Auditory feedback perturbation in children with developmental speech sound disorders

Toward Process-Oriented, Dimensional Approaches for Diagnosis and Treatment of Speech Sound Disorders in Children: Position Statement and Future Perspectives

BACKGROUND

Children with speech sound disorders (SSD) form a heterogeneous group, with respect to severity, etiology, proximal causes, speech error characteristics, and response to treatment. Infants develop speech and language in interaction with neurological maturation and general perceptual, motoric, and cognitive skills in a social-emotional context.

PURPOSE

After a brief introduction into psycholinguistic models of speech production and levels of causation, in this review article, we present an in-depth overview of mechanisms and processes, and the dynamics thereof, which are crucial in typical speech development. These basic mechanisms and processes are: (a) neurophysiological motor refinement, that is, the maturational articulatory mechanisms that drive babbling and the more differentiated production of larger speech patterns; (b) sensorimotor integration, which forms the steering function from phonetics to phonology; and (c) motor hierarchy and articulatory phonology describing the gestural organization of syllables, which underlie fluent speech production. These dynamics have consequences for the diagnosis and further analysis of SSD in children. We argue that current diagnostic classification systems do not do justice to the multilevel, multifactorial, and interactive character of the underlying mechanisms and processes. This is illustrated by a recent Dutch study yielding distinct performance profiles among children with SSD, which allows for a dimensional interpretation of underlying processing deficits.

CONCLUSIONS

Analyses of mainstream treatments with respect to the treatment goals and the speech mechanisms addressed show that treatment programs are quite transparent in their aims and approach and how they contribute to remediating specific deficits or mechanisms. Recent studies into clinical reasoning reveal that the clinical challenge for speech-language pathologists is how to select the most appropriate treatment at the most appropriate time for each individual child with SSD. We argue that a process-oriented approach has merits as compared to categorical diagnostics as a toolbox to aid in the interpretation of the speech profile in terms of underlying deficits and to connect these to a specific intervention approach and treatment target.

Preliminary Speech Perception Performance Profiles of School-Age Children With Childhood Apraxia of Speech, Speech Sound Disorder, and Typical Development

PURPOSE

Limited research exists assessing speech perception in school-age children with speech sound disorder (SSD) and childhood apraxia of speech (CAS); despite early evidence that speech perception may lead to error-prone motor planning/programming. In this study, we examine speech perception performance in school-age children with and without speech production deficits.

METHOD

Speech perception was assessed using the Wide Range Acoustic Accuracy Scale to determine the just-noticeable difference in discrimination for three consonant-vowel syllable contrasts (/bɑ/-/wɑ/, /dɑ/-/gɑ/, /ɹɑ/-/wɑ/), each varying along a single acoustic parameter for seven children with CAS with rhotic errors, seven children with SSD with rhotic errors, and seven typically developing (TD) children.

RESULTS

Findings revealed statistically significant mean differences between perceptual performance of children with CAS when compared to TD children for discrimination of /ɹɑ/-/wɑ/ contrasts. Large effect sizes were also observed for comparisons of /ɹɑ/-/wɑ/ contrasts between children with CAS, SSD, and TD peers. Additionally, large effect sizes were observed for /dɑ/-/gɑ/ contrasts between children with CAS and SSD and TD children despite nonsignificant mean differences in group performance.

CONCLUSIONS

Overall, mean outcome scores suggest that school-age children with CAS and persistent rhotic errors demonstrated less accurate speech perception skills relative to TD children for the /ɹɑ/-/wɑ/ contrasts. However, the relatively small sample sizes per group limit the extent to which these findings may be generalized to the broader population.

Speech sensorimotor relationships in francophone preschoolers and adults: Adaptation to real-time auditory feedback perturbations

PURPOSE

This study investigates the development of sensorimotor relationships by examining adaptation to real-time perturbations of auditory feedback.

METHOD

Acoustic signals were recorded while preschoolers and adult speakers of Canadian French produced several utterances of the front rounded vowel /ø/ for which F2 was gradually shifted up to a maximum of 40%.

RESULTS

The findings indicate that, although preschool-aged children produced overall similar responses to the perturbed feedback, they displayed significantly more trial-to-trial variability than adults. Furthermore, whereas the magnitude of the adaptation in adults was positively correlated with the slope of the perceptual categorical function, the amount of adaptation in children was linked to the variability of their productions in the baseline condition. These patterns suggest that the immature motor control observed in children, which contributes to increased variability in their speech production, plays a role in shaping adaptive behavior, as it allows children to explore articulatory/acoustic spaces and learn sensorimotor relationships.

Do Not Cut Off Your Tail: A Mega-Analysis of Responses to Auditory Perturbation Experiments

PURPOSE

The practice of removing "following" responses from speech perturbation analyses is increasingly common, despite no clear evidence as to whether these responses represent a unique response type. This study aimed to determine if the distribution of responses to auditory perturbation paradigms represents a bimodal distribution, consisting of two distinct response types, or a unimodal distribution.

