Grouping Frequency Components of Vowels: When is a Harmonic not a Harmonic?:

TLDR: In this article, the authors demonstrate that some perceptual grouping operations are performed before the first formant of a vowel is estimated from the amplitudes of its component harmonics, and that the small contribution to vowel quality of a harmonic that starts before a vowel can be increased by adding an additional tone that will in turn form a perceptual group with that part of the harmonic preceding the vowel.

Abstract: When one harmonic of a vowel starts before and stops after the others, its contribution to the vowel's phonetic quality is reduced. Two experiments demonstrate that this reduction cannot be attributed entirely to adaptation. The first experiment shows that a harmonic that starts at the same time as a short vowel but continues after the vowel has ended contributes almost as little to the vowel's phonetic quality as a harmonic that starts before but stops at the same time as the vowel. The second experiment shows that the small contribution to vowel quality of a harmonic that starts before a vowel can be increased by adding an additional tone that will in turn form a perceptual group with that part of the harmonic preceding the vowel. The experiments demonstrate that some perceptual grouping operations are performed before the first formant of a vowel is estimated from the amplitudes of its component harmonics.