate a language mode based on conceptual cues. The representation of a second language is known to be more difficult once native language categories are established, and the acquired first language phonological system influences the production and perception of second language sounds [@Best2007; @Flege1995; @VanLeussen2015]. Escudero's Second Language Linguistic Perception model (L2LP) [@Escudero2005; @VanLeussen2015] postulates that the learners initially create a copy of their L1 phonological system and perceive L2 sounds in terms of L1 categories. As they learn the language, the phonology of this copy is being gradually adjusted in an L2-specific manner by alterating the existing L1 categories or creating new L2 phonetic categories. According to this model, late L2 speakers can form phonetic categories specific to their L2. Along these lines, @Casillas2018 indicate that late L2 learners of intermediate proficiency are also able to display the effects of mode-specific categorization routines when language mode is activated through perceptual cues. However, it remains unknown whether the double phonemic boundary effect is displayed at beginning stages of L2 acquistion and whether conceptual cues can also trigger this shift in adult L2 learners. Answering this question is crucial to identify the factors that play into the development of two phonemic systems.
Perceptual cues help early bilingual speakers in shifting from a phoneme categorization system to another one. @Gonzales2013 investigated how bilinguals perceptually accommodate speech variation across languages. In their experiment, Spanish-English bilinguals and English monolinguals listened to Spanish and English continua of pseudowords ('bafri' and 'pafri') and indicated which of the two "words" was spoken by pressing a key. The language context was manipulated through the instructions and through the phonetic makeup of pseudoword endings. @Gonzales_Lotto2013 found that Spanish-English bilinguals had separate perceptual boundaries depending upon the language-specific continua. The findings suggest that bilinguals adjust perceptual categorization across language contexts by switching between language-specific phonetic systems.
@Casillas2018 found further evidence that bilinguals can maintain separate phonetic systems. Specifically, they explored whether Spanish-English bilinguals and native English speaking L2 learners of Spanish utilized different categorization criteria based on language mode (unilingual, bilingual). Crucially, language mode was only phonetically cued via the stimuli of the VOT continua. The study included 2 experiments. In the first experiment, simultaneous Spanish-English bilinguals and beginning adult learners of Spanish showed language-specific perceptual boundaries in independent unilingual sessions, thus replicating @Gonzales2013, and extending the finding to L2 learners. In the second experiment Spanish-English bilinguals and late learners of Spanish identified stimuli drawn from the VOT continua in a single, bilingual session. Both early and late bilinguals showed mode-specific perceptual normalization criteria in conditions of rapid, random mode switching. Importantly, the study showed that bilinguals can exploit language-specific perceptual processes in real time and that this ability appears to be modulated by language proficiency in late learners.
@Gonzales2019 continued this line of research by examining whether conceptually-based language selection, which is frequent in the spoken modality, is also possible in the listening modality. In their experiment, Spanish-English bilinguals and French-English bilinguals listened to a /b/-/p/ continuum of the beginnings of language neutral pseudowords (Spanish-English: bafri, pafri; French-English: befru, pefru) and indicated which "word" the speaker was beginning to say. The language context was manipulated conceptually through the instructions only. The study showed that both groups displayed different voicing boundaries that corresponded with the language they believed they were hearing. This suggests that conceptually-based perceptual categorization is possible in highly proficient bilinguals.
In sum, previous research suggests that bilinguals can maintain some degree of separation between sound systems. Language-specific perceptual categorization can be phonetically cued in both early and late bilinguals @Gonzales2013; @Casillas2018), and conceptually cued in early bilinguals @Gonzales2019. The present study builds on this line of research by investigating whether the double phonemic boundary effect can be conceptually cued in adult second language learners of different proficiencies.
The present article is a conceptual replication of @Casillas2018. In their study, they compared the double phonemic boundery effect in simultaneous bilinguals and beginner adult L2 learners of Spanish. Results indicated that whereas simultaneous bilinguals display the double phonemic boundery effect when acoustically cued in both bilingual and unilingual modes, adult L2 learners showed the effect in the unilingual mode. When L2 learners were faced with the bilingual mode, only the more proficient learners displayed the effect.
In our replication, we explore whether the double phonemic boundary effect can be conceptually cued in adult second language learners (participants were explicitly instructed that they were hearing English or Spanish) as opposed to acoustic cues (inclusion of the Spanish or English realization of the segment r). Specifically, we explore how late Spanish-English bilinguals categorize the /b/-/p/ acoustic continuum varying in VOT. Importantly, we assessed how L2 proficiency impacts the double phonemic boundary effect in adult learners during unilingual mode.
Specifically, we try to answer the following research questions:
- Can second language learners be conceptually cued to adopt a specific unilingual mode?
- Does L2 proficiency modulate their ability to separate the two phonemic systems?
We predict that speakers will categorize phonemes based on conceptual cues. Additionally, conceptually cued language-specific phonetic categorization develops as a function of language proficiency, such that adult L2 learners of Spanish will display different phonemic boundaries for each language as proficiency in Spanish increases. If these results were born out, then the existence of independent phonemic systems for each language would be confirmed, as well as the shift between language modes based on conceptual cues alone.