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Recent work has led us to the conclusion that the English stop categories /bdg/ and /ptk/ are distinguished by the timing of changes in glottal aperture relative to supra-glottal ariculation. In word-initial position, the environment of current interest to us, this is manifested acoustically by voice onset time, that is, the time interval between the burst that marks release of the stop closure and the onset of quasi-periodicity which reflects laryngeal vibration. For citation forms of words this measure of voice onset time completely separates the two phonemic categories. In running speech, however, the separation is less sharp ; there is some overlap along the dimension of voice onset time. We have examined running speech in some detail to discover the extent to which certain contextual features are responsible for this overlap. It is clear that the presence of a voiceless stop in a stressed syllable makes for a greater lag in the onset of voicing. In unstressed syllables, an environment of high contextual redundancy as well as low functional yield for the phonemic contrast, there is considerable reduction of the distinction along the dimension. A further increase in voicing lag is noted in syllables bearing the final sentence stress. In addition, the farther such a syllable is from the end of the sentence, the less the effect is likely to be. The importance of voice onset time continues to be apparent, even in running speech, although other effects of context remain to be explored.
Lisker et al. (Sun,) studied this question.