Biological Substrates of Speech Development

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Biological Substrates of Speech Development

• Ray D Kent
• University of Wisconsin-Madison
• kent_at_waisman.wisc.edu

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3 Major Themes

• Performance Anatomy
• Structure is shaped partly by function
• Developmental Motor Control
• Early distinction between motor control for
  speech vs. motor control for nonspeech acts
• Action-Perception Linkages
• Actions and the perceptions of those actions are
  fused in cortical representations that are
  present in neonates

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Performance Anatomy
Babbling and early words
Developmental Motor Control
Action-perception Linkages
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Who Babbles?
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Setting the Stage

• How is babbling affected by the ambient language
  (babbling drift)?
• How does babbling relate to early words?
• How is babbling influenced by clinical
  conditions?
• Does babbling have clinical predictive value?

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Effect of Ambient Language

• An effect of ambient language on infant sound
  production has been observed by
• 2 months (Ruzza, Rocca, Boero, Lenti, 2003),
• 6 months (Boysson-Bardies, Sagart, Durand,
  1984),
• 9 months (Boysson-Bardies, Vihman,
  Roug-Hellichjius, Durand, Landberg, Arao,
  1992),
• 10 months (Boysson-Bardies, Halle, Sagart,
  Durand, 1989 Boysson-Bardies, Sagart, Halle,
  Durand, 1986)
• 12 months (Chen Kent, 2005 Grenon, Benner,
  Esling, 2007 Koponen, 2002 Levitt Utman,
  1992 Whalen, Levitt, Wang, 1991).

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Hearing Loss in Infancy

• Research on infants with hearing loss shows that
  their vocalizations differ from those of
  normal-hearing infants by the age of 8 to12
  months of life.
• Specifically, delays in the onset of canonical
  babbling, along with reduced phonetic variation,
  have been reported for infants with hearing loss.
  
• Kent, Netsell, Osberger, Hustedde, 1987
  Koopmans-van Beinum, Clement, van den
  Dikkenberg-Pot, 2001b McGowan, Nittrouer,
  Chenausky, 2008 Oller Eilers, 1988 Scheiner,
  Hammerschmidt, Jurgens, Zwirner, 2006
  Stoel-Gammon Otomo, 1986

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Tracheostomized Infants

• Studies of infants tracheostomized during all or
  part of the period when babbling is expected
• Bleile, Stark, McGowan, 1993 Kamen
  Watson, 1991 Kertoy, Guest, Quart, 1999
  Kraemer, Plante, Green, 2005 Locke Pearson,
  1990.
• As a consequence of the medical intervention, the
  infants in these studies had limited opportunity
  to produce speech-like sounds associated with
  normal phonation and other laryngeal function.
• The general conclusion was that these children
  experienced difficulties with speech and language
  that persisted well beyond the time of
  decannulation

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Babbling as a Predictor of Communication Outcome

• Babbling, especially with regard to its CV and
  consonantal composition, has been demonstrated to
  have predictive value for subsequent speech and
  language outcomes in children with a variety of
  disorders, including
• orofacial clefting (Chapman, Hardin-Jones,
  Halter, 2003 Lohmander-Agerskov, Soderpalm,
  Friede, Lilja, 1998 Scherer, Williams,
  Proctor-Williams, 2008),
• otitis media (Rvachew, Slawinski, Williams,
  Green, 1999),
• expressive language delay (Fasolo, Majorano,
  DOdorico, 2008 Whitehurst, Smith, Fischel,
  Arnold, 1991),
• infants considered at high risk (Oller, Eilers,
  Neal, Cobo-Lewis, 1998).

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The Anatomic Basis of Speech

• The present focus is on the craniofacial system
  in which the vocal tract resides, but the
  laryngeal and respiratory systems cannot be
  neglected
• The human craniofacial anatomy is unique in both
  its macro-anatomy and micro-anatomy
• This anatomy is molded by genetics and by
  function (use)

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Chimpanzee vs Adult Human Vocal Tracts
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The Head, Craniofacial System, and Vocal Tract

• Craniofacial evolution is fundamental to the
  origin of vertebrates (Trainor, 2005)
• there is no theory of segmentation that can
  account for all cephalic iterative structures
  (Northcutt, 2008)
• no structural component has autonomy of form
  (Kean Houghton, 1987)

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Rationale for Research

• Craniofacial malformations are involved in three
  fourths of all congenital birth defects in humans
  (Chai Maxson, Dev Dys, 2006)
• Models of voice and speech production are based
  largely on the anatomy and physiology of adult
  males and do not take account of sex and age
  differences
• We lack a comprehensive theory of speech
  development that exploits available information
  on developmental biology

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Vocal Tract Length
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How Does the Craniofacial System Grow?

