Speech disfluencies in children with developmental dyslexia: How do they differ from typical development?

BACKGROUND: Disfluency is a multifactorial concept that can be linked to several of the language production levels, in both typical and atypical populations. In children, the language system is still developing and few studies have explored disfluency patterns. In typical development (TD), in particular, studies have shown discrepancies according to the language being considered. In neurodevelopmental disorders, such as developmental dyslexia (DD), it is still unclear whether the pattern of disfluency is similar to TD. AIMS: To analyse the type of disfluency and their evolution in French children aged 8-12 years. Also to compare the pattern of disfluency in DD and TD, and to test whether disfluencies were correlated with reading difficulties. METHODS & PROCEDURES: A total of 25 children with DD and 21 children with TD aged 8-12.6 years produced an autobiographical narrative. Seven types of disfluencies were coded: part-word repetitions; repetitions of monosyllabic words; other types of repetitions (words and phrases); filled pauses; revisions-substitutions; revisions-additions; and abandoned utterances. We compared the proportion of each disfluency in DD and TD. Spearman correlations were then performed between disfluencies, reading performance and age. OUTCOMES & RESULTS: The results showed that both DD and TD children mainly produced filled pauses, repetitions of monosyllabic words and substitutions. Both groups displayed a high rate of disfluency (> 10%). No correlations with age were found. Correlations with reading performance were significant in the TD group only. CONCLUSIONS & IMPLICATIONS: The study showed that DD is not characterized by a specific pattern of disfluency. Additionally, disfluency rates were similar in children aged 8-12 years. In contrast to other languages, the current study suggests that French-speaking children have a high rate of disfluency. The study also suggests that disfluency should be interpreted with caution in DD, given that TD children also have a high rate of disfluency. Therefore, it seems important to adapt the pathological threshold of disfluency to the language being spoken in order to avoid an overestimation of the prevalence of these deficits in French-speaking children. WHAT THIS PAPER ADDS: What is already known on this subject TD children produce a high rate of disfluency, which is also influenced by the language being spoken. No study looked at the effect of DD on disfluency production. Nonetheless, problems in reading comprehension and reduced reading experience may impact lexical development and speech fluency. What this paper adds to the existing knowledge In our study, both groups (French-speaking children) produced a substantial amount of disfluency as compared with other languages (> 10%). Additionally, the pattern of disfluency was similar in TD and DD (namely, filled pauses, prolongations repetitions of monosyllabic words and substitutions). In the DD group, disfluency production was not correlated with reading performance. What are the potential or actual clinical implications of this work? These results indicate that it is crucial to consider the language being spoken when examining disfluency in order to avoid an overestimation of language difficulties in some languages, such as in French. Moreover, the production of disfluencies in DD should not be considered as language dysfunction since the pattern of disfluency what quite similar in TD and DD, and did not correlate with their reading difficulties.

Semantic interference affects speech production by increasing disfluencies, not errors.

Several studies have shown that different types of disfluency occur depending on the language production stage at which people experience difficulties. The current study combined a network task and a picture-word interference task to analyse whether lexical-semantic difficulty triggers errors and disfluencies in connected-speech production. The participants produced more disfluencies in the presence of a semantically related distractor word than an unrelated distractor word, while few semantic errors were made. These results support the hypothesis that difficulties at distinct stages of language production lead to distinct patterns of disfluency, with lexical-semantic difficulties leading to self-corrections and silent pauses. The results also have implications for the role of the monitoring system in connected-speech production.

Can object identification difficulty be predicted based on disfluencies and eye-movements in connected speech?

In the current study, we asked whether delays in the earliest stages of picture naming elicit disfluency. To address this question, we used a network task, where participants describe the route taken by a marker through visually presented networks of objects. Additionally, given that disfluencies are arguably multifactorial, we combined this task with eye tracking, to be able to disentangle disfluency related to word preparation from other factors (e.g., stalling strategy). We used visual blurring, which hinders visual identification of the items and thereby slows down selection of a lexical concept. We tested the effect of this manipulation on disfluency production and visual attention. Blurriness did not lead to more disfluency on average and viewing times decreased with blurred pictures. However, multivariate pattern analyses revealed that a classifier could predict above chance, from the pattern of disfluency, whether each participant was about to name blurred or control pictures. Impeding the conceptual generation of a message therefore affected the pattern of disfluencies of each participant individually, but this pattern was not consistent from one participant to another. Additionally, some of the disfluency and eye-movement variables correlated with individual cognitive differences, in particular with inhibition.

