Previous research suggests that multilinguals' languages are constantly co-activated and that experience managing this co-activation changes inhibitory control function. The present study examined language interaction and inhibitory control using a colour-word Stroop task. Multilingual participants were tested in their three most proficient languages. The classic Stroop effect was detected in all three languages, with participants performing more accurately on congruent than on incongruent trials. Multilinguals were faster and more accurate in the within-language-competition condition than in the between-language-competition condition, indicating that additional processing costs are required when stimulus and response languages differ. Language proficiency influenced speed, accuracy and error patterns in multilingual Stroop task performance. These findings augment our understanding of language processing and inhibitory control in multilingual populations and suggest that experience using multiple languages changes demands on cognitive function.

Bilinguals' two languages are both active in parallel, and controlling co-activation is one of bilinguals' principle challenges. Trilingualism multiplies this challenge. To investigate how third language (L3) learners manage interference between languages, Spanish-English bilinguals were taught an artificial language that conflicted with English and Spanish letter-sound mappings. Interference from existing languages was higher for L3 words that were similar to L1 or L2 words, but this interference decreased over time. After mastering the L3, learners continued to experience competition from their other languages. Notably, spoken L3 words activated orthography in all three languages, causing participants to experience cross-linguistic orthographic competition in the absence of phonological overlap. Results indicate that L3 learners are able to control between-language interference from the L1 and L2. We conclude that while the transition from two languages to three presents additional challenges, bilinguals are able to successfully manage competition between languages in this new context.

Many parents express concerns for their children's multilingual development, yet little is known about the nature and strength of these concerns - especially among parents in multilingual societies. This pre-registered, questionnaire-based study addresses this gap by examining the concerns of 821 Quebec-based parents raising infants and toddlers aged 0-4 years with multiple languages in the home. Factor analysis of parents' Likert-scale responses revealed that parents had (1) concerns regarding the effect of children's multilingualism on their cognition, and (2) concerns regarding children's exposure to and attainment of fluency in their languages. Concern strength was moderate to weak, and cognition concerns were weaker than exposure-fluency concerns. Transmission of a heritage language, transmission of three or more languages, presence of developmental issues, and less positive parental attitudes towards childhood multilingualism were associated with stronger concerns. These findings have both theoretical and practical implications: they advance our understanding of parental concerns and facilitate the development of support for multilingual families.