The Effect of Amplitude Enlargement in English Speech on Brain Functions

Some studies have pointed out that music and human voice in high frequency ranges play an important role in activation of brain functions. However, the effect of the high frequency ranges to human brain has not been revealed yet completely. In this study, the authors conducted an experiment to examine whether English speech with enlarged amplitude in a certain frequency range can contribute to better comprehension of English sentences. In this study, a near-infrared spectroscopy (NIRS) system was used to measure relative hemoglobin (Hb) concentration changes in the brain while subjects were listening to English sentences with enhanced amplitude in a certain frequency range. After listening, the subjects responded to a questionnaire with five point scales about the comprehensibility of the English sentences. The NIRS measurement observed the highest brain activation near language processing areas and a portion of the left side of the prefrontal cortex when the subjects were listening to English speech with amplified amplitude in high frequency ranges. This tendency was more obvious for the subjects who had lower English proficiencies. However, questionnaire results showed that English speech with enhanced amplitude in the frequency ranges may not help English learners better comprehend English speech. These results suggest that English speech with enhanced amplitude in the high frequency ranges are more effective for the learners who have lower English proficiency and different factors can affect easier listening to speech in other languages.