Abstract—In this paper, we investigated the speech perception under effects of coarticulation within syllables, including estimating the nuclei and coarticulated transition intervals of phonemes, and investigating the perception of nuclei and coarticulated transition intervals of phonemes within syllables. To complete these objectives, we firstly proposed the folded spectral transition measure to estimate the boundary points between the nuclei interval and coarticulated transition intervals. Then, we conducted experiments to investigate the syllable identification and syllable quality evaluation under effects of coarticulation. The experimental results show that human can identify the syllables with the retaining intervals equal or wider the coarticulated transition intervals. Besides, the experimental results show that the nuclei intervals are still important for speech quality perception; the quality of truncated syllables retaining the two phoneme nucleus and coarticulated transition interval between the two phonemes within syllable is equivalent with the quality of original two-phoneme syllables.