Inhibitory Control of Lexical Selection in Adults who Stutter

The Impact of Executive Functions and Musicality on Speech Auditory-Motor Synchronization in Adults Who Stutter

PURPOSE

Stuttering is a neurodevelopmental disorder that disrupts the timing and rhythmic flow of speech production. There is growing evidence indicating that abnormal interactions between the auditory and motor cortices contribute to the development of stuttering. The present study investigated speech auditory-motor synchronization in stuttering adults and the influential factors behind it as compared to individuals without stuttering.

METHOD

Sixteen Mandarin-speaking adults with stuttering and 19 fluent controls, who were matched for age, gender, and years of musical training, participated in the current study. Their ability to synchronize vocal speech production with accelerating auditory sequences was assessed using the spontaneous speech-to-speech synchronization test (SSS test). Additionally, all participants conducted a series of standardized behavioral tests to evaluate their musicality and executive functions.

RESULTS

Stutterers achieved significantly lower phase locking values in the SSS test compared to nonstuttering controls, indicating a potential rhythmic processing deficit in developmental stuttering. Moreover, the strength of speech auditory-motor synchronization in stutterers was significantly associated with their performance in tasks such as digit span and nonword repetition. This finding further emphasizes the strong link between rhythmic processing and working memory.

CONCLUSIONS

This study provides compelling evidence for the speech rhythmic deficit in individuals with stuttering by incorporating auditory-motor processes. It would offer valuable insights into the intricate relationship between language and the brain and shed light on the potential benefits of cognitive training for speech intervention in individuals with stuttering difficulties.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.27984362.

Exploring the activation of target words in adults who stutter with and without conscious intention to speak: ERP evidence

INTRODUCTION

The primary aim was to determine whether the activation of target words unfolds differently in adults who stutter (AWS) versus typically-fluent adults (TFA) preparing to name pictures. A secondary aim was to explore the influence of conscious intention to speak on this process.

METHOD

18 AWS and 18 TFA completed a picture naming task in which pictures - named at a delay - were followed by auditory probe words that were identical, or unrelated, to the target picture labels. A subset of those participants (15 AWS and 15 TFA) completed a second task in which pictures - judged conceptually at a delay - were followed by auditory probe words that directly named the pictures or were unrelated. Event-related potentials (ERPs) were recorded from probe word onset in each task. It was predicted that the N400 ERP component - an index of lexical processing - would be attenuated to Identity versus Unrelated trials. Between-groups differences in lexical activation (if any) were predicted to result in between-groups differences in the amplitude, latency and/or scalp topography of N400 priming effects.

RESULTS

N400 priming was detected in both tasks for both Groups. In the picture naming task, the N400 priming effect had a more broadly-distributed scalp topography in TFA versus AWS. No between-groups differences were detected in the N400 priming effect in the conceptual judgment task.

CONCLUSIONS

A between-groups difference in the scalp topography of the N400 priming effect in the picture naming task points to a between-groups difference in intention-driven lexical access. Discussion considers how the top-down process of intention - if diminished among AWS - might impact lexical selection and speech motor control.

Exploring the Activation of Target Words in Picture Naming in Children Who Stutter: Evidence From Event-Related Potentials

PURPOSE

Target word activation in picture naming was explored in children who stutter (CWS) and typically fluent children (TFC) using event-related potentials (ERPs).

METHOD

A total of 18 CWS and 16 TFC completed a task combining picture naming and probe word identification. On each trial, a picture-to-be-named was followed by an auditory probe word-to-be-identified; the probe was identical (Identity condition) or Unrelated to the picture name. ERPs were recorded from probe onset. Attenuation of the N400 ERP component was predicted to Identity versus Unrelated trials (N400 priming). Between-groups differences in amplitude, timing, and topography of N400 priming were explored.

RESULTS

Naming was more accurate on Identity versus Unrelated trials. Probe word identification accuracy was not affected by Condition. N400 priming was detected, indicating that self-generated picture names facilitated semantic processing of identical probes. This effect was larger in amplitude in CWS versus TFC. Unexpectedly, an N400-preceding, frontally maximal, positive-going ERP component-associated with expectancy processing-was larger in amplitude to Unrelated versus Identity trials. This effect was smaller in CWS versus TFC.

