What is the reference that sound durations are compared with in speech perception?

Speech segment durations are widely used as cues in the phonetic interpretation of speech (during its perception). To devise a system of quantitative rules for the automatic phonetic interpretation of natural speech it is necessary to know with what reference the speech sound duration is to be compared. An experiment with a specially arranged set of stimuli has shown that durations of adjacent sounds in an utterance, namely vowels, are used as the reference for word stress perception in Russian.