Abstract
In this study, we discuss the principal carrier of speech information. Amplitude envelope of band-limited speeches was modeled by the proposed kernel function, producing three types of syntheses with modifications of the maximal part, the minimal part, and duration of the kernel function. Change of the envelope maxima only deactivated the temporal cortices in the brain by means of near-infrared spectroscopy (NIRS) measurements, which were in accord with the reduction of percentage correct in the dictation test. We hypothesized the integration of the envelope maxima played an important role in speech communication. As for NIRS methods, we regard the observation of hemoglobin maps as the most suitable index for the linguistic ability with following five advantages: (i) completely non-invasive measurements with a brief start-up, (ii) a bedside equipment with silent operation and continuous monitoring, (iii) hemodynamic observation in the cerebral association cortices, (iv) high flexibility in an experimental design because of tolerance for artifacts, and (v) low running costs without addition of supplies.
