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1.  White and Grey Matter Changes in the Language Network during Healthy Aging 
PLoS ONE  2014;9(9):e108077.
Neural structures change with age but there is no consensus on the exact processes involved. This study tested the hypothesis that white and grey matter in the language network changes during aging according to a “last in, first out” process. The fractional anisotropy (FA) of white matter and cortical thickness of grey matter were measured in 36 participants whose ages ranged from 55 to 79 years. Within the language network, the dorsal pathway connecting the mid-to-posterior superior temporal cortex (STC) and the inferior frontal cortex (IFC) was affected more by aging in both FA and thickness than the other dorsal pathway connecting the STC with the premotor cortex and the ventral pathway connecting the mid-to-anterior STC with the ventral IFC. These results were independently validated in a second group of 20 participants whose ages ranged from 50 to 73 years. The pathway that is most affected during aging matures later than the other two pathways (which are present at birth). The results are interpreted as showing that the neural structures which mature later are affected more than those that mature earlier, supporting the “last in, first out” theory.
doi:10.1371/journal.pone.0108077
PMCID: PMC4176722  PMID: 25251441
2.  Predicting stuttering onset 
Pediatrics  2009;123(1):10.1542/peds.2007-3219.
doi:10.1542/peds.2007-3219
PMCID: PMC3879585  PMID: 19117892
3.  Classification of Types of Stuttering Symptoms Based on Brain Activity 
PLoS ONE  2012;7(6):e39747.
Among the non-fluencies seen in speech, some are more typical (MT) of stuttering speakers, whereas others are less typical (LT) and are common to both stuttering and fluent speakers. No neuroimaging work has evaluated the neural basis for grouping these symptom types. Another long-debated issue is which type (LT, MT) whole-word repetitions (WWR) should be placed in. In this study, a sentence completion task was performed by twenty stuttering patients who were scanned using an event-related design. This task elicited stuttering in these patients. Each stuttered trial from each patient was sorted into the MT or LT types with WWR put aside. Pattern classification was employed to train a patient-specific single trial model to automatically classify each trial as MT or LT using the corresponding fMRI data. This model was then validated by using test data that were independent of the training data. In a subsequent analysis, the classification model, just established, was used to determine which type the WWR should be placed in. The results showed that the LT and the MT could be separated with high accuracy based on their brain activity. The brain regions that made most contribution to the separation of the types were: the left inferior frontal cortex and bilateral precuneus, both of which showed higher activity in the MT than in the LT; and the left putamen and right cerebellum which showed the opposite activity pattern. The results also showed that the brain activity for WWR was more similar to that of the LT and fluent speech than to that of the MT. These findings provide a neurological basis for separating the MT and the LT types, and support the widely-used MT/LT symptom grouping scheme. In addition, WWR play a similar role as the LT, and thus should be placed in the LT type.
doi:10.1371/journal.pone.0039747
PMCID: PMC3382568  PMID: 22761887
4.  Comparison of alternative methods for obtaining severity scores of the speech of people who stutter 
Clinical linguistics & phonetics  2011;25(5):368-378.
Purpose
Riley’s Stuttering Severity Instrument (SSI) is widely-used. The manuals allows SSI assessments to be made in different ways (e.g. from digital recordings or whilst listening to speech live). Digital recordings allow segments to be selected and listened to while the entire recording has to be judged when listened to live. Comparison was made between expert judges when they used these digital and live procedures to establish whether one method was more sensitive and reliable than the other.
Method
Five expert judges assessed eight speakers four times each in two judgment conditions (digital versus live). The eight speakers were chosen so that they spanned a wide range of stuttering severity. SSI version 3 (SSI-3) estimates were obtained on all occasions.
Results
An ANOVA showed a three-way interaction between sessions, speakers and condition that indicated that digital and live judgments varied across speakers and across sessions.
