Few studies have focused on mechanisms of developmental change during the prelinguistic period. The lack of focus on early vocal development is surprising given that maternal responsiveness to infants during the first two years has been found to influence later language development. In addition, in a variety of species, social feedback is essential for vocal development. Previous research demonstrated that maternal feedback to prelinguistic vocalizations influenced the production of more developmentally advanced vocalizations, suggesting that effects of maternal responsiveness on vocal development may start during the prelinguistic phase; however, because mothers were instructed how and when to respond to their infants' vocalizations, the timing and type of typical maternal feedback is unknown. In the present study, we analyzed unstructured play sessions for 10 mother-infant dyads to explore the relationship between prelinguistic vocal production and maternal responsiveness. Mothers responded contingently to prelinguistic vocalizations over 70% of the time. Mothers responded with more vocal responses compared to interactive responses (e.g., gazes, smiling, physical contact). Investigation of specific types of vocal responses revealed that mothers responded mainly with acknowledgments to both vowel-like sounds and consonant-vowel clusters. Mothers also showed differential responding to vocalizations that varied in quality. Mothers responded with play vocalizations to vowel-like vocalizations significantly more than to consonant-vowel clusters, whereas they responded with imitations to consonant-vowel clusters more than to vowel-like sounds. Mothers, therefore, appeared to regulate their contingent feedback relative to the speech-like quality of infants' vocalizations which may provide relevant stimulation to guide communicative development. (Contains 1 table and 4 figures.)