The development of the crying state during early infancy.

The development of the crying state was studied in 14 infants from 3 to 18 weeks in two situations: the infant alone and in interaction with the mother. A major transformation occurred in the crying state after 3 months, with the appearance of what is termed interrupted fussing, which consists of rapid alternations between fuss sounds and cooing vocalizations. This change was only found in the alone situation. The functional implications of this finding are discussed within the contexts of motor development and the behavioral state concept.