The functional connectivity of language network across the life span: Disentangling the effects of typical aging from Alzheimer's disease.

Language is usually characterized as the most preserved cognitive function during typical aging. Several neuroimaging studies have shown that healthy aging is characterized by inter-network compensation which correlates with better language performance. On the contrary, language deficits occur early in the course of Alzheimer's disease (AD). Therefore, this study compares young participants, healthy older participants, and prodromal AD participants, to characterize functional connectivity changes in language due to healthy aging or prodromal AD. We first compared measures of integrated local correlations (ILCs) and fractional amplitude of low-frequency oscillations (fALFFs) in language areas. We showed that both groups of older adults had lower connectivity values within frontal language-related areas. In the healthy older group, higher integrated local correlation (ILC) and fALFF values in frontal areas were positively correlated with fluency and naming tasks. We then performed seed-based analyses for more precise discrimination between healthy aging and prodromal AD. Healthy older adults showed no functional alterations at a seed-based level when the seed area was not or only slightly impaired compared to the young adults [i.e., inferior frontal gyrus (IFG)], while prodromal AD participants also showed decreased connectivity at a seed-based level. On the contrary, when the seed area was similarly impaired in healthy older adults and prodromal AD participants on ILC and fALFF measures, their connectivity maps were also similar during seed-to-voxel analyses [i.e., superior frontal gyrus (SFG)]. Current results show that functional connectivity measures at a voxel level (ILC and fALFF) are already impacted in healthy aging. These findings imply that the functional compensations observed in healthy aging depend on the functional integrity of brain areas at a voxel level.

Disfluency patterns in Alzheimer's disease and frontotemporal lobar degeneration.

Disfluencies may reflect various mechanisms: word-finding difficulties, planning strategies, inter-individual cognitive variability, etc. In the current paper, we examined disfluency production in patients with a behavioural variant of Frontotemporal lobar degeneration (bvFTLD), compared to patients with Alzheimer's disease (AD) and healthy older adults. We showed that bvFTLD participants have lower speech rate and produce more incomplete utterances. However, those measures were not correlated with naming and fluency tasks. On the contrary, AD participants did not differ from healthy controls on disfluency production, but discourse measures were correlated with the participants' lexical-semantic impairment. This provides evidence for different causes of disfluency in AD and FTLD, and a distinct role of each disfluency phenomenon.

Language Network Connectivity Increases in Early Alzheimer's Disease.

BACKGROUND: Language production deficits occur early in the course of Alzheimer's disease (AD); however, only a few studies have focused on language network's functional connectivity in mild cognitive impairment (MCI) due to AD. OBJECTIVE: The current study aims to uncover the extent of language alteration at the MCI stage, at a behavioral and neural level, using univariate and multivariate analyses of structural MRI and resting-state fMRI. METHODS: Twenty-four MCI due to AD participants and 24 matched healthy controls underwent a comprehensive language evaluation, a structural T1-3D MRI, and resting-state fMRI. We performed seed-based analyses, using the left inferior frontal gyrus and left posterior temporal gyrus as seeds. Then, we analyzed connectivity between executive control networks and language network in each group. Finally, we used multivariate pattern analyses to test whether the two groups could be distinguished based on the pattern of atrophy within the language network; within the executive control networks, as well as the pattern of functional connectivity within the language network and within the executive control networks. RESULTS: MCI due to AD participants had language impairment during standardized language tasks and connected-speech production. Regarding functional connectivity, univariate analyses were not able to discriminate participants, while multivariate pattern analyses could significantly predict participants' group. Language network's functional connectivity could discriminate MCI due to AD participants better than executive control networks. Most notably, they revealed an increased connectivity at the MCI stage, positively correlated with language performance. CONCLUSION: Multivariate analyses represent a useful tool for investigating the functional and structural (re-)organization of the neural bases of language.

