Tone 2 Pronounced as Tone 4

• It is common that Tone 2 of “卓” was pronounced as Tone 4.
• The native speaker's tone contour presents clear rising trend, from 210Hz to 300Hz.
• The learners' tone contour show obvious falling trend throughout the whole pronunciation, with mean pitch values of 290Hz for starting points and 200Hz for ending points of the tone contour.

• The native speaker's reading of “膜” in the word “視網膜” shows clear rising trend throughout the whole tone contour, ranging from 160Hz at the beginning and 270Hz at the end.
• The learners' reading of “膜” is unstable in terms of pitch value. Most of the pitch contours exhibit falling trend in the middle and then have slight rising or leveling at the end.

Suggestions for teachers:

• remind students to keep raise pitch from the beginning to the end of Tone 2 pronunciation
• encourage students to pronounce Tone 2 decisively, without hesitation