Temporal relationships between gaze and vocal behavior in prelinguistic and linguistic communication.

This work reports longitudinal evaluation of the temporal relationships between gaze and vocal behavior addressed to interactive partners (mother or experimenter) in a free-play situation. Thirteen children were observed at the ages of 1;0 and 1;8 during laboratory sessions, and video recordings of free-play interactions with mother and a female experimenter were coded separately for children's vocal behavior (vocalizations and words) and gaze toward their interactive partners. The difference between the observed and expected co-occurrence of these two communicative behaviors was evaluated by transformation into z-scores. The most important findings are related to differences in the temporal relationship observed at age 1;0 between gaze and vocalizations and at age 1;8 between gaze and words. At the earlier age, the infants who exhibited greater coordination between gaze and vocal behavior than was expected by chance (z-score > +1.96) preferred to look at the interlocutor at the beginning of the vocal turn. Instead, when they were older and began to produce words, they frequently looked at the interlocutor at the end of the vocal turn. These results are interpreted as referring to characteristics of conversational competence in the prelinguistic and lingustic periods. Moreover, looking at the interlocutor at the beginning of the vocal turn at age 1;0 was found to be related to language production at age 1;8, highlighting a significant relationship between conversational competence during the prelinguistic period and language acquisition.