My daughter is almost 4 months old. What types of sounds should she be making? Up until recently, she was cooing a lot and even starting to say ah-goo. But it as if this has all stopped over night. She still makes sounds some, like ahhh, gaaa, and grunting noises, but she used to "coo" back to. Now she just stares at my face and mouth as if she's really focusing on what I'm saying, but she doesn't talk back to me. I think her hearing is fine, because she startles at sudden or loud noises, and she also turns in the direction of my voice. Should I be concerned or do babies often stop cooing and have a quiet period before they begin babbling?
Normally, between 2 and 3 months, children begin to laugh, recognize voices, make lots of vocalizations based on vowels and can distinguish between different tones of voice (happy, angry, etc.). By 4 to 6 months, infants localize sound by turning their heads in the same direction and begin to make sounds from easy consonants ('p', 'd', 'm') and vowels put together. By 9 to 12 months, babbling should be well established and repeated in a sequence (ma-ma-ma). Partly, they do this in response to the sound of their own voices. As they hear their own babbling, they enjoy babbling more.
Children that don't follow this sequence or stop vocalizing for a significant amount of time may be doing so for a few reasons. Has there been a disruptive event in your lives lately? Stress can cause a temporary regression in normal development.
The other possibility is poor or even moderately diminished hearing. Infants who cannot hear themselves babble eventually babble less. Around 6 months is a common time to begin to see this.
Your baby might begin to pick up the frequency of her sounds again soon, but if she doesn't, consider a formal hearing test.