Speech fluency in bilinguals who stutter: Language proficiency and attentional demands as mediating factors.

PURPOSE: The current study examines how speech disfluencies manifest themselves in the two languages of bilingual persons who stutter, starting from the hypothesis that stuttering is associated with an attentional deficit at the level of speech production. METHODS: Twenty-eight bilingual people who stutter performed a spontaneous and a controlled speech production task, once in their dominant and once in their non-dominant language. The controlled production task (i.e. a network description task) was carried out once under a full-attention condition and once under a divided-attention condition where a non-linguistic, pitch discrimination task was performed simultaneously. RESULTS: In both the spontaneous and the controlled speech task, bilingual persons who stutter produced more (typical and stuttering-like) disfluencies in their L2 than in their L1. Furthermore, whereas the typical disfluencies increased when attention was directed away from speech production, stuttering-like disfluencies decreased. This effect was however restricted to L2. In addition, L2 proficiency was generally found to be a predicting factor, with higher proficiency leading to fewer disfluencies. CONCLUSIONS: These results suggest that speaking in a non-dominant language increases both typical and stuttering-like disfluencies in bilingual persons who stutter, but also that these two types of dysfluencies differ regarding their attentional origins. Our findings offer further support for attentional accounts of stuttering and have both theoretical and clinical implications.

Increased functional connectivity supports language performance in healthy aging despite gray matter loss.

Although language is quite preserved from aging, it remains unclear whether age-related differences lead to a deterioration or reorganization in language functional networks, or to different dynamics with other domains (e.g., the multiple-demand system). The present study is aimed at examining language networks, using resting-state functional magnetic resonance imaging in typical aging in relation to language performance. Twenty-three (23) younger adults and 24 healthy older adults were recruited. Volumetric gray matter differences between the 2 groups were assessed using voxel-based morphometry. Then, seed-based analyses, integrated local correlations in core regions of the language network, and within- and between-network connectivity were performed. We expected less extended connectivity maps, local coherence diminution, and higher connectivity with the multiple-demand system in older adults. On the contrary, analyses showed language network differences in healthy aging (i.e., increased connectivity with areas inside and outside language network), but no deterioration, despite widespread atrophy in older adults. Integrated local correlation revealed alterations that were unnoticeable with other analyses. Although gray matter loss was not correlated with language performance, connectivity differences were positively correlated with fluency performance in the older group. These results differ from the literature concerning other cognitive networks in aging in that they show extra internetwork connections without a decrease in intranetwork language connections. This reorganization could explain older adults' good language performance and could be interpreted in accordance with the scaffolding theory of aging and cognition.

An Analysis of Famous Person Semantic Memory in Aging.

BACKGROUND: In contrast to most memory systems that decline with age, semantic memory tends to remain relatively stable across the life span. However, what exactly is stable remains unclear. Is it the quantity of information available or the organization of semantic memory, i.e., the connections between semantic items? Even less is known about semantic memory for celebrities, a subsystem of semantic memory. In the present study, we studied the organization of person-specific semantic memory and its stability in aging. METHODS: We designed a word association task based on a previous study, which consisted in providing the first word that came to the mind of the participants (15 participants for each age group 20-30, 40-50 and 60-70 years old) for 144 celebrities. We developed a new taxonomy of associated responses as the responses associated with celebrities name could in principle be very varied. RESULTS: We found that most responses (>90%) could be grouped into five categories (subjective; superordinate general; superordinate specific; imagery and activities). The elderly group did not differ from the other two groups in term of errors or reaction time suggesting they performed the task well. However, they also provided associations that were less precise and less based on imagery. In contrast, the middle-age group provided the most precise associations. CONCLUSION: These results support the idea of a durable person-specific semantic memory in aging but show changes in the type of associations that elders provide. Future work should aim at studying patients with early semantic impairment, as they could be different from the healthy elders on such semantic association task.

