Verification of Amplitude Enhancement Effects on comprehensions of English speeches and brain functions

As globalization continues rapidly, an effective way of learning English has been interest to non-native speakers as an international language. Our previous study revealed that English speeches with enhanced amplitudes in high frequency ranges activated brain functions in the language processing areas more than original speeches. However, it has been uncovered that the accurate effect of the enhancement and which high frequency ranges induces the activation of brain functions most. In this study, the authors conducted an experiment to examine whether English speeches with enhanced amplitudes in a certain frequency range can contribute to better comprehension of English speeches with different characteristics and to clarify frequency ranges that activate brain functions most. We observed and recorded oxy-hemoglobin (Hb) concentration changes by using near-infrared spectroscopy (NIRS), and also performed an English listening test by using sentences with six different speech characteristics. The result of the experiment showed that Japanese subjects had comprehended the speeches with some of speech characteristics when amplitudes in certain frequency ranges were enlarged. The NIRS measurement also revealed that enhancement of amplitudes in high frequency ranges from 7,000 to 8,500 [Hz] raised the amount of oxy-Hb concentration in the language areas most. These results suggest that depending on combination of enhancement of amplitudes and English speech characteristics, a more effective way of English learning can be attained in terms of brain activation.