Conclusion
The predictions that were upheld were: 1) SSI-3 scores made from digital segements are more sensitive than SSI-3 scores made on the entire live signal; 2) Digital and live judgments vary with respect to speaker’s stuttering severity and across test sessions.
doi:10.3109/02699206.2010.538955
PMCID: PMC3314730  PMID: 21434809
Developmental stuttering; severity estimates; stuttering severity instrument; persistent stuttering; recovered stuttering
5.  Effect of Speaking Environment on Speech Production and Perception 
Environments affect speaking and listening performance. This contribution reviews some of the main ways in which all sounds are affected by the environment they propagate into. These influences are used to assess how environments affect speakers and listeners. The article concludes with a brief consideration of factors that designers may wish to take into account to address the effects.
doi:10.1618/jhes.11.51
PMCID: PMC3024543  PMID: 21258629
Speech production; speech perception; auditory feedback; clear speech; fluency control
6.  Behavioral effects arising from the neural substrates for atypical planning and execution of word production in stuttering 
Experimental neurology  2010;225(1):55-59.
This article reports on an fMRI study that examined the neural bases of atypical planning and execution processes involved in stuttering (Lu et al., 2010). In the study, twelve stuttering speakers and 12 controls named pictures which required single-syllable, multi-syllable, or repeated-syllable word responses, in the scanner. The factors associated with planning and execution were: 1) number of syllable-sized motor programs; and 2) syllable size and onset complexity. Structural equation modeling revealed two parallel neural circuits (the basal ganglia-inferior frontal gyrus, premotor area circuit and the cerebellum-premotor area circuit). These were involved in atypical planning and execution processes in stuttering, respectively. The interface between planning and execution in stuttering involved the angular gyrus. This article discusses the relevance of these findings to behavioral theories that also propose separate planning and execution mechanisms behind stuttering.
doi:10.1016/j.expneurol.2010.06.012
PMCID: PMC3011212  PMID: 20599979
Developmental stuttering; Planning; Execution; Connectivity; EXPLAN
8.  The UCLASS archive of stuttered speech 
Purpose
This letter gives details of two releases of audio recordings available from speakers who stutter that can be accessed on the web. Most of the recordings are from school-age children. These are available on the UCLASS website and information is provided about how to access the site. A description of the recordings and background information about the speakers who contributed recordings to UCLASS Releases One and Two are given. The sample types available in Release One are monolog. Release Two has monologs, readings and conversations. Three optional software formats that can be used with the archive are described (though processing the archive is not restricted to these formats). Some perceptual assessment of the quality of each recording is given. An assessment of the strengths and limitations of the recording archive is presented. Finally, some past applications and future research possibilities using the recordings are discussed.
doi:10.1044/1092-4388(07-0129)
PMCID: PMC2939977  PMID: 19339703
Developmental stuttering; UCL Archive of Stuttered Speech (UCLASS) http://www.speech.psychol.ucl.ac.uk/; PRAAT http://www.praat.org; SFS http://www.phon.ucl.ac.uk/resource/sfs/; CHILDES http://childes.psy.cmu.edu; the Wellcome Trust http://www.wellcome.ac.uk
9.  Dynamic reversibility of hydrodynamic focusing for recycling sheath fluid† 
Lab on a chip  2010;10(15):1952-1959.
The phenomenon of “unmixing” has been demonstrated in microfluidic mixers, but here we manipulate laminar flow streams back to their original positions in order to extend the operational utility of an analytical device where no mixing is desired. Using grooves in the channel wall, we passively focus a sample stream with two sheath streams to center it in a microchannel for optical analysis. Even though the sample stream is completely surrounded by sheath fluid, reversing the orientation of the grooves in the channel walls returns the sample stream to its original position with respect to the sheath streams. We demonstrate the separation of the sample stream from the contiguous sheath streams and the recycling of the sheath fluid using the reversibility of laminar flow. Polystyrene microspheres and fluorescent dye were used to quantify the performance of the unsheathing process. We found that the maximum numbers of microspheres and all of the fluorescent dye were recaptured at sheath recycling levels <92%. The use of this sheathing technique has previously been demonstrated in a sensitive microflow cytometer; the unsheathing capability now provides the opportunity to recover particles from the sensor with minimal dilution or to recycle the sheath fluid for long-term unattended operation.