METHOD

This mega-analysis pooled data from 22 previous studies to examine the distribution and magnitude of responses to auditory perturbations across four tasks: adaptive pitch, adaptive formant, reflexive pitch, and reflexive formant. Data included at least 150 unique participants for each task, with studies comprising younger adult, older adult, and Parkinson's disease populations. A Silverman's unimodality test followed by a smoothed bootstrap resampling technique was performed for each task to evaluate the number of modes in each distribution. Wilcoxon signed-ranks tests were also performed for each distribution to confirm significant compensation in response to the perturbation.

RESULTS

Modality analyses were not significant (p > .05) for any group or task, indicating unimodal distributions. Our analyses also confirmed compensatory reflexive responses to pitch and formant perturbations across all groups, as well as adaptive responses to sustained formant perturbations. However, analyses of sustained pitch perturbations only revealed evidence of adaptation in studies with younger adults.

CONCLUSION

The demonstration of a clear unimodal distribution across all tasks suggests that following responses do not represent a distinct response pattern, but rather the tail of a unimodal distribution.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.24282676.

How to cut the pie is no piece of cake: Toward a process-oriented approach to assessment and diagnosis of speech sound disorders

BACKGROUND

'Speech sound disorder' is an umbrella term that encompasses dysarthria, articulation disorders, childhood apraxia of speech and phonological disorders. However, differential diagnosis between these disorders is a persistent challenge in speech pathology, as many diagnostic procedures use symptom clusters instead of identifying an origin of breakdown in the speech and language system.

AIMS

This article reviews typical and disordered speech through the lens of two well-developed models of production-one focused on phonological encoding and one focused on speech motor planning. We illustrate potential breakdown locations within these models that may relate to childhood apraxia of speech and phonological disorders.

MAIN CONTRIBUTION

This paper presents an overview of an approach to conceptualisation of speech sound disorders that is grounded in current models of speech production and emphasises consideration of underlying processes. The paper also sketches a research agenda for the development of valid, reliable and clinically feasible assessment protocols for children with speech sound disorders.

CONCLUSION

The process-oriented approach outlined here is in the early stages of development but holds promise for developing a more detailed and comprehensive understanding of, and assessment protocols for speech sound disorders that go beyond broad diagnostic labels based on error analysis. Directions for future research are discussed.

WHAT THIS PAPER ADDS

What is already known on the subject Speech sound disorders (SSD) are heterogeneous, and there is agreement that some children have a phonological impairment (phonological disorders, PD) whereas others have an impairment of speech motor planning (childhood apraxia of speech, CAS). There is also recognition that speech production involves multiple processes, and several approaches to the assessment and diagnosis of SSD have been proposed. What this paper adds to existing knowledge This paper provides a more detailed conceptualisation of potential impairments in children with SSD that is grounded in current models of speech production and encourages greater consideration of underlying processes. The paper illustrates this approach and provides guidance for further development. One consequence of this perspective is the notion that broad diagnostic category labels (PD, CAS) may each comprise different subtypes or profiles depending on the processes that are affected. What are the potential or actual clinical implications of this work? Although the approach is in the early stages of development and no comprehensive validated set of tasks and measures is available to assess all processes, clinicians may find the conceptualisation of different underlying processes and the notion of potential subtypes within PD and CAS informative when evaluating SSD. In addition, this perspective discourages either/or thinking (PD or CAS) and instead encourages consideration of the possibility that children may have different combinations of impairments at different processing stages.

Modeling Responses to Auditory Feedback Perturbations in Adults, Children, and Children With Complex Speech Sound Disorders: Evidence for Impaired Auditory Self-Monitoring?

PURPOSE

Previous studies have found that typically developing (TD) children were able to compensate and adapt to auditory feedback perturbations to a similar or larger degree compared to young adults, while children with speech sound disorder (SSD) were found to produce predominantly following responses. However, large individual differences lie underneath the group-level results. This study investigates possible mechanisms in responses to formant shifts by modeling parameters of feedback and feedforward control of speech production based on behavioral data.

METHOD

SimpleDIVA was used to model an existing dataset of compensation/adaptation behavior to auditory feedback perturbations collected from three groups of Dutch speakers: 50 young adults, twenty-three 4- to 8-year-old children with TD speech, and seven 4- to 8-year-old children with SSD. Between-groups and individual within-group differences in model outcome measures representing auditory and somatosensory feedback control gain and feedforward learning rate were assessed.

RESULTS

Notable between-groups and within-group variation was found for all outcome measures. Data modeled for individual speakers yielded model fits with varying reliability. Auditory feedback control gain was negative in children with SSD and positive in both other groups. Somatosensory feedback control gain was negative for both groups of children and marginally negative for adults. Feedforward learning rate measures were highest in the children with TD speech followed by children with SSD, compared to adults.

CONCLUSIONS

The SimpleDIVA model was able to account for responses to the perturbation of auditory feedback other than corrective, as negative auditory feedback control gains were associated with following responses to vowel shifts. These preliminary findings are suggestive of impaired auditory self-monitoring in children with complex SSD. Possible mechanisms underlying the nature of following responses are discussed.

