In their Covert Repair Hypothesis (CRH), Postma and Kolk (1993) proposed that stuttering-like disfluencies arise, in both normal and stuttered speech, as a consequence of speakers‟ attempts to repair phonological-encoding errors before they start to speak. They posited that stutterers are particularly disfluent because they make larger numbers of such errors compared to normally-fluent speakers. To date, however, experimental research has provided little reliable evidence to support or counter this hypothesis. This thesis constitutes a systematic attempt to provide such evidence. Using a tongue-twister paradigm in conjunction with manipulations of auditory masking, it first documents (a) the vigilance with which normally-fluent speakers monitor for such errors; (b) the relative accuracy with which they detect them; and (c) the frequency with which they occur – in both inner and overt speech. A second set of experiments then extends the same investigation to a group of stutterers and matched controls and explores the relationship between the occurrence of participants‟ errors in the experimental paradigm and the frequency of their stuttering-like disfluencies in everyday speaking situations. Together, these experiments reveal that, compared to controls, participants who stutter monitor their speech with similar levels of vigilance; identify phonemic errors with similar degrees of accuracy; and, as predicted by the CRH, produce significantly more errors – in both their inner and overt speech. However, contrary to the predictions of the CRH, no relationship was found between the frequency of such errors in inner speech and the severity of participants‟ disfluencies. In a final set of experiments, a speech-recognition paradigm is employed to explore an alternative hypothesis: that stuttering-like disfluencies can be precipitated, in a speaker, by the mere anticipation that his words will result in communication failure. Results revealed that, for stutterers, stuttering decreased on words that were consistently followed by feedback implying correct recognition, but not on words followed by feedback implying incorrect recognition. For normally-fluent speakers, equivalent correlations were not found. The thesis concludes that slow or impaired phonological encoding may play a role in the development of the disorder. But, once established, the anticipation of communication failure may be a more important factor in determining where and when stuttering-like disfluencies actually occur. It then discusses implications of the experimental findings for hypotheses that posit a connection between phonological encoding and stuttering.

In an effort to improve understanding of the role that support groups such as the National Stuttering Association (NSA) play in helping people who stutter, speech-language pathologists who participate in the NSA were asked to participate in a research survey. Previous research and anecdotal evidence has shown that support groups not only benefit people who stutter, but also the professionals who work with them. Participation in the NSA can enhance SLPs' understanding of stuttering, and their comfort level and competence working with people who stutter. However, the relationship between support groups and professionals has not been adequately studied. / text

This thesis is the pilot study of an ongoing investigation of the organization of the mental lexicon in children with specific language impairment and children who stutter (CWS). The current study analyzes the performance of 8 CWS, ages 4; 11 – 10; 1 and their typically developing age matches (CWNS) on a list recall task adapted from Roediger and McDermott (1995). Talker groups were matched for maternal education level, male to female ratio, and standardized measures of nonverbal intelligence, expressive vocabulary, digit memory, and narrative comprehension and production. Similar to previous reports, the CWS performed significantly lower on a measure of receptive vocabulary and a measure of phonological memory than the CWNS. For both talker groups, there was a positive correlation between age and percentage of correctly recalled words on the list recall task. Older CWNS produced more semantic intrusions than younger CWNS; however the same trend was not demonstrated in CWS. False recall of semantically-related, phonologically-related, and unrelated words was not significantly different between talker groups. These findings provide preliminary evidence of differences between talker groups on a list recall task. The inclusion of a greater number of participants may provide stronger support for the hypothesis that lexical-semantic organization is less efficient in CWS. / text