doi:10.1039/c004696e
PMCID: PMC2919229  PMID: 20480064
10.  Fluorescence-based Sensing of 2,4,6-Trinitrotoluene (TNT) Using a Multi-channeled Poly(methyl methacrylate) (PMMA) Microimmunosensor 
Sensors (Basel, Switzerland)  2010;10(1):876-889.
Fluorescence immunoassays employing monoclonal antibodies directed against the explosive 2,4,6-trinitrotoluene (TNT) were conducted in a multi-channel microimmunosensor. The multi-channel microimmunosensor was prepared in poly (methyl methacrylate) (PMMA) via hot embossing from a brass molding tool. The multi-channeled microfluidic device was sol-gel coated to generate a siloxane surface that provided a scaffold for antibody immobilization. AlexaFluor-cadaverine-trinitrobenzene (AlexaFluor-Cad-TNB) was used as the reporter molecule in a displacement immunoassay. The limit of detection was 1–10 ng/mL (ppb) with a linear dynamic range that covered three orders of magnitude. In addition, antibody crossreactivity was investigated using hexahydro-1,3,5-triazine (RDX), HMX, 2,4-dinitrotoluene (DNT), 4-nitrotoluene (4-NT) and 2-amino-4,6-DNT.
doi:10.3390/s100100876
PMCID: PMC3270874  PMID: 22315573
TNT; immunosensor; fluorescence; PMMA; microchannel; antibody
11.  Development of an operant treatment for content word dysfluencies in persistent stuttering children: Initial experimental data 
A novel behavioral treatment for persistent stuttering is described. Analysis of the dysfluent speech shows that children who emit high rates of stuttering on content words in sentences have a poor prognosis for recovery, compared to those who emit high rates of stuttering on function words. This novel technique aimed to reverse the pattern of dysfluencies noted in such children, and reduce stuttering in the short-term. To this end, dysfluent content words only were subject to an over-correction procedure. In contrast, dysfluent function words were subject to social approval. The results of two studies indicated that these procedures reduced rates of content word stuttering, even at a post-treatment follow-up assessment, for those with severe, and previously intractable, stuttering. These data suggest the efficacy of behavioral interventions for persistent stuttering, and point to the importance of careful delineation between the parts of speech to be subject to various contingencies. However, it remains to be seen whether the treatment efficacy was specifically due to targeting the parts of speech of the stutter-contingent time-outs
PMCID: PMC2777265  PMID: 19920870
operant; over-correction; reinforcement; content words; function words
12.  Microstructure and mineral composition of dystrophic calcification associated with the idiopathic inflammatory myopathies 
Arthritis Research & Therapy  2009;11(5):R159.
Introduction
Calcified deposits (CDs) in skin and muscles are common in juvenile dermatomyositis (DM), and less frequent in adult DM. Limited information exists about the microstructure and composition of these deposits, and no information is available on their elemental composition and contents, mineral density (MD) and stiffness. We determined the microstructure, chemical composition, MD and stiffness of CDs obtained from DM patients.
Methods
Surgically-removed calcinosis specimens were analyzed with fourier transform infrared microspectroscopy in reflectance mode (FTIR-RM) to map their spatial distribution and composition, and with scanning electron microscopy/silicon drift detector energy dispersive X-ray spectrometry (SEM/SDD-EDS) to obtain elemental maps. X-ray diffraction (XRD) identified their mineral structure, X-ray micro-computed tomography (μCT) mapped their internal structure and 3D distribution, quantitative backscattered electron (qBSE) imaging assessed their morphology and MD, nanoindentation measured their stiffness, and polarized light microscopy (PLM) evaluated the organic matrix composition.