The Effect of Somatosensory Input on Word Recognition in Typical Children and Those With Speech Sound Disorder

PURPOSE

Recent work suggests that speech perception is influenced by the somatosensory system and that oral sensorimotor disruption has specific effects on the perception of speech both in infants who have not yet begun to talk and in older children and adults with ample speech production experience; however, we do not know how such disruptions affect children with speech sound disorder (SSD). Response to disruption of would-be articulators during speech perception could reveal how sensorimotor linkages work for both typical and atypical speech and language development. Such linkages are crucial to advancing our knowledge on how both typically developing and atypically developing children produce and perceive speech.

METHOD

Using a looking-while-listening task, we explored the impact of a sensorimotor restrictor on the recognition of words whose onsets involve late-developing sounds (s, ʃ) for both children with typical development (TD) and their peers with SSD.

RESULTS

Children with SSD showed a decrement in performance when they held a restrictor in their mouths during the task, but this was not the case for children with TD. This effect on performance was only observed for the specific speech sounds blocked by the would-be articulators.

CONCLUSION

We argue that these findings provide evidence for altered perceptual motor pathways in children with SSD.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.21809442.

Long-term Average Spectrum and Nasal Accelerometry in Sentences of Differing Nasality and Forward-Focused Vowel Productions Under Altered Auditory Feedback

OBJECTIVES AND BACKGROUND

To investigate whether voice focus adjustments can alter the audio-vocal feedback and consequently modulate speech/voice motor control. Speaking with a forward-focused voice was expected to enhance audio-vocal feedback and thus decrease the variability of vocal fundamental frequency (F0).

MATERIALS AND METHOD

Twenty-two healthy, untrained adults (10 males and 12 females) were requested to sustain vowel /a/ with their natural focus and a forward focus and to naturally read the nasal, oral, and mixed oral-nasal sentences in normal noise-masked auditory conditions. Meanwhile, a miniature accelerometer was externally attached on the noise to detect the nasal vibrations during vocalization. Audio recordings were made and analyzed using the long-term average spectrum (LTAS) and power spectral analysis of F0.

RESULTS

Compared with naturally-focused vowel production and oral sentences, forward-focused vowel productions and nasal sentences both showed significant increases in nasal accelerometric amplitude and the spectral power within the range of 200∼300 Hz, and significantly decreased the F0 variability below 3 Hz, which has been reported to be associated with enhanced auditory feedback in our previous research. The auditory masking not only significantly increased the low-frequency F0 variability, but also significantly decreased the ratio of the spectral power within 200∼300 Hz to the power within 300∼1000 Hz for the vowel and sentence productions. Gender differences were found in the correlations between the degree of nasal coupling and F0 stability as well as in the LTAS characteristics in response to noise.

CONCLUSIONS

Variations in nasal-oral acoustic coupling not only change the formant features of speech signals, but involuntarily influence the auditory feedback control of vocal fold vibrations. Speakers tend to show improved F0 stability in response to a forward-focused voice adjustment.

Pediatric Responses to Fundamental and Formant Frequency Altered Auditory Feedback: A Scoping Review

Purpose

The ability to hear ourselves speak has been shown to play an important role in the development and maintenance of fluent and coherent speech. Despite this, little is known about the developing speech motor control system throughout childhood, in particular if and how vocal and articulatory control may differ throughout development. A scoping review was undertaken to identify and describe the full range of studies investigating responses to frequency altered auditory feedback in pediatric populations and their contributions to our understanding of the development of auditory feedback control and sensorimotor learning in childhood and adolescence.

Method

Relevant studies were identified through a comprehensive search strategy of six academic databases for studies that included (a) real-time perturbation of frequency in auditory input, (b) an analysis of immediate effects on speech, and (c) participants aged 18 years or younger.

Results

Twenty-three articles met inclusion criteria. Across studies, there was a wide variety of designs, outcomes and measures used. Manipulations included fundamental frequency (9 studies), formant frequency (12), frequency centroid of fricatives (1), and both fundamental and formant frequencies (1). Study designs included contrasts across childhood, between children and adults, and between typical, pediatric clinical and adult populations. Measures primarily explored acoustic properties of speech responses (latency, magnitude, and variability). Some studies additionally examined the association of these acoustic responses with clinical measures (e.g., stuttering severity and reading ability), and neural measures using electrophysiology and magnetic resonance imaging.

Conclusion

Findings indicated that children above 4 years generally compensated in the opposite direction of the manipulation, however, in several cases not as effectively as adults. Overall, results varied greatly due to the broad range of manipulations and designs used, making generalization challenging. Differences found between age groups in the features of the compensatory vocal responses, latency of responses, vocal variability and perceptual abilities, suggest that maturational changes may be occurring in the speech motor control system, affecting the extent to which auditory feedback is used to modify internal sensorimotor representations. Varied findings suggest vocal control develops prior to articulatory control. Future studies with multiple outcome measures, manipulations, and more expansive age ranges are needed to elucidate findings.

