Dynamic specification of coarticulated vowels

This chapter summarizes research conducted over a 35 year period on the dynamic specification of vowels. A series of experiments comparing vowels in consonant context with vowels produced in isolation failed to support talker normalization theories that predicted higher accuracy through prior exposure to a talker’s “point vowels.” Instead, these studies showed that vowels in consonant context were more accurately identified than isolated vowels, supporting a dynamic specification of vowels theory over static target theories, leading to the proposal that important information is contained in the formant transitions. Consonant–vowel coarticulation is not a source of “noise”, rather it gives rise to an acoustic array in which the consonants and vowels are cospecified in the time-varying spectral configuration which we call dynamic specification. Subsequent experiments showed high identification accuracy for “silent center vowels” in which the central portion of the CVC syllable was removed by gating. Identification accuracy was not disrupted when the onset and offset portions were produced by different speakers. Vowel identification improved with increasing duration of the onsets or offset portions. Onsets were identified more accurately than offsets but neither was as well identified as the silent center syllables. Collectively these and other experiments summarized herein support the view that the most important source of information for speaker-invariant vowel identity is carried in dynamic specification of vowel onset and offset spectral patterns, with vowel duration also playing a role. Subsequent experiments with North German vowels, which do not exhibit the degree of vowel diphthongization reported in American English dialects, showed that listeners rely on dynamic spectro-temporal information specified by syllable onsets and offsets, in addition to cues provided by inherent vowel duration. Cross-language comparisons are presented from the perspective of adaptive dispersion theory. These comparisons support the view that dynamic properties are perceptually more important in differentiating vowels in languages with large vowel inventories.