Discourse macrolinguistic impairment as a marker of linguistic and extralinguistic functions decline in early Alzheimer's disease.

BACKGROUND: Alzheimer's disease is characterized by macrolinguistic changes. This decline is often analyzed with quantitative scales. AIMS: To analyze discourse production in early Alzheimer's disease (AD) and to identify qualitative markers of macrolinguistic decline. METHODS & PROCEDURES: We analyzed macrolinguistic features of a clinical narrative task along with patients' cognitive changes. To do so, 17 early AD participants and 17 healthy controls were recruited and given a full neuropsychological and language assessment. Narrative discourses produced during the language assessment were transcribed and macrolinguistic features were qualitatively analyzed (i.e., local and global coherence marks and discourse informativeness). Inter-group comparison was complemented by intra-group correlation. As some inter-group comparisons revealed the existence of subgroups of patients, permutation tests were used to investigate how these subgroups differed vis-à-vis cognitive measures. OUTCOMES & RESULTS: Overall, the results indicate that AD participants presented declines in informativeness and global coherence, correlated with declines in memory and executive functions. Permutation tests showed that participants with AD producing referential errors or misinterpretations had a deeper lexical-executive decline and a lower Mini-Mental State Evaluation (MMSE). CONCLUSIONS & IMPLICATIONS: This study shows that two clinically relevant, qualitative signs differ in discourse production between typical ageing and early AD, namely information units and modalizing discourse. It also shows that macrolinguistic assessment is a useful tool for revealing impaired communication and cognition in early AD. Although lexical processing decline probably contributes to patients' macrolinguistic impairment, implications of extralinguistic functioning should be further investigated.

Inter-individual variability in discourse informativeness in elderly populations.

An increasing number of studies focus on discourse production in patients with neurodegenerative diseases and underline its clinical usefulness. However, if this is to be used as a clinical tool, one needs to consider how normal discourse varies within cognitively unimpaired elderly populations. In the current study, the aim has been to investigate discourse macrolinguistic variability. For this, 123 participants aged between 55 and 84 were recruited. A cluster analysis of their discourse macrolinguistic features was conducted. Then, cluster characterisation based on socio-demographic and linguistic performance was tested (fluency, naming, syntax and spelling). This method aims to identify various profiles of speaker and informativeness and then see if inter-individual variability may be related to socio-demographic and/or linguistic aspects. Four clusters of informativeness were found but no socio-demographic features appeared significant. The fourth cluster, defined as 'off topic', had lower performance during linguistic tasks than others and thus the boundary between normality and pathology should be questioned.

Pauses During Autobiographical Discourse Reflect Episodic Memory Processes in Early Alzheimer's Disease.

There is a large body of research on discourse production in Alzheimer's disease (AD). Some studies have focused on pause production, revealing that patients make extensive use of pauses during speech. This has been attributed to lexical retrieval difficulties, but pausing may also reflect other forms of cognitive impairment as it increases with cognitive load. The aim of the present study was to analyze autobiographical discourse impairment in AD from a broad perspective, looking at pausing behavior (frequency, duration, and location). Our first objective was to characterize discourse changes in mild cognitive impairment (MCI) due to AD. Our second objective was to determine the cognitive and neuroanatomical correlates of these changes. Fifteen patients with MCI due to AD and 15 matched cognitively normal controls underwent an ecological episodic memory task, a full neuropsychological assessment, and a 3D T1-weighted MRI scans. Autobiographical discourse collected from the ecological episodic memory task was recorded, transcribed, and analyzed, focusing on pausing. Intergroup comparisons showed that although patients did not produce more pauses than controls overall, they did make more between-utterance pauses. The number of these specific pauses was positively correlated with patients' episodic memory performance. Furthermore, neuroimaging analysis showed that, in the patient group, their use was negatively correlated with frontopolar area (BA 10) grey matter density. This region may therefore play an important role in the planning of autobiographical discourse production. These findings demonstrate that pauses in early AD may reflect a compensatory mechanism for improving mental time travel and memory retrieval.