Results
Some specimens were composed of continuous carbonate apatite containing small amounts of proteins with a mineral to protein ratio much higher than in bone, and other specimens contained scattered agglomerates of various sizes with similar composition (FTIR-RM). Continuous or fragmented mineralization was present across the entire specimens (μCT). The apatite was much more crystallized than bone and dentin, and closer to enamel (XRD) and its calcium/phophorous ratios were close to stoichiometric hydroxyapatite (SEM/SDD-EDS). The deposits also contained magnesium and sodium (SEM/SDD-EDS). The MD (qBSE) was closer to enamel than bone and dentin, as was the stiffness (nanoindentation) in the larger dense patches. Large mineralized areas were typically devoid of collagen; however, collagen was noted in some regions within the mineral or margins (PLM). qBSE, FTIR-RM and SEM/SDD-EDS maps suggest that the mineral is deposited first in a fragmented pattern followed by a wave of mineralization that incorporates these particles. Calcinosis masses with shorter duration appeared to have islands of mineralization, whereas longstanding deposits were solidly mineralized.
Conclusions
The properties of the mineral present in the calcinosis masses are closest to that of enamel, while clearly differing from bone. Calcium and phosphate, normally present in affected tissues, may have precipitated as carbonate apatite due to local loss of mineralization inhibitors.
doi:10.1186/ar2841
PMCID: PMC2787294  PMID: 19857267
13.  Two simple and rugged designs for creating microfluidic sheath flow 
Lab on a chip  2008;8(7):1097-1103.
A simple design capable of 2-dimensional hydrodynamic focusing is proposed and successfully demonstrated. In the past, most microfluidic sheath flow systems have often only confined the sample solution on the sides, leaving the top and bottom of the sample stream in contact with the floor and ceiling of the channel. While relatively simple to build, these designs increase the risk of adsorption of sample components to the top and bottom of the channel. A few designs have been successful in completely sheathing the sample stream, but these typically require multiple sheath inputs and several alignment steps. In the designs presented here, full sheathing is accomplished using as few as one sheath input, which eliminates the need to carefully balance the flow of two or more sheath inlets. The design is easily manufactured using current microfabrication techniques. Furthermore, the sample and sheath fluid can be subsequently separated for recapture of the sample fluid or re-use of the sheath fluid. Designs were demonstrated in poly(dimethylsiloxane) (PDMS) using soft lithography and poly(methyl methacrylate) (PMMA) using micromilling and laser ablation.
doi:10.1039/b719381e
PMCID: PMC2751611  PMID: 18584084
14.  The good, the bad, and the tiny: a review of microflow cytometry 
Analytical and bioanalytical chemistry  2008;391(5):1485-1498.
Recent developments in microflow cytometry have concentrated on advancing technology in four main areas: (1) focusing the particles to be analyzed in the microfluidic channel, (2) miniaturization of the fluid-handling components, (3) miniaturization of the optics, and (4) integration and applications development. Strategies for focusing particles in a narrow path as they pass through the detection region include the use of focusing fluids, nozzles, and dielectrophoresis. Strategies for optics range from the use of microscope objectives to polymer waveguides or optical fibers embedded on-chip. While most investigators use off-chip fluidic control, there are a few examples of integrated valves and pumps. To date, demonstrations of applications are primarily used to establish that the microflow systems provide data of the same quality as laboratory systems, but new capabilities—such as automated sample staining—are beginning to emerge. Each of these four areas is discussed in detail in terms of the progress of development, the continuing limitations, and potential future directions for microflow cytometers.
doi:10.1007/s00216-007-1827-5
PMCID: PMC2746035  PMID: 18228010
Flow cytometry; Microfluidics; Fluid focusing; Integrated optics; Cell sorter
15.  Comparison of acoustic and kinematic approaches to measuring utterance-level speech variability 
Purpose
The spatio-temporal index (STI) is one measure of variability. As currently implemented, kinematic data are used, requiring equipment that cannot be used with some patient groups or in scanners. An experiment is reported that addressed whether STI can be extended to an audio measure of sound pressure of the speech envelope over time, that did not need specialized equipment.