CONCLUSIONS

A larger N400 priming effect in CWS versus TFC reflects a tendency toward more extensive semantic processing in picture naming in CWS. A smaller Condition effect on frontally maximal, positive-going, N400-preceding ERP activity in CWS versus TFC indicates a reduced ability to form expectancies about the lexical and/or phonological identity of probe words in CWS. Both effects may point to inefficient activation of target words in picture naming in CWS.

Statistical Information Affects Spoken Word Recognition of Tone Languages in Stutterers: Evidence From an Auditory-Perceptual Gating Study

PURPOSE

Previous studies have shown that individuals who stutter exhibit abnormal speech perception in addition to disfluent production as compared with their nonstuttering peers. This study investigated whether adult Chinese-speaking stutterers are still able to use knowledge of statistical regularities embedded in their native language to recognize spoken words and, if so, how much acoustic information is needed to trigger this information.

METHOD

Seventeen stutterers and 20 typical, nonstuttering controls participated in a gating experiment. All participants listened to monosyllabic words that consisted of syllables and lexical tones and were segmented into eight successive gates. These words differed in syllable token frequency and syllable-tone co-occurrence probability in line with a Chinese spoken word corpus. The correct syllable-only, correct tone-only, correct syllable-tone word, and correct syllable-incorrect tone responses were analyzed between the two groups using mixed-effects models.

RESULTS

Stutterers were less accurate overall than controls, with fewer correct syllables, tones, and their combination as words. However, stutterers showed consistent and reliable perceptual patterns triggered by statistical information of speech, as reflected by more accurate responses to high-frequency syllables, high-probability tones, and tone errors all in manners similar to those of nonstuttering controls.

CONCLUSIONS

Stutterers' atypical speech perception is not due to a lack of statistical learning. Stutterers were able to perceive spoken words with phonological tones based on statistical regularities embedded in their native speech. This finding echoes previous production studies of stuttering and lends some support for a link between perception and production. Implications of pathological, diagnostic, and therapeutic conditions of stuttering are discussed.

Stuttering-Like Dysfluencies as a Consequence of Long COVID-19

PURPOSE

We present two patients who developed neurogenic stuttering after long COVID-19 related to SARS-CoV-2 infection.

METHODS AND RESULTS

Both patients experienced both physical (e.g., fatigue) and cognitive difficulties, which led to impaired function of attention, lexical retrieval, and memory consolidation. Both patients had new-onset stuttering-like speech dysfluencies: Blocks and repetitions were especially evident at the initial part of words and sentences, sometimes accompanied by effortful and associated movements (e.g., facial grimaces and oro-facial movements). Neuropsychological evaluations confirmed the presence of difficulties in cognitive tasks, while neurophysiological evaluations (i.e., electroencephalography) suggested the presence of "slowed" patterns of brain activity. Neurogenic stuttering and cognitive difficulties were evident for 4-5 months after negativization of SARS-CoV-2 nasopharyngeal swab, with gradual improvement and near-to-complete recovery.

CONCLUSIONS

It is now evident that SARS-CoV-2 infection may significantly involve the central nervous system, also resulting in severe and long-term consequences, even if the precise mechanisms are still unknown. In the present report, long COVID-19 resulted in neurogenic stuttering, as the likely consequence of a "slowed" metabolism of (pre)frontal and sensorimotor brain regions (as suggested by the present and previous clinical evidence). As a consequence, the pathophysiological mechanisms related to the appearance of neurogenic stuttering have been hypothesized, which help to better understand the broader and possible neurological consequences of COVID-19.

Inefficient speech-motor control affects predictive speech comprehension: atypical electrophysiological correlates in stuttering

Listeners predict upcoming information during language comprehension. However, how this ability is implemented is still largely unknown. Here, we tested the hypothesis proposing that language production mechanisms have a role in prediction. We studied 2 electroencephalographic correlates of predictability during speech comprehension-pre-target alpha-beta (8-30 Hz) power decrease and the post-target N400 event-related potential effect-in a population with impaired speech-motor control, i.e. adults who stutter (AWS), compared to typically fluent adults (TFA). Participants listened to sentences that could either constrain towards a target word or not, modulating its predictability. As a complementary task, participants also performed context-driven word production. Compared to TFA, AWS not only displayed atypical neural responses in production, but, critically, they showed a different pattern also in comprehension. Specifically, while TFA showed the expected pre-target power decrease, AWS showed a power increase in frontal regions, associated with speech-motor control. In addition, the post-target N400 effect was reduced for AWS with respect to TFA. Finally, we found that production and comprehension power changes were positively correlated in TFA, but not in AWS. Overall, the results support the idea that processes and neural structures prominently devoted to speech planning also support prediction during speech comprehension.