Current forensic DNA analysis utilizes capillary electrophoresis (CE) to separate short tandem repeat (STR) fragments based on their length. Next generation sequencing (NGS) is the next evolution of forensic DNA profiling, and though dedicated forensics protocols are still fairly new, it is only a matter of time before NGS becomes the new standard for forensic DNA profiling. Stutter has been a problem ever since forensic STR testing was first implemented. The slipped strand mispairing model is the proposed mechanism for how stutter occurs, and it appears to be an intrinsic part of the polymerase chain reaction (PCR). Samples that were run via the ForenSeq™ DNA Signature Prep Kit were amplified using the DNA Primer Mix A (DPMA) and then sequenced on a MiSeq FGx™ Forensics Genomics System. Samples were also amplified using the GlobalFiler™ PCR Amplification kit and fragment separation was done via capillary electrophoresis. Stutter ratios were calculated by dividing the read count /relative fluorescence unit of the stutter allele by the read count / relative fluorescence unit of the parent allele. Stutter ratio comparisons were made between the ForenSeq™ and GlobalFiler™ kits as well as between the parents and the children in the family pedigree, though only samples tested using the ForenSeq™ kit were used. Comparison of overall stutter ratios revealed that the ForenSeq™ kit produced higher stutter across all STR loci, except for D13S317 and D2S441, when compared to the GlobalFiler™ kit. The different chemistries between the two kits, potential usage of different polymerases, and the fact that the ForenSeq™ kit requires two rounds of amplification can serve as likely explanations for this difference. There was also quite a bit of variability observed for the stutter ratios between loci in the samples run using the ForenSeq™ kit. Possible explanations for this could be that the cluster generation step could produce more clusters for some stutter products over others. Comparison of the stutter ratios for the pedigree obtained from the Coriell Institute revealed no differences between the parents and the respective alleles inherited by the children when tested with the ForenSeq™ kit. Some loci showed a difference between the parent and children, but that could simply be due to the sample size. The utilization of NGS for STR testing can result in two alleles of the same length but different sequences, called isoalleles. Analysis of isoalleles present at D21S11 in the children samples from the Coriell Institute pedigree showed that the isoalleles had different mean stutter ratios. The results open the possibility of potentially utilizing sequence-specific stutter filters in the ForenSeq™ Universal Analysis Software. The model of the longest uninterrupted stretch (LUS) has been around for some time, though recently the block length of missing motif (BLMM) has been proposed as a better predictor for stutter ratios. The results of stutter ratio analysis at D21S11 show that as the length of the BLMM increases, so too does the stutter ratio.

Despite the prevalent utilization of capillary electrophoresis (CE) in the analysis of short tandem repeats (STRs) to generate deoxyribonucleic acid (DNA) profiles for forensic comparisons, the method is not without its inherent drawbacks. Massively parallel sequencing (MPS) is still a relatively novel technology in the forensics field, but contains the capacity to address current challenges faced by the traditional CE approach - such as degraded samples, low template DNA, and artifacts - while also providing additional information such as isoalleles, same-length alleles with sequence variation, and ancestry, mixture, and phenotyping-informative single nucleotide polymorphisms (SNPs). One of the principal ongoing challenges faced by both technologies is the presence of artifacts such as stutter, a byproduct of slipped strand mispairing during amplification of STRs, which can further complicate interpretation of DNA profiles. Understanding and predicting the behavior of stutter is important in establishing appropriate thresholds to distinguish these artifacts from true alleles. With complex MPS data, new approaches in characterizing stutter have been established such as the BLMM and simplified sequence. In this study, twenty-one oral samples from individuals belonging to the same family were constructed into libraries containing 58 STR regions and 98 identity SNPs using Verogen’s Forenseq™ DNA Signature Prep Kit and sequenced on the MiSeq FGx™ Forensics Genomics System. Isoallele and stutter sequences were extracted from the data and simplified using the longest uninterrupted stretch (LUS), block length of missing motif (BLMM) and simplified sequence approaches. It was found that the stutter ratio for the 11 isoallele pairs at the D13S317 locus did not follow the linear correlation with increasing LUS. Instead, the isoallele with the higher LUS demonstrated equal or lower stutter ratios. Additionally, three different stutter patterns were identified for the same locus. Based on the provided pedigree, ten different relations were defined and the amount of allele sharing between the individuals in the pedigree was analyzed with and in the absence of isoallelic information to determine its impact on predicting relatedness. It was found that there was an average of 1.3% difference across the ten defined categories when isoalleles were taken into consideration. However, the difference in the percentage of shared alleles was not found to be significant for each of the relations category between the results before and after the consideration of isoallelelic data.