Method
STI indices of variability were obtained from lip track (L-STI) and amplitude envelope (E-STI) signals. These measures were made concurrent whilst either fluent speakers or speakers who stutter repeated “Buy Bobby a puppy” 20 times.
Results
L-STI and E-STI correlated significantly. STI reduced with age for both L-STI and E-STI. E-STI scores and L-STI scores discriminated successfully between fluent speakers and speakers who stutter.
Conclusion
The amplitude envelope over time STI scores can be used to obtain an STI score. This STI score can be used in situations where lip movement STI scores are precluded.
doi:10.1044/1092-4388(2009/07-0167)
PMCID: PMC2719598  PMID: 19564436
Speech development; spatio-temporal index (STI); speech kinematics; stuttering; articulatory undershoot
16.  Multi-wavelength microflow cytometer using groove-generated sheath flow 
Lab on a chip  2009;9(13):1942-1950.
A microflow cytometer was developed that ensheathed the sample (core) fluid on all sides and interrogated each particle in the sample stream at four different wavelengths. Sheathing was achieved by first sandwiching the core fluid with the sheath fluid laterally via fluid focusing. Chevron-shaped groove features fabricated in the top and bottom of the channel directed sheath fluid from the sides to the top and bottom of the channel, completely surrounding the sample stream. Optical fibers inserted into guide channels provided excitation light from diode lasers at 532 and 635 nm and collected the emission wavelengths. Two emission collection fibers were connected to PMTs through a multimode fiber splitter and optical filters for detection at 635 nm (scatter), 665 nm and 700 nm (microsphere identification) and 565 nm (phycoerythrin tracer). The cytometer was capable of discriminating microspheres with different amounts of the fluorophores used for coding and detecting the presence of a phycoerythrin antibody complex on the surface of the microspheres. Assays for Escherichia coli were compared with a commercial Luminex flow cytometer.
doi:10.1039/b822442k
PMCID: PMC2719160  PMID: 19532970
17.  The effects of bilingualism on stuttering during late childhood 
Objectives
To document distinct patterns of language use by bilingual children (use of an alternative language exclusively, LE, or along with English, BIL). To establish how these patterns affect onset of stuttering, school performance and recovery rate relative to monolingual speakers who stutter (MONO).
Design
Clinical referral sample with cases classified by speech-language therapists. Supplementary data obtained from speech recordings, interviews with child and family.
Setting
South-East England, 1999-2007.
Participants
Children aged 8-12 plus who stuttered (monolingual and bilingual) and fluent bilingual controls (FB).
Main outcome measures
Participants’ stuttering history, SATS scores, measures of recovery or persistence of stuttering.
Results
The sample of 317 children had 69 bilinguals (prevalence rate of bilingualism in the stuttering sample was 21.8%). 38 children used a language other than English primarily or exclusively in the home and 36 of these (94.7%) bilinguals who stuttered did so in both their languages. There were fewer LE than BIL stuttering children at time of first referral to clinic (of the bilinguals who stuttered, 15/38, 39.5%, were LE and 23/38, 60.5%, were BIL). The reverse was the case in the fluent control sample (of the bilinguals who did not stutter, 28/38, 73.7%, were LE and 10/38, 26.3%, were BIL). The association between stuttering and bilingual group (LE/BIL) was significant by χ2 and this is consistent with a higher chance of stuttering for BIL than LE speakers. For speakers who stuttered, age of stuttering onset for LE and BIL was similar to that reported for MONO groups (4 years 9 months, 4 years 10 months and 4 years 3 months for LE, BIL, MONO respectively) and males were affected in each of these groups to about the same extent (the male/female ratio was 4.1:1, 4.75:1 and 4.43:1 for LE, BIL and MONO respectively). For the 29 children who were old enough to complete the assessments, educational achievement at key stages one and two was not affected by either form of bilingualism relative to the MONO and fluent bilingual groups. For these same children, recovery rate for LE and MONO controls was significantly higher by χ2 than for those who were BIL since birth (recovery rate for LE and MONO together was 55%, and for BIL was 25%).
