To explain how the ear can recognize a vowel sound as the same vowel, even though it is sounded at different pitches, the idea of vocal formants is invoked. This is data from Benade showing that an "Ah" vowel involves a similar envelope of harmonics when sounded at different frequencies.

To explain how the ear can recognize a vowel sound as the same vowel, even though it is sounded at different pitches, the idea of vocal formants is invoked. This is data from Backus showing that an "EE" vowel involves a similar envelope of harmonics when sounded at different frequencies. Formants occur at about 300 Hz and about 2300 Hz for each sound.

To explain how the ear can recognize different vowel sounds, the idea of vocal formants is invoked. This is a conceptualization only; no scaling to the inner ear was done. The place theory suggests that the ear distinguishes pitches based on the location of maximum excitation along the basilar membrane of the inner ear. So the ear acts as a sound analyzer which can detect differences in harmonic content by the different amounts of excitation at different places along the basilar membrane. Since sustained vowel sounds differ primarily in their harmonic content, this offers a mechanism by which the ear can distinguish them.