Figure 1. Stimuli and experimental design.

(A) Synthesized vowel stimuli/a/, /e/, /i/, and/u/in the F1–F2 space. (B) The standard stimuli shared the relative flat pitch contour but differed in formant, intensity, and level of pitch. There were 120 different combinations of standard stimuli (4 vowels * 3 intensities * 10 pitch levels). Two deviant types were defined, the rising deviant (T2) and the falling deviant (T4). Within each deviant type, the stimuli differed in formant, intensity, and level of pitch. There were 36 different combinations of stimuli (4 vowels * 3 intensities * 3 pitch levels) for each deviant type.