Conclusions
There was an increased chance of stuttering onset for BIL children. The chances of recovery from stuttering were lower for BIL speakers than for LE and MONO speakers.
doi:10.1136/adc.2007.134114
PMCID: PMC2597689  PMID: 18782846
Bilingualism; persistence; recovery; stuttering
18.  Temporal and spatial variability in speakers with Parkinson's Disease and Friedreich's Ataxia 
Speech variability in groups of speakers with Parkinson's disease (PD) and with Friedreich's ataxia was compared with healthy controls. Speakers repeated the same phrase 20 times at one of two rates (fast or habitual). A non-linear analysis of variability was performed which used some of the principles behind the spatio-temporal index (STI). The STI usually employs variation in lip displacement over repetitions of the same utterance and a linear analysis of such signals is conducted to represent the combined variation in spatial and temporal control. When working with patients, audio measures (here we used speech energy) are preferred over kinematics ones as they are minimally disruptive to speech. Non-linear methods allow spatial variability to be estimated separately from temporal variability. The results are tentatively interpreted as showing that PD speakers were distinguished from healthy control speakers in spatial variability and ataxic speakers were distinguished from controls in temporal variability. These findings are consistent with the speech symptoms reported for these disorders. We conclude that the non-linear analysis using the speech energy measure is worth investigating further as it is potentially revealing of the differences underlying these two pathologies.
PMCID: PMC2661058  PMID: 19330039
19.  An investigation into the influences of age, pathology and cognition on speech production 
Changes in speech rate have long been identified as a prominent sign of dysarthria. At the same time, such changes have been reported in the literature on normal ageing. This study aimed to provide information on the speech rate behaviour in the three participant groups, comprising speakers with Parkinson's Disease (PD), healthy age matched control speakers (CON), and an older non-dysarthric group with mild cognitive decline (DEM).
The analysis revealed that the CON and PD group performed similarly for articulation rate whereas the DEM speakers spoke significantly more slowly. This relationship was reversed for pausing behaviour, where the DEM and CON groups performed similarly whilst the PD speakers produced a higher degree of pause time. All groups could change their articulation rate significantly from habitual to slow and fast conditions. However, the groups differed in the amount of change, with CON speakers showing the greatest and DEM the smallest amount of differences in articulation rate. The data did not identify clear performance predictors. However, there was a suggestion that the speakers' cognitive skills had an impact on their speech performance.
PMCID: PMC2661059  PMID: 19330040
20.  The effects of delayed and frequency shifted feedback on speakers with Parkinson's Disease 
Delayed auditory feedback (DAF) has been assessed as a rate reduction and intelligibility enhancing tool in patients with Parkinson's Disease (PD) for some time. However, there are contradictory results in the literature regarding the success of this device. Also, little is known about the effects of DAF on speech other than influences on speech rate and intelligibility. Frequency shifted feedback (FSF) is known to produce more natural sounding speech than DAF and to improve the fluency of persons who stutter. However, there are currently no studies reporting how PD speakers perform under FSF.
The aim of this study was to investigate the effects of both types of altered feedback on the speech of PD and control participants on a broad range of measures. The performance of 16 PD speakers and 11 control speakers in a reading task under DAF, FSF and no altered feedback (NAF) are reported in this paper.