Background: Speech rate plays an essential role in overall speech intelligibility in fluent speakers and is an important variable affecting fluency in people who stutter (PWS). There are no normative speech rate data for South African English (SAE). In PWS, attempts to manipulate speech rate for improved fluency have mostly focused on articulation rate. Revisiting the role of pauses in speech rate and the manipulation of both frequency and duration of pauses was deemed necessary to investigate a potentially valuable alternative strategy to assist PWS in rate reduction and possible improved fluency. Aims: The aims of this study were to investigate the speech rate and pause use for first language (L1) and second language (L2) SAE fluent speakers and PWS in both monologue and reading tasks. In addition, this study investigated if the manipulation of pause use could increase fluency in L1 and L2 PWS given six sessions of pause instruction in SAE. Methods: 80 fluent speakers (40 L1 SAE and 40 L1 isiZulu) and 14 PWS (7 L1 SAE and 7 L1 isiZulu) were asked to engage in a 2-minute monologue and a reading task in order to calculate the mean speech rate, frequency of pauses and average pause duration for each group. Following baseline measures, the 14 PWS were randomly assigned to either immediate or delayed intervention consisting of 6 sessions addressing manipulation of pauses. A crossover treatment design allowed for repeated measures of speech rate and pause use across three data collection periods. Results: Results revealed L1 and L2 SAE fluent speakers differed significantly in speech rate and frequency of pauses in reading and in pause length in the monologue. L1 and L2 PWS differed in frequency of pauses in reading. L1 fluent speakers and PWS differed in speech rate and both measures of pause use in reading. L2 fluent speakers and PWS differed in frequency of pauses in the monologue. Results from the crossover intervention for the PWS revealed a significant decrease in percentage syllables stuttered (% SS) for the delayed treatment group and a clinically significant decrease in % SS for both groups, in conjunction with a reduced speech rate that could be linked to increased frequency and/or average duration of pauses. Conclusions: This study presented speech rate and pause use norms for both fluent speakers and PWS, L1 and L2 SAE speakers that may provide useful guidelines for speech language pathologists in South Africa. Additionally, the intervention results for PWS presented efficacy data for six sessions of pause manipulation with measurable findings for improved fluency.

The aim of this study was to investigate how young adults who stutterer allocate attentional resources during two linguistic stages in picture naming, specifically lemma and lexeme retrieval. This study reports on behavioral and brain electrophysiological data collected during a simple auditory oddball task and a Dual Picture-Word Interference/Tone Monitoring Task.

