Changes in infants' cries as a function of time in a cry bout.

The present study examines changes in cry sounds over the course of a relatively long bout of crying. Specifically, differences in acoustic characteristics of 5 cries from early and 5 cries from late in a prolonged cry bout were assessed. The results indicated that several features changed in means and/or variances between early and late in the bout. A subset of 9 acoustic features was chosen to evaluate changes in the interrelations of features over time. Cries from late in the bout appeared to result from a smaller number of factors, which were more readily interpretable in terms of a standard model of cry production. Thus, it appears that as infants' level of arousal or distress changes, so do the acoustic features of their cries. Further, the results support the notion that bouts of crying settle into a "basic" or regular cry whose acoustic features provide a reasonable match with a theoretical model of cry production.