Santiago Barreda
Assistant Professor, Department of Linguistics, UC Davis

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How do vowel formant-patterns vary between speakers, within category?

The information presented here was collected from two large vowel datasets, Peterson and Barney (1952) and Hillenbrand et al. (1995). This data comprises productions from 215 unique speakers, 76 adult females, 78 adult males, and 61 children of either sex.

The figures below show average productions for different vowel categories from two large datasets.


Individual tokens are plotted below. Obviously, there is a lot of variation around vowel-category means. However, ellipses generally point in the same direction and are closely aligned with the lines on the figures. These lines indicate the direction of variation in which F1 and F2 increase by a single scale-factor.



If all of the tokens in the figures above are centered around their category-means and superimposed, we get a figure like the one on the right.

The ellipse enclosing tokens shows the orientation of the distribution, the solid line is the line in which variation in F1 is equal to variation in F2, and the dotted line indicates the major axis of the ellipse (denoting the primary direction of variation). The major axis of the ellipse differs from the solid line by only 2°.

This suggests that within-category variation in formant-patterns is primarily according to a single scale-factor. In fact, an analysis presented in Barreda & Nearey (2013) indicates that around 80% of variation in formant-patterns occurs along this dimension.