Petitto has sought to find the answers to these questions through intensive studies of hearing babies acquiring spoken languages (English or French) and deaf babies acquiring signed languages (American Sign Language, ASL, or Langue des Signes Québécoise, LSQ), from the ages of birth through 48 months. A prevailing view about the biological foundations of language has been that very early language acquisition is tied to speech.Universal regularities in the timing and structure of infants’ vocal babbling and first words were taken as evidence that the brain must be attuned to perceiving and producing spoken language, per se, in early life. A frequent answer to the question “how does early human language acquisition begin?” was that it was the result of the development of the neuroanatomical and neurophysiological mechanisms involved in the perception and the production of speech.
One novel implication here is that language modality, be it spoken or signed, is highly plastic and may be neurologically set after birth. Note that this brain sensitivity, which Petitto has discovered to be processed in the brain’s Superior Temporal Gyrus (STG) in very young infants (and beyond), renders infants with the units over which they can tacitly perform important distributional (“statistical”) analyses, which, in turn, enable them to derive core knowledge of the patterning at the heart of natural language phonology, syntax, and phonotactic organization. Another benefit of this brain sensitivity is this: in addition to all else, it permits the child to solve the “problem of reference” (that is, to “discover” the discrete unit in the continuous linguistic stream, so that he or she may learn its meanings).Since Petitto began her study of language acquisition and the mechanisms that support it in the brains of young children, it has become accepted that babies are born with a propensity to acquire language. Whether the language comes as speech or sign language, it does not appear to matter to the brain. As long as the language input has the above crucial properties, human babies will attempt to acquire it.
Timing Milestones in Early Human Language Acquisition: Summary of Findings
Deaf children exposed to signed languages from birth, acquire these languages on an identical maturational time course as hearing children acquire spoken languages. Deaf children acquiring signed languages do so without any modification, loss, or delay to the timing, content, and maturational course associated with reaching all linguistic milestones observed in spoken language.Beginning at birth, and continuing through age 3 and beyond, speaking and signing children exhibit the identical stages of language acquisition.
These include the (a) “syllabic babbling stage” (7-10 months) as well as other developments in babbling, including “variegated babbling,” ages 10-12 months, and “jargon babbling,” ages 12 months and beyond, (b) “first word stage” (11-14 months), (c)”first two-word stage” (16-22 months), and the grammatical and semantic developments beyond.Communicative gestures versus language. Surprising similarities are also observed in deaf and hearing children’s timing onset and use of gestures as well. Signing and speaking children produce strikingly similar pre-linguistic (9-12 months) and post-linguistic communicative gestures (12-48 months). Deaf babies do not produce more gestures, even though linguistic “signs” (identical to the “word”) and communicative gestures reside in the same modality, and even though some signs and gestures can be formationally and referentially similar. Instead, deaf children consistently differentiate linguistic signs from communicative gestures throughout development, using each in the same ways observed in hearing children.
Throughout development, signing and speaking children also exhibit remarkably similar complexity in their language utterances, as well as similar types of gestures.The discovery of manual babbling. The regular onset of vocal babbling – the CV (consonant-vowel) alternation “bababa” and other repetitive, syllabic sounds that infants produce – has led researchers to conclude that babbling represents the “beginning” of human language acquisition (specifically, language production). Babbling – and thus early language acquisition in our species – was said to be determined by the development of the anatomy of the vocal tract and the neuroanatomical and neurophysiological mechanisms subserving the motor control of speech production
