Foreign language side effect when inner language is suspected to accompany thinking: Lowered thinking ability in daily verbal communication

抄録

Foreign language side effect (FoLSE) refers to a temporary decline of thinking ability while nonproficient foreign language is being used. This decline is produced by stronger interference between thinking and a heavier cognitive load of foreign language processing. Although FoLSE was shown to occur in laboratories, it may not occur in daily verbal communication when thinking is accompanied by inner language. The reason is as follows: In general, the more similar two concurrent cognitive tasks, the stronger their mutual interference. Inner language is usually experienced as effortless native language. When outer language used in verbal communication is native language, it is more similar to inner native language. Therefore, outer native language is expected to produce stronger interference with inner native language involved in thinking, and thus could produce a larger reduction in thinking performance. This larger reduction due to outer native language may cancel out the reduction due to outer foreign language (FoLSE). To examine this possibility, Japanese college students performed verbal and thinking tasks concurrently in two dual-task experiments. The verbal task was presented in either Japanese (native language) or English (foreign language). The thinking task was always presented in Japanese (native language). Past empirical studies strongly suggested that inner language should be evoked in the employed thinking tasks (i.e., validity judgment on categorical syllogism and intelligence test problems that loaded heavily on verbal factors of intelligence). The results revealed that performance in the thinking task was lower when the verbal task was presented in the foreign language. This means that FoLSE was stronger than the interference between the inner and outer native language. It follows that FoLSE is likely to occur in daily verbal communication as well even when it is accompanied by inner language.