Response patterns to vowel formant perturbations in children

Auditory feedback is an important component of speech motor control, but its precise role in developing speech is less understood. The role of auditory feedback in development was probed by perturbing the speech of children 4-9 years old. The vowel sound /ɛ/ was shifted to /æ/ in real time and presented to participants as their own auditory feedback. Analyses of the resultant formant magnitude changes in the participants' speech indicated that children compensated and adapted by adjusting their formants to oppose the perturbation. Older and younger children responded to perturbation differently in F₁ and F₂. The compensatory change in F₁ was greater for younger children, whereas the increase in F₂ was greater for older children. Adaptation aftereffects were observed in both groups. Exploratory directional analyses in the two-dimensional formant space indicated that older children responded more directly and less variably to the perturbation than younger children, shifting their vowels back toward the vowel sound /ɛ/ to oppose the perturbation. Findings support the hypothesis that auditory feedback integration continues to develop between the ages of 4 and 9 years old such that the differences in the adaptive and compensatory responses arise between younger and older children despite receiving the same auditory feedback perturbation.

Auditory feedback experience in the development of phonetic production: Evidence from preschoolers with cochlear implants and their normal-hearing peers

Previous work has found that preschoolers with greater phonological awareness and larger lexicons, who speak more throughout the day, exhibit less intra-syllabic coarticulation in controlled speech production tasks. These findings suggest that both linguistic experience and speech-motor control are important predictors of spoken phonetic development. Still, it remains unclear how preschoolers' speech practice when they talk drives the development of coarticulation because children who talk more are likely to have both increased fine motor control and increased auditory feedback experience. Here, the potential effect of auditory feedback is studied by examining a population-children with cochlear implants (CIs)-which is naturally differing in auditory experience. The results show that (1) developmentally appropriate coarticulation improves with an increased hearing age but not chronological age; (2) children with CIs pattern coarticulatorily closer to their younger, hearing age-matched peers than chronological age-matched peers; and (3) the effects of speech practice on coarticulation, measured using naturalistic, at-home recordings of the children's speech production, only appear in the children with CIs after several years of hearing experience. Together, these results indicate a strong role of auditory feedback experience on coarticulation and suggest that parent-child communicative exchanges could stimulate children's own vocal output, which drives speech development.

A Pilot Single-Case Experimental Design Study of Rapid Syllable Transition Treatment for Italian Children With Childhood Apraxia of Speech

Background The Rapid Syllable Transition (ReST) treatment is an effective intervention designed to address the planning and programming disorder found in childhood apraxia of speech. To date, no study has considered its use with children who speak languages other than English. Aim This pilot study aimed to examine the use of ReST treatment with Italian children. We hypothesized that the ReST approach would improve the overall accuracy of the targeted behaviors of lexical stress, smoothness, and phonemic accuracy, whereas phonemic and phonetic accuracy of untreated items would remain stable. Method Two monolingual Italian-speaking children with childhood apraxia of speech received therapy in 12 one-hour sessions, 2-3 times per week, using a single-case experimental design. The treatment procedures used in English were replicated in Italian with one change: In English, two stress patterns are treated. Italian commonly uses three stress patterns; therefore, the stimuli were modified accordingly. Accuracy of articulation, lexical stress, and smoothness were assessed at pretreatment and 1 day, 1 week, and 4 months posttreatment in treated and untreated pseudowords and in real words and sentences. Results Both children improved on treated pseudowords and real words with moderate effect sizes, but only one child generalized to untreated pseudowords. Maintenance of treatment results was observed in both participants. Articulation of control phonemes did not change. Conclusions ReST treatment in Italian is feasible, and a treatment effect was found, showing that its use may be valid in languages other than English. Further research is required. Supplemental Material https://doi.org/10.23641/asha.14348060.

Compensation to Altered Auditory Feedback in Children With Developmental Language Disorder and Typical Development

Purpose Developmental language disorder (DLD), an unexplained problem using and understanding spoken language, has been hypothesized to have an underlying auditory processing component. Auditory feedback plays a key role in speech motor control. The current study examined whether auditory feedback is used to regulate speech production in a similar way by children with DLD and their typically developing (TD) peers. Method Participants aged 6-11 years completed tasks measuring hearing, language, first formant (F1) discrimination thresholds, partial vowel space, and responses to altered auditory feedback with F1 perturbation. Results Children with DLD tended to compensate more than TD children for the positive F1 manipulation and compensated less than TD children in the negative shift condition. Conclusion Our findings suggest that children with DLD make atypical use of auditory feedback.

