| Abstract | The corpus callosum is the largest white matter structure of the human brain, and it enables interhemispheric transfer of information. Research has shown that bilinguals have larger anterior regions of the corpus callosum when compared to monolinguals. Besides, as a potential consequence of age-related thinning of the corpus callosum, and therefore less facilitated interhemispheric transfer, older monolingual adults seem to experience less interference from contradicting stimuli when bilaterally displayed. The current study aimed to investigate whether bilinguals, due to a larger corpus callosum, would experience more interference from bilaterally displayed contradicting stimuli and whether age-related decline in interference would be mediated by bilingualism. Using a divided-field Stroop task, four groups of younger (18-25 years) and older (65-85 years) monolinguals and bilinguals were tested with spatially separated target and distracter stimuli in an online experiment. The stimuli consisted of a word written in black and a coloured rectangle. As expected, all groups showed a significant Stroop effect across both experiments. For the older bilinguals, the Stroop effect was significantly larger in the bilateral condition than in the unilateral condition, while there was no difference between the two for all other groups. Consistent with our hypothesises, the findings suggest that older bilinguals experience more interference from contradicting stimuli in the bilateral display when compared to their monolingual peers. This could be explained by increased white matter integrity through lifelong bilingualism and would indicate that older bilinguals are less able to inhibit the distracter stimulus in a bilateral display compared to older monolinguals.
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