Biological Substrates of
Speech Development
Ray D Kent
University of Wisconsin-Madison
[email protected]
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
Performance Anatomy
Developmental Motor Control
Action-perception Linkages
Babbling and
early words
Who Babbles?
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?
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).
Hearing Loss in Infancy
• Research on infants with hearing loss shows that
their vocalizations differ from those of normalhearing 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; StoelGammon & Otomo, 1986]
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
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, & D’Odorico,
2008; Whitehurst, Smith, Fischel, & Arnold, 1991),
– infants considered at high risk (Oller, Eilers, Neal, & CoboLewis, 1998).
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)
Chimpanzee vs Adult Human Vocal Tracts
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)
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
Vocal Tract Length
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.
MRI
High-speed CT
Craniofacial anatomy shaped
by biomechanical forces
Scammon’s Morphogenetic Schedules
1960s
Genetics
Molecular
biology
Embryology
Moss’s Functional
Matrix theory
1800s
1930s
Bosma’s theory of
Performance Anatomy
Developmental Performance Anatomy
based on advances in biology
1970s
Today
Tension
Original status
Compression
Shear
Original status
Bending
Original status
Torsion
Neural
Lymphatic
Lingual
Somatic
Tissue Growth Types, based on Scammon
Lingual
(Vorperian & Kent)
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.
Bosma’s 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
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
*
FM
Female
13y 6m
Source: Dr. Christel Hummert
Mouth breather; Enlarged pharyngeal tonsil (adenoid)
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.
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)
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.
Palatal Shapes
Typically developing
Down syndrome
3-D modeling Based on Imaging Data
Yellow -- mandible
Blue -- vocal tract
Red -- palate
Green -- hyoid bone
Performance
anatomy
Speech motor
control
Action-perception
linkage
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
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)]
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).
Mammalian Muscle Fibers, cont.
– The remaining forms are found in fast
skeletal muscle:
– Type IIA is found in most fast
oxidative-glycolytic (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
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 coexpress two or more isoforms, and these
have special relevance to the craniofacial
muscles where they are found in unusual
proportions.
Soft palate
Lips
Tongue
Mandible
Vocal Folds
Pharynx
Muscles of the tongue
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Anterior
IIC/IM
IM/IIC
IIAB
IIB
IIA
I
Mid Ant Mid Post Posterior
Percentage of muscle area formed by
different fiber types
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.
Masticatory Muscles
Temporalis
Masseter
Pterygoid
Large number of hybrid fibers
Mylohyoid
Geniohyoid
Digastric
Fewer hybrid fibers and fewer
fibers expressing MyHC-I,
MyHC-fetal, & MyHC-cardiac alpha
More fibers expressing MyHC-IIA
Korfage, Brugman, and Van Eijden (2000)
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.
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)
Palatal muscles
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Pal-phar
IIC/IM
IIAB
IIB
IIA
I
Uvular
Fast Movements
LVP
TVP
Slower, more
continuous movements
Stal & Lindman, J. Anat., 2000
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.
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
Performance
anatomy
Speech motor
control
Action-perception
linkage
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
“Monkey see”
“Monkey do”
Dalai Llama Neurons
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.
Mirror Neurons and Autism
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
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
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.
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