Basque-Spanish Bilingual Aphasia: A Case-Study to Reveal Frequency-Based, Language-Agnostic Lexical Organization in Bilinguals

This study investigated whether language serves as the primary organizational axis dividing lexico-semantic representations in multilingual individuals, or whether language is a subsidiary feature to dominant organizing principles identified in monolingual individuals. To address this question, we examined the influence of two well-established principles of language organization-frequency and concreteness-on naming accuracy in a post-stroke bilingual individual with anomic aphasia (PWA). The participant, a highly proficient Basque-Spanish bilingual, underwent MRI scanning to delineate the extent and location of the lesion and completed a naming-by-definition task in both languages, along with a control group of 24 age-matched bilinguals. Stimuli were orthogonally varied by frequency (high/low) and concreteness (high/low). Generalized linear mixed models revealed main effects of both frequency and concreteness on naming accuracy. Notably, while healthy controls showed a robust concreteness effect-with concrete words yielding higher accuracy-the PWA exhibited a disproportionately larger impairment for low-frequency words. This pattern, consistent with the lesion's location to the inferior temporal gyrus, highlights a specific vulnerability of frequency-based lexical representations following temporal lobe damage. Importantly, the bilingual PWA demonstrated strikingly similar error rates across languages, yet an item-level analysis revealed that the specific words affected differed between the two languages. These findings (i) clarify the role of the inferior temporal gyrus in lexical organization, (ii) suggest that bilinguals possess an integrated lexical system governed by general cognitive principles, and (iii) challenge the notion that language itself is the dominant axis of organization in the bilingual mind/brain.