• The human head is a complex anatomical system
  consisting of uniquely shaped elements and a
  variety of tissue types.

High-speed CT
MRI
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Craniofacial anatomy shaped by biomechanical
forces
1800s
1930s
Scammons Morphogenetic Schedules
Mosss Functional Matrix theory
Bosmas theory of Performance Anatomy
1970s
1960s
Genetics Molecular biology Embryology
Developmental Performance Anatomy based on
advances in biology
Today
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Torsion
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Neural
Lymphatic
Lingual
Somatic
Tissue Growth Types, based on Scammon
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Lingual
(Vorperian Kent)
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Moss Functional Matrix

• The functional matrix is primary and the
  presence, size, shape, spatial position, and
  growth of any skeletal unit is secondary,
  compensatory, and mechanically obligated to
  changes in the size, shape, spatial position of
  its related functional matrix (Moss, 1968).
• The functional matrix incorporates relevant soft
  tissues, including muscles, glands, nerves, and
  the spaces.

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Bosmas Functional Anatomy

• Bosma (1975, 1976) theorized that the vocal tract
  has a performance anatomy, meaning that its
  structure is determined by how the system is
  used.
• He further suggested that different models of
  speech production would be required to account
  for different ages of development

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Long-face Syndrome aka adenoid facies
Increased vertical height in lower third of
face Excessive dento-alveolar height Gummy
smile High arched palate Steep mandibular plane
Cause Nasal obstruction
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FM Female 13y 6m
Source Dr. Christel Hummert
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Recent Clinical Evidence

• (1) Individuals with large volumes of the
  masseter and medial pterygoid muscles have
  relatively flat mandibular and occlusal planes,
  along with small gonial angles.
• (2) Congenital Fiber-Type Disproportion myopathy
  is associated with a narrow maxillary arch,
  labial incompetence, severe skeletal open bite,
  and weakness of the masticatory muscles.
• (3) Children with obstructive sleep apnea have
  increased overjet, reduced overbite, and narrower
  upper and shorter lower dental arches.
• 4) Compared to a control group, children who
  received activator-headgear Class II treatment
  for at least 9 months had a greater reduction in
  ANB angle, a greater increase in pharyngeal area,
  pharyngeal length, and the smallest distance
  between the tongue and posterior pharyngeal wall.
• (5) Children with otitis media with effusion have
  an altered facial morphology, as reflected in
  measures of anterior cranial base length, upper
  facial height, size of the hard palate, facial
  depth, facial axis, mandibular length, and
  inferior pharyngeal airway.
• (6) Individuals with Duchenne muscular dystrophy
  have an altered craniofacial morphology that
  appears to result from an imbalance of strength
  in the orofacial muscles.

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Lamina Propria of Vocal Folds

• A recent study of unphonated vocal folds in three
  young adults evinced abnormalities in vocal fold
  mucosa presumably due to the lack of mechanical
  stimulation normally provided by phonation
• The vocal fold mucosae were hypoplastic and
  rudimentary, lacking a vocal ligament, Reinke's
  space, and layered structure.
• (Sato, Nakashima, Nonaka, Harabuchi, 2008)

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Developmental Performance Anatomy

• Endogenous and exogenous factors combine to
  influence postnatal craniofacial development.
• It is likely that the craniofacial and
  extraocular muscles have distinct patterns of
  gene expression.
• Interaction between genetics and extrinsic
  factors begins in embryology, where morphogenesis
  depends on the reactions of cells to the
  conditions created by their own growth and the
  growth of proximal cells.

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Palatal Shapes
Down syndrome
Typically developing
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3-D modeling Based on Imaging Data
Yellow -- mandible Blue -- vocal tract Red --
palate Green -- hyoid bone
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Speech motor control
Performance anatomy
Action-perception linkage
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Emergence of Speech Motor Control

• A popular conception is that motor control for
  speech builds on pre-existing motor control for
  nonspeech behaviors (e.g., feeding)
• This idea is a core assumption to MacNeilage and
  Davis Frame-Content Theory
• Recent evidence prompts a reconsideration of this
  idea

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Speech and Nonspeech Motor Development

• The central conclusion of several studies is
  that, early in infancy, speech-like movements are
  distinct from movements for nonspeech behaviors.
  
• Accordingly, speech motor control appears to
  develop in parallel with nonspeech motor
  functions, rather than being derived from them.
• Moore Ruark, 1996 Ruark Moore, 1997
  Steeve, Moore, Green, Reilly, McMurtrey, 2008
  Wilson, Green, Yunusova, Moore, 2008)

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Mammalian Muscle Fibers

• There are at least nine different mammalian MyHC
  isoforms.
• Embryonic and neonatal are developmental isoforms
  
• Cardiac alpha and beta are "slow" forms expressed
  in the heart. The cardiac beta is also found in
  slow skeletal muscle fibers (in which case it is
  called type I).

