Atypical neural functions underlying phonological processing and silent rehearsal in children who stutter

Speech-induced suppression of evoked auditory fields in children who stutter

Auditory responses to speech sounds that are self-initiated are suppressed compared to responses to the same speech sounds during passive listening. This phenomenon is referred to as speech-induced suppression, a potentially important feedback-mediated speech-motor control process. In an earlier study, we found that both adults who do and do not stutter demonstrated a reduced amplitude of the auditory M50 and M100 responses to speech during active production relative to passive listening. It is unknown if auditory responses to self-initiated speech-motor acts are suppressed in children or if the phenomenon differs between children who do and do not stutter. As stuttering is a developmental speech disorder, examining speech-induced suppression in children may identify possible neural differences underlying stuttering close to its time of onset. We used magnetoencephalography to determine the presence of speech-induced suppression in children and to characterize the properties of speech-induced suppression in children who stutter. We examined the auditory M50 as this was the earliest robust response reproducible across our child participants and the most likely to reflect a motor-to-auditory relation. Both children who do and do not stutter demonstrated speech-induced suppression of the auditory M50. However, children who stutter had a delayed auditory M50 peak latency to vowel sounds compared to children who do not stutter indicating a possible deficiency in their ability to efficiently integrate auditory speech information for the purpose of establishing neural representations of speech sounds.

Non-linguistic auditory processing and working memory update in pre-school children who stutter: an electrophysiological study

Non-linguistic auditory processing and working memory update were examined with event-related potentials (ERPs) in 18 children who stutter (CWS) and 18 children who do not stutter (CWNS). Children heard frequent 1 kHz tones interspersed with rare 2 kHz tones. The two groups did not differ on any measure of the P1 and N1 components, strongly suggesting that early auditory processing of pure tones is unimpaired in CWS. However, as a group, only CWNS exhibited a P3 component to rare tones, suggesting that developmental stuttering may be associated with a less efficient attentional allocation and working memory update in response to auditory change.

Effects of word frequency and phonological neighborhood characteristics on confrontation naming in children who stutter and normally fluent peers

In a prior study (Newman & Bernstein Ratner, 2007), we examined the effects of word frequency and phonological neighborhood characteristics on confrontation naming latency, accuracy and fluency in adults who stutter and typically fluent speakers. A small difference in accuracy favoring fluent adults was noted, but no other patterns differentiated fluent speaker responses from those obtained from the adults who stutter. Because lexical organization or retrieval differences might be more easily observed in less mature language users, we replicated the experiment using 15 children who stutter (ages 4;10 16;2) and age- and gender-matched peers. Results replicated the earlier study: the two groups of participants showed strikingly similar patterns of responses based on word frequency and neighborhood characteristics. There were also no differences in naming accuracy overall between the two groups. Given our results and those of other researchers who have explored the impact of neighborhood variables on lexical retrieval in people who stutter, we suggest that differences between language production in PWS and fluent speakers are not likely to involve atypical phonological organization of lexical neighborhoods.

EDUCATIONAL OBJECTIVES

After reading this article, the reader will be able to: (1) define and illustrate words that have differing frequency and phonological neighborhood characteristics; (2) evaluate whether or not children who stutter appear to organize their mental lexicons differently than those of children who are typically fluent; (3) suggest future areas of research into language processing in people who stutter.

Non-linguistic auditory processing in stuttering: evidence from behavior and event-related brain potentials

Auditory processing deficits are hypothesized to play a role in the disorder of stuttering (e.g. Hall, J. W., & Jerger, J. (1978). Central auditory function in stutterers. Journal of Speech and Hearing Research, 21, 324-337). The current study focused on non-linguistic auditory processing without verbal responses to explore the relationship between behavior and neural activity in the absence of cognitive demands related to language processing and articulatory planning for speaking. A pure-tone, oddball paradigm was utilized to compare behavioral accuracy and reaction times for adults who stutter (AWS) and normally fluent speakers (NFS). Additionally, event-related potentials elicited by brief standard and target tones were compared for the two groups. Results revealed that, as a group, AWS tended to perform less accurately compared to the NFS and were slower to respond to target stimuli. However, inspection of individual data indicated that most of the AWS performed within the range of normally fluent speakers while a small subset of AWS were well outside the normal range. This subgroup of AWS also demonstrated early perceptual processes (as indexed by N100 and P200 amplitudes) indicative of reduced cortical representation of auditory input. The P300 mean amplitudes elicited in AWS tended to be reduced overall compared to those of the NFS, suggesting the possibility of weaker updates in working memory for representations of the target tone stimuli in AWS. Taken together, these findings point to the possibility that a subset of AWS exhibit non-linguistic auditory processing deficits related to altered cortical processing.

EDUCATIONAL OBJECTIVES

After reading this article, the reader will be able to: (1) summarize research findings of non-linguistic auditory processing in stuttering; (2) discuss the relationship between behavioral performance for auditory processing and the underlying event-related brain potentials; (3) discuss the importance of analyses of individual versus group data in stuttering; and (4) summarize how the findings of this study relate to a multifactorial model of stuttering.

Stuttering and natural speech processing of semantic and syntactic constraints on verbs

PURPOSE

Previous findings from event-related brain potentials (ERPs) indicate that adults who stutter (AWS) exhibit processing differences for visually presented linguistic information. This study explores how neural activations for AWS may differ for a linguistic task that does not require preparation for overt articulation or engage the articulatory loop for silent speech.

METHOD

Syntactic and semantic processing constraints were examined in AWS and adults who are normally fluent (AWNF) by assessment of their behavioral performance and ERPs in a natural speech listening task.

RESULTS

AWS performed similarly to AWNF in identifying verb-agreement violations and semantic anomalies, but ERPs elicited by syntactic and semantic constraints indicated atypical neural functions for AWS. ERPs of the AWNF displayed an expected N400 for reduced semantic expectations and a typical P600 for verb-agreement violations. In contrast, both N400s and P600s for the semantic and verb-agreement conditions were observed in the ERPs of the AWS.

CONCLUSIONS

The findings suggest that AWS may engage semantic-syntactic mechanisms more generally for semantic and syntactic processing. These findings converge with earlier studies using visual stimuli to indicate that whereas linguistic abilities are normal in AWS, underlying brain activity mediating some aspects of language processing may function differently.