Duration as a cue to the perception of a phrase boundary

The presence of a phrase boundary is often marked in speech by phrase-final lengthening-a lengthening of the final stressed syllable of the phrase and pause at the phrase boundary. The present study investigates (a) whether listeners use the feature of phrase-final lengthening to parse syntactically ambiguous sentences such as "Kate or Pat and Tony will come," where the position of a phrase boundary after "Kate" represents one meaning, and after "Pat" another meaning, and (b) whether listeners use phrase-final lengthening directly to parse the sentence or indirectly via the effect that phrase-final lengthening has on the rhythm of the feet (the onsets of the stressed syllables) of the sentence. Four experiments are reported in which listeners are asked to judge the meaning of sentences which have been temporally manipulated so that the foot which originally did not contain the crucial phrase boundary is lengthened by (i) inserting a pause at the "false" phrase boundary experiment I, (ii) inserting a pause and lengthening the final stressed syllable at the "false" phrase boundary experiments II, (iii) lengthening all segments contained in the foot experiment III, and (iv) lengthening only the conjunction within the foot experiment IV. The results indicate that both rhythm of the inter-stress intervals and the presence of phrase-final lengthening influence listeners' perception of a phrase boundary, although the stress rhythm appears to be the more powerful perceptual cue.