A Temporary Decline of Thinking Ability During Foreign Language Processing

It was predicted that the use of a foreign language should cause a temporary decline of thinking ability because the heavier processing load imposed by a foreign language than by a native language should produce stronger interference with thinking to be performed concurrently. A divided-attention experiment with Japanese-English and English-Japanese bilinguals confirmed this prediction: performance in a thinking task (i.e., calculation) declined when a concurrent linguistic task (i.e., question-answering) had to be performed in their respective foreign languages. This decline is distinguished from foreign language processing difficulty per se because the thinking task involved no foreign language use. The decline was also observed in another divided-attention experiment employing a different type of thinking task, that is, spatial reasoning problems adopted from intelligence tests.