1. C. F. Hockett in Animal Sounds and Communication W. E. Lanyon and W. N. Tavolga Eds. (American Institute of Biological Sciences Washington DC 1960) pp. 392–430.
2. Babbling occurs during the period of roughly 7 to 12 months of age.
3. The Articulatory Basis of Babbling
4. First (single) words are produced during the period of roughly 12 to 18 months of age.
5. B. L. Davis P. F. MacNeilage C. L. Matyear in preparation.