The results showed that all groups responded to altered feedback in a similar way and showed a prominent reduction of speech rate. The conditions evoked changes in pause frequency (increases), loudness levels (increases), pitch variation (increases) and intelligibility and naturalness (decreases) for all or some of the groups. Few effects could be observed on articulation/pause time ratio, pause duration, pitch range, and speech rhythm. Previous reports on differences in susceptibility of PD speaker to altered feedback were confirmed and some speakers benefited from the system despite the negative group results for intelligibility and naturalness. In general, FSF resulted in performance closer to the NAF state than DAF on all variables, and for those PD speakers who benefited from altered feedback, the FSF condition evoked the greatest improvement.
PMCID: PMC2661057  PMID: 19330038
21.  Lexical Priming of Function Words and Content Words with Children Who Do and Do Not Stutter 
The specific mechanisms that underlie childhood stuttering are not fully understood. The current study investigated these mechanisms by comparing the effect on fluency of priming different components of a short sentence. The main findings were that 1. Both children who stutter (CWS) (n=12, M age = 6;3) and children who do not stutter (CWNS) (n=12, M age = 6;6) were more fluent after function word priming than content word priming, 2. This effect was significantly greater for CWS than for CWNS, and 3. After function word priming, CWS produced content words with significantly longer duration than did CWNS. These findings are discussed in relation to two competing theories of stuttering: the Covert Repair Hypothesis (Kolk & Postma, 1997) and the developmentally focused model of Howell and Au-Yeung (2002).
doi:10.1016/j.jcomdis.2008.01.004
PMCID: PMC2635535  PMID: 18407286
22.  Lexical priming of function words and content words with children who do, and do not, stutter 
Journal of Communication Disorders  2008;41(6-5):459-484.
The specific mechanisms that underlie childhood stuttering are not fully understood. The current study investigated these mechanisms by comparing the effect on fluency of priming different components of a short sentence. The main findings were that: (1) both children who stutter (CWS) (n = 12, M age = 6;3) and children who do not stutter (CWNS) (n = 12, M age = 6;6) were more fluent after function word (FW) priming than content word (CW) priming, (2) this effect was significantly greater for CWS than for CWNS, and (3) after FW priming, CWS produced CWs with significantly longer duration than did CWNS. These findings are discussed in relation to two competing theories of stuttering: the covert repair hypothesis (CRH) [Kolk, H., & Postma, A. (1997). Stuttering as a covert repair phenomenon. In R. F. Curlee & G. M. Siegel (Eds.), Nature and treatments of stuttering: New directions (pp. 182–203). Needham Heights, MA: Allyn & Bacon] and the developmentally focused model of Howell and Au-Yeung [Howell, P., & Au-Yeung, J. (2002). The EXPLAN theory of fluency control and the diagnosis of stuttering. In E. Fava (Ed.), Current issues in linguistic theory series: Pathology and therapy of speech disorders (pp. 75–94). Amsterdam: John Benjamins].
Learning outcomes: After reading this article, the reader will be able to: (1) understand which linguistic levels can be primed in children who stutter; (2) see why EXPLAN predicts asymmetrical effects on fluency when function or content words are primed; (3) appreciate the distinguishing characteristics of CRH and EXPLAN theories.
doi:10.1016/j.jcomdis.2008.01.004
PMCID: PMC2635535  PMID: 18407286
23.  The Use of Structural Equation Modeling in Stuttering Research: Concepts and Directions 
This article provides a brief introduction to the history and applications of the class of data analytic techniques collectively known as Structural Equation Modeling (SEM). Using an example based on psychological factors thought to affect the likelihood of stuttering, we discuss the issues of specification, identification, and model fit and modification in SEM. We also address points relating to model specification strategies, item parceling, advanced modeling, and suggestions for reporting SEM analyses. It is noted that SEM techniques can contribute to the elucidation of the developmental pathways that lead to stuttering.
PMCID: PMC2493410  PMID: 18677423
Structural equation modeling; LISREL; stuttering models
24.  Structural and functional abnormalities of the motor system in developmental stuttering 
Brain : a journal of neurology  2007;131(Pt 1):50-59.
