Two current theories of vowel normalization imply that vowel formant frequencies of one speaker can be related to those of another by a simple translation along a tonotopic frequency axis [T. M. Nearey, J. Acoust. Soc. Am. 85, 2088--2113 (1989)]. Theory A uses a Bark scale, while theory B uses a log-frequency (musical) scale. To compare these theories, a baseline continuum is first constructed that spans the range appropriate for the front vowels of an adult male speaker. In test series A, the formant frequencies are translated upward by 1.2 Bark, corresponding to the difference between average adult male and average female and child values from a vowel data base. In test series B, an upward translation of 0.2 natural log units is made, based on the corresponding average values in a log space. (Fundamental frequencies are also changed by the appropriate average value in the appropriate scale.) Each theory predicts its associated continuum will be identical to the baseline set, while that of the rival theory will show systematic distortion. Results of perceptual experiments will be presented that evaluate the phonetic distortion of the two test continua empirically.