Glottalization, reduction, and acoustic variability in function words in American English
Laura C. Dilley, Meisam Khalil Arjmandi, Zachary Ireland, Christopher C. Heffner, Mark A. Pitt · The Journal of the Acoustical Society of America · 2016
Function words vary widely in pronunciation; understanding this variation is essential for accurate cognitive modeling of lexical perception and production, as well as for computer speech applications. This study analyzed acoustic variation in pronunciation of vowel-initial words a, are, our, and or, as well as her, which has a vowel-initial variant, [ɚ]. Sentences were constructed in which each function word was preceded by a phonetically similar open syllable rhyme, with which the word was expected to sometimes blend spectrally. Twenty-nine participants uttered 100 sentences in a casual speaking style. The degree of clarity of function word onsets was measured, focusing on evidence of onset discontinuities: glottal onset gestures (e.g., low fundamental frequency, F0; amplitude dips) for vowel-initial words a, are, our, and or, and, for her, of /h/ (e.g., root-mean-square amplitude, amplitude differences of first and second harmonics). Results showed that a substantial proportion of the time, function words lacked any detectable acoustic onset discontinuity. When discontinuities did occur before vowel-onset function words, there was a high degree of acoustic variability in those realizations. These findings highlight the challenges for speech perception to identify word onsets and/or to overcome variability in recognizing words. [Work supported by NSF Grant BCS-1431063.]