This study found that segment duration is perceived categorically in Japanese. Using a speech time-scale modification algorithm, PICOLA plus 2, the nonword /kesonato/ pronounced by a native Japanese male was manipulated to generate stimulus continua. The durations of /s/, /n/, /a/, and /t/ closure interval were manipulated in four continua. In the first experiment, three stimulus pairs which had the same disparity in duration were selected from the short, long, and middle region of each continuum. Forty-eight randomized trials were presented to twenty native Japanese, who were asked individually to distinguish the stimuli by the ABX method. Pairs from the short and long regions of the continua were not accurately discriminated while pairs from the middle region were. In the second experiment, 44 stimuli were selected from every continuum. They were presented to the subjects for identification in Hiragana (Japanese characters). The second result demonstrated the existence of a moraic phoneme boundary paralleling the discrimination peak in the first experiment. This research concluded that native Japanese perceive the duration of relatively steady-static sounds categorically. And also it is suggested that native Japanese utilize an automatic duration detection routine.
