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Which neural circuits underlying spoken language may be inefficient or vulnerable to disruption? One of the functions
that often seems to be atypical in stuttering is sensorimotor processing, particularly auditory-motor processing. Because
auditory processing plays a major role in infants' use of the sounds of adult speech and the sounds of their own babbling, a
dysfunction in this area would obviously have an influence on the development of interacting neuronal circuits for speech
and language production. The sounds of adult speech give infants auditory targets to aim for when they are learning to
speak. The sensorimotor activity in babbling helps a child develop internal models that specify what articulatory gestures are
needed to produce desired auditory targets (Guenther, Ghosh, & Tourville, 2006; Hickok & Poeppel, 2007; Neilson &
Neilson, 1987, 2005a, 2005b). Moreover, the auditory information from babbling allows the child to adapt his internal
auditory-articulatory model to his rapidly growing speech production mechanism (Callan, Kent, Guenther, & Vorperian,
2000). Because these circuits are self-organizing, they may develop a variety of solutions to the auditory processing
problem. Some individuals may use homologous right-hemisphere structures for auditory processing, others may continue to
use inefficient areas of the left hemisphere, and still others may try to do both.
Four of the brain imaging studies described in Chapters 2 and 3 suggest problems in the very pathways that would be
expected to support sensory-motor modeling for speech. The findings of Sommer, Koch, Paulus, Weiller, and Buchel (2002),
Chang, Erickson, Ambrose, Hasegawa-Johnson, and Ludlow (2008), Watkins, Smith, Davis, and Howell (2008), and
Cykowski and colleagues (2010) suggest that individuals who stutter have less dense bidirectional fiber tracts between
sensory and motor areas. If these fiber tracts are less dense, they are probably less efficient for rapid transmission of signals.
Let's step through the process of speech production to see why this matters. Remember that according to the inverse internal
model theory of speech production, when individuals plan to generate a word or phrase, they use the inverse internal model
system (see Fig. 6.2) to generate motor commands (including making an efference copy—a copy used to rapidly produce a
hypothetical output of the motor commands for error-correction purposes) based on the sensory target they are trying to
produce. However, this inverse internal modeling system depends on continuous back-and-forth communication between
sensory and motor areas. Sensory areas supply information about the current tension in muscles and positions of speech
structures, while motor areas use this information to plan and carry out the motor commands to speech system muscles to
produce speech output. Then sensory areas analyze both the efference copy of the motor plans as well
Which neural circuits underlying spoken language may be inefficient or vulnerable to disruption? One of the functions
that often seems to be atypical in stuttering is sensorimotor processing, particularly auditory-motor processing. Because
auditory processing plays a major role in infants' use of the sounds of adult speech and the sounds of their own babbling, a
dysfunction in this area would obviously have an influence on the development of interacting neuronal circuits for speech
and language production. The sounds of adult speech give infants auditory targets to aim for when they are learning to
speak. The sensorimotor activity in babbling helps a child develop internal models that specify what articulatory gestures are
needed to produce desired auditory targets (Guenther, Ghosh, & Tourville, 2006; Hickok & Poeppel, 2007; Neilson &
Neilson, 1987, 2005a, 2005b). Moreover, the auditory information from babbling allows the child to adapt his internal
auditory-articulatory model to his rapidly growing speech production mechanism (Callan, Kent, Guenther, & Vorperian,
2000). Because these circuits are self-organizing, they may develop a variety of solutions to the auditory processing
problem. Some individuals may use homologous right-hemisphere structures for auditory processing, others may continue to
use inefficient areas of the left hemisphere, and still others may try to do both.
Four of the brain imaging studies described in Chapters 2 and 3 suggest problems in the very pathways that would be
expected to support sensory-motor modeling for speech. The findings of Sommer, Koch, Paulus, Weiller, and Buchel (2002),
Chang, Erickson, Ambrose, Hasegawa-Johnson, and Ludlow (2008), Watkins, Smith, Davis, and Howell (2008), and
Cykowski and colleagues (2010) suggest that individuals who stutter have less dense bidirectional fiber tracts between
sensory and motor areas. If these fiber tracts are less dense, they are probably less efficient for rapid transmission of signals.
Let's step through the process of speech production to see why this matters. Remember that according to the inverse internal
model theory of speech production, when individuals plan to generate a word or phrase, they use the inverse internal model
system (see Fig. 6.2) to generate motor commands (including making an efference copy—a copy used to rapidly produce a
hypothetical output of the motor commands for error-correction purposes) based on the sensory target they are trying to
produce. However, this inverse internal modeling system depends on continuous back-and-forth communication between
sensory and motor areas. Sensory areas supply information about the current tension in muscles and positions of speech
structures, while motor areas use this information to plan and carry out the motor commands to speech system muscles to
produce speech output. Then sensory areas analyze both the efference copy of the motor plans as well
Which neural circuits underlying spoken language may be inefficient or vulnerable to disruption? One of the functions
that often seems to be atypical in stuttering is sensorimotor processing, particularly auditory-motor processing. Because
auditory processing plays a major role in infants' use of the sounds of adult speech and the sounds of their own babbling, a
dysfunction in this area would obviously have an influence on the development of interacting neuronal circuits for speech
and language production. The sounds of adult speech give infants auditory targets to aim for when they are learning to
speak. The sensorimotor activity in babbling helps a child develop internal models that specify what articulatory gestures are
needed to produce desired auditory targets (Guenther, Ghosh, & Tourville, 2006; Hickok & Poeppel, 2007; Neilson &
Neilson, 1987, 2005a, 2005b). Moreover, the auditory information from babbling allows the child to adapt his internal
auditory-articulatory model to his rapidly growing speech production mechanism (Callan, Kent, Guenther, & Vorperian,
2000). Because these circuits are self-organizing, they may develop a variety of solutions to the auditory processing
problem. Some individuals may use homologous right-hemisphere structures for auditory processing, others may continue to
use inefficient areas of the left hemisphere, and still others may try to do both.
