Vowels are distinguished by formant frequencies controlled by tongue, jaw, and lips

Evidence

Apart from the vocal folds, we have several other control parameters, including the position of the tongue, jaw, and lips. These constrict or expand the diameter of the vocal tract at various places along its length and thereby control the resonant frequencies of the vocal tract. The resonances, called formants, must be placed at distinct frequencies for distinct vowels. — Eric J. Heller, Why You Hear What You Hear- An…, 1638

Categorization

• DEFINE: Defines formants as vocal tract resonances that distinguish vowels.
• XREF: connects to: Vowel identification depends on formant peaks being representable in the output spectrum. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1368