Shared spatial representations for physical locations and location words in bilinguals' primary language.

For monolinguals, the Simon effect is eliminated when Simon task trials are intermixed with ones in which participants respond to the words left and right with incompatibly mapped keypresses. For bilingual Dutch/French speakers, this result has been shown to occur when the words are in Dutch (their first and primary language), but not when they are in French. To dissociate the influence of order in which the languages were learned from whether the language was the primary one currently being used, we tested bilinguals who learned Spanish or Vietnamese as their first language but for whom English became their primary language. For both groups, the incompatible location-word mapping influenced performance of the Simon task when the words were in English but not when they were in the first language. These findings indicate that the strength of language, not order of acquisition, is the critical factor.