What type of vocal play emerges at around 4-7 months of age?

The correct answer highlights the developmental stage where infants begin to experiment with their vocal abilities. At around 4-7 months, infants typically engage in manipulation of pitch and loudness as part of their early vocal play. This stage is characterized by a growing ability to control their vocalizations, leading them to explore different sounds and variations in their voice.

This vocal play is crucial for language development, as it lays the groundwork for later speech and communication skills. By experimenting with pitch and loudness, infants not only begin to understand how their voice works but also learn about expressiveness, which will be essential for effective communication in their future interactions.

Although other types of vocalizations like canonical babbling and squeals can emerge around this age, manipulation of pitch and loudness specifically refers to the broader exploration of sound qualities and variations that can set the stage for more complex babbling and speech development in the future. Grunting and sighing may occur as a part of a baby's general expressions, but they do not involve the same level of vocal exploration as manipulating pitch and loudness.