Duration and fundamental frequency correlates of phrase boundaries in productions by children and adults.

Two experiments examined how children and adults produce acoustic correlates for phrase boundaries during speech. Adult and children (ages 5 and 7) were asked to describe groupings of colored blocks, first in a relatively spontaneous manner and next under more structured conditions designed to elicit grouping information concerning "which blocks go together." In the spontaneous condition, adults gave elaborate descriptions of block positions and color, whereas children produced short descriptions such as "pink, green, white;" "pink, green, and white;" and "pink and green and white." In the structured condition, all subjects produced utterances corresponding to three syntactic bracketings of the phrase "pink and green and white:" [pink and (green and white)]; [(pink and green) and white]; and [pink and green and white]. Acoustic analyses indicated that adults reliably control both duration and fundamental frequency (F0) to signal phrase boundaries, whereas children of both age groups demonstrate little evidence of either type of information being used. We interpret these finding as suggesting that children as old as age 7 do not produce prosodic cues for this type of standing ambiguity in their everyday speech. Possible reasons for this lack of phrase boundary prosodic correlates are examined.