Interlanguage Dissimilarity Enhances the Decline of Thinking Ability During Foreign Language Processing

This study tested a hypothesis that the “foreign language effect” is larger when similarity between a foreign language and a native language is less. Foreign language effect refers to a temporary decline of thinking ability during foreign language processing, a decline that is distinguished from foreign language processing difficulty per se. In the first of two divided‐attention experiments, we compared 16 adult native speakers of German and 16 of Japanese given English as a common foreign language; in the second, we compared 16 adult native speakers of Korean and 16 of English given Japanese as a common foreign language. The participants performed a thinking task (addition) and a linguistic task (question‐answering) in parallel. The thinking task contained no foreign language; the linguistic task was presented in either the native language or the foreign language. In accordance with the hypothesis, the foreign language effect (denned by lower performance in the thinking task when the linguistic task was in the foreign language) was larger in both cases for those whose native language was less similar to the common foreign language.