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Mammalian Muscle Fibers, cont.

• The remaining forms are found in fast skeletal
  muscle
• Type IIA is found in most fast oxidative-glycolyti
  c (FOG) fibers
• Type IIB and type IIX in fast glycolytic (FG)
  fibers. These are relatively rare and appear to
  be expressed primarily in the extraocular,
  laryngeal, masticatory, and lingual muscles.
• Type IIM and extraocular

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Muscle Fiber Types

• Isoforms isted in order of contraction speed,
  from slow to fast
• I - IC - IIC - IIAC - IIA - IIAB - IIB IIX
• In addition, hybrid muscle fibers co-express two
  or more isoforms, and these have special
  relevance to the craniofacial muscles where they
  are found in unusual proportions.

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Soft palate
Lips
Tongue
Mandible
Vocal Folds
Pharynx
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Muscles of the tongue
Percentage of muscle area formed by
different fiber types
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Lingual Muscles

• Stal et al. noted that the muscle fiber
  composition of the tongue differs from that in
  the limb, orofacial, and masticatory muscles.
• The predominance of type II fibers and regional
  heterogeneity were interpreted as a means for
  fast and flexible actions in positioning and
  shaping the tongue. The combination of type I,
  IIA, and IM/IIC fibers may contribute to lingual
  bending.

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Masticatory Muscles
Temporalis Masseter Pterygoid
Large number of hybrid fibers
Fewer hybrid fibers and fewer fibers expressing
MyHC-I, MyHC-fetal, MyHC-cardiac alpha More
fibers expressing MyHC-IIA
Mylohyoid Geniohyoid Digastric
Korfage, Brugman, and Van Eijden (2000)
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Masticatory Muscles

• Koolstra (2002) notes that the human masticatory
  system seems to have more muscles than are needed
  for its purposes.
• The apparent surfeit of muscles is
  understandable when it is recognized that the
  masticatory system meets both mechanical and
  spatial requirements.

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Masticatory Muscles Distinctive Properties

• Contain at least four different isoforms of
  myosin heavy chain
• Have a continuous range of contraction speeds
• Have a high oxidative capacity and are therefore
  very fatigue resistant

(Weijs, 1997)
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Palatal muscles
Fast Movements
Slower, more continuous movements
Stal Lindman, J. Anat., 2000
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A New Pharyngeal Muscle

• Mu and Sanders (2008) describe a a newly
  discovered muscle, the cricothyropharyngeus
• This muscle has unusual MyHC isoforms including
  slow-tonic, alpha-cardiac, neonatal, and
  embryonic.
• They believed that this muscle may have a
  specialized function in speech, which may explain
  its uniqueness to humans.

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Muscle Properties

• Speech muscles have properties that seem
  highly suited to their specialized roles in
  phonation and articulation
• Fatigue resistance
• Rapid shortening
• Very slow shortening
• Functional variation within and across muscles

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Speech motor control
Performance anatomy
Action-perception linkage
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Looking to the Future --Neuroscience
As for the future of the field, I think language
development will be covered at different levels
in several disciplines. There is very exciting
brain research going on right now for instance
the discovery of mirror neurons provides a new
way of interpreting early imitative behaviour.
IASCL - Child Language Bulletin - Vol 26, July
2006
Jean Berko Gleason
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Monkey see
Monkey do
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Dalai Llama Neurons
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Mirror Neurons (aka Dalai Llama neurons)

• Discovered by Iaccomo Rizzolati of the University
  of Parma in 1995.
• V.S. Ramachandran predicted that mirror neurons
  would do for psychology what DNA did for biology
  by providing a unifying framework and help
  explain a host of mental abilities that have
  hitherto remained mysterious and inaccessible to
  experiments.

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Mirror Neurons and Autism
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Action-Perception Networks

• Can explain seemingly precocious imitative
  behaviors, such as neonates imitating adult
  facial gestures
• Can account for aspects of vocal imitation in
  infancy
• Provide a basis for the efficient learning of
  behaviors
• May be a neural foundation for language
  development

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Developmental Profile Based on Fagan

• 7 months onset of canonical babbling
• 9 months - maximum frequency of repetitions per
  utterance, after which frequency of repetitions
  declined
• 8.4 months - the mean age of onset of word
  comprehension
• 11.8 months - first word production

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Babbling

• Babbling is a behavior based on a developmental
  anatomy that is shaped in part by its uses.
  Babble helps to create the anatomy for adult
  speech.
• Babbling draws on action-perception linkages
  present to some degree at birth but are refined
  with experience to create internal models that
  guide speech production.