What Acoustic Studies Tell Us About Vowels in Developing and Disordered Speech

Purpose Literature was reviewed on the development of vowels in children's speech and on vowel disorders in children and adults, with an emphasis on studies using acoustic methods. Method Searches were conducted with PubMed/MEDLINE, Google Scholar, CINAHL, HighWire Press, and legacy sources in retrieved articles. The primary search items included, but were not limited to, vowels, vowel development, vowel disorders, vowel formants, vowel therapy, vowel inherent spectral change, speech rhythm, and prosody. Results/Discussion The main conclusions reached in this review are that vowels are (a) important to speech intelligibility; (b) intrinsically dynamic; (c) refined in both perceptual and productive aspects beyond the age typically given for their phonetic mastery; (d) produced to compensate for articulatory and auditory perturbations; (e) influenced by language and dialect even in early childhood; (f) affected by a variety of speech, language, and hearing disorders in children and adults; (g) inadequately assessed by standardized articulation tests; and (h) characterized by at least three factors-articulatory configuration, extrinsic and intrinsic regulation of duration, and role in speech rhythm and prosody. Also discussed are stages in typical vowel ontogeny, acoustic characterization of rhotic vowels, a sensory-motor perspective on vowel production, and implications for clinical assessment of vowels.

Compensatory and adaptive responses to real-time formant shifts in adults and children

Auditory feedback plays an important role in speech motor learning, yet, little is known about the strength of motor learning and feedback control in speech development. This study investigated compensatory and adaptive responses to auditory feedback perturbation in children (aged 4-9 years old) and young adults (aged 18-29 years old). Auditory feedback was perturbed by near-real-time shifting F1 and F2 of the vowel /ɪː/ during the production of consonant-vowel-consonant words. Children were able to compensate and adapt in a similar or larger degree compared to young adults. Higher token-to-token variability was found in children compared to adults but not disproportionately higher during the perturbation phases compared to the unperturbed baseline. The added challenge to auditory-motor integration did not influence production variability in children, and compensation and adaptation effects were found to be strong and sustainable. Significant group differences were absent in the proportions of speakers displaying a compensatory or adaptive response, an amplifying response, or no consistent response. Within these categories, children produced significantly stronger compensatory, adaptive, or amplifying responses, which could be explained by less-ingrained existing representations. The results are interpreted as both auditory-motor integration and learning capacities are stronger in young children compared to adults.

The Neurocognition of Developmental Disorders of Language

Developmental disorders of language include developmental language disorder, dyslexia, and motor-speech disorders such as articulation disorder and stuttering. These disorders have generally been explained by accounts that focus on their behavioral rather than neural characteristics; their processing rather than learning impairments; and each disorder separately rather than together, despite their commonalities and comorbidities. Here we update and review a unifying neurocognitive account—the Procedural circuit Deficit Hypothesis (PDH). The PDH posits that abnormalities of brain structures underlying procedural memory (learning and memory that rely on the basal ganglia and associated circuitry) can explain numerous brain and behavioral characteristics across learning and processing, in multiple disorders, including both commonalities and differences. We describe procedural memory, examine its role in various aspects of language, and then present the PDH and relevant evidence across language-related disorders. The PDH has substantial explanatory power, and both basic research and translational implications.

An N-of-1 Randomized Controlled Trial of Interventions for Children With Inconsistent Speech Sound Errors

Purpose The aim of this study was to test the hypothesis that children with inconsistent speech errors would respond differentially to 1 of 3 specific interventions depending on their primary underlying impairment: Children with deficient motor planning were expected to respond best to an auditory-motor integration (AMI) intervention, and children with deficient phonological planning were expected to respond best to a phonological memory and planning (PMP) intervention. Method Twelve participants were diagnosed with a motor planning (n = 7) or phonological planning (n = 5) deficit based on a comprehensive assessment, which included the Syllable Repetition Task as an important source of diagnostic evidence. An N-of-1 randomized controlled trial was used. Each child experienced all 3 interventions: AMI, PMP, and control (CTL); however, these interventions were randomly allocated to sessions within weeks (3 sessions per week × 6 weeks for 18 sessions). The AMI intervention procedures targeted knowledge of the acoustic-phonetic target and integration of auditory and somatosensory feedback during speech practice. The PMP intervention procedures targeted segmenting and recompiling the phonological plan for each word. The CTL intervention was standard drill practice. The child was taught 5 pseudowords in a meaningful context in each intervention condition. Results Same-day (SD) probes assessed transfer from taught pseudowords to untaught real words, and next-day (ND) probes assessed retention of that learning. Nonparametric resampling tests with pooling of p values across children with the same diagnosis were used to assess the results. Pooled p values indicated a significant benefit of AMI over PMP for the group with a motor planning deficit (p = 2.01E-04 for SD probes and 2.97E-03 for ND probes) and a significant benefit of PMP over AMI for the group with a phonological planning deficit (p = 1.22E-02 for SD probes and 1.32E-02 for ND probes). Response to the CTL intervention was variable within groups. Conclusion In this study, the child's underlying psycholinguistic deficit helped to predict response to intervention.