Summary
Though stuttering is manifest in its motor characteristics, the cause of stuttering may not relate purely to impairments in the motor system as stuttering frequency is increased by linguistic factors, such as syntactic complexity and length of utterance, and decreased by changes in perception, such as masking or altering auditory feedback. Using functional and diffusion imaging, we examined brain structure and function in the motor and language areas in a group of young people who stutter. During speech production, irrespective of fluency or auditory feedback, the people who stuttered showed overactivity relative to controls in the anterior insula, cerebellum and midbrain bilaterally and underactivity in the ventral premotor, Rolandic opercular and sensorimotor cortex bilaterally and Heschl’s gyrus on the left. These results are consistent with a recent meta-analysis of functional imaging studies in developmental stuttering. Two additional findings emerged from our study. First, we found overactivity in the midbrain, which was at the level of the substantia nigra and extended to the pedunculopontine nucleus, red nucleus and subthalamic nucleus. This overactivity is consistent with suggestions in previous studies of abnormal function of the basal ganglia or excessive dopamine in people who stutter. Second, we found underactivity of the cortical motor and premotor areas associated with articulation and speech production. Analysis of the diffusion data revealed that the integrity of the white matter underlying the underactive areas in ventral premotor cortex was reduced in people who stutter. The white matter tracts in this area via connections with posterior superior temporal and inferior parietal cortex provide a substrate for the integration of articulatory planning and sensory feedback, and via connections with primary motor cortex, a substrate for execution of articulatory movements. Our data support the conclusion that stuttering is a disorder related primarily to disruption in the cortical and subcortical neural systems supporting the selection, initiation and execution of motor sequences necessary for fluent speech production.
doi:10.1093/brain/awm241
PMCID: PMC2492392  PMID: 17928317
speech dysfluency; functional imaging; diffusion tensor imaging; basal ganglia; ventral premotor cortex
25.  Late childhood stuttering 
Purpose
A longitudinal study was conducted on 76 children which examined risk factors that led children who stutter at around age eight to persist in the disorder when they reached age twelve.
Method
All children were verified as stuttering at the first assessment on the basis of a clinical referral and a further clinical assessment. When they reached twelve, they were classified as persistent or recovered on the basis of parent, child and researcher assessments. A range of measures was taken at the two age-points for determining risk factors for persistence/recovery.
Results
More males than females were affected. There was no evidence for persistence and recovery to run in families. At first referral all speakers who stuttered had high stuttering severity ratings and high proportions of dysfluencies in their speech (particularly those involving repetitions of whole words). At age 12 plus, the severity ratings of the recovered speakers and dysfluency counts dropped. The persistent speakers continued to have high severity ratings and produced more part-word dysfluencies. Temperament, measured at first assessment, differed between all stutterers and fluent controls and, when persistent and recovered speaker groups were examined separately, recovered speakers were less adaptable than persistent speakers; persistent speakers had more intense moods than controls; recovered speakers were less adaptable than controls. Detection of backward masking stimuli at 12 plus did not differ between all the children who stuttered and controls but when speakers who stuttered were differentiated by recovery group, persistent speakers had poorer backward masking thresholds than recovered speakers. Performance in motor tasks controlled by the cerebellum was assessed at 12 plus. There were indications of poor cerebellar control in speakers who persisted compared with the recovered speakers.
Conclusion
The tendency for more males than females to stutter was confirmed. Different patterns in speech were observed: Severity ratings of the recovered speakers dropped by age 12 plus. The severity ratings for the persistent speakers remained high at 12 plus and dysfluency types tended to change from whole to part words over time. Persistent and recovered speakers differed on temperamental performance at initial assessment, and performed differently on sensory and motor tasks at age 12 plus.
doi:10.1044/1092-4388(2008/048)
PMCID: PMC2405819  PMID: 18506043

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