Abstract:

Voluntary language switching refers to the language switching that occurs spontaneously among bilinguals. While forced language switching tasks require bilinguals to select language based on external cues (e.g., color of frames or national flags), voluntary switching tasks provide a context where bilinguals may freely select their intended language on any given trial (e.g., via instructions). It echoes the dense code-switching context described in the Adaptive Control Hypothesis (Green & Abutalebi, 2013), where bilinguals rely more on opportunistic planning and less on conflict monitoring or interference suppression. By contrast, forced switching tasks parallel the dual-language context, which places higher demands on executive control processes such as interference suppression, goal maintenance, and conflict monitoring. Indeed, recent studies suggest that, compared with forced language switching,voluntary language switching does not necessarily impose a cognitive burden. As a result, switching cost can be markedly reduced or even eliminated when switching is driven by bottom-up lexical access or when speakers have full freedom to maintain language consistency.
Neuroimaging evidence indicates that voluntary language switching is characterized by distinct neural activation patterns in contrast to forced language switching. It differs both in the intensity of neural activation and in the temporal locus of inhibitory control. Voluntary switching not only engages brain regions implicated in inhibitory control (e.g., the right inferior frontal gyrus) but also recruits additional areas associated with self-initiated decision-making (e.g., the medial prefrontal cortex). More specifically, the process unfolds in distinct temporal stages. During the early phase of language selection, voluntary switching recruits neural mechanisms related to free decision-making (e.g., bilateral frontoparietal and medial prefrontal cortices). In contrast, during the later stages of speech execution, it elicits reduced activation in classical language control regions.In naturalistic contexts, the reduced reliance on inhibitory control may facilitate a more efficient allocation of neural resources. These findings highlight the critical role of intention formation and prospective planning, rather than inhibitory control per se, in voluntary switching. Taken together, the evidence suggests that voluntary switching relies more heavily on mechanisms of intention generation and anticipatory planning than on reactive inhibition.
Bilingual control in voluntary language switching is shaped by second language(L2) proficiency, contextual factors, and individual executive control abilities. L2 proficiency influences language selection preferences and may modulate the extent of proactive control at the global level. Contextual factors—including non-linguistic contexts (e.g., interlocutor settings and emotional states) and linguistic contexts (e.g., sentence contexts)—may induce adaptive changes of both proactive and reactive language control at the global and local levels. Furthermore, voluntary switching is also closely associated with domain-general executive control components, such as inhibitory control, working memory, and conflict monitoring. Importantly, different forms of voluntary switching (e.g., conscious vs. unconscious; intra-sentential vs. inter-sentential) may recruit distinct cognitive control mechanisms. Furthermore, individual differences—including age and patterns of language use—can significantly moderate these relationships. Therefore, the Adaptive Control Hypothesis may require further refinement by incorporating dynamic individual and contextual factors—such as individual language use habits and socio-cultural norms—to more adequately capture the complexities of real-world bilingual communication.
Future research on voluntary language switching should integrate individual factors (e.g., language proficiency, usage habits, executive control) and contextual factors (e.g., sentence context, interlocutors) to develop more refined and dynamic models of bilingual control. While existing work has begun to probe the mechanisms and determinants of voluntary switching, further advances will require methodological innovation and broader research approaches. In particular, future studies should connect complex behavioral patterns in naturalistic social contexts with standardized laboratory measures to better elucidate the underlying neural mechanisms. For instance, functional near-infrared spectroscopy (fNIRS) and virtual reality (VR) technologies could be utilized to construct multimodal conversational scenarios. Longitudinal designs are also needed to examine the long-term effects of voluntary switching on cognitive development and neural adaptation. Moreover, it remains unclear how comprehension and production differ and interact in voluntary switching and examine how they jointly shape cognitive control. The cognitive costs associated with producing and comprehending spontaneous code-switching may be a key factor influencing the communicative efficiency for both interlocutors. This line of research may shed light on the distinction between domain-specific and shared control processes and provide insights for bilingual education and second language learning.

Key words: voluntary language switching, forced language switching, inhibitory control, context, executive control