Formant Pattern Ambiguity of Vowel Sounds

The formant frequencies of a particular vowel vary according to the speaker group and to coarticulation. Therefore, overlapping formant patterns of different vowels are commonly related to sex and age differences and to coarticulation, and are considered to concern mainly the F1-F2 pattern of adjacent vowels. However, several studies have reported indications of a correlation between the lower formant frequencies and F0, as well as of the appearance of different formant numbers relevant to vowel identity. As a consequence, the overlap between formant patterns of different vowels might be more substantial than has traditionally been assumed. Within the present study, therefore, the extent to which a given formant pattern can represent different vowels was investigated for natural Swiss German vowels produced monotonously and in isolation by men, women and children at F0 of 85-870 Hz. Similar formant patterns were found for vocalizations of different vowels with both small and large phonetic distances, and within the entire frequency ranges of the formants relevant for phoneme identity. For vowel sounds displaying ambiguous formant patterns, the main spectral characteristics related to differences in their perceptual identity were found to concern F0 and relative formant amplitudes. Results are given in exemplary vowel series, and consequences for the psychophysics of the vowel are discussed.