FIG. 20.  The onset frequency of the formant transition into a vowel is plotted as a function of the vowel target frequency for 16 vowel nuclei before /g/, after Klatt (1979b). Each data point is an average of six tokens from a single speaker. Open circles indicate front vowels, crosses indicate back unrounded vowels, and solid circles indicate rounded vowels. Within each vowel class, data points are well fit by a straight line, confirming the existence of a locus theory equation, see text.