Describes a study of three infants whose parents presented vocal models for the infants to imitate. Parents presented vocal models both with and without social praise. Infants showed systematic increases in matching after praise was introduced. Nonmatching vocalizations did not increase with introduction of praise. Findings demonstrate generalized…

Examined the role of exposure to speech in children's vocabulary growth. Characterized vocabulary growth rates for children from 14 to 26 months of age. Found a relation between individual differences in vocabulary acquisition and variations in the amount of a mother's speech to her children. (BC)