Adults Who Stutter Show Diminished Word Fluency, Regardless of Mode

PURPOSE

Language abilities have long been thought to be weaker in adults who stutter (AWS) compared to adults who do not stutter (AWNS). However, it is unknown whether modality affects language performance by AWS in time pressure situations. This study aimed to examine lexical access and retrieval abilities of AWS in oral and typed modes.

METHOD

Fifteen AWS and 15 well-matched AWNS completed computer-administered letter fluency tasks. Adults were asked to orally produce words that began with one of two letter targets and type words that began with one of two alternate letters. Conditions were counterbalanced across participants.

RESULTS

Generalized linear mixed-effects models were evaluated to determine the effects of group (AWS/AWNS), mode (oral/typed), and expressive vocabulary on letter fluency performance. Group predicted letter fluency such that AWS generated fewer items on both the oral and typed letter fluency tasks. Mode did not impact letter fluency results. Expressive Vocabulary Test scores predicted letter fluency similarly in both AWS and AWNS.

CONCLUSIONS

AWS were not penalized by oral task demands. AWS generated fewer items on the letter fluency tasks regardless of response mode, suggesting that they have weaker lexical access abilities. Furthermore, better expressive vocabulary skills were associated with better letter fluency performance in both groups.

Cognitive control of action naming in adults who stutter

PURPOSE

Based on previous evidence that cognitive control of lexical selection in object (noun) naming operates differently in adults who stutter (AWS) versus typically-fluent adults (TFA), the aim was to investigate cognitive control of lexical selection in action (verb) naming in AWS.

METHOD

12 AWS and 12 TFA named line drawings depicting actions using verbs. Half of the pictures had high-agreement action names and the other half low-agreement action names. Naming accuracy and reaction times (RT), and event-related potentials (ERPs) time-locked to picture onset, were compared between groups.

RESULTS

Naming RTs were slower for low- versus high-agreement trials, and the magnitude of this effect was larger in AWS versus TFA. Delta-plot analysis of naming RTs revealed that individual differences in selective inhibition were associated with the agreement effect on naming RTs in AWS but not TFA. Action naming elicited frontal-central N2 activity in both agreement conditions in TFA but not AWS. Additionally, a later, posterior P3b component was affected by agreement in TFA only. In AWS, low-agreement action naming elicited frontal P3a activation.

CONCLUSIONS

Results suggest that cognitive control of action name selection was qualitatively different between groups. In TFA, cognitive control of lexical selection in action naming involved nonselective inhibition, as well as more efficient working memory updating on high- versus low-agreement trials. In AWS, cognitive control of low-agreement action naming involved increased focal attention. Individual differences in selective inhibition may have moderated cognitive control of action naming in AWS.

Verbal Response Inhibition in Adults Who Stutter

Purpose Adults who stutter (AWS) often attempt, with varying degrees of success, to suppress their stuttered speech. The ability to effectively suppress motoric behavior after initiation relies on executive functions such as nonselective inhibition. Although previous studies found that AWS were slower to inhibit manual, button-press response than adults who do not stutter (AWNS), research has yet to confirm a consistent relationship between manual and verbal inhibition. No study has examined verbal inhibition ability in AWS. The purpose of this study, therefore, is to compare verbal response inhibition between AWS and AWNS, and compare verbal response inhibition to both the overt stuttering and the lived experience of stuttering. Method Thirty-four adults (17 AWNS, 17 AWS) completed one manual and three verbal stop-signal tasks. AWS were assessed for stuttering severity (Stuttering Severity Instrument-Fourth Edition: SSI-4) and experience with stuttering (Overall Assessment of the Speaker's Experience With Stuttering [OASES]). Results Results indicate no correlation between manual and verbal inhibition for either group. Generalized linear mixed-model analyses suggested no significant group differences in manual or verbal inhibition. Manual and verbal inhibition did not predict SSI-4 in AWS. However, verbal inhibition was uniquely associated with OASES scores. Conclusion Although underlying manual and verbal inhibition was comparable between AWS and AWNS, verbal inhibition may be linked to the adverse experience of stuttering rather than the overt symptoms of stuttering severity. Supplemental Material https://doi.org/10.23641/asha.15145185.