Interaction between two factors that influence vowel duration

It is well known that stressed vowels are shorter before voiceless consonants than before voiced, and that stressed vowels are shorter before an unstressed syllable in a bisyllabic word than in a monsyllabic word. A set of test materials was designed to study the interaction between these two rules. Results suggest that vowels become strongly incompressible beyond a certain amount of shortening and that vowel duration modification rules should have the form Do = k (Di − Dmin)+Dmin, where Di is the input duration to the rule, Do is the output duration of the rule, Dmin is the minimum duration for the vowel, and the scale factor k is greater than zero and depends on the particular rule. The data indicate that Dmin is about 45% of the inherent duration of a given vowel.