Natural vs forced language switching: Free selection and consistent language use eliminate significant performance costs and cognitive demands in the brain.

Bilinguals are known to switch language spontaneously in everyday conversations, even if there are no external requirements to do so. However, in the laboratory setting, language control is often investigated using forced switching tasks, which result in significant performance costs. The present study assessed whether switching would be less costly when performed in a more natural fashion, and what factors might account for this. Mandarin-English bilinguals engaged in language switching under three different contexts with varied task demands. We examined two factors which may be characteristic of natural switching: (i) freedom of language selection; (ii) consistency of language used to name each item. Participants' brain activities were recorded using magnetoencephalography (MEG), along with behavioural measures of reaction speed and accuracy. The natural context (with both free selection and consistent language use for each item) produced better performance overall, showing reduced mixing cost and no significant switch cost. The neural effect of language mixing was also reversed in this context, suggesting that freely mixing two languages was easier than staying in a single language. Further, while switching in the forced context elicited increased brain activity in the right inferior frontal gyrus, this switch effect disappeared when the language used to name each item was consistent. Together, these findings demonstrate that the two factors above conjointly contribute to eliminating significant performance costs and cognitive demands associated with language switching and mixing. Such evidence aligns with lexical selection models which do not assume bilingual production to be inherently effortful.

Evaluating automatic creaky voice detection methods.

There is growing interest in research on the non-modal voice quality, creaky voice; however, its identification often relies on time-consuming manual annotation, leading to a recent focus on automatic creak detection methods. Various automatic methods have been proposed, which rely on varying types and combinations of acoustic cues for creak detection. In this paper, we compare the performance of three automatic tools, the AntiMode method, the Creak Detector algorithm, and the Roughness algorithm, against manual annotation of creak using data from 80 Australian English speakers. We explore the possibility that tools used in combination may yield more accurate creak detection than individual tools used alone. Based on method comparisons, we present options for researchers, including an "out-of-the-box" approach, which supports combining automatic tools, and propose additional steps to further improve creak detection. We found restricting analysis to sonorant segments significantly improves automatic creak detection, and tools performed consistently better on female speech than male speech. Findings support previous work showing detection may be optimised by performing a creak probability threshold sweep on a subset of data prior to applying the Creak Detector algorithm on new datasets. Results provide promising solutions for advancing efficient large-scale research on creaky voice.

Effects of Glottalisation, Preceding Vowel Duration, and Coda Closure Duration on the Perception of Coda Stop Voicing.

English has multiple potential acoustic cues to coda stop voicing, including the duration of the preceding vowel, the coda closure duration, and, in some varieties, glottalisation. Glottalisation associated with coda stops appears to be a recent change to Australian English (AusE) with younger speakers using glottalisation more than older speakers in production. Here we report on a study designed to examine AusE-speaking listeners' perception of cues to coda stop voicing. Listeners were presented with audio stimuli in which preceding vowel duration, coda closure duration, and the relative proportions of the rhyme that these occupy were manipulated and co-varied with the presence or absence of glottalisation. The results show that listeners used preceding vowel duration to cue coda stop voicing, and that coda closure duration was a weaker cue to voicing when not varied in conjunction with preceding vowel duration. In addition, glottalisation facilitated increased perception of coda voicelessness, even when paired with very long preceding vowels, which otherwise signal coda voicing. Although age-related differences in production have previously been reported, we found that both older and younger listeners used glottalisation similarly in perception. These results may provide support for a sound change led by a shift in perception.

Glottalisation, coda voicing, and phrase position in Australian English.

Glottalisation is an important cue to coda stop voicelessness, particularly for younger Australian English speakers who utilise glottalisation more than older speakers, suggesting a recent sound change. However, most previous studies of glottalisation in this variety of English have focussed on single word utterances, raising questions about whether glottalisation in those studies may have been prosodically conditioned rather than specific to the coda stop: Could the observed effect have been due to phrase-final creaky voice, which is acoustically similar to coda-related glottalisation? This study therefore explored the differential effects of phrase position on the production of glottalisation. Phrase-medially (where phrase-final creaky voice is not expected to occur), results confirmed previous findings that glottalisation cues coda stop voicelessness and that it does so more frequently for younger compared to older speakers. In phrase-final position, rates of glottalisation increased, but older speakers appeared more similar to younger speakers in use of glottalisation, suggesting that the change towards the increased use of glottalisation may be nearing completion in this prosodic position. Younger speakers appear to represent a more advanced stage of the change extending the use of glottalisation from phrase-final to phrase-medial position.

Neuro-dynamics of executive control in bilingual language switching: An MEG study.

Bilinguals have a remarkable ability to juggle two languages. A central question in the field is concerned with the control mechanisms that enable bilinguals to switch language with ease. Theoretical models and neuroimaging evidence suggest that a range of control processes are at play during language switching, and their underlying neural mechanisms are closely related to executive function. What remains unclear is when these control processes are engaged in language switching. In this study, we used magnetoencephalography (MEG) to examine the brain activity while unbalanced Mandarin-English bilinguals performed a digit-naming task with cued language switching. Following presentation of the language cue, an asymmetrical switch effect was observed in the left inferior frontal gyrus (IFG), where switch-related increase in evoked brain activity was larger for switching into the non-dominant language. Following presentation of the naming target, evoked brain activity in the right IFG was larger when naming was required in the non-dominant language compared to the dominant language. We conclude that control processes take place in two stages during language switching, with the left IFG resolving interference following cue presentation and the right IFG inhibiting competing labels following target presentation.