3 to 6 months
Around three to four months infants produce nasals, liquids (mainly trills), and friction noises produced in the back of the throat. Between 4 and 6 months the infant's vocalizations will include a variety of new and different sounds. The infant will playfully explore the vocal mechanism by producing "raspberries", squeals, growls, yells, whispers, bilabial trills, snorts, and isolated vowel-like sounds. Vocalizations will be produced that mainly consist of vowels with intonation patterns that are not consistent with adult speech patterns.
An infant will also begin marginal babbling during this stage. "In marginal babbling, long series of segments are found in which consonantal and vocalic elements both occur but they do not resemble syllables of adult speech in their durational aspects or other articulatory features" (Stark, 1980, p. 74).
Clip 1. The infant is exploring the range of sounds he can produce. He produces nasalized vowels, long vowels, squeals, and raspberries.
Clip 2. The infant produces marginal babbling and isolated long vowels.
Clip 3. The infant produces squeals along with another example of marginal babbling. He is beginning to produce more adult-like intonation.
Clip 4. The infant produces marginal babbling during this sample.