Deaf babies also babble, which suggests that babbling is:

1. Deaf babies babble in the same patterns as hearing babies. 2. So babbling cannot be simply imitation of sounds heard. 3. It is a natural part of the process of language development. 4. Deaf babies babble somewhat less and start later, but that is not a delay in language. **Why not the others:** Deaf babies cannot hear sounds to imitate, and their babbling is not a delay sign; it is simply later and less frequent. _Source: Wikipedia, "Language acquisition", section "Sensitive period" (revision 1375526787)_