Dissertation Defense: Erika Exton (HESP)
Evaluating the role of acoustic cues in identifying the presence of a code-switch
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Abstract: Code-switching (switching between languages) is common in bilingual speech directed to infants and children. In adult-directed speech (ADS), acoustic-phonetic properties of one language may transfer to the other language close to a code-switch point; for example, English stop consonants may be more Spanish-like near a switch. This acoustically-natural code-switching may be easier for bilingual listeners to comprehend than code-switching without these acoustic changes; however, it effectively results in the languages being more phonetically similar at the point of a code-switch, which could make them difficult for an unfamiliar listener to distinguish. The goal of this research was to assess the acoustic-phonetic cues to code-switching available to listeners unfamiliar with the languages by studying the perception and production of these cues.
In Experiment 1 Spanish-English bilingual adults (particularly those who hear code-switching frequently), but not English monolingual adults, were sensitive to natural acoustic cues to code-switching in unfamiliar languages and could use them to identify language switches between French and Mandarin. Such cues were particularly helpful when they allowed listeners to anticipate an upcoming language switch (Experiment 2). In Experiment 3 monolingual children appeared unable to continually identify which language they were hearing. Experiment 4 provides some preliminary evidence that monolingual infants can identify a switch between French and Mandarin, though without addressing the utility of natural acoustic cues for infants.
The acoustic detail of code-switched speech to infants was investigated to evaluate how acoustic properties of bilingual infant-directed speech (IDS) are impacted by the presence of and proximity to code-switching. Spanish-English bilingual women narrated wordless picture books in IDS and ADS, and the voice onset times of their English voiceless stops were analyzed in code-switching and English-only stories in each register. In ADS only, English voiceless stops that preceded an English-to-Spanish code-switch and were closer to that switch point were produced with more Spanish-like voice onset times than more distant tokens. This effect of distance to Spanish on English VOTs was not true for tokens that followed Spanish in ADS, or in either direction in IDS, suggesting that parents may avoid producing these acoustic cues when speaking to young children.
