Month 2

Cooing and melodic vowel sounds, typically “uuuu” and “ aaaa”^{3,14, 107}

Reciprocal vocal play³

Guttural and gurgling sounds¹⁴

Greater variation in cry (pitch and loudness of sound) in association with physiological state^{6, 18}

Shows interest in sounds¹⁴

Sound in conjunction with movement⁶

Quiets to and turns to localize sound¹⁴