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      Baby hands that move to the rhythm of language: hearing babies acquiring sign languages babble silently on the hands

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      Cognition
      Elsevier BV

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          Abstract

          The "ba, ba, ba" sound universal to babies' babbling around 7 months captures scientific attention because it provides insights into the mechanisms underlying language acquisition and vestiges of its evolutionary origins. Yet the prevailing mystery is what is the biological basis of babbling, with one hypothesis being that it is a non-linguistic motoric activity driven largely by the baby's emerging control over the mouth and jaw, and another being that it is a linguistic activity reflecting the babies' early sensitivity to specific phonetic-syllabic patterns. Two groups of hearing babies were studied over time (ages 6, 10, and 12 months), equal in all developmental respects except for the modality of language input (mouth versus hand): three hearing babies acquiring spoken language (group 1: "speech-exposed") and a rare group of three hearing babies acquiring sign language only, not speech (group 2: "sign-exposed"). Despite this latter group's exposure to sign, the motoric hypothesis would predict similar hand activity to that seen in speech-exposed hearing babies because language acquisition in sign-exposed babies does not involve the mouth. Using innovative quantitative Optotrak 3-D motion-tracking technology, applied here for the first time to study infant language acquisition, we obtained physical measurements similar to a speech spectrogram, but for the hands. Here we discovered that the specific rhythmic frequencies of the hands of the sign-exposed hearing babies differed depending on whether they were producing linguistic activity, which they produced at a low frequency of approximately 1 Hz, versus non-linguistic activity, which they produced at a higher frequency of approximately 2.5 Hz - the identical class of hand activity that the speech-exposed hearing babies produced nearly exclusively. Surprisingly, without benefit of the mouth, hearing sign-exposed babies alone babbled systematically on their hands. We conclude that babbling is fundamentally a linguistic activity and explain why the differentiation between linguistic and non-linguistic hand activity in a single manual modality (one distinct from the human mouth) could only have resulted if all babies are born with a sensitivity to specific rhythmic patterns at the heart of human language and the capacity to use them.

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          Most cited references40

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          Language within our grasp

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            The frame/content theory of evolution of speech production.

            The species-specific organizational property of speech is a continual mouth open-close alternation, the two phases of which are subject to continual articulatory modulation. The cycle constitutes the syllable, and the open and closed phases are segments-vowels and consonants, respectively. The fact that segmental serial ordering errors in normal adults obey syllable structure constraints suggests that syllabic "frames" and segmental "content" elements are separately controlled in the speech production process. The frames may derive from cycles of mandibular oscillation present in humans from babbling onset, which are responsible for the open-close alternation. These communication-related frames perhaps first evolved when the ingestion-related cyclicities of mandibular oscillation (associated with mastication [chewing] sucking and licking) took on communicative significance as lipsmacks, tonguesmacks, and teeth chatters--displays that are prominent in many nonhuman primates. The new role of Broca's area and its surround in human vocal communication may have derived from its evolutionary history as the main cortical center for the control of ingestive processes. The frame and content components of speech may have subsequently evolved separate realizations within two general purpose primate motor control systems: (1) a motivation-related medial "intrinsic" system, including anterior cingulate cortex and the supplementary motor area, for self-generated behavior, formerly responsible for ancestral vocalization control and now also responsible for frames, and (2) a lateral "extrinsic" system, including Broca's area and surround, and Wernicke's area, specialized for response to external input (and therefore the emergent vocal learning capacity) and more responsible for content.
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              The role of audition in infant babbling.

              The traditional belief that audition plays only a minor role in infant vocal development depends upon evidence that deaf infants produce the same kinds of babbling sounds as hearing infants. Evidence in support of this position has been very limited. A more extensive comparison of vocal development in deaf and hearing infants indicates that the traditional belief is in error. Well-formed syllable production is established in the first 10 months of life by hearing infants but not by deaf infants, indicating that audition plays an important role in vocal development. The difference between babbling in the deaf and hearing is apparent if infant vocal sounds are observed from a metaphonological perspective, a view that takes account of the articulatory/acoustic patterns of speech sounds in all mature spoken languages.
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                Author and article information

                Journal
                Cognition
                Cognition
                Elsevier BV
                00100277
                August 2004
                August 2004
                : 93
                : 1
                : 43-73
                Article
                10.1016/j.cognition.2003.10.007
                15110725
                73103ec7-5bfe-41c8-a393-7002be5de7d8
                © 2004

                https://www.elsevier.com/tdm/userlicense/1.0/

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