Lexical and prosodic cues in the comprehension of relative certainty.

This study examined the development of children's comprehension of the use of intonation and belief verbs to mark the relative certainty with which a speaker makes a statement. Subjects were presented with a task in which they had to guess the location of an object hidden in one of two boxes over a series of trials. As clues to location, the children were presented with contrasting pairs of statements by two puppets. In the first experiment with 30 children at each of three, four, five and six years of age, statements in each pair differed either with respect to the belief term included - know, think or guess - or with respect to terminal pitch contour - rising or falling. Results showed that three-year-olds did not use any information reliably to determine the location of the object, four-year-olds treated falling pitch as a more reliable indicator of location than rising pitch, and older children responded on the basis of the belief terms but not on the basis of prosody. In Experiment 2, 40 children at each of three, four and five years heard statements which differed with respect to both belief verbs and prosody. In one condition falling intonation was paired with the more certain belief term in each pair, and rising intonation with the less certain pair. In a second condition, the pairings were reversed. Results showed that, while four-year-olds could tell the difference between know and think, they could not use intonation information to determine the location. Five-year-olds used both lexical and prosodic information, with prosodic cues modulating the effects of lexical. Taken together, these experiments show that prosodic and lexical cues start to be used by children to interpret relative speaker certainty at about the same time developmentally, but that lexical cues initially appear to dominate while prosodic ones modulate their effects. Finally, it is argued that children's understanding of prosody will be best revealed in contexts in which they are required to respond to the pragmatic function of verbal stimuli rather than to the lexical content.