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Figure 3. Noninvasive reflective motion capture markers are applied on Fiona’s face, lips, and jaw (lefi). The movement of the
markers are tracked in three dimensions, and the resulting model (right) can be analyzed in various ways to better understand
speech production and development. Photo from Iennell Vick, 2014.
years of childhood. At 12 months of age, movement of the infants and young children compared with adults. More-
lower jaw is the primary driver that brings the lips together for over, the structures are growing rapidly and nonuniformly
the “b” sound. By two years of age, the lower lip and upper lip throughout the period of speech development (Vorperian et
start to contribute in equal measure to each other, but the jaw al., 2005). Acoustically, the output from the growing speech
is still the primary driver. At six years of age, children use both production system is continually changing during this pe-
the lower lip and jaw equally to achieve lip closure for the “b,” riod so that the same configuration at one stage will pro-
with less movement from the upper lip, quite similar to the duce a different sound than at subsequent stages (Menard
strategy used by adults (Green et al., 2000). In addition to the et al., 2004). This challenge creates a tension between what
lack of differentiation in structures in early vocal productions, the child is able to produce with limited control, which is far
the movement of the jaw is much more ballistic, lacking the from perfect, and the desire to produce target sounds like
fine control observed in older children (Green et al., 2002). the adult model (McAllister Byun et al., 2016).
If is Clea? ‘hat the earliest vocalizations are accomplished by As the child builds maps within the brain that associate its
sunplifying the more complex movements produced by adults . . . . . .. »
_ _ own ability to produce a sound that is somethuig like ba

to generate sounds that approximate the adult versions. The with ‘he adult word «ban» R Creams a fmmdafion on which
infant and toddler are, then, reducing the degrees of freedom . . . l .

_ _ _ its early words will build. These earliest syllable shapes, pro-
of the system using the linuted control that they have mas- . . . .

d G_ k I duced during the babbling stage, facilitate the eventual pro-
tare ( ‘C E‘ a " 2008)' duction of words that contain these very sounds (Vihman,
All of this control develops uniquely in children because of 2013). The motoric and anatomic constraints of the baby’s
the highly individualized constraints within each child. For system are the most likely determinants of these early pro-
example, tongue control and coordination develops later ductions and preferences, not the speech sounds the baby
than jaw control and many children seem to babble pre- hears most frequently from its caregiver (Majorano et al.,
dominantly with jaw-driven segments like “ba” and “ma,” 2014). The baby’s own babbling provides the most frequent
but other children babble more complex sounds like “l€’ input to the auditory target map-building system in the
and “g,” as reported by Stoel-Gammon and Cooper (1984). brain (Tourville and Guenther, 2010).

Regardless, all babies face the same challenge of attempting

to mimic the sounds they hear from adults with much dif- The First’. Vllord

ferent equipment. That is, the size and relative proportion Considering, now, the skills, limitations, and babbling habits

of the speech-producing structures are vastly different in of a baby at 12 months, we come to the moment of the first
Fall 2013 | Acoustic: Tnduy | 4:1

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