Determining Frequency Importance Function for Speech Intelligibility of Persian Monosyllabic Words and the List of Quick Speech in Noise in Persian Language

Background and Aim: The Frequency Importance Function (FIF) is the main component of the Speech Intelligibility Index (SII) for a certain language. The FIF indicates the relative importance of each frequency band as it contributes to speech intelligibility. This study was conducted to determine the FIF for the Persian monosyllabic words and the list of Quick Speech in Noise (QSIN) in Persian language. Methods: In this exploration study, 34 monolingual Persian-speaking subjects aged  25–40 years with normal hearing (17 males) were included. The FIF was evaluated for 100 monosyllabic words and 30 sentences of Persian QSIN under 180 different auditory conditions. The speech recognition scores were calculated and crossover frequencies were determined. Then, the relative transfer function was extracted and FIFs were calculated. Results: The findings showed that for monosyllabic word material, the FIF had three peaks at 178, 1787, and 4467 Hz and for Persian QSIN, the FIF had an initial peak at about 141 Hz followed by a peak at about 1800 Hz. According to the results, the frequency range 891–8913 Hz is very important for recognition of the Persian words. Moreover, the mean crossover frequencies for the Persian sentences was 1446 Hz. Conclusion: For monosyllabic word material in the Persian language, the FIF at 708–1778 Hz is very important for recognition of the Persian monosyllabic words. For sentence material in the Persian Language, the FIF at 708–4467 Hz has the highest importance for recognition of Persian sentences. Keywords: Frequency importance function; speech intelligibility index; monosyllabic word; quick speech in noise list; Persian language