Selective cognitive effects of multilingualism emerge in visuospatial working memory in later life.

Epidemiological literature suggests that speaking multiple languages can delay the onset of neurodegenerative conditions such as Alzheimer's disease. Cognitive and neuroscientific explanations, however, remain inconclusive. While some studies have found behavioural and neural effects of being multilingual (compared to monolingual) for working memory, inhibitory control, and attention across the lifespan, others have found no such evidence. An emerging focus on nuanced, dimensional measures of language experience, direct comparison of tasks within the same experiment, and a direct comparison of stimulus modality (visuospatial versus auditory processing) could potentially resolve these mixed findings. The present study investigated whether multilingual experience, measured continuously via the Language History Questionnaire (LHQ-3), was associated with domain-specific cognitive performance in both auditory and visuospatial modalities in a lifespan sample (N = 94, aged 18-83). Participants completed working memory (N-back), inhibitory control (Simon), and attention (Attention Network and Dichotic Listening) tasks in both auditory and visuospatial formats. Generalised additive models revealed no significant associations between multilingual experience and cognitive performance for auditory and most visuospatial tasks. However, a significant interaction between multilingual language diversity and age was found for visuospatial working memory, with older multilingual adults demonstrating higher accuracy and faster response times. These findings suggest that the cognitive effects of multilingualism may be age-, domain-, and modality-specific rather than universal. Neuroprotective associations observed in epidemiological and neuroimaging studies may therefore reflect mechanisms beyond direct behavioural performance, such as neural reserve or compensation.