There is a systematic relationship between stress accent and vocalic identity in spontaneous English discourse (the Switchboard corpus of telephone dialogues). Low vowels are much more likely to be fully accented than their high vocalic counterparts. And conversely, high vowels are far more likely to lack stress accent than low or mid vocalic segments. Such patterns imply that stress accent and vowel height are bound together at some level of lexical representation. Vocalic duration appears to be the primary acoustic cue associated with stress accent, and the association between vowel height and accent level is most clearly observed in this dimension, particularly for diphthongs and the low, tense monophthongs. Together, the data suggest that vocalic duration plays an exceedingly important role in understanding spoken language.

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Bibliographic reference.  Hitchcock, Leah / Greenberg, Steven (2001): "Vowel height is intimately associated with stress accent in spontaneous american English discourse", In EUROSPEECH-2001, 79-82.