Modern DNA analysis is possible due to the discovery of repeating microsatellite regions in DNA and successful implementation of the polymerase chain reaction (PCR) in laboratories. PCR amplification chemistries that contain short tandem repeat (STR) loci are sensitive. As a result, the discrimination power within human identification sciences has increased in recent years. Despite these advances, cellular admixtures are commonly collected, and the resultant “DNA mixture profile” is difficult to interpret as it is often encumbered by low-signals and allele drop-out. Regularly detected PCR artifacts can further complicate interpretation. One commonly encountered artifact is stutter, the result of strand slippage during PCR. Stutter can be of two types: forward and reverse. Reverse stutter (or back stutter) is the most prevalent and is one repeat unit shorter (n - 1) than the template strand. In contrast, forward stutter is one repeat unit longer (n + 1). If a reverse stutter amplicon is produced there is the distinct possibility that a stutter product of stutter may occur. This artifact is usually referred to as double-back stutter (DBS) or n - 2 stutter. Recently there has been renewed interest in examining signal approaching baseline levels. As the sensitivity of the process improves, so does the probability of detecting DBS. Therefore, studies that examine the peak height distributions, rarity, stutter signal-to-noise distances and the general impact of DBS on the signal are warranted. Models simulating PCR, and the entire forensic DNA process, have been created by this laboratory. The work presented herein builds upon a preexisting model; specifically, the dynamic model was extended such that DNA profiles consisting of 21 autosomal STRs, consistent with the GlobalFilerTM multiplex, are simulated. Furthermore, this expansion incorporated a three-type Galton-Watson branching process allowing DBS to be added to the simulated electropherogram (EPG). The in silico model was used to simulate the amplification of a 1:43 and 1:73 mixture at a total DNA concentration of 0.3 and 0.5 ng, respectively. We chose these extreme mixture ratios because the signal from these minor contributors would be most susceptible to DBS effects from the major contributor. A total of 1200 alleles from each contributor were simulated at each target, and effects of DBS on the signal from the minor contributor were characterized. At 0.3 and 0.5 ng both the noise and stutter signal histograms are right-skewed and a Kolmogorov-Smirnov (KS) test indicates that the noise and DBS were significantly different (p-value < 4x10-6). The average peak height of DBS for all loci in both scenarios were less than 50 RFU (Relative Fluorescence Units), and the DBS ratios ranged from 0.29 to 2.15% of the main allele, with the median ratios less than 0.5%. A per locus analytical threshold (AT) was calculated for both the 0.3 and 0.5 ng targets using two k-values: 3 and 4. The k-value is chosen based on the Type I risk assessment, wherein increasing the k-value increases AT. The percentage of DBS peaks greater than AT when k = 3 for the mixtures amplified at 0.3 and 0.5 ng ranged from 0 to 7.08% and 0 to 10.50%, respectively. Interestingly, when k = 4 the percentage of DBS peaks greater than AT for 0.3 and 0.5 ng reduced to 0 to 1.08% and 0 to 0.17%, respectively. This suggests that modeling DBS in continuous systems may not be necessary if the laboratory continues to rely on a system that requires an AT of sufficient strength. However, with the advent of Bayesian or machine learning-based approaches to analyzing EPGs, thus removing AT in its entirety, a complete understanding of the prevalence of DBS is necessary. This work shows that DBS from an extreme major using our laboratory protocols is not likely to be in the same signal regime as the signal from alleles; however, it does show that signal from DBS is significantly different from noise. Therefore, the software expert pair should be carefully considered during the validation stage and laboratories should consider DBS during interpretation, especially if enhanced post-PCR parameters are implemented into the forensic laboratory process.

In the ongoing discussion of treatment efficacy, some researchers have argued for the use of evidence from randomized controlled trials while others have argued the case for the use of non-randomized designs (Ingham 2003) in the study of the treatment of stuttering. Few attempts have been made to integrate findings from the research on stuttering intervention {Andrews, et al.1980; Howard, Nye, & Vanryckegbem, 2005; Herder, Howard, Nye & Vanryckeghem 2006; Thomas and Howell, 2001). Since the usual approach to the study of treatment efficacy uses experimental and quasi-experimental sources, a summary of the data available from single subject design {SSD) studies would seem warranted. The purpose of this project was to conduct a systematic review and meta-analysis of the effectiveness of stuttering treatment for children and adults by summarizing studies and determining an overall effect by calculating the percentage of non-overlapping data points (PND). The resulting review provides a summary of the effects of stuttering treatment, the nature of the treatment program characteristics and their associated effectiveness, and a general mapping of the research landscape in stuttering treatment terms of its' strengths and weaknesses and areas of need for future research.

This report was developed to: a) enhance the clinician’s understanding of transfer and maintenance as it relates to stuttering, b) explore the unique challenges that face the school-aged population, c) examine research outside of the field that may be of benefit for school-aged stuttering clients, and d) provide the clinician with examples and activities that will facilitate the transfer and maintenance of stuttering treatment. The report will include a brief discussion of transfer and maintenance. The remainder of the report will focus on facilitating transfer and maintenance by increasing motivation, self-efficacy, realistic goal setting, and self-regulation. / text