Speech Production From a Developmental Perspective

Purpose Current approaches to speech production aim to explain adult behavior and so make assumptions that, when taken to their logical conclusion, fail to adequately account for development. This failure is problematic if adult behavior can be understood to emerge from the developmental process. This problem motivates the proposal of a developmentally sensitive theory of speech production. The working hypothesis, which structures the theory, is that feedforward representations and processes mature earlier than central feedback control processes in speech production. Method Theoretical assumptions that underpin the 2 major approaches to adult speech production are reviewed. Strengths and weaknesses are evaluated with respect to developmental patterns. A developmental approach is then pursued. The strengths of existing theories are borrowed, and the ideas are resynthesized under the working hypothesis. The speech production process is then reimagined in developmental stages, with each stage building on the previous one. Conclusion The resulting theory proposes that speech production relies on conceptually linked representations that are information-reduced holistic perceptual and motoric forms, constituting the phonological aspect of a system that is acquired with the lexicon. These forms are referred to as exemplars and schemas, respectively. When a particular exemplar and schema are activated with the selection of a particular lexical concept, their forms are used to define unique trajectories through an endogenous perceptual-motor space that guides implementation. This space is not linguistic, reflecting its origin in the prespeech period. Central feedback control over production emerges with failures in communication and the development of a self-concept.

A Psycholinguistic Framework for Diagnosis and Treatment Planning of Developmental Speech Disorders

BACKGROUND

Differential diagnosis and treatment planning of developmental speech disorders (DSD) remains a major challenge in paediatric speech-language pathology. Different classification systems exist, in which subtypes are differentiated based on their theoretical cause and in which the definitions generally refer to speech production processes. Accordingly, various intervention methods have been developed aiming at different parts of the speech production process. Diagnostic classification in these systems, however, is primarily based on a description of behavioural speech symptoms rather than on underlying deficits.

PURPOSE

In this paper, we present a process-oriented approach to diagnosis and treatment planning of DSD. Our framework comprises two general diagnostic categories: developmental delay and developmental disorder. Within these categories, treatment goals/targets and treatment methods are formulated at the level of processes and rules/representations.

CONCLUSION

A process-oriented approach to diagnosis and treatment planning holds important advantages, offering direct leads for treatment aimed at the underlying impairment, tailored to the specific needs of the individual and adjusted to the developmental trajectory.

An Investigation of Compensation and Adaptation to Auditory Perturbations in Individuals With Acquired Apraxia of Speech

Two auditory perturbation experiments were used to investigate the integrity of neural circuits responsible for speech sensorimotor adaptation in acquired apraxia of speech (AOS). This has implications for understanding the nature of AOS as well as normal speech motor control. Two experiments were conducted. In Experiment 1, compensatory responses to unpredictable fundamental frequency (F0) perturbations during vocalization were investigated in healthy older adults and adults with acquired AOS plus aphasia. F0 perturbation involved upward and downward 100-cent shifts versus no shift, in equal proportion, during 2 s vocalizations of the vowel /a/. In Experiment 2, adaptive responses to sustained first formant (F1) perturbations during speech were investigated in healthy older adults, adults with AOS and adults with aphasia only (APH). The F1 protocol involved production of the vowel /ε/ in four consonant-vowel words of Australian English (pear, bear, care, dare), and one control word with a different vowel (paw). An unperturbed Baseline phase was followed by a gradual Ramp to a 30% upward F1 shift stimulating a compensatory response, a Hold phase where the perturbation was repeatedly presented with alternating blocks of masking trials to probe adaptation, and an End phase with masking trials only to measure persistence of any adaptation. AOS participants showed normal compensation to unexpected F0 perturbations, indicating that auditory feedback control of low-level, non-segmental parameters is intact. Furthermore, individuals with AOS displayed an adaptive response to sustained F1 perturbations, but age-matched controls and APH participants did not. These findings suggest that older healthy adults may have less plastic motor programs that resist modification based on sensory feedback, whereas individuals with AOS have less well-established and more malleable motor programs due to damage from stroke.

Speech Impairment in Boys With Fetal Alcohol Spectrum Disorders

BACKGROUND

Fetal alcohol spectrum disorders (FASD) are a highly prevalent spectrum of patterns of congenital defects resulting from prenatal exposure to alcohol. Approximately 90% of the cases involve speech impairment. Yet, to date, no detailed symptom profiles nor dedicated treatment plans are available for this population.

PURPOSE

This study set out to chart the speech and speech motor characteristics in boys with FASD to profile the concomitant speech impairment and identify possible underlying mechanisms.

METHOD

Ten boys with FASD (4.5-10.3 years old) and 26 typically developing children (4.1-8.7 years old; 14 boys, 12 girls) participated in the study. Speech production and perception, and oral motor data were collected by standardized tests.

RESULTS

The boys with FASD showed reduced scores on all tasks as well as a deviant pattern of correlations between production and perception tasks and intelligibility compared with the typically developing children. Speech motor profiles showed specific problems with nonword repetition and tongue control.

CONCLUSIONS

Findings indicate that the speech impairment in boys with FASD results from a combination of deficits in multiple subsystems and should be approached as a disorder rather than a developmental delay. The results suggest that reduced speech motor planning/programming, auditory discrimination, and oral motor abilities should be considered in long-term, individually tailored treatment.

