Newborns' repertoire of sounds is extremely limited: they cry, sneeze, sigh,burp, and smack their lips. At about 6 to 8 weeks of age, infants begin to coo —producing drawn-out vowel sounds, such as "ooohh" or "aaahh." They click, smack, blow raspberries, squeal—all with apparent fascination and delight. Through this practice, infants gain motor control over their vocalizations. While their sound repertoire is expanding, infants become increasingly aware that their vocalizations elicit responses from others, and they begin to engage in dialogues of reciprocal cooing with their caregivers. Indeed, infants with more responsive caregivers are more likely to use more mature vocalization patterns