The robustness of speech-like vocalization in typically developing infants and infants with autism

Human infants produce speech-like vocalizations ("volubility") at very high rates, 4-5 per minute during waking hours across the first year, far exceeding rates of our ape relatives.

We document volubility in 127 typically developing (TD) infants, 44 with autism (ASD), and 21 with non-autism developmental delay (DD) through longitudinal recordings and human coding.

Families of 302 infants (110 not yet diagnosed or with other diagnoses) supplied 8.6 all-day recordings across the first year. Trained coders analyzed 21 randomly-selected 5-minute segments per recording, counting speech-like vocalizations, cries, and laughter.

Infants in all groups (including those with other diagnoses or not yet diagnosed) showed volubility of 4-5 per minute for the first year, but boys showed higher volubility than girls in the TD, ASD, and DD groups. While volubility was relatively stable across the first year for both boy and girl TD infants, volubility fell in both ASD and DD boys, while being more stable for girls.

Strong similarities in volubility were seen across all groups, but male infants diagnosed with ASD or DD showed falling volubility across the first year, a pattern not seen in TD infants.