Aging and Sex Influence Cortical Auditory-Motor Integration for Speech Control

It is well known that acoustic change in speech production is subject to age-related declines. How aging alters cortical sensorimotor integration in speech control, however, remains poorly understood. The present event-related potential study examined the behavioral and neural effects of aging and sex on the auditory-motor processing of voice pitch errors. Behaviorally, older adults produced significantly larger vocal compensations for pitch perturbations than young adults across the sexes, while the effects of sex on vocal compensation did not exist for both young and older adults. At the cortical level, there was a significant interaction between aging and sex on the N1-P2 complex. Older males produced significantly smaller P2 amplitudes than young males, while young males produced significantly larger N1 and P2 amplitudes than young females. In addition, females produced faster N1 responses than males regardless of age, while young adults produced faster P2 responses than older adults across the sexes. These findings provide the first neurobehavioral evidence that demonstrates the aging influence on auditory feedback control of speech production, and highlight the importance of sex in understanding the aging of the neuromotor control of speech production.

Timing variability of sensorimotor integration during vocalization in individuals who stutter

Persistent developmental stuttering affects close to 1% of adults and is thought to be a problem of sensorimotor integration. Previous research has demonstrated that individuals who stutter respond differently to changes in their auditory feedback while speaking. Here we explore a number of changes that accompany alterations in the feedback of pitch during vocal production. Participants sustained the vowel /a/ while hearing on-line feedback of their own voice through headphones. In some trials, feedback was briefly shifted up or down by 100 cents to simulate a vocal production error. As previously shown, participants compensated for the auditory pitch change by altering their vocal production in the opposite direction of the shift. The average compensatory response was smaller for adults who stuttered than for adult controls. Detailed analyses revealed that adults who stuttered had fewer trials with a robust corrective response, and that within the trials showing compensation, the timing of their responses was more variable. These results support the idea that dysfunctional sensorimotor integration in stuttering is characterized by timing variability, reflecting reduced coupling of the auditory and speech motor systems.

Assessing speech correction abilities with acoustic analyses: Evidence of preserved online correction in persons with aphasia

Purpose: Disorders of speech production may be accompanied by abnormal processing of speech sensory feedback. Here, we introduce a semi-automated analysis designed to assess the degree to which speakers use natural online feedback to decrease acoustic variability in spoken words. Because production deficits in aphasia have been hypothesised to stem from problems with sensorimotor integration, we investigated whether persons with aphasia (PWA) can correct their speech acoustics online. Method: Eight PWA in the chronic stage produced 200 repetitions each of three monosyllabic words. Formant variability was measured for each vowel in multiple time windows within the syllable, and the reduction in formant variability from vowel onset to midpoint was quantified. Result: PWA significantly decreased acoustic variability over the course of the syllable, providing evidence of online feedback correction mechanisms. The magnitude of this corrective formant movement exceeded past measurements in control participants. Conclusion: Vowel centreing behaviour suggests that error correction abilities are at least partially spared in speakers with aphasia, and may be relied upon to compensate for feedforward deficits by bringing utterances back on track. These proof of concept data show the potential of this analysis technique to elucidate the mechanisms underlying disorders of speech production.

Abnormal Speech Motor Control in Individuals with 16p11.2 Deletions

Speech and motor deficits are highly prevalent (>70%) in individuals with the 600 kb BP4-BP5 16p11.2 deletion; however, the mechanisms that drive these deficits are unclear, limiting our ability to target interventions and advance treatment. This study examined fundamental aspects of speech motor control in participants with the 16p11.2 deletion. To assess capacity for control of voice, we examined how accurately and quickly subjects changed the pitch of their voice within a trial to correct for a transient perturbation of the pitch of their auditory feedback. When compared to controls, 16p11.2 deletion carriers show an over-exaggerated pitch compensation response to unpredictable mid-vocalization pitch perturbations. We also examined sensorimotor adaptation of speech by assessing how subjects learned to adapt their sustained productions of formants (speech spectral peak frequencies important for vowel identity), in response to consistent changes in their auditory feedback during vowel production. Deletion carriers show reduced sensorimotor adaptation to sustained vowel identity changes in auditory feedback. These results together suggest that 16p11.2 deletion carriers have fundamental impairments in the basic mechanisms of speech motor control and these impairments may partially explain the deficits in speech and language in these individuals.

Perception-production relations in later development of American English rhotics

It is known that some adult listeners have more sharply defined perceptual categories than others, and listeners with more precise auditory targets are also more precise in their production of contrasts. There is additionally evidence that children who have not yet mastered production of a contrast show diminished performance on perceptual measures of the same contrast. To date, however, few studies have investigated developmental perception-production relations using the fine-grained measures typical of adult studies. Existing evidence suggests that perception and production can be closely connected in development, but this relationship may break down as perception and articulation mature at different rates. This study evaluated perception and production of the English /r-w/ contrast in 40 typically-developing children aged 9-14. Perceptual sensitivity was measured with a logistic function fitted over responses in a forced-choice identification task using two synthetic 10-step continua from rake to wake. Participants also produced rhotic and non-rhotic words. Across participants, there was a significant correlation between perceptual acuity and rhoticity in production, although this effect was only observed for one of two continua tested. These results provide preliminary evidence compatible with the hypothesis that children with a more refined auditory target for a sound also produce that sound more accurately.

