While there are no clinical trials that have explored the explicit connection between
reading and speech production (as the current study is proposing) the print-to-speech
model provides a framework for understanding how the recognition of visual word forms
(i.e., reading) is built upon acquisition and production of speech. Knowledge of how a
word sounds and feels when produced (i.e., auditory and somatosensory feedback,
respectively) scaffolds the development of knowledge about what a word looks like. This
notion that reading development is heavily dependent on oral language skills follows from
many studies providing evidence that oral language skills (i.e., vocabulary, syntax) and
phonological awareness skills are predictors of both typical and deficient reading
ability. Further, there are several nonclinical studies that provide convincing evidence
that this connection needs to be better understood.
For example, children with apraxia of speech, a motor speech disorder that results in an
impaired ability to plan and/or program the sequential movements required for speech that
is not attributable to deficits in motor physiology (e.g., weakness, or spasticity) or
deficits in language (i.e., reduced comprehension), are 1) at a high risk of developing a
reading impairment and 2) have increased sensorimotor deficits. An investigation from
2009 evaluated the performance of 38 children with suspected apraxia of speech (CAS) on
the Sensory Profile, a standardized assessment of sensory processing in children.
Children with CAS had atypical sensory processing in five sensory factors, including oral
sensory sensitivity. Increased oral sensory sensitivity in comparison to typically
developing children has also been reported in children with specific language impairment,
autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD). In
computational modelling, it has also been reported that the core impairment in CAS may be
impaired feedforward commands secondary to reduced or degraded oral sensitivity, which
fits well within the print-to-speech framework. An investigation of oral form
discrimination performance in children with CAS (i.e., identification of geometric shapes
in the mouth) reported that children with CAS scored significantly lower than typically
developing children. Lower discrimination abilities are proposed to be an indicator of
poor somatosensory function.
It has also been reported that sensory cueing approaches (which place emphasis on the
relation between movements and auditory and somatosensory information via auditory,
touch, pressure, kinesthetic and proprioceptive cues) are the most effective for
treatment of CAS. Such results suggest that sensory cueing approaches either target the
underlying impairment directly (i.e., restorative) or compensate for deficits (i.e.,
compensatory). The identification of sensory difficulties in children with CAS is
important to understand speech characteristics and treatment efficacy in this population.
These findings warrant additional investigations to understand if and to what extent
somatosensory processing contributes to speech production and reading deficiencies in
healthy and impaired adult and pediatric populations.
The investigators have found that oral form discrimination performance in adults is
related to their reading performance and previously attempted to determine the influence
of speech production feedback on reading performance by measuring reading performance in
adults while adding an additional motor component (i.e., lollipop, bite bar, lidocaine).
These somatosensory perturbations have the potential to alter and/or decrease the sensory
feedback from the articulators in the mouth.
It was found that the lollipop had a facilitatory effect (i.e., faster response times) in
the orthographic lexical decision tasks but no effect on the phonological lexical
decision tasks or picture categorization tasks. In contrast, the lidocaine had a
facilitatory effect (i.e., faster response times) in the phonological lexical decision
tasks, but no facilitatory effects on the orthographic lexical decision tasks or picture
categorization. Finally, the bite bar did not impact performance in any of the three
tasks. However, it is not known if these effects (i.e., lollipop, bite bar, lidocaine)
hold for an adult population with reading disorders. While completing these tasks under
these conditions, brain activity will be measured using an functional near-infrared
spectroscopy (fNIRS) system.
The approved investigational product is Lidocaine Hydrochloride Oral Topical Solution 2%
USP. This oral topical anesthetic will temporarily numb the participant's articulators.
This clinical trial will be conducted in compliance with this described protocol, good
clinical practice (GCP) guidelines and the applicable regulatory requirement(s).