Vowel Fundamental and Formant Frequency Contributions to English and Mandarin Sentence Intelligibility

The current study investigated spectral components of vowels that contribute to Mandarin and English sentence intelligibility. Sentences were processed to preserve various amounts of vowel information. Processing parameters ensured similar proportions of speech preserved between the two languages. In the first experiment, speech segments, primarily containing vocalic cues, were processed to flatten fundamental frequency (F0) cues. In the second experiment, sine-wave speech synthesis was used to coarsely code speech to retain only amplitude and frequency variation associated with the first three formants. Results demonstrated remarkable similarity between Mandarin and English sentence intelligibility with flattened F0 sentences. In contrast, the intelligibility of English sentences surpassed that of Mandarin sentences for sine-wave speech. Combined with earlier reports of superior intelligibility of Mandarin sentences with full spectrum vowels, these results highlight significant contributions of Mandarin F0 information, likely related to lexical tone. In contrast, English listeners may rely more on frequency and/or amplitude variation of the formants.