Speech Sound Disorders: What's Motor Got To Do With It?

Speech sound disorders (SSDs) are commonly viewed as involving impaired articulation and/or phonological skills. Speech language pathologists working with individuals with (SSDs) assess the articulation of speech sounds and the coordination of articulatory structures with other components of the speech mechanism, including the phonatory, respiratory, and resonatory subsystems. The sound system of the language and the rules that govern how phonemes are combined are equally critical for clinicians to explore. While the terms “articulation” and “phonology” provide clinicians with a framework for classification, children who are broadly identified with (SSDs) may also display characteristics of a motor speech impairment, which can obscure the decision making process with respect to both diagnosis and treatment. One such motor speech disorder is childhood apraxia of speech (CAS). The focus of this paper is to discuss motor speech deficits in children and to review research that aims to distinguish motor speech patterns in children with (SSDs) with and without CAS. We will also address the relationship between emerging speech motor and linguistic skills.

Visual Feedback of Tongue Movement for Novel Speech Sound Learning

Pronunciation training studies have yielded important information concerning the processing of audiovisual (AV) information. Second language (L2) learners show increased reliance on bottom-up, multimodal input for speech perception (compared to monolingual individuals). However, little is known about the role of viewing one's own speech articulation processes during speech training. The current study investigated whether real-time, visual feedback for tongue movement can improve a speaker's learning of non-native speech sounds. An interactive 3D tongue visualization system based on electromagnetic articulography (EMA) was used in a speech training experiment. Native speakers of American English produced a novel speech sound (/ɖ/; a voiced, coronal, palatal stop) before, during, and after trials in which they viewed their own speech movements using the 3D model. Talkers' productions were evaluated using kinematic (tongue-tip spatial positioning) and acoustic (burst spectra) measures. The results indicated a rapid gain in accuracy associated with visual feedback training. The findings are discussed with respect to neural models for multimodal speech processing.

Transfer Effect of Speech-sound Learning on Auditory-motor Processing of Perceived Vocal Pitch Errors

Speech perception and production are intimately linked. There is evidence that speech motor learning results in changes to auditory processing of speech. Whether speech motor control benefits from perceptual learning in speech, however, remains unclear. This event-related potential study investigated whether speech-sound learning can modulate the processing of feedback errors during vocal pitch regulation. Mandarin speakers were trained to perceive five Thai lexical tones while learning to associate pictures with spoken words over 5 days. Before and after training, participants produced sustained vowel sounds while they heard their vocal pitch feedback unexpectedly perturbed. As compared to the pre-training session, the magnitude of vocal compensation significantly decreased for the control group, but remained consistent for the trained group at the post-training session. However, the trained group had smaller and faster N1 responses to pitch perturbations and exhibited enhanced P2 responses that correlated significantly with their learning performance. These findings indicate that the cortical processing of vocal pitch regulation can be shaped by learning new speech-sound associations, suggesting that perceptual learning in speech can produce transfer effects to facilitating the neural mechanisms underlying the online monitoring of auditory feedback regarding vocal production.

Reliance on auditory feedback in children with childhood apraxia of speech

Children with childhood apraxia of speech (CAS) have been hypothesized to continuously monitor their speech through auditory feedback to minimize speech errors. We used an auditory masking paradigm to determine the effect of attenuating auditory feedback on speech in 30 children: 9 with CAS, 10 with speech delay, and 11 with typical development. The masking only affected the speech of children with CAS as measured by voice onset time and vowel space area. These findings provide preliminary support for greater reliance on auditory feedback among children with CAS.

LEARNING OUTCOMES

Readers of this article should be able to (i) describe the motivation for investigating the role of auditory feedback in children with CAS; (ii) report the effects of feedback attenuation on speech production in children with CAS, speech delay, and typical development, and (iii) understand how the current findings may support a feedforward program deficit in children with CAS.

Behavioral, computational, and neuroimaging studies of acquired apraxia of speech

A critical examination of speech motor control depends on an in-depth understanding of network connectivity associated with Brodmann areas 44 and 45 and surrounding cortices. Damage to these areas has been associated with two conditions-the speech motor programming disorder apraxia of speech (AOS) and the linguistic/grammatical disorder of Broca's aphasia. Here we focus on AOS, which is most commonly associated with damage to posterior Broca's area (BA) and adjacent cortex. We provide an overview of our own studies into the nature of AOS, including behavioral and neuroimaging methods, to explore components of the speech motor network that are associated with normal and disordered speech motor programming in AOS. Behavioral, neuroimaging, and computational modeling studies are indicating that AOS is associated with impairment in learning feedforward models and/or implementing feedback mechanisms and with the functional contribution of BA6. While functional connectivity methods are not yet routinely applied to the study of AOS, we highlight the need for focusing on the functional impact of localized lesions throughout the speech network, as well as larger scale comparative studies to distinguish the unique behavioral and neurological signature of AOS. By coupling these methods with neural network models, we have a powerful set of tools to improve our understanding of the neural mechanisms that underlie AOS, and speech production generally.