Four of the brain imaging studies described in Chapters 2 and 3 suggest problems in the very pathways that would be
expected to support sensory-motor modeling for speech. The findings of Sommer, Koch, Paulus, Weiller, and Buchel (2002),
Chang, Erickson, Ambrose, Hasegawa-Johnson, and Ludlow (2008), Watkins, Smith, Davis, and Howell (2008), and
Cykowski and colleagues (2010) suggest that individuals who stutter have less dense bidirectional fiber tracts between
sensory and motor areas. If these fiber tracts are less dense, they are probably less efficient for rapid transmission of signals.
Let's step through the process of speech production to see why this matters. Remember that according to the inverse internal
model theory of speech production, when individuals plan to generate a word or phrase, they use the inverse internal model
system (see Fig. 6.2) to generate motor commands (including making an efference copy—a copy used to rapidly produce a
hypothetical output of the motor commands for error-correction purposes) based on the sensory target they are trying to
produce. However, this inverse internal modeling system depends on continuous back-and-forth communication between
sensory and motor areas. Sensory areas supply information about the current tension in muscles and positions of speech
structures, while motor areas use this information to plan and carry out the motor commands to speech system muscles to
produce speech output. Then sensory areas analyze both the efference copy of the motor plans as well Which neural circuits underlying spoken language may be inefficient or vulnerable to disruption? One of the functions
that often seems to be atypical in stuttering is sensorimotor processing, particularly auditory-motor processing. Because
auditory processing plays a major role in infants' use of the sounds of adult speech and the sounds of their own babbling, a
dysfunction in this area would obviously have an influence on the development of interacting neuronal circuits for speech
and language production. The sounds of adult speech give infants auditory targets to aim for when they are learning to
speak. The sensorimotor activity in babbling helps a child develop internal models that specify what articulatory gestures are
needed to produce desired auditory targets (Guenther, Ghosh, & Tourville, 2006; Hickok & Poeppel, 2007; Neilson &
Neilson, 1987, 2005a, 2005b). Moreover, the auditory information from babbling allows the child to adapt his internal
auditory-articulatory model to his rapidly growing speech production mechanism (Callan, Kent, Guenther, & Vorperian,
2000). Because these circuits are self-organizing, they may develop a variety of solutions to the auditory processing
problem. Some individuals may use homologous right-hemisphere structures for auditory processing, others may continue to
use inefficient areas of the left hemisphere, and still others may try to do both.
Four of the brain imaging studies described in Chapters 2 and 3 suggest problems in the very pathways that would be
expected to support sensory-motor modeling for speech. The findings of Sommer, Koch, Paulus, Weiller, and Buchel (2002),
Chang, Erickson, Ambrose, Hasegawa-Johnson, and Ludlow (2008), Watkins, Smith, Davis, and Howell (2008), and
Cykowski and colleagues (2010) suggest that individuals who stutter have less dense bidirectional fiber tracts between
sensory and motor areas. If these fiber tracts are less dense, they are probably less efficient for rapid transmission of signals.
Let's step through the process of speech production to see why this matters. Remember that according to the inverse internal
model theory of speech production, when individuals plan to generate a word or phrase, they use the inverse internal model
system (see Fig. 6.2) to generate motor commands (including making an efference copy—a copy used to rapidly produce a
hypothetical output of the motor commands for error-correction purposes) based on the sensory target they are trying to
produce. However, this inverse internal modeling system depends on continuous back-and-forth communication between
sensory and motor areas. Sensory areas supply information about the current tension in muscles and positions of speech
structures, while motor areas use this information to plan and carry out the motor commands to speech system muscles to
produce speech output. Then sensory areas analyze both the efference copy of the motor plans as well
as the actual speech output to correct errors and update the internal model.
Rapid information flow between sensory and motor areas is critical for accurate and fluent speech. If there is a delay in
the information needed to generate the motor plans and execute them, repetitions may occur. This often happens after the
speaker produces the first sound, syllable, or word. This sound or syllable of the utterance is usually fluent because it can be
based on already obtained sensory information about the resting state of the speech system structures. But new information
is needed to go forward—information required for production of the next sound, syllable, or word. However, that
information is often delayed because it depends on rapid updating of information about the new state of the speech system
(sensory analysis) and the rapid analysis of the sound just produced (comparison of efference copy of motor commands and
feedback of actual output). Again, see Figure 6.2 for a description of the process.
This description of dyssynchrony in the assembly of components of speech and language production is intended only as
a possible explanation of primary stuttering, which is a stage of stuttering characterized by relatively relaxed repetitions and
occasional prolongations that typically occur, as Bloodstein (2001, 2002) has suggested, at the beginnings of phrases or
sentences. As indicated in the paragraph above, the first sound or syllable may be fluent but the second is often a repeat of
the first, li-like this. Most children who begin to stutter outgrow their primary disfluencies as their speech and language
systems mature or as they develop effective ways to work around the problem. Other children, however, react to their
primary stuttering by increasing the speed and tension of their disfluencies. They go on to develop the characteristics of
secondary stuttering: blocks, escape behaviors, and avoidance reactions. Why? And why do some children begin to stutter
with blocks rather than repetitions? The answer, I think, can be found in the temperament of these children, interacting with
the processes of learning.