Formant measurements show sex and age differences in the formant patterns of a single vowel category. Comparisons of the formant frequency values of men, women and children indicate low, middle and high values, respectively (Chiba & Kajiyama 1941, Potter & Steinberg 1950, Peterson & Barney 1952). The differences are found for all vowel categories, and they have generally been interpreted as a consequence of different vocal tract size.