In this era of globalization, a second language (which is often English in Japan) has become prevalent and important. To investigate whether cerebral hemodynamics could represent the speech comprehension level of a learned language, we measured the brain activation of 46 non-fluent Japanese learners of English using functional near-infrared spectroscopy while performing speech comprehension tasks. Tasks were given in three languages: English (second language), Japanese (native language), and Chinese (unknown language). Analyses of the hemodynamic responses showed that the activated areas for the English task were widely distributed in the bilateral frontal and temporal regions, and this was more evident than for the Japanese and Chinese tasks. This suggests that comprehension of a second language involves more cognitive and/or attentional load. Moreover, particularly in the English tasks, there were significant differences in activations between the cases when participants correctly answered questions and the cases when they did not. These results suggest that the hemodynamic response can provide the information needed to estimate the speech comprehension level of a learned language.
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