Dynamic specification of coarticulated German vowels: perceptual and acoustical studies

To examine the generality of Strange's Dynamic Specification Theory of vowel perception, two perceptual experiments investigated whether dynamic (time-varying) acoustic information about vowel gestures was critical for identification of coarticulated vowels in German, a language without diphthongization. The perception by native North German (NG) speakers of electronically modified /dVt/ syllables produced in carrier sentences was assessed using the "silent-center" paradigm. The relative efficacy of static target information, dynamic spectral information (defined over syllable onsets and offsets together), and intrinsic vowel length was investigated in listening conditions in which the centers (silent-center conditions) or the onsets and offsets (vowel-center conditions) of the syllables were silenced. Listeners correctly identified most vowels in silent-center syllables and in vowel-center stimuli when both conditions included information about intrinsic vowel length. When duration information was removed, errors increased significantly, but performance was relatively better for silent-center syllables than for vowel-center stimuli. Acoustical analyses of the effects of coarticulation on target formant frequencies, vocalic duration, and dynamic spectro-temporal patterns in the stimulus materials were performed to elucidate the nature of the dynamic spectral information. In comparison with vowels produced in citation from /hVt/ syllables by the same speaker, the coarticulated /dVt/ utterances showed considerable "target undershoot" of formant frequencies and reduced duration differences between tense and lax vowel pairs. This suggests that both static spectral cues and relative duration information for NG vowels may not remain perceptually distinctive in continuous speech. Analysis of formant movement within syllable nuclei corroborated descriptions of German vowels as monophthongal. However, an analysis of first formant temporal trajectories revealed distinct patterns for tense and lax vowels that could be used by listeners to disambiguate coarticulated NG vowels.